Paleontological Discoveries in the Chorrillo Formation (Upper Campanian-Lower Maastrichtian, Upper Cretaceous), Santa Cruz Province, Patagonia, Argentina

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Rev. Mus. Argentino Cienc. Nat., n.s. 21(2): 217-293, 2019 ISSN 1514-5158 (impresa) ISSN 1853-0400 (en línea)

Paleontological discoveries in the Chorrillo Formation (upper Campanian-lower Maastrichtian, Upper Cretaceous), Santa Cruz Province, Patagonia, Argentina

Fernando. E. NOVAS1,2, Federico. L. AGNOLIN1,2,3, Sebastián ROZADILLA1,2, Alexis M. ARANCIAGA-ROLANDO1,2, Federico BRISSON-EGLI1,2, Matias J. MOTTA1,2, Mauricio CERRONI1,2, Martín D. EZCURRA2,5, Agustín G. MARTINELLI2,5, Julia S. D´ANGELO1,2, Gerardo ALVAREZ-HERRERA1, Adriel R. GENTIL1,2, Sergio BOGAN3, Nicolás R. CHIMENTO1,2, Jordi A. GARCÍA-MARSÀ1,2, Gastón LO COCO1,2, Sergio E. MIQUEL2,4, Fátima F. BRITO4, Ezequiel I. VERA2,6, 7, Valeria S. PEREZ LOINAZE2,6 , Mariela S. FERNÁNDEZ8 & Leonardo SALGADO2,9

1 Laboratorio de Anatomía Comparada y Evolución de los Vertebrados. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Avenida Ángel Gallardo 470, Buenos Aires C1405DJR, Argentina - fernovas@yahoo. com.ar. 2 Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina. 3 Fundación de Historia Natural “Felix de Azara”, Universidad Maimonides, Hidalgo 775, C1405BDB Buenos Aires, Argentina. 4 Laboratorio de Malacología terrestre. División Invertebrados Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Avenida Ángel Gallardo 470, Buenos Aires C1405DJR, Argentina. 5 Sección Paleontología de Vertebrados. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Avenida Ángel Gallardo 470, Buenos Aires C1405DJR, Argentina. 6 División Paleobotánica. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Avenida Ángel Gallardo 470, Buenos Aires C1405DJR, Argentina. 7 Área de Paleontología. Departamento de Geología, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria (C1428EGA) Buenos Aires, Argentina. 8 Instituto de Investigaciones en Biodiversidad y Medioambiente (CONICET-INIBIOMA), Quintral 1250, 8400 San Carlos de Bariloche, Río Negro, Argentina. 9 Instituto de Investigación en Paleobiología y Geología de la Universidad Nacional de Río Negro, General Roca, Río Negro, Argentina

Abstract: The first fossil remains of vertebrates, invertebrates, plants and palynomorphs of the Chorrillo Formation (Austral Basin), about 30km to the SW of the town of El Calafate (Province of Santa Cruz), are described. Fossils include the elasmarian (basal Iguanodontia) Isasicursor santacrucensis gen. et sp. nov., the large titanosaur Nullotitan glaciaris gen. et sp. nov., both large and small Megaraptoridae indet., and fragments of sauropod and theropod eggshells. The list of vertebrates is also composed by the Neognathae Kookne yeutensis gen. et sp. nov., two isolated caudal vertebrae of Mammalia indet., and isolated teeth of a large mosasaur. Remains of fishes, anurans, turtles, and snakes are represented by fragmentary material of low taxonomical value, with the exception of remains belonging to Calyptocephalellidae. On the other hand, a remarkable diversity of terrestrial and freshwater gastropods has been documented, as well as fossil woods and palinological assemblages. The Chorrillo Formation continues south, in the Las Chinas River valley, southern Chile, where it is called Dorotea Formation. Both units share in their lower two thirds abundant materials of titanosaurs, whose remains cea- se to appear in the upper third, registering only elasmarians (Chorrillo Formation) and hadrosaurs (Dorotea Formation). Above both units there are levels with remains of invertebrates and marine reptiles. It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent. In contrast, these taxa are dominant components in sedimentary units of central and northern Patagonia (e.g., Allen, Los Alamitos, La Colonia formations). Such differences could reflect, in part, a greater antiquity (i.e., late Campanian-early Maastrichtian) for the Chorrillo fossils, or, more probably, different environmental conditions. Thus, knowledge of the biota of the southern tip of Patagonia is expanded, particularly those temporarily close to the K-Pg boundary.

Key words: Chorrillo Formation, Southern Patagonia, Late Cretaceous, fossils

Resumen: Hallazgos Paleontológicos en la Formación Chorrillo (Campaniano-Maastrichtiano, Cretácico Superior), Provincia de Santa Cruz, Patagonia, Argentina. Se describen los primeros restos fósiles de vertebrados, invertebrados, plantas y palinomorfos de la Formación Chorrillo (Cuenca Austral), aflo- rante unos 30km al SW de la localidad de El Calafate (Provincia de Santa Cruz). Los fósiles de dinosaurios no avianos incluyen el elasmariano (Iguanodontia basal) Isasicursor santacrucensis gen. et sp. nov., el titanosaurio 218 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

gigante Nullotitan glaciaris gen. et sp. nov., Megaraptoridae indet. de tamaños pequeño y grande, y fragmentos de cáscaras de huevo pertenecientes a saurópodos y terópodos. La lista de vertebrados se compone también del Neognathae Kookne yeutensis gen. et sp. nov., dos vértebras caudales aisladas de Mammalia indet., y dientes aisla- dos de un mosasaurio de gran tamaño. Han sido colectados también restos de peces, anuros, tortugas y serpientes los cuales están representados por material fragmentario de escaso valor taxonómico, con la excepción de restos pertenecientes a Calyptocephalellidae. Por otra parte, ha sido documentada una notable diversidad de gasteró- podos terrestres y dulceacuícolas, así como leños fósiles y asociaciones palinológicas. La Formación Chorrillo se continúa hacia el sur, en el valle del río Las Chinas, Chile, en donde es denominada Formación Dorotea. Ambas unidades comparten en sus dos tercios inferiores abundante material de titanosaurios, cuyos restos dejan de apa- recer en el tercio superior, registrándose solo elasmarianos (Fm Chorrillo) y hadrosaurios (Fm Dorotea). Por en- cima de ambas unidades existen niveles con restos de invertebrados y reptiles marinos. Llama la atención que los dinosaurios de los dos tercios inferiores de las formaciones Chorrillo y Dorotea estén representados por titanosaurios basales de gran tamaño y celurosaurios Megaraptoridae, estando ausentes los Saltasaurinae, Aeolosaurinae y Abelisauridae, los cuales son componentes dominantes en las unidades sedimentarias del Maastrichtiano de la provincia de Chubut y del norte patagónico (p.ej., formaciones Allen, Los Alamitos y La Colonia, por ejemplo). Estas diferencias podrían reflejar, en parte, una mayor antigüedad (i.e., Campaniano tardío -Maastrichtiano tem- prano) para los fósiles de Chorrillo. Se amplía así el conocimiento de las biotas del extremo sur de Patagonia, en particular de aquellas temporalmente cercanas al límite K-Pg.

Palabras clave: Formación Chorrillo, Patagonia austral, Cretácico Tardío, fósiles. ______

INTRODUCTION mains, including a partial ulna and a shed tooth, forming part of the Paleontological Collection of The Chorrillo Formation (Upper Cretaceous, the Museo Argentino de Ciencias Naturales, in Campanian-Maastrichtian; Arbe, 2002; Nullo et Buenos Aires. al., 2006) extensively crops out to the south of Recent explorations carried out in La Anita Centinela River, Santa Cruz Province, southern and Alta Vista farms, approximately 30 km SW Patagonia, Argentina (Figure 1). The Chorrillo from El Calafate city, allowed relocation of the Formation extends NE to SW as a narrow titanosaur specimen discovered by Nullo, but band with a maximum E-W width of 2 kms. also resulted in the discovery of novel vertebrate The Chorrillo Formation continues southward remains, which are described below. The explora- on the Chilean side, being partially equivalent tions were carried out on from January 13th-17th to the Dorotea Formation (Upper Cretaceous, and March 14th-19th, 2019. Campanian-Maastrichtian; Macellari et al., The complex topography of the region made 1989; Vogt et al., 2014; González Abarca, 2015; the access somewhat difficult, even for 4x4 ve- Manriquez et al., 2019). hicles, thus long and exhausting walks were re- Feruglio (in Fossa Mancini et al., 1938) was quired to reach the fossil sites. Notwithstanding the first to call “Estratos de Chorrillo” (i.e., such circumstantial inconveniences, a rich collec- “Chorrillo Beds”) to these rocks cropping out tion of fossils made up by large titanosaur bone to the south of the Argentino Lake, indicating fragments, theropod remains, medium-sized the presence of fossil logs and dinosaur bones ornithopods, tiny vertebrate bones, gastropods, (Feruglio, 1944-45). Aside from these citations and plant remains, starts to be amassed from concerning the presence of unspecified dinosaur this southern region of the Argentine Patagonia. remains, the first to discover a partial sauropod The fossil remains studied below, the first to be skeleton was Francisco Nullo in 1980, then geo- formally described from the Chorrillo Formation, logist of Argentine Geological Survey, while ex- shed valuable information on a wide variety of ploring the top of the hills of the Alta Vista farm Late Cretaceous organisms in the southern cone, (“estancia”). Nullo informed on the discovery complementing the fossil record that has been to the renowned paleontologist José Bonaparte, obtained from equivalent stratigraphic levels in who collected a partial cervical vertebra of such the geographically close Las Chinas River Valley, titanosaur specimen (see description below). in southern Chile (Leppe et. al., 2014; González Bonaparte illustrated the titanosaur bones -still Abarca, 2015; Manriquez et al., 2019). yielding on the ground- in a popular book about South American dinosaurs (Bonaparte, 1996). GEOLOGICAL SETTING From the same locality, Bonaparte also collected (but did not describe) some isolated theropod re- We follow the stratigraphic interpretations Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 219 expressed by Nullo et al. (2006) in recognizing 2005; Nullo et al., 2006). In sum, the dinosaur- in the study area the following stratigraphic bearing, continental deposits of the Chorrillo succession (from bottom to top): Alta Vista, La Formation exposed at the top of the high pla- Anita, La Irene, Chorrillo, and Calafate forma- teaus of the La Anita and Alta Vista ranges, may tions. Both Alta Vista and La Anita bedrocks be early Maastrichtian in age. Evidence from the form the high cliffs of the homonymous farms. equivalent Dorotea beds supports, however, that The dinosaur-bearing beds of the Chorrillo the lower thirds of the Chorrillo Formation be Formation form continuous outcrops on the high late Campanian, at least (see below). plateaus on the top of these hills (Figure 1). In The Argentine sequence formed by both the Argentina these beds extend to the international continental Chorrillo and the marine Calafate border with Chile, close to the “Hito Baguales formations resembles the sedimentary unit that 2” (Figure 1; Nullo et al., 2006). The top of the in southern Chile is named as Dorotea Formation Chorrillo Formation laterally inter-fingers and (F. Nullo, pers. comm.). As Cecioni (1957) and is overlaid by the marine Calafate Formation Katz (1963) have noted, rock units cropping out (Marensi et al. 2004; Odino Barreto et al., 2018). on both sides of the international border are The rock succession comprehended by La Anita, inseparable from a formational point of view. La Irene and Chorrillo formations conforms an This observation also applies for Chorrillo plus upper Campanian-early Maastrichtian regressi- Calafate (on the Argentine side) and Dorotea (in ve episode, started with the deltaic deposits of Chile), which exhibit almost the same lithological the La Anita Formation, and followed upwards characteristics and fossil content. The Dorotea by braided and meandering fluvial deposits of Formation includes basal and middle sections the La Irene and Chorrillo formations (Arbe & equivalent to Chorrillo, and an upper section res- Hechem, 1984; Macellari et al., 1989; Nullo et al., embling, both lithologically and in fossil content, 2006; Moyano Paz et al., 2018; Tettamanti et al., to the Calafate Formation. 2018). The stratigraphic succession of the Chorrillo Tettamanti et al., (2018) synonymized Cerro Formation is made up by intercalated levels of Fortaleza, La Anita, La Irene, and Chorrillo for- greenish and reddish sandstones, intercalated by mations under the name of “Upper Cretaceous some conglomeratic banks. Important is to say Continental Deposits”. We concur with these that the following description is tentative, re- authors in interpreting these lithologically simi- quiring for more detailed stratigraphic and sedi- lar beds as part of a same diachronic episode of mentological surveys. Immediately above the La Campanian through Maastrichtian continental Anita beds, the base of the Chorrillo Formation sedimentation. However, we prefer to keep the is characterized by green mudstones with frag- original lithostratigraphic names for these units, mentary plant remains. Following upwards there waiting for more paleovertebradological infor- is a bank of conglomerates and coarse sandsto- mation from both Chorrillo and Cerro Fortaleza nes containing abundant fossil wood and badly beds, eventually offering more confident age de- preserved leaves. These stratigraphic levels with terminations for these beds. abundant plant remains are replaced upwards Regarding the age of the Chorrillo Formation, by the already mentioned greenish and reddish it has to be no older than the underlying Early sandstone levels, with an approximate thickness Campanian Alta Vista beds (the age of which of 250m (Nullo et al., 2006), containing dinosaur is based on abundant marine invertebrates; and other vertebrate remains. Such succession is Blasco et al., 1980; Nullo et al., 2006) and the capped by a meter thick sandstone bank, green Maastrichtian La Irene Formation (the age of in color, bearing abundant specimens of tiny bi- which is based on palynological assemblages; valves (approximately 2-3 cm long), including Povilauskas et al., 2008). Moreover, the Chorrillo ostreids, mytilids and pectinids (see below for Formation inter-fingers to the SE with the taxonomic identification). The sequence of gree- shallow marine deposits of the Cerro Cazador nish and reddish sandstones is cyclic and mono- Formation (Macellari, 1988), which yielded the tonous, thus being difficult to recognize discrete associated presence of Eubaculites and Maorites, members. interpreted as early Maastrichtian in age (Nullo We informally separate the Chorrillo beds et al., 2006). The Chorrillo Formation is overlaid into three “levels”, but this arbitrary subdivision by the marine Calafate Formation, considered to pends on future sedimentological studies. The ti- be late Maastrichtian based on dinoflagelate cysts tanosaur bones originally discovered by F. Nullo association (Marenssi et al., 2004; Guler et al., come from the lower third of the formation, but 220 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 remains of titanosaurs of similar size also come MATERIALS AND METHODS from the middle portion of the unit. A thick bank of conglomerates exposes on the base of Study area the upper third of the Chorrillo Formation, and The fossil remains come from different above it repeats again the alternate sequence of spots and stratigraphic levels, within an area greenish and reddish sandstones bearing dino- of approximately 2000 m2 (Figure 1). The fossil saur remains. The upper levels of the Chorrillo spots are the following: Formation yielded abundant remains of diffe- -Nullo site (locality 1): Yielded six titano- rent individuals of a single species of a basal saur bone accumulations, which do not neces- iguanodontian, mixed with several shed teeth of sarily correspond with discrete individuals. a large, indeterminate mosasaur. The sequence Stratigraphically it corresponds to the lower ends with a conglomeratic level (approximately third of the Chorrillo Formation. one-meter-thick), overlaid by a bank (roughly -Titanosaur tibia site (locality 2): This place one meter thick) made up by slender and elon- provided a single, well preserved titanosaur ti- gate bivalves (Gryphaeostrea cf. G. callophyla bia, titanosaur eggshells, sauropod teeth, the- Ihering, 1903 and Cubitostrea cf. C. ameghinoi ropod eggshells, avian coracoid, snake vertebra, Ihering, 1902, indeterminate Mytilidae and and fish teeth. This site yielded the woods descri- Pectinidae; D. Pérez, B.Santelli, and M.Álvarez, bed above. Stratigraphically it corresponds to the pers. comm.). This couple of banks (conglomerate lower third of the Chorrillo Formation. plus bivalves) represents the base of the Calafate -Megaraptorid site (locality 3): This place pro- Formation. vided fragments of a single large, indeterminate For southern Chile, Manriquez et al., (2019) Megaraptoridae, represented by 2 vertebrae, described the stratigraphic sequence of the proximal pubis and rib fragments. Invertebrate Dorotea Formation and its fossil content. At the bioturbations were found in close proximity. base of the formation, they identified leaf impres- Stratigraphically this locality corresponds with sions of a variety of taxa; from the middle section the middle portion of the Chorrillo Formation. (exposed in a fossil spot they name “Saurópodo”) -Puma cave site (locality 4): 50 specimens they described (in addition to plants) titanosaur, of terrestrial molluscs have been collected from ornithischian, and bird bones, turtle and frog mid-levels of the Chorrillo beds, in close proxi- fragments, and mammal and theropod teeth. The mity to mammalian, turtle, snake, ornithopod paper by Manriquez et al. (2019) does not specify and theropod bone remains, and sauropod teeth. the taxonomic referral of the fossils collected, and Six articulated caudal vertebrae of a large titano reference of the completeness of the collected nosaur come from 10 m far from this fossil spot. materials is offered. However, such fossil assem- All these specimens were produced by the same blage from the “Saurópodo Member” looks simi- stratigraphic level, corresponding to the middle lar to the lower and mid-sections of the Chorrillo portion of the Chorrillo Formation. Formation. Interesting is to say that the levels -Ornithopod site (locality 5): Association of of “Saurópodo Member” are comprehended by different sized specimens corresponding to a radiometric datings below (74.9my) and above single, new species of an elasmarian ornithopod, (71.7my), thus strongly suggesting these depo- represented by vertebrae, phalanges, a, and me- sits correspond to the Campanian-Maastrichtian tatarsals. Found in close association with seven boundary (Manriquez et al., 2019). mosasaur teeth. Stratigraphically it corresponds In sum, general aspect of Chorrillo plus to the upper third of the Chorrillo Formation, Calafate beds resembles the sequence of Dorotea roughly 20 meters below the beds with marine beds, suggesting these units represent a same molluscs (interpreted as the base of the Calafate sedimentary sequence. However, precise corre- Formation). lation between these beds requires further stratigraphy survey of the entire region. Besides, Collected material future exploration and study also need to be The collected materials belong to the collec- done to elucidate if the Chorrillo Formation is tion of the Museo Padre Molina, Río Gallegos, equivalent or not with the dinosaur-bearing, Santa Cruz province. Some specimens, coming continental deposits of the Cerro Fortaleza from the same site and stratigraphic levels, were Formation (radimetrically dated as Campanian; collected in 1981 by J.F. Bonaparte and are housed Sickman et al., 2018), exposed north of Argentino at the Vertebrate Paleontology Collection, Museo Lake, on both margins of the La Leona River. Argentino de Ciencias Naturales “Bernardino Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 221

Figure 1. Map showing studied area. Numbers 1 through 5 indicate the localities from which fossil specimens were collected.

Rivadavia” (MACN), Buenos Aires. died using light Microscopy (Olympus BX51). At least 25 measures were taken, and data is given Specimen preparation as the mean and standard deviation, and range Vertebrates were extracted and prepared as (in parenthesis). For the generic classification of is the usual technique in vertebrate paleontology. the studied woods we followed the key for fossil Most bones here described do not need mecha- genera proposed by Philippe & Bamford (2008). nical preparation because they were found free Descriptive terminology used here follows the of sediment in most cases. The bones that were IAWA list of microscopic features for softwood embedded in sedimentary matrix were prepared identification (Baas et al., 2004), with the addi- with mechanical hammers at the Laboratorio tion of terms defined in Philippe and Bamford de Anatomía Comparada y Evolución de los (2008), seriation and contiguity indices propo- Vertebrados preparation lab. sed by Pujana et al. (2016). Pit counting me- The fossil woods were thin-sectioned in thod follows suggestions made by Philippe et al. transverse (TS), longitudinal tangential (TLS) (2013). The palynological samples were treated and longitudinal radial (RLS) sections, and stu- following standard techniques for extraction and 222 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 concentration of palynomorphs (Volkheimer & Referred material: MPM 21517, isolated tooth Melendi, 1976). Observations were made with an (locality 2) (Figure 2 H). Olympus BX-51 microscope while photographs Description: This is a lanceolate and acute were taken with an Olympus DP25 digital came- tooth, with vitreous enamel surface. Under the ra. Coordinates of the illustrated specimens are enamel layer there is a relatively thick layer of given as England Finder coordinates. dentine constituted by vascular canals. At its base, the tooth is not crenulated, indicating the Institutional abbreviations absence of plicidentine. Tooth crown possesses MPM, Paleontological Collection, Museo elongated, narrow peduncles which are constrict- Regional Provincial “Padre Molina”, Río Gallegos, ed below the apex. The apex is formed by a short, Santa Cruz province, Argentina; MACN-Pv, translucent, and flattened acrodin cap with both Paleontological Vertebrate Collection, RN, Río acute mesial and distal carinae. Negro Collection, Museo Argentino de Ciencias Comments: The combination of lanceolate Naturales “Bernardino Rivadavia”, Buenos teeth lacking plicidentine at its base (presence of Aires, Argentina. plicidentine is typical of lepisosteiforms; Cione, 1987; Grande, 2010) and a translucent cap with SYSTEMATIC PALEONTOLOGY mesial and distal carinae is diagnostic of vida- lamiine amiiform fishes (Grande & Bemis, 1998; Vertebrata Cuvier, 1812 Martinelli et al., 2013). In spite of such similari- Teleostei Müller, 1844 ties, the isolated nature of MPM 21517 precludes Genus and species indeterminate a more accurate determination. The fossil record of Mesozoic amiiforms in the Referred material: MPM 21516, three crush- southern Hemisphere is strongly biased (Grande ing tooth crowns (locality 4) (Figure 2E-G). & Bemis, 1998; Martinelli et al., 2013; Brito et Description: Three isolated crushing teeth al., 2017). From the southern cone, only three lo- crowns have been collected. The largest one calities have yielded amiid remains (Bogan et al., is 13mm in diameter. They are subcircular in 2010, 2013), of which only two (i.e., El Anfiteatro contour in occlusal view, with a gently convex and Cerro Tortuga localities, Río Negro province, occlusal surface, and a concave ventral surface. Argentina; Bogan et al., 2010) belong to the Late The tooth bases show concentric growth lines on Cretaceous. Because of their fragmentary nature, the ventral side. these remains from Río Negro have indetermi- Comments: Crushing teeth similar to those nate affinities below family level. Present report, described here resemble pharyngeal teeth of if correctly identified, constitutes an important semionotiforms, sparids, sciaenoids, and bas- addition to the meager record of the clade for the al percoids, among others (e.g., Cione, 1987). continent, and may represents the southernmost Similar teeth were previously reported from record for Amiiformes. the Maastrichtian Loncoche (González Riga, 1999; Previtera & González-Riga, 2008), Los Anura Fischer von Waldheim, 1813 Alamitos (Cione, 1987), and Allen (Martinelli & Genus and species indeterminate Forasiepi, 2004) formations. The semionotiform genus Lepidotes, was repeatedly reported from Referred material: MPM 21518, isolated tibio- Argentina, and South America (Arratia & Cione, fibula (locality 4) (Figure 2D). 1996). These semionotiforms bear crushing vom- Description: The distal halves of a tibia and a erine teeth, with short roots and exceptionally fibula have been collected. These bones are sepa- broad and rounded crowns, thus differing from rated by a narrow and relatively shallow longi- the low crowns with concave roots here described tudinal groove. The distal end of each bone is (see Jain, 1985). Information at hand forbids re- subcircular in cross-section. Based on preserved ferral of crushing teeth from the Chorrillo beds fragments, the tibiofibula may have been mea- to any particular teleostean clade. sured 25 mm when complete. Comments: The presence of an elongate and Amiiformes Hay, 1929 fused tibiofibula is a feature diagnostic of Amiidae Bonaparte, 1838 anurans (Jenkins & Shubin, 1998). However, cf. Vidalamiinae Grande & Bemis, 1998 the morphology of the distal half of tibiofibula Genus and species indeterminate lacks diagnostic features to offer a more precise allocation within the clade. Present specimen, to- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 223

Figure 2. Fishes, anurans, and turtles. (A-C), Indeterminate Calyptocephalellidae, MPM 21519, distal end of right humerus with eroded distal margin in anterior (A), posterior (B), and medial (C) views. (D) Indeterminate anuran, MPM 21518, incomplete tibiofibula. (E-G) Indeterminate Teleostei, MPM 21516, tooth crown in lateral (E), occlusal (F), ventral (G) views. (H) cf. Vidalamiinae indet., MPM 21517, isolated tooth in side view. (I-K) Indeterminate Chelidae, carapace fragments. (I) Plastral fragment. (J) Incomplete costal plate. (K) Middle peripheral plate. Abbreviations: ab, articular ball; ue, ulnar epicondyle; vf, ventral fossa. Scale bar: 5 mm. gether with remains described below, represents The distal articular ball, as well as both epicon- the southernmost records for a fossil frog from dyles, are distally eroded. The humeral shaft is the Late Mesozoic. subtriangular in cross-section, with a relatively sharp crest running along its medial margin, Calyptocephalellidae Reig, 1960 which probably ended in a well-developed deltoid Genus and species indeterminate crest as it occurs in living anurans. The distal end of humerus bears a ball-shaped and ventrally Referred material: MPM 21519, distal end of projected articular condyle, bordered by similar- right humerus with eroded distal margin (local- sized, flange-like, and transversely expanded ul- ity 4) (Figure 2A-C). nar and radial epicondyles. The ulnar epicondyle Description: The distal end of the humerus (1.5 shows a flattened anterior surface that is sepa- mm in maximum transverse width), probably rated from the articular ball by a shallow groove. belongs to an adult individual, as suggested by The radial epicondyle is broader than the ulnar degree ossification and well-finished structures. epicondyle and its anterior surface is concave 224 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 and crescent-shaped in anterior view. The ven- Testudines Linnaeus, 1758 tral fossa is not clearly outlined. Chelidae Gray, 1825 Comments: MPM 21519 exhibits the following Genus and species indeterminate unique combination of features, only observed in the extant genus Calyptocephalella (Báez, Referred material: Chelid materials include 1987; Otero et al., 2014): 1) distal articular ball MPM 21520 (consisting in two peripheral and one large and placed at the center of the distal end; costal plates; locality 2), MPM 21521 (consisting 2) prominent, subequal-sized and flange-like ra- of an anterior peripheral, one mid-peripheral, dial and ulnar epicondyles, resulting in a roughly three posterior peripherals, fragment of plastral symmetrical distal end; 3) humeral shaft distally bridge, three incomplete costal plates, and distal unexpanded; 4) poorly defined ventral fossa. The end of radius; locality 4) (Figure 2 I-K). Based on locality and size differences, specimens belong to incomplete nature of MPM 21519 does not allow at least two different individuals. referral the specimen beyond the family level. Description: In both localities, available speci- The Mesozoic record of anurans in South mens were found in an area of few square me- America is patchy. Basal anurans of the clade ters. However, the different degree of preserva- Pipoidea have been recorded from the Early tion and different size of the specimens indicate Cretaceous of Brazil (Carvalho et al., 2019) the presence of different individuals. The plates and from mid-to Late Cretaceous localities of resemble each other in being relatively thin and Brazil and Argentina (see Báez, 2000). The re- in having a similar ornamentation, suggesting cord of neobatrachians is also restrictive, be- that all belong to the same taxon. Largest avail- ing currently represented by nearly complete able plates suggest a maximum carapace length specimens from the Early and Late Cretaceous of 40cm, approximately. Peripheral plates are of Brazil (e.g., Báez & Perí, 1989; Báez et al., relatively small and dorsoventrally thin. Mid- 2009, 2012), and disarticulated specimens from peripherals show relatively small and shallow Campanian-Maastrichtian localities in Chubut costal fossae. There is no suture for the contact and Río Negro provinces of Argentina (i.e., Báez, with costal plates. Plate decoration consists of 1987; Martinelli & Forasiepi, 2004; Muzzopappa small and well-defined polygonal figures, sepa- & Baez, 2009; Agnolin, 2012). rated by anastomosed sulci. In some sections the Most neobatrachians are represented by polygones became smaller, conferring the plate highly fragmentary remains assigned to the non- a rugose texture. Preserved costal plates are in- monophyletic clade “Leptodactylidae”, and most completely preserved. They show ornamentation of them have been assigned (or related with) the similar to that of peripheral plates, but polygones living Helmeted toad Calyptocephalella (Báez, are more elongate. 1987; de la Fuente et al., 2007; Agnolin, 2012), Comments: In spite of the incomplete nature, the only extant member of Calyptocephalellidae. available specimens can be referred with confi- This genus is currently restricted to a single dence to Chelidae, based on the combined presence species, Calyptocephalella gayi, being ende- of free peripheral plates lacking firm contact with the costal ones, and external surface decoration mic from the temperate region of south-central consisting of dichotomizing sulci and polygones Chile (Otero et al., 2014). However, during the (Broin & De la Fuente, 1993; Lapparent de Broin Mesozoic and Cenozoic, calyptocephalellids & De la Fuente, 2001; Lapparent de Broin, 2003). were geographically widespread, with possible Plates here described are indistinguishable from reports from Late Cretaceous of India, Africa those reported by Broin (1987) under the name and Madagascar (see Agnolin, 2012). In South of “Chelidae indet. Nº 3”, and by Gasparini & de America, Calyptocephalellids are recorded from la Fuente (2000) as “Chelidae indet. Nº5”, from Late Cretaceous to Miocene beds, in several loca- the Maastrichtian Los Alamitos and La Colonia lities along the Patagonia of Argentina and Chile formations (Río Negro and Chubut provinces, re- (Agnolin, 2012; Otero et al., 2014). Because of spectively). its great antiquity, calyptocephalellids were considered as being part of the “ancient assembla- Squamata Oppel, 1811 ge” or “Andean-Antarctic” batrachofaunas that Serpentes Linnaeus, 1758 inhabited the southern end of South America Genus and species indeterminate during the Mesozoic, up to Miocene times (Vuilleumier, 1968; Cei, 1980; see Agnolin, 2012). Referred material: MPM 21522, partial mid- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 225

Figure 3. Serpentes indet. (MPM 21522) partial mid-posterior vertebra in anterior (B), posterior (B), lateral (C), ventral (D) and dorsal (E) views. Abbreviations: ct, cotyle; izr, interzygapophiseal ridge; hk, haemal keel; lf, lateral foramen; prz, prezygapophysis; pk, pseudo keel; scf, subcentral foramen; scr, subcentral ridge; sy, synapophisis; vf, ventral foramen. Scale bar: 5 mm. posterior vertebra (locality 4) (Figure 3). ted, about 40-50° from the sagittal plane. At the Description: MPM 21522 is a small vertebra, base of the facet there is a well-defined and small 7mm long, consisting of centrum, left prezygopo- fossa. The prezygapophiseal accessory process is physis, and ventral region of the neural canal. absent and the interzygapophyseal rim is sha- As in most snakes, it shows an anteroventrally llow. facing articular cotyle, subcentral ridges, grooves The posterior articular condyle is below the and foramina and synapophyses. This element level of paradiapophysis. The neural canal seems is identified as a precloacal vertebra because of taller than in anterior view, and is sub-triangular the absence of pleurapophyses, lymphapophyses, in contour. A small portion of the posterodorsal and hemapophyses (LaDuke, 1991). It shares a surface of the vertebral centrum is preserved, combination of characters present in middle and and bears no medial keel. posterior precloacals (wide and shallow haemal The centrum has a parallelogram-shaped keel, elongated vertebral centrum, and synapo- profile in lateral view, with the posterior region physes with a strong lateral component ventrally in a lower level than the anterior region. The pa- located). radiaphophysis is massively built, with no clear In anterior view the articular cotyle is sub- differentiation from the both dia- and parapo- circular in contour. The neural canal was dorso- physes. The paradiapophysis is sub-rectangular ventrally low and with a subtriangular contour in in contour and is postero-ventrolaterally faced, anterior view. There are two well-defined paraco- with a strong lateral component. Posterior to it, tylar foramina, located close and at mid height at mid-length of the vertebral length, there is a of the cotyle. The foramina are situated within lateral foramen. The diapophyseal region is wi- shallow paracotylar fossae, adjacent to the left der and more posteriorly placed than the parapo- side of the cotyle. The prezygapophysis has the physeal region. Posterior to the paradiapophysis articular facet inclined about 20° above the hori- there is a moderately developed subcentral ridge zontal plane, and barely surpass the lateral mar- that laterally surrounds the subcentral fossa. gin of the paradiapophysis (=synapophysis). The The haemal keel is low and ventrally concave, ventral margin of the synapophysis is lower than and the subcentral foramina are not visible due the ventral margin of the articular cotyle. the great depth of the subcentral fossa. In dorsal view, the prezygapophyseal facet is In ventral view, the vertebral centrum is suboval-shaped, with its main axis obliquely orien- triangular shaped, its lateral margins converging 226 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 posteriorly. The haemal keel is transversely wide MPM 21522, madtsoiids, and Najash (Rage & and is hourglass shaped, with the anterior region Wagner, 1999; Albino, 2000; Scanlon, 2006; La transversely wider than the posterior half. The Duke et al., 2010; Mohabey et al., 2011; Zaher et subcentral fossae are well developed and latera- al., 2009). lly delimit the haemal keel. On the ventral surfa- The haemal keel present in MPM 21522 is ce of the haemal keel there are present two fora- low and wide, similar to the condition of poste- mina. Between them there is a pseudo-keel that rior precloacal vertebrae in most madtsoiids and extends all the length of the haemal keel. This anilioiids. It is flanked by two small subcentral pseudo-keel is poorly-developed, but distinctive. foramina, as occurs in posterior precloacal verte- Comments: Albino (Albino, 1986, 1987, 1994; brae of Dinilysia (MACN-RN 116). Furthermore, see also Martinelli & Forasiepi, 2004) described MPM 21522 differs from all known madtsoiids several serpent taxa based on isolated vertebrae and other fossil snakes because of the presence from the Latest Cretaceous (Maastrichtian) of a pseudo-keel, flanked by two foramina loca- Los Alamitos Formation, Rio Negro province. ted on slits, on the ventral surface of the haemal These specimens belong to basal snakes of the keel. A somewhat similar condition is found in “madtsoiid” grade. More recently, Gómez et al. Colombophis and in the supposed tropidophiid (2008) described from coeval beds the “anilioid” Dunnophis (Rage, 1984), where the haemal keel Australophis anilioides from northern Patagonia. is wide and flat and two subcentral foramina In spite of this relative rich record, they restrict are present on the ventral surface of the keel; to the NW corner of Patagonia. Thus, present however, there is no presence of a pseudo-keel report extends paleogeographic distribution of (Rage, 1984; Hsiou et al., 2010). Rage (2013) re- these reptiles up to the southern region of South ported for Paraungaliophis a ventral longitudi- America. nal keel producing a shallow sagittal ridge, but In spite of being incomplete, the specimen this keel differs from MPM 21522 in being sharp MPM 21522 shows a combination of characters and restricted to the posterior end of the keel. unique among snakes. Presence of a paracotylar Another distinguishable feature of MPM 21522 foramen is shared with madtsoiids, Dinilysia, is that the foramina present on the ventral sur- several specimens of Colombophis (Simpson, face are placed in a slit, similar to the anilioiid 1933; Albino, 1986, 1994, 2000; Rage & Wagner, Hoffstetterella, where the subcentral fossa of the 1999; Scanlon, 2006), boiids (Albino, 2010), and anterior and mid precloacal vertebra are located it is variably present among anilioids (Hsiou et within slits (Rage, 1998). al., 2019). Paracotylar foramina are absent in The synapophyses of MPM 21522 is well de- Najash, Menarana, and most anilioiids (Rage, veloped and the diapophyseal and parapophyseal 1984, 1998; Gómez et al., 2008; Zaher et al., 2009; regions are plesiomorphically poorly differentia- La Duke et al., 2010). As occurs in the madts- ted. This condition is also present in Alamitophis, oiids Madtsoia, Adinophis, and Alamitophis, Colombophis, Anilius and Coniophis (Rage, 1984; MPM 21522 presents two paracotylar foramina Albino, 1994; Hsiou et al., 2010). On the contrary, (Simpson, 1933; Albino, 1994; La Duke et al., the synapophyses in most of the madtsoiids and 2010; Pritchard et al., 2014). the anilioiid Hoffstetterella are well-defined into Resembling Dinilysia, and the madtsoiids para- and diapophyseal regions (Simpson, 1933; Alamitophis (Albino, 1986; MACN-RN 27,38), Rage, 1998; Zaher et al., 2009; La Duke et al., Nidophis, Menarana and Madtsoia pisduren- 2010; Mohabey et al., 2011; Vasile et al., 2013; sis (La Duke et al., 2010; Mohabey et al., 2011; Pritchard et al., 2014; Rio & Mannion, 2017), a Vasile et al., 2013), the prezygapophysis of MPM derived condition found in all alethinophidian 21522 extends slightly beyond the lateral mar- snakes (Rieppel et al., 2002; Apesteguía & Zaher, gin of the synapophysis. In Colombophis and 2006). anilioiids (Rage, 1984, 1998; Hsiou et al., 2010) As in Dinilysia, Najash, and the madts- the prezygapophyses extend much further than oiids Madtsoia madagascarensis, Nidophis and the synapophisys, whereas the reverse condi- Menarana (Zaher et al., 2009; La Duke et al., tion applies for Najash, Adinophis, Gigantophis, 2010; Vasile, 2013), the subcentral ridges and Nanowana, Patagoniophis and several Madtsoia fossae in MPM 21522 are well developed. This species (Scanlon, 1997; Rage, 1998; Zaher et contrast with some madtsoiids (e.g., Madtsoia, al., 2009; La Duke et al., 2010; Pritchard et al., Gigantophis, Adinophis) and most anilioids 2014). The absence of a prezygapophiseal acces- (Simpson, 1933; Rage, 1998; Gómez et al., 2008; sory process is a plesiomorphic feature shared by Mohabey et al., 2011; Pritchard et al., 2014; Rio Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 227

& Mannion, 2017; Hsiou et al., 2010) which have ture of MPM 21523, comparisons are limited. poorly defined subcentral ridges and fossae. However, its size and general morphology closely In lateral view, a lateral foramen can be obser- resembles Rionegrophis madtsoioides (Albino, ved in most madtsoiids and anilioiids (Simpson, 1986). MPM 21523 shows a well-developed and 1933; Rage, 1998; Albino, 2000; Zaher et al., narrow haemal keel, similar to some madts- 2009; La Duke et al., 2010; Vasile et al., 2013; oiids and the anilioiid Hoffstetterella brasiliensis Pritchard et al., 2014). (Scanlon, 1997; Rage, 1998; Vasile et al. 2013), The interzygapophyseal constriction in MPM whereas Dinilysia and Najash show a notably 21522 is shallow as in Dinilysia, Madtosoia pis- wider haemal keel (Zaher et al. 2009; MACN-RN durensis and most anilioiids (Rage, 1998; Gómez 2019). Further, the synapophysis of MPM 21523 et al., 2008; Mohabet et al., 2011), which differ resembles most madtsoiids synapophyses becau- from Najash, Colombophis and most madtsoiids, se the diapophysis is wider than the parapophy- where it is notably deep (Simpson, 1933; Rage, sis. 1998; Zaher et al., 2009; La Duke et al., 2010; Presence of a well-developed keel present Vasile et al., 2013; Rio & Mannion, 2017; Hsiou on the dorsal surface of the centrum is shared et al., 2010). with Alamitophis and Rionegrophis madtsoioi- In spite of its distinctiveness, MPM 21522 is des (Albino, 1986; MACN-RN 27, 32). However, here regarded as an indeterminate Serpentes be- MPM 21523 differs from Alamitophis and resem- cause of its fragmentary condition. bles Rionegrophis in the presence of a subtriangular-shaped centrum when viewed dorsally or cf. Rionegrophis madtsoioides Albino, ventrally. 1986 In gross-morphology and main features MPM 21523 resembles Rionegrophis madtsoioides. Referred materials: MPM 21523, partial ver- However, its fragmentary nature precludes a tebra (locality 2) (Figure 4). clear determination, and thus is identified here Description: Description: MPM 21523 is an in- as cf. Rionegrophis madtsoioides. complete vertebra, approximately 14 mm long as preserved. As in most snakes, the cotyle faces an- Squamata Oppel, 1811 teroventrally, the subcentral ridges and grooves Mosasauridae Gervais, 1852 are well-defined, and synapophysis are present. Genus and species indeterminate The vertebra corresponds to the precloacal region because of the absence of pleurapophyses, Referred material. MPM 21524, seven isolated lymphapophyses, and hemapophyses (LaDuke, teeth (locality 5) (Figure 5). 1991). Due to the tall and narrow haemal keel, Description. Seven mosasaur teeth have been and the absence of a hypoapophysis, this element collected from the upper levels of the Chorrillo corresponds to the mid-precloacal region. Formation, all of them coming from a single fos- The cotyle is notably deep and dorsolaterally sil spot which also yielded ornithopod remains flanked by a deep paracotylar foramen. The distal (described below). We assume these teeth, found end of the prezygapophysis is missing, thus the in close association, belong to a single mosasaur presence of a prezygapophyseal process remains individual. Available teeth share the following unknown. In dorsal view, the prezygapophysis combination of characters supporting their refer- shows a subtriangular contour, its major axis ral as to Mosasauridae (Hornung & Reich, 2015): forming an angle about 45° with the sagittal pla- 1) crowns bearing distal and mesial carinae, 2) ne. The paradiaphophysis is widely exposed; the different level of enamel striation, 3) crown po- diapophysis region of the synapophysis is more lygonal-shaped in cross-section, and 4) crown tip developed and more posteriorly located than the posteriorly curved. parapophyseal region of the synapophysis. Available teeth can be sorted into two di- The condyle is prominent, sub-circular sha- fferent types, in accordance with size, enamel ped in posterior view, and slightly dorsally poin- ornamentation and morphology. One type is re- ted. The ventral surface of centrum exhibits on presented by fragments of three large teeth, the its posteriormost region an haemal keel, flanked best preserved of which has an almost complete by two small depressions, probably representing crown (Figure 5A-C), being 44 mm in total height the posterior portion of the subcentral grooves. and 20 mm in diameter at its base. The basal Subcentral ridges are present. quarter of these teeth is devoid of enamel, stria- Comments. Due to the fragmentary na- tions, and carinae, indicating proximity to bone 228 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 4. cf. Rionegrophis madtsoiids (MPM 21523), one partial vertebrae in dorsal (A, C), anterior (B), lateral (D), posterior (E) and ventral (F) views. Abbreviations: ct, cotyle; cn, condyle; dk, dorsal keel; pcf, paracotylar foramina; prz, prezygapophysis; scr, subcentral ridge; sy, synapophisis; vk, ventral keel. Scale bar: 5 mm. attachment (Figure 5). The crowns are conical- secondary striae. Labially, the crowns exhibit shaped, being only slightly distally curved in side three main convex prism faces (sensu Hornung view. Tooth crowns lack striations on their api- & Reich, 2015), which are absent on the lingual cal quarter, but show a gently convex wear facet. surface. Crown bases are elliptical in cross-section, with The second tooth type is represented by an the labial side strongly convex and lingual side almost complete tooth crown (Figure 5D,E). It is slightly more flattened than the opposite side. small sized (total height 15mm, basal diameter Mesial and distal carinae are sharp and devoid 10mm), subtriangular-shaped in side view, and of serrations, being the distal carina stronger elliptical in cross-section. Both mesial and distal than the mesial one. Applying the terminology margins are slightly convex. The labial side of the for enamel ornamentation used by Hornung & crown is smooth and devoid of ornamentation, Reich (2015) these crowns have primary and se- whereas the lingual side bears fine basal striae. condary striae with no ramifications, with some The base of this tooth is devoid of enamel. of the primary striae converging adapically with Comments. The Campanian-Maastrichtian fos- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 229

Figure 5. Mosasauridae indet. (MPM 21524). Tooth types 1 (A-C) and 2 (D-E) in mesial (A), distal (B), basal (C, E), and lingual views. Abbreviations: e1, primary striation; e2, secondary striation; ca, carina; wf, wear facet. Scale bars: 10 mm. sil record of mosasaurs described for southern Teeth of Mosasaurus aff. M. hoffmani from Patagonia and Antarctic Peninsula includes re- the Late Cretaceous of Río Negro province mains referred as to mosasaurines, halisaurines, (Fernández et al., 2008) differ from those re- tylosaurines, and plioplatecarpines (Ameghino, ported here in having lingual surface wider, and 1893; Gasparini & Del Valle, 1981; Martin et al., enamel surface smooth. Teeth of “Liodon argen- 2002; Otero et al., 2017). Most of them are based tinus” (Ameghino, 1893), from the Cenomanian upon shed teeth and isolated vertebrae, and have Mata Amarilla Formation, Pari Aike, Santa Cruz been considered of dubious affinities by Novas province, share with those collected in Chorrillo et al. (2002). Currently, only two taxa have been beds in bearing both anterior and posterior cari- confidently identified on the basis of cranial, den- nae, but differ in being more laterally compres- tal and postcranial remains: Taniwhasaurus ant- sed, with stronger carinae and serration in the arcticus (Novas et al., 2002; Fernandez & Martin, anterior carina. 2007) and Kaikaifilu hervei (Otero et al., 2017), In sum, MPM 21523 could not be referred both of them belonging to Tylosaurinae. Teeth of to any of the previously listed Patagonian and Taniwhasaurus antarcticus (Novas et al., 2002) Antarctic mosasaur taxa, and thus they are con- differ from those reported here in having slen- sidered as Mosasauridae indet. derer and posterolingually curved crowns, nar- Some authors (e.g., Lindgren, 2005; rower striae, and feebly developed unserrated Fernández, 2008; Lindgren & Siverson, 2002, carinae. Besides, teeth here described resemble 2004) have conferred a great taxonomic value the large Antarctic mosasaur Kaikaifilu on their to mosasaur shed teeth, taking them as enough large size, overall shape and cross section of the evidence for the presence of a particular mosa- crown. However, teeth of Kaikaifilu bear only a saur family, or even mosasaur genera. However, mesial carina and are more finely striated. we agree with Caldwell and Diedrich (2005) in Several tooth remains from the Late that the taxonomic importance of dentition has Cretaceous of Antarctica have been reported as been overestimated. For example, the presence belonging to indeterminate mosasaurines (e.g., of strong facets has been considered diagnostic Martin, 2006; Martin and Crame, 2006). These for mosasaurines, instead the presence of deep teeth differ from those here described in being striations was interpreted distinctive for plio- more labiolingually compressed, with enamel platecarpines (e.g., Martin & Crame, 2006). surface smooth, and prism faces greater and However, as indicated by specimens from the flatter. Besides, isolated teeth from Antarctica Chorrillo beds, these characters are vague and referred as to tylosaurines and platecarpines are present in many non-related taxa. It has been (e.g., Martin, 2006; Martin & Crame, 2006) con- shown that tooth morphology varies along den- sist on poorly preserved materials, precluding tal series of a single individual (see for example detailed comparisons with present specimens. Konishi et al., 2012), and some taxa display up 230 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 to four distinct tooth types along the jaws (e.g., ticulation between the first and second sacral Schulp et al., 2004; Thevenin, 1896; Otero et al., vertebrae in ventral view; 3) tibia with strongly 2017). Further, ontogenetic changes have been proximally projected and thickened cnemial also recognized in mosasaur literature (Lindgren crest, 4) lateral condyle of tibia with an addi- & Siverson, 2004). In sum, we consider that the tional anterolateral process; and 5) metatarsal II taxonomic value of isolated mosasaur teeth have with a proximally displaced collateral ligament to be taken with caution. pit on its lateral surface. Regarding the possible paleoenvironmental The preserved elements of the hindlimb, significance of mosasaur teeth, it is outstanding especially metatarsals are more robust than their close taphonomic association with ornitho- other elasmarians of comparable size, such as pod bones. The presence of mosasaur remains Morrosaurus and Talenkauen. is suggestive of marine influence during the en- Horizon and Locality. Collected specimens tombing of basal iguanodontians. This resembles come from locality 5. the El Puesto “member” of the upper third of the Etymology. Isasicursor honors the skilled Dorotea Formation, which yielded hadrosaurs technician Marcelo P. Isasi (Conicet - MACN), remains (Jujihara et al., 2014; Soto Acuña et al., who discovered the remains of this new iguano- 2014), immediately below marine levels with dontian, and cursor, meaning runner in Latin; aquatic fossils (including mosasaurs; Soto Acuña santacrucensis, in regards to Santa Cruz, the et al., 2016). Argentine province where fossils were found.

Dinosauria Owen, 1842 Description Ornithischia Seeley, 1887 Cervical vertebra (Figure 8). The only recov- Ornithopoda Marsh, 1881 ered cervical vertebra of Isasicursor is represent- Euiguanodontia Coria & Salgado, 1996 ed by the anterior third of a centrum. In anterior Elasmaria Calvo, Porfiri & Novas, 2007 view the articular surface is concave and roughly hexagonal in contour. The parapophyses are rep- Isasicursor santacrucensis gen. et sp. nov. resented by poorly developed processes, subtri- Figure 6 angular in contour when viewed from the side. Ventral to the parapophyses the lateral surfaces Holotype. MPM 21525, proximal end of left tibia of centrum are transversely concave. In ven- (Figure 7). The specimen comes from locality 5. tral view, there is a sharp ventral longitudinal Paratypes: MPM 21526, incomplete cervical keel, a condition considered synapomorphic for centrum; MPM 21527, two dorsal vertebrae; Elasmaria (Rozadilla et al., 2019). MPM 21528, sacrum lacking sacral 3rd; MPM Dorsal vertebrae (Figure 8). Two incomplete 21529, 30 caudal vertebrae; MPM 21530, proxi- dorsal vertebrae are preserved. The centra are mal end of right scapula ; MPM 21531, distal laterally compressed, conferring an hourglass half of left humerus; MPM 21532, iliac process contour in ventral view. In lateral view, the ven- of left pubis; MPM 21533, set of juvenile speci- tral margin of the centra possesses ventral but- mens represented by proximal end of right femur tresses near the anterior and posterior articular , three proximal end of left femora, three distal surfaces, with a concave margin between them. end of left femora, and two fragments of femur The anterior and posterior articular surfaces are mid-shaft; MPM 21534, distal end of tibia; MPM slightly concave and oval in contour. They are 21535, proximal and distal end of metatarsal II; dorsoventrally taller than transversely wide, in- MPM 21536, distal end of left metatarsal III; dicating these centrae correspond to the mid-dor- MPM 21537, proximal and distal ends of meta- sal series. The ventral surface bears a stout ven- tarsal IV; MPM 21538, nearly complete meta- tral keel, as occurs in most basal ornithopods in- tarsal IV of a juvenile individual; MPM 21539, cluding elasmarians (i.e., Coria & Salgado, 1996; pedal phalanges I-1, II-1, IV-2/IV-3; MPM 21540, Martínez, 1998; Coria & Calvo, 2002; Novas et six pedal ungual phalanges; MPM 21541, pedal al., 2004; Calvo et al., 2007; Coria et al., 2013; phalanges II-2 and III-2 of juvenile individuals. Ibiricu et al., 2014; 2019; Cruzado-Caballero et As for the holotype, all the referred specimens al., 2019; Rozadilla et al., 2019). Some vascular come from locality 5. foramina are present on the lateral and ventral Diagnosis. Medium-sized elasmarian ornitho- surfaces of the centra. pod having the following autapomorphies: 1) Sacral vertebrae (Figure 9). The sa- ventrally arched sacrum; 2) peg-and-socket ar- crum is represented by six disarticulated Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 231

Figure 6. Isasicursor santacrucensis gen. et sp. nov. Skeletal reconstruction and body shape, indicating the discovered bones in white. centra,corresponding to sacrals 1,2 and 4, 5 and end of the centrum bears sacral rib facets, which 6. They lack signs of fusion and pneumatization, expand laterally resulting in the transversely and the intervertebral attachment surfaces are widest portion of the bone. The sacral rib facet ornamented by radiating grooves. is anteroposteriorly short, with a rugose attach- The sacrum is relatively stout, with ventral ment surface. The ventral surface of centrum margin is strongly arched in side view, a condi- has a smooth longitudinal keel, which projects tion absent in other known elasmarians. The first anteriorly into a peg-like process that fits into sacral is box-shaped and is the transversely wider the socket present in the posterior surface of the element of the series. In ventral view, its anterior first sacral. On the sides of this ventral keel there margin is notably transversely wide and presents are subparallel and shallow longitudinal grooves. large, fan-like transverse processes that bear ar- The anterior articular surface of the centrum is ticulation facets for the sacral ribs. This strong suboval in contour, with the main axis trans- lateral projection is shared with Jeholosaurus versely oriented. The posterior articular surface and Anabisetia (Cambiaso, 2007; Han et al., is suboval in contour, being slightly transversely 2012), whereas in Macrogryphosaurus these pro- wider than the anterior half of centrum. jections are feebly developed and in Sektensaurus The third sacral is not preserved. The fourth are totally absent (Ibiricu et al., 2019; Rozadilla sacral is box-shaped and its lateral surface bears et al., 2019). The articular surface for ribs is oval laterally projected processes for the attachment in contour and bears a rugous surface, being dor- with the sacral ribs on its anterior and posterior solaterally facing. The anterior articular surface ends. The anterior attachment for the sacral rib of the centrum is kidney-shaped, dorsoventrally is more dorsally located and anteroposteriorly low and transversely wide. The posterior sur- elongated than the posterior one. These surfaces face has a dorsoventrally oriented groove that are concave and rugose. The ventral surface of ends in a socket-like pit on its ventral margin. centrum shows a shallow median longitudinal This pit articulates with a process located on groove. A low median ridge exists near its ante- the anteroventral surface of the second sacral, rior end. The anterior articular surface of cen- resulting in a peg-and socket articulation. In trum is rugose and sub-quadrangular in contour, other elasmarians, such as Gasparinisaura and instead the posterior articular surface is hexag- Sektensaurus the contact between both elements onal-shaped and transversely wider than the an- is nearly flat (Ibiricu et al., 2019; Rozadilla et al., terior one. 2019). On the ventral surface, this sacral has a The fifth sacral vertebra is box-shaped, with shallow ventral keel located at the bottom of a a trapezoidal outline in ventral view, its anterior wide and shallow longitudinal groove. Some nu- end transversely wider than its posterior one. tritious foramina occur on the ventral and lat- The floor of the neural canal is narrow and bears eral surfaces of the centrum. an oval pit at mid-length. Sacral rib facets are an- The second sacral centrum is box-shaped and teroposteriorly elongate and located at the ante- transversely compressed, which results in an rior half of the bone. These articulation surfaces hourglass outline in ventral view. The posterior are suboval in contour and show strong rugosi- 232 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 7. Isasicursor santacrucensis gen. et sp. nov. Femur (MPM 21533a) in (A) anterior, (B) posterior, (C) lateral, (D) medial, (E) proximal and (F) distal views. Tibia (MPM 21525a) in (G) lateral, (H) medial, (I) anterior, (J) posterior, (K) proximal and (L) distal views. Abbreviations: cc, cnemial crest; fib, fibular facet; ff, flexor fossa; fh, femoral head; gt, greater trochanter; itg, intertrochanteric groove; lc, lateral condyle; lp, lateral process; mc, medial condyle. Scale bar: 10 cm. ties on its attachment surface. Posterior and dor- posterior surface of the preceding vertebra. The sal to the sacral rib facets, the centrum becomes posterior articular surface is sub-quadrangular transversely narrower. The ventral surface of in contour, dorsoventrally high and transversely centrum bears a shallow and wide longitudinal narrower than the anterior articular surface. groove, with a low and smooth ridge restricted The sixth sacral vertebra is represented by a to its anterior margin. The anterior articular weathered centrum. The centrum is box-shaped, surface is suboval in contour, dorsoventrally low with a wide and shallow longitudinal ventral and transversely wide. Its dorsal edge has an an- groove. Few nutritious foramina exist on its lateral terior process that fits into the concavity of the and ventral surfaces. The anterior articular sur- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 233

Figure 8. Isasicursor santacrucensis gen. et sp. nov. Selected vertebral elements. Cervical vertebra (MPM 21526) in (A) anterior, (B) ventral and (C) lateral. Dorsal Vertebra (MPM 21527) in (D) lateral, (E) anterior, (F) posterior and (G) ventral views. Proximal caudal vertebra (MPM 21529) in (H) lateral, (I) anterior, (J) dorsal and (K) ventral views. Middle caudal vertebra (MPM 21529) in (L) lateral, (M) ventral and (N) anterior views. Posterior caudal vertebra (MPM 21529) in (O) lateral, (P) ventral and (Q) anterior views. Abbreviations: di, diapophysis; hf, haemal facet; lk, lateral keel; nc, neural canal; ns, neural suture; vg, ventral groove; vk, ventral keel. Scale bar: 5 cm. face is sub-rectangular in contour. There is a small Caudal vertebrae (Figure 8). Thirty caudal prominence at the lateral margin that contacts a vertebrae, corresponding to different individu- shallow concavity present at the posterior articu- als, have been recovered. These vertebrae belong to the anterior, median and posterior portions lar surface of the preceding vertebra, resulting in of the tail. Anterior caudal vertebrae are robust a shallow peg and socket articulation. The pos- and slightly amphicoelous. The neural arches terior articular surface is subcircular in contour. preserve the base of the diapophyses, which is 234 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 suboval in cross-section. The centra are dors- 2002; Cruzado-Caballero et al., 2019; Rozadilla et oventrally taller than anteroposteriorly long; al., 2019). Near the coracoidal suture the medial they are laterally concave, resulting in a spool- surface of the scapula is covered by numerous shaped profile in ventral view. In lateral view, the ligament scars. The coracoidal articular facet is ventral margin of the centra shows an extensive sub-rhomboidal in outline and strongly rugose. haemal facet, which is sub-triangular in contour Humerus (Figure 10). The left humerus is rep- and strongly anteroventrally oriented. The ven- resented by isolated and incomplete shaft and tral surface of the centra bears a deep longitu- distal end. The shaft is laterally bowed, as sy- dinal groove. Shallow longitudinal striations are napomorphic for Elasmaria (e.g., Anabisetia, present near both anterior and posterior articu- Notohypsilophodon, Talenkauen, Trinisaura, lar surfaces. Sektensaurus, Mahuidacursor; Martínez, 1998; Mid-caudals are represented by isolated cen- Coria & Calvo, 2002; Novas et al., 2004; Coria tra. These are slightly amphicoelous, and dors- et al., 2013; Ibiricu et al., 2014; 2019; Cruzado- oventrally lower and anteroposteriorly longer Caballero, 2019; Rozadilla et al., 2019). The del- than in anterior caudals. The lateral surface topectoral crest is reduced and represented by a shows lateral longitudinal ridges, which become low ridge, its lateral surface crossed by longitudi- sharper towards the distal end of the tail. In nal muscle scars, as diagnostic for Elasmaria (e.g., ventral view, the centra are hourglass-shaped Anabisetia , Notohypsilophodon, Talenkauen, and show a ventral longitudinal groove, which Trinisaura, Sektensaurus, Mahuidacursor; becomes deeper towards the distal end of the Martínez, 1998; Coria & Calvo, 2002; Novas et tail. The haemal facet is relatively smaller than al., 2004; Coria et al., 2013; Ibiricu et al., 2014; in anterior caudals. The anterior and posterior 2019; Cruzado-Caballero, 2019; Rozadilla et al., articular surfaces are subcircular in contour and 2019), in contrast with the well-developed del- sub-equal in size and shape. topectoral crest present in most ornithopods, Vertebrae of the distal section of the tail re- including Gasparinisaura (Coria & Salgado, semble those of the middle section, excepting for 1996; Rozadilla et al., 2019). The anterior sur- being anteroposteriorly longer and with more face of the humeral shaft is concave, while the prominent lateral longitudinal ridges, resulting posterior one is convex. The medial surface bears hexagonal-shaped in cross-section. The ventral an oval nutritious foramen. The shaft is reni- longitudinal groove is well developed and bound- form in cross-section. The distal end of the bone ed by two subparallel longitudinal ridges. Distal is slightly transversely expanded. The anterior caudals are indistinguishable from other basal surface of the bone is deeply concave proximal ornithopods (e.g. Gasparinisaura, Anabisetia, to the distal condyles. In distal view, the lateral Talenkauen, Macrogryphosaurus, Diluvicursor, condyle is more extensive than the medial one. Sektensaurus, Trinisaura, Jeholosaurus; Coria The flexor fossa is transversely wider than the & Salgado, 1996; Cambiaso, 2007; Calvo et al., extensor one. 2007; Barrett et al., 2011; Han et al., 2012; Pubis. The pubis is only represented by the ili- Barrett, 2016; Herne et al., 2018; Ibiricu et al., ac process. This process is oval in cross-section. 2019; Rozadilla et al., 2019). The articular margin is almost flat and slightly Scapula (Figure 10). The right scapula is rep- projected ventrally in a short process, being not resented by its proximal end. It is anteroposte- fused with the obturator process, indicating a riorly extensive, with thick acromial process. posteriorly opened obturator foramen, resem- It narrows anteriorly, showing a wide and flat bling the condition of basal ornithopods (e.g., dorsal surface. The acromial process is laterally Hypsilophodon, Gasparinisaura, Anabisetia, expanded, forming the deltoid rim, which delim- Trinisaura; Galton, 1974a; Coria & Calvo, 2002; its the dorsal margin of a shallow deltoid fossa. Cambiaso, 2007; Barrett et al., 2011; Coria et al., The glenoid cavity is severely damaged. It is ven- 2013). trolaterally oriented and its anterior margin is Femur (Figures 7, 11). The femora are repre- delimited by a shallow supraglenoid fossa. This sented by several specimens, including a proxi- fossa is subcircular in contour and is ornamented mal end belonging to a juvenile individual. The by small striations, being relatively shallow, as femoral head is not preserved, but the neck is occurs in Gasparinisaura and Trinisaura (Coria well-defined. The greater trochanter is com- & Calvo, 2002; Coria et al., 2013), whereas in pletely preserved only in the juvenile specimen. Anabisetia, Talenkauen and Mahuidacursor it In proximal view, the lateral margin of the great- shows a deep supraglenoid fossa (Coria & Calvo, er trochanter is sigmoidal in outline. In lateral Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 235

Figure 9. Sacrum of Isasicursor santacrucensis gen. et sp. nov. (MPM 21528) in (A) anterior, (B) dorsal, (C) ventral, (D) right, (E), left and (F) posterior views. I-VI indicates anteroposterior position in vertebral series. Abbreviations: f, vascular foramen; p, peg; pit, pit; p-s, peg and socket articulation; s, scar; sr, sacral rib; vg, ventral groove; vk, ventral keel. Scale bar: 3 cm. view, this trochanter is proximally convex, and is Salgado, 1996; Coria & Calvo, 2002; Coria et al., medially delimited by the groove that separates 2013; Rozadilla et al., 2016). it from the lesser trochanter. This indicates that The lateral surface near the proximal end the lesser trochanter was not fused to the major shows a bump ornamented with longitudinal one, a condition different from Gasparinisaura scars, which likely represents the anchoring of (Coria & Salgado, 1996). The lesser trochanter the for the M. iliofemoralis externus. The an- is represented by its base, indicating that to- terior surface between the greater trochanter wards its anterior end it was notably narrow, a and the femoral head is concave. The femo- condition shared with Morrosaurus, Anabisetia, ral shaft is subtriangular in cross-section, be- Trinisaura and Gasparinisaura (Coria & ing posteriorly flat and anteriorly narrow. 236 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 10. Isasicursor santacrucensis gen. et sp. nov. Scapula (MPM 21530) in (A) lateral (B), medial and (C) coracoidal views. Humerus (MPM 21531) in (D) anterior, (E) posterior, (F) medial and (G) lateral views. Abbreviations: dc, deltopectoral crest; df, deltoid fossa; dr, deltoid rim; ef, extensor fossa; ff, flexor fossa; gl, glenoid fossa; hf, humeral foramen; lc, lateral condyle; mc, medial condyle; sgf, supraglenoid fossa. Scale bar: 10 cm.

The distal end of the femur is transversely as well as in more derived Iguanodontia (Cooper, expanded. In distal view, the medial condyle is 1985; Coria & Calvo, 2002; Norman 2004; transversely wider than the lateral one. This Norman et al., 2004; Rozadilla et al., 2016). The asymmetry is present in many elasmarians, such medial condyle has a sub-rectangular outline, as Anabisetia, Morrosaurus and Kangnasaurus, and slightly tapers posteriorly. In medial view, Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 237

Figure 11. Isasicursor santacrucensis gen. et sp. nov. Selected juvenile materials. Right femur (MPM 21533b) in (A) anterior, (B) posterior, (C) lateral (D) medial and (E) proximal views. Left tibia (MPM 21534b) in (F) anterior, (G) posterior, (H) lateral (I) medial and (J) distal views. Metatarsal II in (K) anterior, (L) posterior, (M) lateral (N) medial and (O) distal views. Metatarsal IV (MPM 21538b) in (P) anterior, (Q) posterior, (R) lateral (S) medial (T) proximal and (U) distal views. Abbreviations: cp, collateral pit; fib, fibular facet; gt, greater trochanter; ig, intertrochanteric groove; lc, lateral consyle; lf, lateral fossa; lr, lateral ridge; lt, lesser trochanter; mf, medial fossa; pc, plantar crest; sIII, surface for mtt III. Scale bar: 3 cm. 238 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 the medial condyle is posteriorly expanded and Notohypsilophodon, Hypsilophodon, Zalmoxes, its medial surface is smoothly concave. The Trinisaura, and the iguanodontian Ouranosaurus lateral condyle is gently laterally projected, re- (Galton, 1974a; Cooper, 1985; Coria & Salgado, sulting in a well-defined longitudinal groove on 1996; Cambiaso, 2007; Godefroit et al., 2009; its lateral surface. This groove separates the Barrett et al., 2011; Han et al., 2012; Ibiricu et lateral condyle from the tibiofibular crest. The al., 2014; Bertozzo et al., 2017; Rozadilla et al., medial condyle is not laterally expanded as in 2019). The lateral surface of the lateral condyle Morrosaurus and Kangnasaurus (Cooper, 1985; is convex and rugose. The posterior margin of Rozadilla et al., 2016). The anterior surface of the lateral condyle is defined by a dorsoventrally the bone lacks a well-developed extensor fossa, oriented groove. There is a notch between the a condition shared with many basal ornitho- lateral and the posteromedial processes. The pods, such as Thescelosaurus, Hypsilophodon, medial surface of the cnemial crest is posteriorly Jeholosaurus, Gasparinisaura, Trinisaura, delimited by a low prominence. The tibial shaft is Notohypsilophodon and “Fulgurotherium” oval in cross-section on its proximal third. (Galton, 1974a,b; Molnar & Galton, 1986; Coria The distal end of tibia of Isasicursor is trans- & Salgado, 1996; Coria et al., 2013; Martínez, versely expanded and anteroposteriorly com- 1998; Han et al., 2012; Ibiricu et al., 2014), pressed. The distal malleoli are weathered. Both while Anabisetia, Morrosaurus, Kangnasaurus, have a subtriangular outline in anterior view and Tenontosaurus, Rhabdodontidae, Dryosauridae are distally rounded, as occurs in related taxa and Ankylopollexia show a well-developed exten- with the exception of Morrosaurus, in which the sor groove (Cooper, 1985; Sereno, 1986; Coria & medial condyle has a sharp trapezoidal outline Calvo, 2002; Norman, 2004; Norman et al., 2004; (Cooper, 1985; Coria & Salgado, 2002; Cambiaso Godefroit et al., 2009; Rozadilla et al., 2016). In 2007; Ibiricu et al., 2014; Rozadilla et al., 2016). posterior view, the flexor fossa is deep and lim- The lateral malleolus is transversely wider and ited laterally and medially by stout ridges that more distally projected than the medial one. The end in the distal condyles. anterior surface of the lateral malleolus bears Tibia (Figure 7, 11). The proximal end of the a mound-like longitudinal crest, as occurs in tibia is anteroposteriorly expanded, its proxi- Talenkauen and Anabisetia (Cambiaso, 2007; mal surface is medially inclined and exhibits a Rozadilla et al., 2019). Lateral to this crest there rugose surface. The cnemial crest is anteriorly is a smoothly concave surface for contact with extended and is strongly proximally projected, the fibula. This crest and concave surfaces are resulting in a subtriangular profile in lateral shallower in the juvenile specimen. The posterior view. This trait is unique for Isasicursor, differ- surface of the lateral malleolus is concave. In the ent from the remaining ornithopods in which juvenile specimen of Isasicursor, the lateral mal- the cnemial crest does not project further leolus is anteroposteriorly narrower. The medial proximally than the articular surface of the malleolus is subtriangular in distal view, concave tibia (e.g. Gasparinisaura, Notohypsilophodon, anteriorly and convex posteriorly, lacking the Tenontosaurus, Ouranosaurus; Coria & Calvo, anterior curvature present in Morrosaurus and 1996; Tennant, 2013; Ibiricu et al., 2014; Trinisaura (Barrett et al., 2011; Rozadilla et al., Bertozzo et al., 2017), or has a distally deflected 2016). The distal malleoli are separated anteri- anterior margin (e.g. Anabisetia, Talenkauen, orly by a shallow anterior intermalleolar fossa Morrosaurus, Zalmoxes; Coria & Calvo, 2002; and posteriorly by a thick intermalleolar crest. Godefroit et al., 2009; Rozadilla et al., 2016, The anterior intermalleolar fossa is shallower in 2019). The cnemial crest of Isasicursor is the juvenile specimen. transversely thickened and shows a proximally Metatarsals (Figures 11, 12). Metatarsal II of rounded apex. In lateral view, the lateral crest Isasicursor is represented by isolated proximal shows a straight anterior margin. In Isasicursor and distal ends. The proximal end is antero- it is more extensive than in Kangnasaurus, posteriorly expanded and transversely com- Talenkauen and Morrosaurus (Cooper, 1985; pressed a condition that was previously consid- Novas et al., 2004; Rozadilla et al., 2016, 2019). ered synapomorphic for Elasmaria by Rozadilla The lateral condyle is subtriangular in proximal et al. (2016, 2019). However, metatarsal II of view. It shows a well-developed process at the Isasicursor is not as expanded anteroposteriorly anterolateral corner, being absent in other basal as in Anabisetia and Diluvicursor (Coria & Calvo, ornithopods such as Gasparinisaura, Anabisetia, 2002; Herne et al., 2018). The lateral surface of Talenkauen, Jeholosaurus, Kangnasaurus, metatarsal II shows a flattened surface for artic- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 239

Figure 12. Isasicursor santacrucensis gen. et sp. nov. Metatarsal I in (A) anterior, (B) posterior, (C) lateral, (D) medial and (E) distal views. Proximal (above) and distal end (below) of metatarsal II (MPM 21535a) in (F) anterior, (G) posterior, (H) lateral, (I) medial (J) proximal and (K) distal views. Metatarsal III (MPM 21536) in (L) anterior, (M) posterior, (N) lateral, (O) medial and (P) distal views. Proximal (above) and distal end (below) of metatarsal IV (MPM 21537) in (Q) anterior, (R) posterior, (S) lateral, (T) medial (U) proximal and (V) distal views. Abbreviations: cp, collateral pit; ef, extensor fossa; f, foramen; ff, flexor fossa; ics, intercondylar sulcus; sI, surface for the mtt I; sIII, surface for the mtt III. Scale bar: 3 cm. 240 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 ulation with the medial surface of metatarsal III. sharp longitudinal keel. The anterior surface of The anterior surface of the bone is transversely the shaft is smooth, while the posterior one pos- thicker than the posterior one and is more lat- sesses an oblique ridge that runs from the medial erally expanded. The distal end of metatarsal II margin to the lateral distal condyle. The distal has a sub-rectangular outline in distal view. The end is strongly anteroposteriorly expanded. In anterior surface is smooth and bears a rounded anterior view, the articular surface lacks a well- distal articular surface that is distally convex. defined extensor groove. In lateral view, there is The posterior surface has a deep flexor groove. a shallow collateral pit that is suboval in contour The lateral surface is deeply concave and bears and with a strongly anteriorly projected anterior a distinct and deep collateral ligamental pit that articular surface. In distal view, the articular sur- is proximally located. This condition is absent in face has sub-parallelogram outline, with its another elasmarians and may constitute an auta- terior margin more laterally projected than the pomorphy of Isasicursor. The lateral condylid posterior one. The posterior margin is medially is transversely thicker than the medial one. In projected, forming a lip-like process that proj- an available juvenile metatarsal II (MPM 21535) ects laterally, a condition shared with Anabisetia both extensor and flexor grooves and collateral and Trinisaura (Cambiaso, 2007; Barrett et al., ligamental pits are shallower. 2011). This projection posteriorly bounds the Metatarsal III is only represented by its dis- outer collateral pit. In posterior view a shallow tal end. The articular surface is asymmetrical in flexor groove separates both condylids. shape, being proximally expanded at its medial MPM 21538 is proximodistally short and surface. The distal condylids are separated by transversely stout. In related taxa, such as a well-developed intercondylar groove. In distal Gasparinisaura, Anabisetia and Morrosaurus, view, the condyles are asymmetrical, the medial the adult specimens possess a more slender one being larger than the lateral one, resem- metatarsal IV than in different-sized Isasicursor bling the condition of Anabisetia (Coria & Calvo, specimens (see Coria & Salgado, 1996; Cambiaso, 2002; Cambiaso, 2007), but differing from that of 2007; Rozadilla et al., 2016). Morrosaurus, which shows a notably larger lat- Phalanges (Figure 13). Pedal toes of Isasicursor eral condylid (Rozadilla et al., 2016). The lateral are represented by several damaged phalanges surface of the bone has a deep and sub-circular belonging to several individuals. Available pha- collateral pit, while the medial one is shallower. langes are relatively stout and short, with a flat- Metatarsal IV is represented by several ele- tened ventral surface and wide and deep collat- ments of different specimens. The most com- eral ligamental pits. plete metatarsal IV belongs to a juvenile speci- Phalanx I-1 is represented by its distal end. men, while larger specimens are represented by The distal trochlea is well developed, with low isolated proximal and distal ends. The proximal condyles divided by a deep intercondylar groove. end is transversely expanded and is subtrian- The preserved portion of the shaft is slender gular in proximal view, with a tapering lateral and the distal trochlea is strongly transversely surface, as occurs in Gasparinisaura, Anabisetia, expanded. Deep and sub-circular collateral pits Thescelosaurus and Trinisaura (Galton, 1974b; are present. Phalanx II-1 shows a concave and Coria & Salgado, 1996; Coria & Calvo, 2002; subtriangular-shaped proximal articular surface. Barrett et al., 2011), whereas in Talenkauen, The proximal end narrows distally. The medial Morrosaurus and Styracosterna the lateral sur- surface has several muscular scars near its proxi- face is rounded (Norman, 2004; Rozadilla et al., mal surface, which are continuous ventrally with 2016; 2019). The proximal surface is gently con- a ventral ridge. In ventral view, the proximal cave and its posterior margin is more proximally portion of this phalanx possesses two collateral extended than the anterior one. The medial ridges, in which the medial one is more robust surface is deeply concave with a narrow proxi- and ventrally extended. The lateral ridge is shal- mal groove that receives the lateral process of lower and more laterally projected. These ridges metatarsal III. Distal to this groove, the medial are separated by a proximal concavity. The shaft surface of the bone shows a flat contact for the is sub-rectangular in cross-section. Three nota- lateral surface of metatarsal III. The anterior bly anteroposteriorly short phalanges from digit and posterior surfaces of the proximal end of the IV were recovered. We identify these elements as bone are flattened and smooth. In cross section, IV-2/IV-3? The proximal surface is weathered, but the bone is subtriangular proximally and oval shows a well-developed dorsoventral ridge sepa- distally. The lateral margin of the shaft shows a rating it symmetrically, as occurs in phalanges of Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 241

Figure 13. Isasicursor santacrucensis gen. et sp. nov.Pedal phalanx IV-2/IV-3? (MPM 21539) in (A) proximal, (B) dorsal, (C) lateral and (D) ventral views. Ungual phalanx (MPM 21540) in (E) proximal, (F) dorsal, (G) lateral and (H) ventral views. Abbreviations: ce, collateral expansions; cp, collateral pit; mr, median ridge; st, striations; vl, ventral lip. Scale bar: 3 cm. the fourth digit in other elasmarians (Rozadilla with the lateral articular surface larger than the et al., 2019). The ventral margin of the proximal medial one. The dorsal margin of the articular surface is proximally projected, forming a well- surface projects proximally into a proximal lip. developed posteroventral process. The distal tro- The blade is dorsoventrally flattened, and slight- chlea is well-defined and is proximally delimited ly medially curved. The dorsal surface is smooth by a transversely oriented groove. In the dorsal and convex, while the ventral one is flat. The un- surface of the bone there is a small extensor pit gual possesses two flattened longitudinal step- proximal to the distal articular surface. Distal like expansions that are dorsally delimited by a condyles are well developed and separated by a longitudinal collateral groove. The distal end of deep intercondylar groove. Deep collateral pits the ungual is notably acute. The ungual is deco- occur at the sides of each distal condyle. These rated with striations near its proximal and distal phalanges are anteroposteriorly short, as oc- ends and on the ventral surface. The flexor tu- curs in Talenkauen and derived iguanodontians bercle is represented by a poorly developed and (Norman et al., 2004; Norman 2004; Rozadilla et transversely expanded bump, decorated with al., 2019), whereas more basal ornithopods and muscle-scar striations. The overall morphology smaller elasmarians show proportionally longer of these phalanges resembles that of other basal pedal phalanges (Coria & Calvo, 2002; Cambiaso, ornithopods (e.g., Norman et al., 2004; Canudo et 2007; Coria et al., 2013). al., 2013), but contrasting with the blunt hoof- At least six pedal unguals were recovered. We like unguals of styracosternan ornithopods (e.g., tentatively identify the most complete elements Norman 2004; Horner et al., 2004). as unguals of the third digit. The proximal surface Comments. The morphology of the proximal is suboval in proximal view, being transversely end of femur and humerus shows synapomor- wider than dorsoventrally deep. This surface is phic features supporting Isasicursor belongs to asymmetrically divided by a dorsoventral ridge, the Elasmaria (e.g., cervical vertebrae laterally 242 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 compressed and with a sharp ventral keel; lat- Surman, 1979; Bonaparte et al., 1984; Juarez- erally bowed humerus with a rudimentary del- Valieri et al., 2010; Coria et al., 2012; Cruzado- topectoral crest; femur with greater trochanter Caballero & Powell, 2017). These dinosaurs were showing a sigmoidal lateral margin in proximal outstanding components of the South American view; and metatarsal II laterally compressed “Allenian vertebrate assemblage” (see Leanza in proximal view; Rozadilla et al., 2016; 2019). et al., 2004), which includes other herbivorous Among elasmarians, Isasicursor shows unique dinosaurs such as titanosaurs and ankylosaurs features in several elements, especially the proxi- (Bonaparte, 1986). In a global context, the re- mal end of tibia and sacrum, indicating that it cord of Campanian-Maastrichtian basal ornitho- is a clearly distinctive and diagnosable taxon. pods suggests a decline in diversity with respect Its size is similar to that of larger taxa, such as to previous times, whereas hadrosaurs exhibit Sektensaurus, Morrosaurus, Talenkauen and a notorious “evolutionary explosion” during Macrogryphosaurus. However, the incomplete the end of the Late Cretaceous (Horner et al., nature and dissociated preservation of available 2004). In that time span, basal ornithopods are material precludes the recognition of the rela- nearly exclusively represented by the European tionships of Isasicursor within Elasmaria. Rhabdodontidae and the North American The Upper Cretaceous record of basal iguan- Thescelosauridae (Weishampel et al., 2003; Boyd odontians from Argentina and Antarctica in- et al., 2009; Ősi et al., 2012; Boyd, 2015). The cludes the Cenomanian-Turonian Talenkauen same seems to be true for South America, where and Anabisetia, and the Campanian Trinisaura ornithopods are only represented by small to me- and Morrosaurus from Antarctica (Coria et al., dium sized elasmarians. 2013), whereas Sektensaurus has a poorly con- The discovery of diverse elasmarian in strained age that ranges from Coniacian to Campanian-Maastrichtian beds of Patagonia Maastrichtian (Ibiricu et al., 2018). Previous re- and Antarctica (e.g. Trinisaura, Morrosaurus, ports of Campanian-Maastrichtian basal ornitho- Sektensaurus, Isasicursor; Ibiricu et al., 2010; pods from Northern Patagonia were dismissed 2019; Coria et al., 2013; Rozadilla et al., 2016) (Agnolin et al., 2010). In this way, Isasicursor suggest that some of these basal ornithopods co- constitutes the first Maastrichtian basal iguano- existed with hadrosaurs. This, together with the dontian from the southern cone. much smaller size of elasmarians, suggests that Ornithopods are frequently recorded as ta- some kind of niche partitioning occurred among phonomic associations composed by several indi- Gondwanan ornithopods (see Brett-Surman, viduals (e.g, Horner & Makela, 1979; Salgado et 1979; Case et al., 2000). al., 1997; Andrzejewski et al., 2019). Isasicursor is known from several specimens corresponding Sauropoda Marsh, 1878 to different sizes that likely represent different Titanosauriformes Salgado, Calvo & Coria, 1993 ontogenetic stages, found together in a reduced Titanosauria Bonaparte & Coria, 1993 fossiliferous spot (i.e., a bed roughly 5 m long Genus and species indeterminate and 0.50 m thick). This leads to the interpretation that this taxon had a gregarious behavior, Referred material: MPM 21542, three isolated at least at the time of their death. In South teeth (locality 4). America the finding of different individuals in Description. Available teeth lack the tip of close association is common, as demonstrated by the crown and most of the enamel. They are Talenkauen santacrucensis, in which the holo- pencil-like as typical for titanosaurs (e.g. García type specimen was found associated with a neo- & Cerda, 2010). The enamel is smooth and the natal tooth (Egerton et al., 2013), and Anabisetia teeth are subcircular in cross-section. There is and Gasparinisaura which are known from sev- no clear difference in thickness between crown eral individuals (Salgado et al., 1997; Coria & and root. Calvo, 2002). This may indicate that Isasicursor Comments. The general crown outline is similar and other elasmarians were gregarious, a condi- in the three collected teeth, including a pencil- tion well-known among their Laurasian counter- like general aspect with poor labiolingual com- parts (Andrzejewski et al., 2019). pression and lacking mesial and distal carinae. Hadrosaurs appear in the South American These are features typical of titanosaur dentition fossil record at the Campanian-Maastrichtian (García & Cerda, 2010). Further, the absence of time span, being represented by abundant re- needle-like teeth and lack of strong enamel or- mains corresponding to different species (Brett- namentation, argue against rebbachisaurid af- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 243 finities for the collected specimens (Salgado et Diagnosis. Large titanosaurian sauropod diag- al., 2004). In sum, MPM 21542 is regarded as nosable on the basis of the following combina- Titanosauria indet. tion of characters (autapomorphies marked with an asterisk*): 1) anterior caudal centra notably ?Colossosauria González Riga, Lamanna, Otero, anteroposteriorly short, its transverse diameter Ortíz, Kellner and Ibiricu, 2019 duplicating its anteroposterior length; 2) proximal and mid-caudal centra with lateral and ven- Nullotitan glaciaris gen. et sp. nov. tral surfaces profusely excavated by large blind Figure 14 depressions*; 3) mid-caudal vertebrae with lateral surface with a tabicate large fossa below the Holotype. MACN-PV 18644 and MPM 21542, transverse process; 4) centra of all available cau- the specimen consists of isolated cervical cen- dal vertebrae lacking signs of pneumatization; 5) trum (presumably Cv3; MACN-PV 18644), frag- mid-caudals with a deep ventral longitudinal fur- mentary cervical rib shaft, dorsal rib shaft frag- row surrounded by two longitudinal thick ridges; ments, several caudal vertebrae, fragmentary left 6) fibula with a pronounced sigmoid curvature scapula, proximal and distal ends of right femur, when viewed anteriorly or posteriorly*; and 7) almost complete right tibia, fibula, and astrag- distal end of tibia strongly anteroposteriorly com- alus. The holotype specimen comes from local- pressed and more transversely expanded than in ity 1. It also includes an isolated cervical cata- other titanosaurs. logued with collection number MACN-PV 18644 Etymology. Nullotitan, in honor of geologist by J. F. Bonaparte in 1981, and then catalogued Francisco E. Nullo, discoverer of the holotype as cf. Antarctosaurus. Later, Bonaparte et al. specimen, and titan, powerful giant; the specific name glaciaris refers to the majestic Perito (2002) interpreted this titanosaur as related with Moreno Glacier, observable from the excavation Aeolosaurus; Powell (2003), instead, referred the site. material as to Titanosauridae indet. Remarks. Fossil remains of sauropods from Referred specimens. The following specimens Chorrillo beds, albeit fragmentary, consist of were collected from other nearby localities, from bones, teeth and egg-shell fragments. Bones that levels above and below the holotype: 1) MPM are here referred as to Nullotitan glaciaris were 21545, complete humerus, lacking cortex of mid- found broken and forming different bone accu- shaft, partial rib, and vertebra, which were found mulations, spread over 100 square meters on a preserved ex situ, about 100 meters far from the slope surface. All collected elements belong to place of the holotype specimen. These elements large titanosaur sauropods, and no overlapping were found relatively high on the slope, indi- bones exist among these five discrete bone accu- cating they correspond to a different individual mulations. The available bones that were found than the holotype. Further, the humerus belongs in situ, come from a reduced spot of hard green to an individual smaller than the holotype. 2) sandstone exposed at the top of the slope; in MPM 21546 (locality 1), isolated and partially contrast, the remaining sets of bones were col- preserved distal caudal centra. 3) MPM 21547 lected down on the slope, and were exposed ex (locality 5), sequence of five mid-caudal verte- situ, but some of them still preserving bits of the brae with their respective haemal arches, found green sandstone exposed on the top of the slope. articulated in situ. This specimen still remains No dermal ossifications have been discovered in in the field. 4) MPM 21548 (locality 2), isolated Chorrillo beds, either isolated or in association complete left tibia. 5) MPM 21549 (locality 2), with bone remains. proximal to mid-caudal centrum, found ex situ Description. Almost all the collected titano- some meters far from the isolated tibia. saur bones belong to large sized individuals. Stratigraphic provenance. All aforemen- Estimated length of the holotype specimen al- tioned specimens come from the lower and middle most probably surpassed 20 meters long, based sections of the Chorrillo Formation, being absent on extrapolations of available elements with the from the upper third of this unit. The upper-most fairly complete titanosaurs Dreadnoughtus and record is from locality 4, which was found from Patagotitan (Lacovara et al., 2014; Carballido et beds lying above a thick conglomerate bank. This al., 2017). later specimen is not yet numbered, still remaing Cervical vertebra (Figure 15). Neck verte- in the field. This later specimen still remains un- brae are represented just by a single, incomplete numbered, waiting to be excavated from the field. centrum, collected by J. F. Bonaparte in 1981 244 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 14. Nullotitan glaciaris gen. et sp. nov. Silhouette showing the recovered elements.

(MACN-PV 18644). It is elongate (45cm long) and represented by incomplete centra, with limited dorsoventrally low (22cm). The centrum is opist- information regarding transverse processes and hocoelous. The parapophyses are tabular shaped, neural arches. Location of each of these isolat- dorsoventrally depressed, and anteroposteriorly ed elements along the caudal series is tentative extended. The sides of the centrum are deeply and based on the ratio between anteroposterior excavated between parapophysis and diapophy- length vs. transverse width of centra, contour of sis, bearing a large and elliptical pleurocoel at the centra (i.e., proportional development of primary bottom of the excavation. In anterior view the and secondary lateral surfaces), presence and vertebra is cross-shaped, due to the development relative development of articular surfaces for of para- and diapophyses bounding the centrum. haemal arches, degree of convexity of the poste- There are subhorizontally oriented longitudinal rior articulation of centrum, and profusion and ridges that run from diapophyses to parapo- size of blind perforations on lateral and ventral physes. The ventral surface of centrum is flat- surfaces. In contrast with cervical elements, all tened and smooth, as is usual in basal sauropods available caudals are apneumatic, and the inter- (Tazoudasaurus, Shunosaurus, Patagosaurus), nal tissue is compact. basal macronarians (Camarasaurus), and titano- Proximal caudals characterize for the following saurs (Malawisaurus, Rapetosaurus, Isisaurus, combination of features: 1) anteroposteriorly Trigonosaurus, Neuquensaurus and Saltasaurus), short centra; 2) centrum transversely wide and and unlike some basal Titanosauriformes elliptical-shaped in anterior view; 3) lateral and (Giraffatitan, Paluxysaurus and Tendaguria) ventral surfaces profusely excavated by large, and diplodocoids (Apatosaurus, Diplodocus and blind perforations; 4) centrum lateral surface Limaysaurus) where it is transversely concave. (below transverse process) steeply inclined ven- This combination of features suggests it may cor- trally and medially; 5) transverse processes respond to Cv3. The internal structure is camel- dorsoventrally deep and anteroposteriorly com- late, as occurs in some basal Titanosauriformes pressed. Mid-caudals exhibit: 1) squared-shaped (Giraffatitan), basal somphospondylians (Erketu, centra in side view; 2) ball-shaped distal articu- Ligabuesaurus, Phuwiangosaurus), titanosaurs lar surface; 3) centra with a deep ventral longi- (Mendozasaurus, Malawisaurus, Rapetosaurus, tudinal furrow; 4) blind excavations reduced in Isisaurus, Trigonosaurus, Alamosaurus, size, but still abundant in number; 5) transverse Neuquensaurus, Saltasaurus) and some diplodo- processes reduced in size, cone-shaped, and lo- cids (Apatosaurus and Diplodocus), and unlike cated at centrum mid-height. Finally, distal cau- other sauropods where inner pneumaticity of the dals exhibit: 1) relatively elongate centra; and cervical centrum is absent (e.g., Patagosaurus) 2) posterior articular surface cone-shaped and or present but with several small and complex transversely wide in posterior view. internal cavities (Camarasaurus, Limaysaurus). Regarding the distribution among Caudal vertebrae (Figures 16-18). The holo- Titanosauria of the blind, apneumatic excava- type of Nullotitan glaciaris includes different tions which do not enter inside the centrum, caudal elements, corresponding to proximal and there are some cases in which similar depres- middle section of the tails. Most of them are only sions exist (see Martinelli et al., 2011). For ex- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 245

Figure 15. Nullotitan glaciaris gen. et sp. nov. Cervical vertebra (MACN Pv 18644) in left lateral (A), dorsal (B), posterior (C), right lateral (D), and longitudinal section (E) views. Abbreviations: di, diapophysis; fo, fossa; na, neural arch; nc, neural canal; pa, parapophysis; pl, pleurocoele. Scale bar: 10 cm. ample, in Drusilasaura the ventral surface surrounded by a well-developed rim. The dorsal of Cd4? exhibits a pair of large elliptical open- part of transverse processes extends dorsally, well ings which were considered autapomorphic for above level of neural arch. Transverse processes this species (Navarrete et al., 2011). Similarly, are cranially concave and caudally convex. On its Salgado (1996) reported on caudals 2 through 4 cranial surface, the transverse process bears a of Pellegrinisaurus the presence of small holes on pair of large, eye-shaped, blind excavations. On each side of the centrum. However; in Nullotitan the surface behind the transverse process, there the excavations are larger than in other titano- is only one of these excavations. Below the trans- saurs, and much more abundant. verse processes, the centrum becomes strongly The following description of caudal elements constricted due to the ventromedial slope of positions the ventral surface of centrum on the the lateral surface. Notably, this lateroventral horizontal plane. The dorsoventral axis of cen- surface of the centrum exhibits large and blind, trum (especially in proximal caudals) is vertically randomly distributed perforations, consisting positioned, and forming a right angle with the in fossae separated by ridges. The lateroventral ventral surface of centrum. Thus, the floor of surface of centrum forms an inflexion with the the neural canal results inclined ventrodistally flattened ventral surface. The ventral surface of (in side view) with respect to ventral surface the centrum is perforated by isolated longitudi- of centrum. This means that the caudal series, nally oriented, blind depressions, which develop when reconstructed articulated in line with the on the posterior half of the bone. sacrum, show the neural canal inclined, accom- The cranial articular surface is deeply con- panying the dorsoventral lowering of vertebrae. cave. The distal articular cone is eroded, so its Caudal 1st? (Figure 16). It is represented by caudal projection is difficult to discern; howev- most of its centrum and the base of the neural er, it seems to have been hemispheric, as usual arch. The later one occupies a central to cranial among titanosaurs. position in lateral view, similar to other titano- The neural canal is oval-shaped, with its floor saurs (e.g., Patagotitan; Carballido et al., 2017). concave that widens posteriorly (in dorsal view). The centrum is 40 cm in transverse width, 34 cm The later region is highly vascularized, as sug- in dorsoventral depth, and 22 cm in anteroposte- gested by abundant foramina. On the posterior rior length (but probably 25 cm when complete). surface of the base of neural arch, there is a me- Transverse processes are broken at their bases dian fossa immediately above the neural canal. but revealing a prominent vertical structure. No facets for haemal arches are present. They are dorsoventrally deep, extending over Caudal 2nd? (Figure 17). It is represented by the the dorsal half of the lateral centrum surface. In dorsal half of centrum and the badly preserved side view it is seen that the transverse process bases of the neural arch, including the base of occupies a central position on the lateral surface the right transverse process. As in Cd1st, the of the vertebra. The anterior articular surface is centrum is anteroposteriorly very short, but 246 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 16. Nullotitan glaciaris gen. et sp. nov. Caudal vertebrae?1st (A-D) and ?2nd (E-G) (MPM 21542) in anterior (A, E), posterior (B, F), right lateral (C, G), and ventral (D) views. Abbreviations: lg, longitudinal groove; tp, transverse process. Scale bar: 10 cm. transversely wide. The transverse processes are face are more elongate and deeper than those of eroded, but the preserved portions indicate they the lateral surface. The ventral surface of cen- were dorsoventrally deep. However, they are trum is almost flat. shallower than in Cd1st, due to the lower margin The base of prezygapophysis indicates that in a higher position on the lateral surface. The it was anterodorsally projected. The base of the cranial and caudal surfaces of the transverse pro- spinoprezygapophyseal lamina, the only portion cess are concave-convex, as in Cd1st. Regarding preserved, is nearly horizontal and sharp. On the the blind depressions, they are similar to those of internal surface of neural arch, behind the base Cd1st. The cranial articular surface seems more of prezygapophysis, and above the intraprezyga- concave than in Cd1st. The floor of the neural pophyseal lamina (TPRL), there is an elongate canal is fan-shaped in dorsal view, being trans- fossa. The floor of neural canal is flat; it widens versely expanded towards the rear. posteriorly as in the remaining proximal caudals. Caudal 4th? or 5th? (Figure 18). It is represented Due to poor preservation, there is no evidence of by most of the centrum and base of neural arch facets for articulation with the haemal arches. and base of left prezygapophysis. The centrum is Mid-caudals (Figure 18). Possible caudals 11 dorsoventrally and transversely smaller than the and 12 are preserved. Because it is not easy to caudals previously described, but it is anteropos- elucidate the respective position of these verte- teriorly as long as these centra. The lateral sur- brae, we describe them together. They are ap- face of centrum orientates lateroventrally. The proximately half the size of the available proxi- base of right transverse process is sub-conical, mal caudals. The base of the neural arch occu- and it locates immediately below level of neural pies most of the anteroposterior length of cen- canal. Due to the higher position of transverse trum (discounting the hemispherical posterior process, the lateral surface of centrum is more de- articular surface). The floor of the neural canal veloped than in more proximal caudals. In sharp exhibits foramina and longitudinal grooves on difference from more proximal caudals, the base its posterior half. The centrum is damaged along of the transverse process reaches the anterior the anterior articular rim. The caudal surface margin of centrum, thus the later results devoid is hemispherical, but slightly eccentric in side of a lateral surface in front the transverse pro- view, with the maximum convexity on the dor- cess. Regarding the blind depressions, they are sal half. In distal view, the contour of the articu- similar to those of more proximal caudals, being lar surface is sub-quadrangular, with the major more developed towards the posterior margin of axis vertically oriented. The lateral surface has a centrum. Blind depressions on the ventral sur- large fossa below the transverse process, as well Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 247

Figure 17. Nullotitan glaciaris gen. et sp. nov. Caudal vertebrae ?11th (A-D), ?15th (E-H), ?16th (I-M), ?20th (N-Q), and ?21th (R, S) (MPM 21542). The elements are figured in anterior (A, E, I, Q, R), lateral (B, H, M, P, S), dorsal (C, L), ventral (D, G, K, O), posterior (F, J, N) views. Abbreviations: cn, neural canal; tp, transverse process; fo, fossa; h, haemal facet; gr, groove; na, neural arch. Scale bar: 10 cm. as deep blind depressions, which are located on and with a flat surface surrounding it. the central region of the centra. In caudal 15, the articulation for the haemal The ventral surface exhibits a deeply exca- arches, placed on the posteroventral border of vated central depression, flanked by strong lon- centrum, are closer to each other (5 cm) than in gitudinal ridges. The inner side of these ridges caudal 16th (6-7 cm); the primary lateral surfac- exhibits randomly distributed, and longitudi- es (Salgado & García, 2002) are dorsoventrally nally elongate foramina, which are much smaller oriented and dorsoventrally deeper (7cm) than in that the blind fossae described for the proximal caudal 16th (4cm), where they are ventrally ori- caudals. Facets for articulation with the haemal ented. According to the interpretation of Salgado arches are present. Transverse processes are lo- and García (2002), this would indicate that the cated at level of neural canal, and the preserved M. caudofemoralis extended distally as much as bases suggest they were robust. caudal 16th. Caudals 15th and 16th (Figure 18). They are Distal caudal centra (Figure 18). No complete quadrangular in caudal view, being wider than distal centra are available. The centra are pro- tall, different from the mid-caudals described coelous, and notably dorsoventrally compressed. above. The posterior surface is less spherical The anterior articular surface is subcircular in than in previous caudals, and the spherical ar- contour. The posterior articular surface is kid- ticulation is placed on the center of the surface ney-shaped and shows an eccentric distal cone, 248 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 18. Nullotitan glaciaris gen. et sp. nov. Distal caudal vertebrae (MPM 21542) in dorsal (A), lateral (B), ventral (C), posterior (D), anterior (E) views. Abbreviations: cn, neural canal; co, articular cone; ri, ridge. Scale bar: 10 cm. dorsally displaced. At least in caudal 19th, the is estimated in 0.28, being comparable to that primary lateral surfaces are constrained to the of Epachthosaurus (RI=0.27), Mendozasaurus, ventral face of centrum. (R=0.24; Martínez et al., 2004; Mannion & Haemal arches. Haemal arches are represent- Otero, 2012), Patagotitan (RI estimated=0.28; ed by two single elements. They are rod-shaped Carballido et al., 2017), and Notocolossus (RI and proximally opened. In lateral view they show =0.28; González Riga et al., 2016). These hu- a gentle sigmoid curvature. meral proportions differ from the robust hu- Scapula (Figure 19). The central portion of a meri (RI more than 0.28) of Dreadnoughtus left scapula is preserved (the following descrip- (RI=0.33), Neuquensaurus (RI=0.35, Salgado et tion assumes the long axis of scapula as vertically al., 2005; Otero, 2010), Saltasaurus (RI=0.36; oriented). This portion of the scapula lacks both Powell, 2003), and Opisthocoelicaudia (RI=0.41; glenoidal and acromial regions. It is a plate-like Borsuk-Bialynicka, 1977). Bonaparte et al. (2002) bone, medially concave and laterally convex. The considered the humerus of Nullotitan similar to most notable feature preserved on this fragmen- Aeolosaurus rionegrinus (Powell, 2003) in their tary scapula is a medial tubercle with a muscle slender proportions, but the RI of the latter one scar located dorsal to the level of the acromial can not calculated because the humerus is in- process and close to the anterior margin of the complete. bone. The tubercle is triangular-shaped, with The humeral deltopectoral crest of Nullotitan is the apex oriented ventrally. Such prominence markedly expanded distally as it occurs in practi- has been also reported in other titanosauriforms cally all sauropods. In Nullotitan, the greater an- (e.g., Wintonotitan, Alamosaurus; D´Emic, 2012; terior expansion of the lower portion of the delto- Poropat et al., 2015). A ventromedial process is pectoral crest is placed at nearly 25% of the total observed on the ventral margin of the scapula, length of the bone beginning from the top. This as reported in Ligabuesaurus (Bonaparte et al., means a shorter deltopectoral crest, with values 2006). more similar to those of basal titanosaurs such as Humerus (Figure 20). A fairly complete right hu- Paralititan and Epachthosaurus the ratio is near- merus (MPM 21545) is available. It measures 114 ly 31% (Smith et al., 2001; Martínez et al., 2004). cm in total length, 44 cm in maximum proximal In other forms, in turn, the deltopectoral crest width, and 40 cm of maximum distal width (mid- is more distally extended, such as in Elaltitan shaft is damaged, and its reconstructed maximum (36%; Mannion & Otero, 2012), Dreadnoughtus width is estimated in 25 cm). The robust index (RI; (37%), Patagotitan (33.6%; Carballido et al., maximum distal width/total length) of Nullotitan 2017), Narambuenatitan and Mendozasaurus Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 249

Figure 19. Nullotitan glaciaris gen. et sp. nov. Left scapula (MPM 21542) in lateral (A), and medial (B) views. Abbreviations: bl, blade; tu, tubercle; vp, ventral process. Scale bar: 10 cm.

(35%; Filippi et al., 2011; González Riga et al., insertion of adductor muscles. The tibial condyle 2018). is more conical-shaped (in cranial view) than the Femur (Figure 21). The femoral head and neck more rounded lateral condyle. Also, the later are poorly preserved. They seem to be proximo- one is carved by deep sulci, giving a brain-like medially elongate, describing an obtuse angle aspect, different from the tibial condyle with a with the longitudinal axis of femur, a condition less marked decoration. Both the tibiofibular typical for titanosauriforms (González Riga et crest and the posterior projection of the medial al., 2019). condyle are broken at their bases. The distal The femur shaft shows a minimum width end of femur described above resembles that of of about 44 cm, and the distal end of the right Mendozasaurus. Notably, the femur shaft (imme- femur is 53 cm in maximum transverse diam- diately proximal to the distal condyles) is highly eter, with globe-shaped, sub-equal articular con- compressed anteroposteriorly (10cm). dyles, 28 cm in anteroposterior diameter. They Tibia (Figure 22). The tibia of the holotype are separated through a marked anteroposterior (MPM 21542) consists of a right element, broken constriction, visible in distal aspect. This separa- and slightly distorted. It measures 105 cm in to- tion is also evident on the cranial surface, which tal length, and 44 cm in maximum distal width. exhibits a shallow distal concavity. In correla- It exhibits remarkable features interpreted as tion, the cranial surface of distal femur forms a diagnostic for the species (see below). A second wide, shallow but deeply grooved, extensor sul- tibia (MPM 21548), discovered in isolation, is cus. Articular condyles are not extended on the tentatively referred as to the same genus and cranial surface of the distal end. Subequal distal species, although its features do not completely condyles may indicate that Nullotitan is close to agree with those of the holotype. the lithostrotian clade (Upchurch et al., 2004), The tibia of Nullotitan is robust. As in other ti- but the lack of dorsomedial beveling of the dis- tanosaurs, the distal end of tibia of Nullotitan is tal condyles onto the cranial side of the shaft transversely expanded to twice midshaft breadth excludes it from Saltasaurinae (Wilson, 2002). (Ullman & Lacovara, 2016) and the proximal The medial surface of distal femur is flat but end is anteroposteriorly expanded. However, strongly decorated by proximodistally oriented the distal end of tibia of Nullotitan is strongly ridges almost probably corresponding with the anteroposterior compressed and more trans- 250 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 20. Nullotitan glaciaris gen. et sp. nov. Right humerus (MPM 21546) in anterior (A), lateral (B), posterior (C), medial (D), distal (E), and proximal (F) views. Abbreviations: dp, deltopectoral crest; hh, humeral head; lc, lateral condyle; mc, medial condyle. Scale bar: 10 cm. versely expanded than in other titanosaurs (e.g., Lacovara, 2016). The sigmoid curve present in Mendozasaurus; González Riga et al., 2019), sug- both Nullotitan and Dreadnoughtus is exaggerat- gesting that may constitute an autapomorphic ed in lateral view, for the notable anteroposterior trait of Nullotitan. expansion of both proximal and distal ends of the Fibula (Figure 23). A nearly complete right fibu- bone. In lateral view, the proximal margin of the la is available. The fibula of Nullotitan measures fibula is nearly horizontally oriented, as occurs 109 cm long, being a bit longer than the fibula of in Dreadnoughtus (Ullman & Lacovara, 2016), Dreadnoughtus (103 cm; Lacovara et al., 2014). Mendozasaurus (González Riga et al., 2018), The fibula of Nullotitan is rubust (RI=0.4), more Saltasaurus (Powell, 2003), and Neuquensaurus than Neuquensaurus (RI=0.172-0.232; Otero, (Otero, 2010), and unlike other titanosaurs such 2010), but less than in Uberabatitan (0.6). as Uberabatitan (Salgado & Carvalho, 2008; The anterior margin of the bone is straight, Silva Junior et al., 2019) in which it is posteri- whereas the posterior one is strongly sigmoid, orly inclined. On the lateral surface, there is the much more than in other titanosaurs (for in- tubercle for the M. iliofibularis. stance, Uberabatitan, Mendozasaurus, Elaltitan; Astragalus (Figure 24). As usual among sauro- Salgado & Carvalho, 2008; Silva Junior et al., pods, the astragalus is conical-shaped, with an 2019; González Riga et al., 2018; Mannion & excavated lateral surface for articulation with Otero, 2012). The fibular shaft is also strongly the calcaneum and the fibula, and a pointed end sigmoidal in posterior view, with the lateral sur- oriented medially, which is partially broken and face markedly convex at level of the biceps tu- coincident with the medial expansion of the dis- bercle (Figure 23C). In general terms, the fibula tal end of tibia. Apparently, the medial expansion is similar to that of Dreadnoughtus (Ullman & of astragalus was more developed in Nullotitan Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 251

Figure 21. Nullotitan glaciaris gen. et sp. nov. Proximal (A-B) and distal (C-D) ends of right femur (MPM 21542) in anterior (A, C), and posterior (B, D) views. Abbreviations: eg, extensor groove; lc, lateral condyle; lbu, lateral bump; mc, medial condyle; ne, neck. Scale bar: 10 cm. than in Uberabatitan (Salgado & Carvalho, 2008; to the greater trochanter; and femoral shaft an- Silva Junior et al., 2019). The ascending process teroposteriorly compressed (Salgado et al., 1997; of the astragalus is low. Mannion et al., 2013; González Riga et al., 2019). Comparisons. Because of the paucity of the Furthermore, presence of subequal-sized con- available materials, the phylogenetic position dyles on distal femur may suggest lithostrotian of Nullotitan among titanosaurs is difficult to affinities for Nullotitan (Upchurch et al., 2004). discern. This taxon exhibits features diagnosing Characters of Colossosauria present in Nullotitan Titanosauria, as well as characteristics of less in- are: deltopectoral mediolateral thickness of ante- clusive clades such as Lithostrotia, Colossosauria, rior attachment surface with distal half medio- and Lognkosauria (González Riga et al., 2019). laterally expanded relative to proximal half and a In addition, Nullotitan lacks features diagnosing value near 0.15 of minimum mediolateral width the derived titanosaur clades Saltasauridae and vs. proximodistal length (González Riga et al., Aeolosaurini. 2019). Nullotitan exhibits the following titanosau- Proximal caudals of Nullotitan are notably rian features: caudal vertebrae procoelous, with anteroposteriorly short, showing awl-like trans- neural arches located on the anterior half of verse processes and a slightly convex posterior centrum; femur medially bowed on its proximal articular surface. This combination of traits is end; presence of a prominent lateral bulge distal also shared with most lognkosaurians (González 252 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 22. Nullotitan glaciaris gen. et sp. nov. Tibia (A-F) right tibia of MPM 21542 specimen and (G-J) left tibia of MPM 21548 specimen. The elements are figured in anterior (A, G), medial (B, H), posterior (C, I), lateral (D, J), proximal (E) and distal (F) views. Abbreviations: aspa, ascending process for astragalus; cc, cnemial crest; pc, proximal condyle; pvp, posteroventral process; ri, ridge. Scale bar: 10 cm.

Riga et al., 2019). 2017). In addition, Patagotitan shows a ventral As follows, we compare Nullotitan with other pocket at the base of centrum, which is absent in gigantic members of the colossosaurian clade n Nullotitan. Notocolossus, Futalognkosaurus, Lognkosauria (sensu Carballido et al., 2017; Dreadnoughtus and Puertasaurus show verte- González Riga et al., 2019). This clade is actu- brae that are proportionally anteroposteriorly ally composed by the genera Argentinosaurus, longer than Nullotitan, with a distal articular Futalognkosaurus, Mendozasaurus, surface more spherical. Also, in Notocolossus Notocolossus, Patagotitan, Puertasaurus, and Futalognkosaurus the transverse pro- Dreadnoughtus and Drusilasaura (Carballido cesses are more dorsally located on the sides et al., 2017; González Riga et al., 2018, 2019). of centra (Lacovara et al., 2014). As occurs in Patagotitan, Futalognkosaurus, and Notocolossus Patagotitan, the mid-caudals show a large fos- show the first caudal transverse processes with sa below transverse process (Carballido et al., a notably dorsoventrally narrow base, a condi- 2017). However, in Nullotitan this fossa is tabi- tion not observed in Nullotitan (Carballido et al., cated by an obliquely oriented ridge of bone. Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 253

Figure 23. Nullotitan glaciaris gen. et sp. nov. Right fibula (MPM 21542) in anterior (A), lateral (B), posterior (C), medial (D), proximal (E), and distal (F) views. Abbreviations: it, iliofibularis tubercle; mf, medial fossa. Scale bar 10 cm.

As already said, proximal caudal centra dis- and elliptical-shaped blind excavations on the tinguish for the presence of profuse blind exca- proximal caudals of Nullotitan (as well as other vations. These are considered autapomorphic for titanosaurs) may have anchored thick tendons the new species. Small vascular foramina were of hypaxial and epaxial muscles. If this interpre- reported in caudal vertebrae of some titanosaurs tation proves to be correct, then it represents a (Mannion & Calvo, 2011; Mannion et al., 2013), different anatomical adaptation for tail support but are much smaller than in Nullotitan. The and movement control than that known in other excavations in caudals of Nullotitan are elon- dinosaurs. gate and subparallel to the main axis of the tail. Humeral proportions of Nullotitan (RI=0.28) On proximal caudals, the excavations are rela- are more gracile in comparison with the ro- tively large (i.e., 5 cm long in a centrum 22 cm bust humerus exhibited by Dreadnoughtus long), but are reduced or absent in more distal (RI=0.33), Elaltitan and Argyrosaurus (Huene, caudals. Such excavations are randomly distrib- 1929; Powell, 2003; Mannion & Otero, 2012; uted over centrum surface, being different from Lacovara et al., 2014; González Riga et al., 2019). the symmetrical ventral perforations present in Although Nullotitan exhibits a RI similar to that some titanosaurs, such as Pellegrinisaurus and of Notocolossus, this genus exhibits a humerus Drusilasaura (Salgado, 1996; Navarrete et al., with markedly asymmetrical proximal margin 2011). Clearly, the perforations do not invade in anterior view (nearly straight laterally but the vertebral centrum. Such pattern of blind strongly expanded and rounded proximomedi- randomly distributed excavations, resemble the ally) (González Riga et al., 2019), features absent excavations observed on the nuchal crest of felids in Nullotitan. (Duckler, 1997), which are produced by muscu- The proximal end of the femur is strongly me- lar activity, particularly overstretched muscles dially bent in Nullotitan, forming a large convex that create depressions (due to bone necrosis) surface that is not present in Dreadnoughtus, at attachment sites. In humans, this pattern is Mendozasaurus, and Patagotitan. In respect evidenced in athletic individuals who place high to robustness of femur, Nullotitan resembles strain on selected active muscles and have skele- more Dreadnoughtus than Patagotitan and tal responses at attachment sites in consequence Mendozasaurus, which show a more elongate (Duckler, 1997). Our best guess is that such large and narrow femur. The fibula of Nullotitan is 254 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 24. Nullotitan glaciaris gen. et sp. nov. Right astragalus (MPM 21542) in dorsal (A), ventral (B), anterior (C), lateral (D), posterior (E), and medial (F) views. Abbreviations: ap, ascending process; df, dorsal fossa; fc, calcaneum facet; tf, tibial facet. Scale bar: 10 cm. different from that of other large titanosaurs, et al., 2019). In this regard, the ventral aspect including Dreadnoughtus and Argentinosaurus of the caudal vertebrae of Nullotitan is unique (Bonaparte & Coria, 1993), in being strongly sig- in that the proximal and distal caudals show moidal in both anterior and lateral views. a relatively flat ventral surface of centrum, In the case of Drusilasaura, the few overlap- whereas mid-caudals exhibit a deep longitudi- ping elements preclude proper comparisons with nal furrow surrounded by two thickened ridges. Nullotitan. Both taxa share proximal caudals Presence of deep ventral furrow in Nullotitan strongly anteroposteriorly compressed with awl- should not be confused with the deep pneumatic like transverse processes that extend towards excavations present in derived titanosaurs such the vertebral centrum, a longitudinal ventral as Saltasaurus and Rocasaurus (Powell, 2003; groove delimited by thick ridges, and distal cau- Salgado & Azpelicueta, 2000). dals dorsoventrally compressed (Navarrete et al., Besides, caudal vertebrae of Nullotitan dif- 2011). However, Drusilasaura apomorphically fers from the caudal type reported for aeolosau- shows two large ventral foramina that are ab- rines (i.e., Aeolosaurus patagonicus and A. col- sent in Nullotitan. Further, Drusilasaura lacks huehuapensis; Powell, 2003; Casal et al., 2007; the blind fossa present along the lateral surface Martinelli et al., 2011) because in the latter ones of caudal vertebrae of Nullotitan. the neural arches are strongly inclined anteriorly Nullotitan differs from saltasaurids (sensu and have a more developed procoelous condition. Gonzáles-Riga et al., 2019) in having proximal Thus, the sum of features of the caudal vertebrae caudals anteroposteriorly short, with posterior of Nullotitan clearly distinguishes it from other articular surfaces slightly convex, and apneumat- Late Cretaceous derived titanosaurs from South ic centra. These are plesiomorphic traits indicat- America. ing that Nullotitan is not related with saltasau- In sum, although the scarcity of currently rids, which usually have caudal vertebrae with available materials of Nullotitan precludes a dorsoventrally depressed and strongly procoelous clear taxonomic referral, its anatomical details centra, and highly pneumatic centra and neural (mainly from the caudal vertebrae), support arches (e.g., Powell, 1993; Salgado et al., 1997; it as a valid gen. et sp.. Also, the large size of Bonaparte et al., 2000; Salgado & Azpelicueta, Nullotitan, in joint with the lack of saltasaurid 2000; Rose, 2007; Taylor, 2009; González Riga and aeolosaurine features, plus all the character- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 255 istics listed above suggest its placement among torids as Aerosteon and Murusraptor, in which colossosaurian titanosaurs. these surfaces become progressively deeper posteriorly. Large paired pleurocoels are present on Theropod dinosaurs both sides of the centrum; they are separated Remains of theropod dinosaurs (including by a wide and oblique septum, a diagnostic fea- birds) collected in the Chorrillo beds include sev- ture of Megaraptoridae (Novas et al., 2013). The eral isolated bones and a single tooth identified pleurocoels penetrate the centrum medially and as Megaraptoridae indet., as well as some pedal slightly ventrally. The internal structure of the phalanges referred with doubts to Noasauridae centrum is camellate, as occurs in other meg- and Unenlagiidae. Besides, eggshell fragments araptorids (e.g, Orkoraptor, Megaraptor; Calvo et are described as belonging to Theropoda indet. al., 2004; Novas et al., 2008; Benson et al., 2010, Available evidence, albeit fragmentary, clearly 2012; Porfiri et al., 2014). shows that the dinosaur fauna from the Chorrillo An isolated transverse process is interpreted as Formation was taxonomically diverse, formed belonging to a dorsal vertebra. It is oval in cross by clades also documented in other regions of section, and with camellate internal structure. Patagonia and Gondwana, but with an apparent Distally the process bears a concave and oval dominance of megaraptorids over other theropod surface for articulation with the rib tuberculum. groups. From the equivalent Dorotea Formation The articular surface of the process is proportion- in Chile, Manriquez et al. (2019) mention the dis- ally much bigger than in the cervical vertebrae of covery of theropod teeth, but no details on their other theropods. phylogenetic affinities was given. Caudal vertebra. This element is represented by the right side of a neural arch, including the Coelurosauria Huene, 1914 base of the transverse process and the base of Megaraptora Benson, Carrano and Brusatte, the postzygapophysis. The presence of a tall neu- 2010 ral arch suggests it corresponds to the proximal Megaraptoridae Novas et al., 2013 third of the tail. As in other vertebral elements, Megaraptoridae gen. et sp. indet. 1 this neural arch possesses a camellate internal structure. The preserved part of the neural arch Referred material. MPM 21545, fragmentary appears to be dorsoventrally more depressed specimen composed of a posterior dorsal cen- than in Aoniraptor and Murusraptor (Coria & trum, transverse process of a dorsal vertebra, Currie, 2016; Motta et al., 2016), but similar to partial neural arch of a caudal vertebra, frag- Megaraptor and Orkoraptor (Novas, 1998; Novas ments of two indeterminate vertebrae, rib frag- et al., 2008). The transverse process is robust, ments and proximal end of pubis (locality 3) dorsoventrally tall and posterolaterally directed. (Figure 25). The specimen was found in a 5x3 m Below it there is the anterior centrodiapophyseal surface area. lamina, which is robust and anteroventrally di- Horizon. Base of the upper third of the Chorrillo rected, delimiting anteriorly the prezygadiapo- Formation, lying above a thick bank of conglom- physeal-centrodiapophyseal fossa, and posterior- erates. ly the centrodiapophyseal fossa. The presence of Description. Available elements belong to a two laminae delimiting three fossae is observed megaraptorid similar in size to Aerosteon (Sereno in other megaraptorids such as Aoniraptor, et al., 2008), approximately 8-9 meters in whole Orkoraptor, Murusraptor, and Megaraptor length. (Calvo et al., 2004; Novas et al., 2008; Coria & Dorsal vertebrae. The isolated centrum is in- Currie, 2016; Motta et al., 2016). In contrast, in complete, lacking most of its dorsal portion. It other theropod groups (e.g., abelisaurids, car- probably corresponds to a posterior dorsal verte- charodontosaurids, tyrannosaurids) the neural bra, with transverse width vs maximum length arch lacks these laminae below the transverse ratio of 1.16, almost the same as dorsal 10th of process. Interestingly, the anteroventral limit Aerosteon. The anterior articular surface of cen- of the prezygadiapophyseal-centrodiapophyseal trum is concave, but the posterior one is flat. fossa is made up by an anteroposteriorly wide The lateral surfaces are remarkably concave, as and anteriorly inclined lamina. This robust lam- occurs with other big-sized theropods (Brochu, ina is observed in Aoniraptor, Murusraptor and 2003; Sereno & Brusatte, 2008). Ventrally, the Megaraptor, but not in Aerosteon and Orkoraptor. centrum is smooth and transversely convex. This The postzygapophysis is small and slightly lon- condition is observed in other big-sized megarap- ger than wide. Above it, the postspinal laminae 256 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 25. Megaraptoridae indet. (MPM 21545). (A-D) Partial dorsal centrum in dorsal (A), ventral (B), posterior (C) and right lateral (D) views. (E-G) Isolated dorsal transverse process in anterior (E), posterior (F) and distal (G) views. (H-K) Partial caudal neural arch in left lateral (H), dorsal (I), right lateral (J) and anterior (K) views. (L-O) Proximal end of right pubis in lateral (L), medial (M), anterior (N) and proximal (O) views. Abbreviations: acdl, anterior centrodiapophyseal lamina; pcdl, posterior centrodiapophyseal lamina; pl, pleurocoel. Scale bars 3 cm Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 257 ascends vertically and delimits the postspinal tral surfaces are concave. Laterally, the centrum fossa. This fossa is narrow and does not show in- shows a rounded fossa with an anterior pleuro- terspinous ligament tuberosity. coel and a posterior pleurofossa separated by an Pubis. The pubis is represented by the proxi- oblique septum, as it occurs in other megarap- mal end of the right bone. Its lateral surface is torans (e.g., Fukuiraptor, Aerosteon, Megaraptor, convex, while the medial one is both anteropos- Murusraptor, Tratayenia). The centrum is quad- teriorly and dorsoventrally concave. The medial rangular in side view, devoid of articular surfaces surface shows vertical striations probably for for both ribs and haemal arches, thus indicating ligament attachment. The anterior margin is it may correspond to the posterior dorsals. Also, transversely thick and convex in cross-section, the ventral surface is smooth and transversely whereas the posterior margin is thin and sharp. convex, contrasting with the caudal vertebrae The pubis is oval in proximal view, with a rugose of megaraptorans, which possess strong ventral articular surface for the iliac pedicle, and seems keels (Méndez et al., 2012; Motta et al., 2016). morphologically less complex than in other meg- Furthermore, in this element the posterior ar- araptorans, such as Aerosteon or Murusraptor ticular surface is flat but the anterior one shows (Sereno et al., 2008; Coria & Currie, 2016). The a moderate concavity.In dorsal view, the floor of proximal margin of pubis seems simple, lacking the neural canal is shallow and has a constant differentiation into acetabular, ischiadic and iliac transverse width. This condition is observed articular surfaces present in another megarap- in isolated dorsal centra of the megaraptorids torids. Aerosteon and Murusraptor (Sereno et al., 2008; Discussion. MPM 21545 exhibits the following Coria & Currie, 2016), while the caudal centra of megaraptorid synapomorphies: 1) dorsal cen- these theropods have a neural canal constricted tra with two pleurocoels separated by a septum around mid-length. In lateral view, the centrum (Novas et al., 2013); and 2) two centrodiapophy- is squared-shaped in outline, contrasting with seal laminae separating three fossae below the other megaraptorids, in which the centrum is transverse process of the anterior-middle caudal shorter and taller (e.g., Megaraptor Aerosteon, vertebrae (Calvo et al., 2004). This morphology Murusraptor, Tratayenia; Sereno et al., 2008; is absent in other theropods such as ceratosaurs, Coria & Currie, 2016; Porfiri et al., 2014, 2018). spinosaurids, allosauroids, tyrannosauroids, and However, Wilson et al. (2016) noted that this fea- ornithomimosaurs. ture seems size-dependant, and may be related with the fact that all of the above mentioned Megaraptoridae gen. et sp. indet. 2 megaraptorids are 8-10 meters long. Comments. Up to now, the Patagonian record Referred material. MPM 21546, isolated dor- of Megaraptoridae corresponds to large-sized sal centrum (locality 4) (Figure 26). animals, approximately 8-9 m long. For their Description. This small vertebra measures 2.72 size and relative abundance, these theropods cm long, 2.43 cm tall, and 2.79 cm wide. It is in- may have constituted the main predators during ternally pneumatized through a complex pattern the Early Maastrichtian in southern Patagonia. of lateral pleurocoels, similar to those of meg- Even juveniles may have played an important araptoran theropods (e.g., Sereno et al., 2008). ecological role in these southern dinosaur fau- Based on extrapolations with complete theropods nas, considering that the specimen here reported (e.g., Allosaurus; Madsen, 1976), we estimate attained a whole length of, at least, 2 m. This this specimen being approximately three meters means that megaraptorids probably preyed upon long. The maturity of the specimen is uncertain, different sized herbivore dinosaurs (small to me- but the small size of the element together with dium sized elasmarians, and bigger titanosau- the lack of fusion with the neural arch suggests rids) in the course of their ontogeny. it corresponds to a juvenile. This vertebra is even smaller than those of the juvenile specimen of Megaraptoridae gen. et sp. indet. 3 Megaraptor namunhuaquii described by Porfiri et al. (2014). Referred material. MACN-Pv 19066, iso- The centrum has a slightly concave anterior lated shed tooth crown, presumably com- articular surface and a flat posterior one, as oc- ing from the lower levels of the Chorrillo curs in posterior dorsal vertebrae of megarapto- Formation (Figure 27). Collected by J. F. rids (e.g., Murusraptor, Aerosteon; Sereno et al., Bonaparte in 1981 on the same large area were 2008; Coria & Currie, 2016). The lateral and ven- the holotype of Nullotitan glaciaris was found. 258 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 26. Megaraptoridae indet. (MPM 21546). (A-F) Posterior dorsal centrum in left lateral (A), ventral (B), posterior (C), right lateral (D), dorsal (E) and anterior (F) views. Abbreviations: pl, pleurocoel. Scale bar: 3 cm.

Description. MACN-PV 19066 is represented ticles of MACN-PV 19066 is higher than that in by a shed tooth crown that lacks its apex, a por- Fukuiraptor kitadaniensis (3−4 denticles per tion of the mesial margin, and some denticles in mm; Azuma & Currie, 2000), Orkoraptor burkei the distal margin. The crown is slightly curved (3−4 denticles per mm; Novas et al., 2008) and to the right in distal view and the mesial carina Megaraptor namunhuaiquii (3−4 denticles is displaced to the right of the distal one, thus in- per mm; MUCPv 595). The denticles are mesi- dicating that the tooth represents a left anterior odistally deeper and apicobasally tall and their maxillary or dentary dental piece. The crown has main axis is orthogonal to the distal edge of the an apicobasal height of 19.0 mm, a basal labio- crown, resembling the condition in the above lingual width of 6.8 mm, and a basal mesiodistal mentioned megaraptorans. The distal denticles length of 10.7 mm. of MACN-Pv 19066 have a rounded edge and are The crown is distinctly recurved in labial separated from each other by short interdenticu- and lingual views, with the apex being located lar sulci that do not extend as blood grooves, as distally to the base, as occurs in other meg- occurs in megaraptorids (e.g., Australovenator, araptorans (e.g. Fukuiraptor: Azuma & Currie, Megaraptor, Orkoraptor, Murusraptor; Hocknull 2000; Australovenator, Hocknull et al., 2009; et al., 2009; Porfiri et al., 2014; Novas et al., 2008; Megaraptor, Porfiri et al., 2014; Orkoraptor, Coria & Currie, 2016). In contrast, at least some Novas et al., 2008; Murusraptor, Coria & Currie, check tooth crowns of the non-megaraptorid 2016). The entire labial surface of the crown is Fukuiraptor have well-defined, oblique -basally apicobasally and mesiodistally convex, whereas oriented- blood grooves (Azuma & Currie, 2000). the distal one-third of the lingual surface is api- The mesial surface is considerably labiolingual- cobasally concave. This concavity produces the ly broader than the distal one and has a carina slight curvature of the crown in distal view. The which extends along the total length of the crown. rest of the lingual surface is homogeneously con- The carina reaches the apicalmost preserved por- vex. The distal margin of the crown possesses tion of the crown and lacks denticles, as occurs a sharp carina that begins 1 mm from the base in Megaraptor (Porfiri et al., 2014), Orkoraptor and reaches the apicalmost preserved portion (Novas et al., 2008) and Murusraptor (with ex- of the crown. This carina is serrated along its ception of the premaxillary teeth of this species; entire length, with a rather constant density of Coria & Currie, 2016). In contrast, Fukuiraptor five denticles per mm. Thus, the density of den- (Azuma & Currie, 2000) and Australovenator Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 259

Figure 27. Megaraptoridae indet. (MACN-Pv 19066), isolated shed tooth crown in (A), labial; (B), lingual; (C), mesial; (D), distal; (E), apical; and (H), basal views. F, G, selected anatomical details. Abbreviations: ds, distal serrations; mc, mesial carina. Scale bar: 1 cm.

(Hocknull et al., 2009) possess denticles on both distally recurved crown, with apex located distal mesial and distal carina. As far as it is preserved, to the base, and absence of mesial serrations. The the enamel of MACN-Pv 19066 is smooth, with- Chorrillo Formation megaraptorid tooth differs out wrinkles or wear facets. In contrast, exten- from those of other megaraptorids in its higher sive wear facets, but not wrinkles, are usually density of distal denticles and the absence of an present in other megaraptorids (e.g. Novas et 8-shaped cross-section at the base of the crown al., 2008; Hocknull et al., 2009). The base of the (Novas et al., 2013). Although MACN-PV 19066 crown is sub-oval in cross-section, with a labial suggests the presence of a previously unknown margin distinctly more convex than the lingual megaraptorid taxon we refrain of erecting a new one. There is no labiolingual constriction of the species because of the fragmentary condition of base of the crown, contrasting with the eight- the megaraptorid specimens currently known shaped cross-section of the base of the crowns from the Chorrillo Formation. of the megaraptorids Orkoraptor (Novas et al., 2008), Murusraptor (Coria & Currie, 2016) and Abelisauroidea Bonaparte and Novas, 1985 Megaraptor (Porfiri et al., 2014). Noasauridae Bonaparte and Powell, 1980 Comments. MACN-PV 19066 can be referred to Gen. et sp. indet. Megaraptoridae because of the presence of the following combination of characters: strongly Referred material. MPM 21547, isolated right 260 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 pedal phalanx IV-2? (locality 4) (Figure 28). Referred material. MPM 21548, pedal ungual Description. The non-ungual pedal phalanx is of digit II; MPM 21549, phalanx III-2. (locality 4) almost complete, lacking the ventral portion of (Figure 28). the distal condyles. The bone is 15 mm long and 8 Description. MPM 21548 consist on the proxi- mm high proximally. The element is proximodis- mal portion of the ungual phalanx of right pedal tally short, dorsoventrally deep, and transversely digit II, lacking its proximodorsal lip. The ungual narrow. The proximal articular surface of the is laterally compressed, being 9.9 mm in trans- phalanx has a dorsoventral keel separating two verse width, comparable in size with the corre- concavities, the medial one being slightly wider spondent ungual of Neuquenraptor argentinus than the lateral one. Proximally, the phalanx has (MCF PVPH 77; Novas & Pol, 2005; Brisson et a well-developed ventral projection, sub-triangu- al., 2017). It is elliptical-shaped in cross-section, lar in contour as viewed from above. The phalanx with collateral grooves asymmetrically placed, as is ventrally flat and smooth. Dorsally is trans- typical of paravians (Rauhut & Werner, 1995). versely narrower with respect to the ventral sur- The lateral surface is flat, while the medial one face, a condition resembling other abelisauroids is dorsoventraly convex. The proximoventral (e.g., Novas & Bandyopadhyay, 2001; Novas et al. flexor tubercle is well-developed and shows ru- 2004; Brissón Egli et al., 2016). Distally, the me- gosities on its ventral surface, as typically oc- dial condyle is more developed than the lateral curs among paravian theropods (e.g., Ostrom, one. The lateral collateral ligament pit is wider 1969). The proximal articular surface presents and deeper than the medial one. a well-defined dorsoventral keel separating two Comments. The pedal phalanx MPM 21547 re- sub-equals concavities. The ventral margin of sembles Noasauridae in being transversely nar- ungual forms a cutting edge that is continuous row and dorsoventrally deep, a condition shared with the lateral surface of the ungual blade. The with Velocisaurus and Vespersaurus (Brissón cutting edge is medially displaced, as it also oc- Egli et al., 2016; Langer et al., 2019). Further, curs in other paravians (e.g., Neuquenraptor, a well-developed, transversely thick, and pos- Deinonychus, Velociraptor, Buitreraptor; Ostrom, teriorly extended posterodorsal process is also 1969; Norell & Makovicky, 1999; Makovicky et shared with noasaurids, including Noasaurus, al., 2005; Brisson Egli et al., 2017). The longi- Ligabueino, Velocisaurus and Vespersaurus tudinal collateral grooves are proximally forked, (Langer et al., 2019), constituting a synapo- depicting the characteristic horizontal oriented morphic feature of Noasauridae (Agnolin & “Y”-shaped groove. Chiarelli, 2010). However, in the case for the Besides, specimen MPM 21549 is a complete phalanx here described the ventral projection pedal non-ungual phalanx, probably correspond- proximally surpasses the level of the dorsal lip, ing to pedal phalanx III-2. It was found nearby contrasting with known noasaurids in which MPM 21548 and their sizes are congruent to the projections are sub-equal in proximal ex- refer them to a single individual. Phalanx MPM tension (e.g., Laevisuchus, Noasaurus; Novas 21549 measures 45 mm long and 19 mm high, be- & Bandyopadhyay, 2001, Sampson et al., 2001, ing larger than that of Neuquenraptor (Brisson Novas et al., 2004; Agnolin & Chiarelli, 2010; Egli et al., 2017). Brissón Egli et al., 2016). The proximal articular surface lacks the me- Noasaurids have been recorded in differ- dial keel and shows a sub-triangular contour, ent Late Cretaceous localities of Gondwana, in- with a straight ventral margin. The proximodor- cluding India (Novas & Bandyopadhyay, 2001; sal lip has a sub-triangular profile in dorsal view, Novas et al., 2004), Africa (Sampson et al., 2001) proximally surpassing the level of the articular and South America (Bonaparte & Powell, 1980; surface. The proximal articular surface is gen- Bonaparte, 1991; Brissón Egli et al., 2016; Langer tly concave. The proximal portion of the ventral et al., 2019; Martinelli et al., 2019). Present speci- surface has a rugose and flat shelf. Distally, the men constitutes the southernmost record for this extensor fossa is wide. The distal condyles are theropod family, and forms part of a small-sized circular-shaped in lateral view and have wide theropod fauna also integrated by megaraptorids collateral ligament pits. In lateral view, the dis- and unenlagiids (see below). tal condyles slightly surpass the dorsal margin of the body of the phalanx. Paraves Sereno, 1997 Comments. Unenlagiids were recorded in NW Unenlagiidae Bonaparte, 1999 Patagonia and NW Argentina (Agnolin and Gen. et sp. indet. Novas, 2013). MPM 21548 and MPM 21549 con- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 261

Figure 28. Theropod pedal elements. (A-C), isolated noasaurid right pedal phalanx IV-2? (MPM 21547) in medial (A-B) and dorsal (C) views; (D-H), Unenlagiid pedal elements. Right pedal phalanx III-2 (MPM 21549, D) and right pedal ungual of digit II (MPM 21548, E-G) in lateral (D), ventral (E, F), and medial (G-H) views. Abbreviations: cp, colateral pit; ft, flexor tubercle; mvc, medioventral crest; pdp, posterodorsal process; pvp, posteroventral process. Scale bar: 10 cm stitute the southernmost unenlagiid record for Holotype. MPM 21550, incomplete right cora- South America. This unenlagiid, similar in size coid lacking sternal end and proximal end dam- and shape to Neuquenraptor, expands the mea- aged (locality 2) (Figure 29). gre record of Maastrichtian unenlagiids from Diagnosis. Medium-sized derived ornithurine Argentina, up to the date represented by the diagnosable on the basis of the following unique combination of characters (autapomorphies large bodied Austroraptor (Novas et al., 2009). marked by an asterisk*): 1) robust coracoidal shaft with well-defined and proximodistally ex- Aves Linnaeus, 1758 tended procoracoid process; 2) ligamentum cora- Ornithurae Haeckel, 1866 coscapulare ventralis forming a well-defined scar, resulting in a notch that separates the scapular Kookne yeutensis nov. gen. et sp. cotyla from the facies articularis humeralis; 3) 262 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 facies articularis humeralis ovoidal in shape, is narrow and bifurcates in two main ridges that with its distal half more transversely expanded delimit a well-defined and cup-shaped impressio than the proximal half; 4) cup-shaped impression for the acrocoracohumeral ligament. The dorsal for the acrocoracohumeral ligament, with thick- crest becomes proximally prominent and medi- ened and well-defined margins*. ally wraps the triosseous canal. Etymology. “Kookne”, mythological swan com- The lateral surface of the coracoid shows a sub- panion of the Aonikenk hero Elal; and yeutensis, triangular flattened surface with its tip pointing from “yeut”, “mountain” in Aonikenk language. distally. This surface is ventrally delimited by a Description. Kookne yeutensis is represented by very narrow but conspicuous ridge corresponding an isolated coracoid lacking the sternal end and with the M. supracoracoidei. Distal to this ridge, showing badly damaged acrocoracoidal process. there is preserved the proximalmost portion of The coracoid is robust, and belongs to a medium- the intermuscular ridge between the M. coraco- sized bird, the size of a tern (maximum preserved brachialis caudalis and M.supracoracoideus (see proximodistal length of coracoid is 23.4 mm, mi- Jasinoski et al., 2006). nor coracoidal transverse width is 4.8 mm, and In medial view the coracoid shows a very deep the preserved transverse width at level of scapu- and wide triosseal canal. This is represented by lar cotyla is 6.3 mm). The distal end of the bone the excavation for the M.supracoracoidei which exhibits a transverse linear ridge for the impres- forms a deep groove that is distally extended as a sion of the M. sternocoracoidei. This ridge is narrow sulcus reaching the distal end of the pro- obliquely oriented and runs from the laterodistal coracoidal process. Proximally, this groove shows to the medioproximal edges of the bone. a dorsal depression that is subcircular in contour. The procoracoid process is present, but lacks Comments. The coracoid is one of the most di- its distal tip. It is represented by an acute lamina. agnostic elements of the avian skeleton (Hope, This process is relatively dorsoventrally short, 2002). Because of its taphonomical attributes, distally extending as a narrow but well-defined the coracoid is the most commonly preserved ele- ridge, constituting the medial edge of the distal ment among Mesozoic birds (see Higgins, 1999; half of the coracoid. Distal to the procoracoid pro- Longrich et al., 2011). In spite of being repre- cess there is a strap-like impression for the M. sented by a single, isolated coracoid, Kookne is subscapularis, as is observed in modern anseri- referred to derived Ornithurae by having an forms (e.g., Anas) and Maaqwi (McLachlan et al., acrocoracoid process that curves medially to em- 2017). At the base of the procoracoidal process brace a wide and deep triosseal canal, and a broad there is a small, ellipsoidal-shaped foramen for furcular articulation (Agnolin, 2010; McLachlan the N. supracoracoidei. This foramen penetrates et al., 2017). Within Ornithurae, the coracoid is the bone dorsally and leaves the bone medially, similar to Palintropus, Ichthyornis, and more within the supracoracoidei groove. This foramen derived forms in having a ligament scar on the is distal to the medial margin of the scapular dorsal surface of the acrocoracoid (Longrich, cotyla, and is slightly recessed. 2009). As occurs in Ichthyornis and crown Aves The scapular cotyla is roughly subtriangular it exhibits a triosseal canal passing ventral to in contour. The margins of the cotyle are nota- the scapular articular facet (McLachlan et al., bly thick, especially the lateral and distal ones. 2017). Further, Kookne is more derived than Laterally, the distal margin of the cotyle is de- Ichthyornis, and resembling crown Aves, in hav- limited by a notch formed by the scar of the ing the following features: humeral articular ligamentum coracoscapulare ventralis. This scar facet anteriorly displaced relative to the scapu- separates the scapular cotyle form the articular lar articular facet, scapular and humeral facets surface for the humerus. The humeral articular well-separated each other, and acrocoracoid that surface is relatively large, roughly ovoidal in con- medially wraps the triosseal canal (Hope, 2002; tour and its surface is slightly concave. Its distal Agnolin, 2010; McLachlan et al., 2017). In sum, half is transversely wider than its proximal half. all features exhibited by Kookne are shared with The lateral margin is slightly thickened. Its dis- derived Ornithurae, mostly Neornithes. In this tal end is more proximally located than the distal way, we refer Kookne to crown birds. level of the scapular cotyla and is delimited by Mesozoic Neornithines or stem-Neornithines the scar of the ligamentum coracoscapulare ven- are scarce in the fossil record. Most taxa are tralis. The humeral articular surface is laterodor- grouped within Cimolopterygidae (Longrich, sally oriented and slightly proximally tilted. The 2009; Agnolin, 2010; Longrich et al., 2011; proximal edge of the humeral articular surface McLachlan et al., 2017), Palintropidae (Brodkorb, Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 263

Figure 29. Kookne yeutensis gen. et sp. nov. Right coracoid (MPM 21550; holotype) in dorsal (A), lateral (B), ventral (C) and medial (D) views. Abbreviations: fah, facies articularis humeralis; fas, facies articularis scapularis; ial, impression for the acrocoracohumeral ligament; imcc, impressio for the m. coracobrachialis caudalis; imsc, impressio for the m. supracoracoideus; imss, impressio of the m. subscapularis; imst, impressio for the m. sternocoracoidei; lcsv, ligamentum coracoscapularis ventralis; nsc, foramen for n. supracoracoidei; pcr, procoracoidal process; tc, triosseal canal. Scale bar: 1 cm

1970; Hope, 2002), and Vegaviidae (Agnolin et al., ventral margin is straight (instead of strongly 2017). Kookne does not fit with any previously concave as in Vegavis and Maaqwi) resulting in a named derived ornithurine from the Mesozoic. subvertically oriented acrocoracoid process. It differs from Palintropus and kin by a large Cimolopterygids are a widespread clade of number of features, including retention of a Cretaceous and possibly Paleogene birds that well-developed procoracoidal process, foramen include a large variety and diversity of mor- for N.supracoracoidei proximally located at the photypes (Longrich, 2009). Most cimoloptery- base of the procoracoid process, scapular facet gids are based on isolated and often fragmented not laterodistally positioned, and ventral margin coracoids, with a wide morphological divergence. with a straight anterior edge (Hope, 2002). However, cimolopterygids share some common Further, Kookne differs from Vegaviidae in traits that are absent in Kookne. For example, lacking thickened bone cortex on the coracoid and Cimolopteryx and Lamarqueavis show a very in having more gracile proportions (McLachlan large and distally located foramen for the N. su- et al., 2017). Detailed comparisons with Vegavis pracoracoidei, procoracoid process laminar and resulted in the following differential features: in dorsoventrally extended, and humeral articu- Kookne the procoracoid is more ventrally extend- lar surface dorsoventrally oriented (Brodkorb, ed, the humeral facet is dorsolaterally faced (in- 1963; Hope, 2002; Agnolin, 2010). This com- stead of being laterally faced as in Vegavis), the bination of characters is absent in Kookne. 264 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Iaceornis is a purported neornithine coming in contour, and foramen for N. supracoracoidei from the Late Cretaceous of USA, and described more distally located (Hope, 2002; De Pietri et by Hope (2002) under the name of Apatornis (see al., 2016). This combination of traits is absent also Clarke, 2004). It was previously referred in Kookne. In addition, Kookne differs from the to Galloanseres (Hope, 2002; Clarke, 2004). It early Paleocene anseriform Conflicto in retaining sharply differs from Kookne in having a notably a foramen for the N. supracoracoidei, humeral elongate omal end, with proportionately smaller shaft more robust, and scapular facet ovoidal, acrocoracoid and humeral facet, and a narrow among other minor details (see Tambussi et al., scapular cotyla and shallower triosseal canal 2019). (Hope, 2002; Clarke, 2004). In spite of its fragmentary nature, Kookne Among neornithines, Kookne shows a combi- represents an important addition to the fossil re- nation of characters (e.g., well-developed acroco- cord of Late Cretaceous birds from the in South racoid and procoracoid processes, well-developed America and Antarctica. Most relevant evidence foramen for N. supracoracoidei, coracoidal shaft comes from NW Argentina, NW Patagonia, and relatively short and stout) clearly distinguishing Antarctic Peninsula (e.g., Agnolin, 2010; Agnolin it from ratites, tinamids, galliforms, gruiforms et al., 2017). Bird remains have been also re- and podicipediforms (Hope, 2002). Further, corded from the Dorotea Formation (Manriquez the coracoid of Kookne differs from that of et al., 2019). Kookne expands avian diversity for Charadriiformes in that the humeral facet is not the southern extreme of Patagonia, and demon- large and ovate, the foramen for the N. supraco- strates, in join with Lamarqueavis and Vegavis, racoidei is not caudally recessed from the scap- that an important morphological divergence ex- ular cotyla, and the scapular cotyla is not par- isted in the southern cone during Maastrichtian ticularly large and subcircular in contour (Hope, times (Agnolin et al., 2006; Agnolin, 2010; Clarke 2002). Further, in charadriiforms the humeral et al., 2016). This also supports the idea (firstly facet and coracoidal shaft are usually medially expressed by Chatterjee, 2002) that the Southern tilted (Hope, 2002). Hemisphere played a key role in the origin and Kookne is reminiscent of Anseriformes in early evolution of modern birds. sharing several derived features, including: transverse linear ridges within the impressio Dinosaur eggshells sternocoracoidei (Ericson, 1997; Mayr & Smith, Abundant dinosaur eggshells have been re- 2001); expanded articular surface for the furcula corded from the lower and middle sections of (a feature recovered diagnostic for Anseriformes the Chorrillo Formation. Dinosaur egg-shell in recent analyses; Clarke et al., 2016); ventral fragments of two types have been collected from border of sulcus for the M. supracoracoidei co- Titanosaur tibia (locality 2) and Puma Cave (lo- lumnar-shaped, and increasing in diameter to- cality 4) sites. The microstructural patterns ob- wards the clavicular facet; and well-defined fossa served in the eggshells agrees with that previous- within the supracoracoideus groove (Hope, 2002), ly described for sauropods (i.e., Fusioolithidae) and well-excavated acrocoracohumeralis impres- and theropods (i.e., Prismatoolithidae). sion (Mayr & Smith, 2001). In Kookne the ligamentum coracoscapulare ventralis forms a well- Oofamily Fusioolithidae Fernández & Khosla, defined scar, a feature shared with Anseriformes 2015 (Hope, 2002). A similar condition is observed Fusioolithus Fernández & Khosla, 2015 in Ceramornis (figured as “lateral fossa” by Fusioolithus ichnosp. Longrich et al., 2011), but in this case the fossa is notably wider and crescent-shaped. In sum, this Referred material. MPM 21543, thirty four combination of characters strongly suggests an- eggshells collected from locality 4; MPM 21544, seriform affinities for Kookne. However, its frag- twenty two eggshells collected from locality 2 mentary nature makes this referal tentative. (Figure 30). Most frequently cited Latest Cretaceous Description. The outer eggshell surface displays anseriforms belong to Presbyornithidae. a compactitubercular ornamentation with coales- Presbyornithid coracoid, as exemplified by cent nodes, showing partial fusion of shell units Presbyornis and Telmatornis. is characterized by into more nodes (Figure 30A,B,E), with pore ap- a notably elongate neck and narrow humeral fac- ertures located in the depressions among them. et which is proximodistally expanded and notably The eggshell is 0.97 mm thick and each node is flattened, scapular facet large and subcircular about 0.7 mm in diameter. The pore system is Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 265

Figure 30. Dinosaur eggshells. (A-B, E) Fusioolithus sp. eggshell fragment (MPM 21543). A, external view; B, radial section; E, radial section showing the microstructure of the sample. (C-D, F) Prismatoolithidae eggshell fragment (MPM 21551) (C) external view; (D) radial section; (F) radial section under MEB showing three main structural layers: mammillary, prismatic and external. Abbreviations: CL, continuous layer; ML, mammillary layer. Scale bar 1 mm in A-E, 200 µm in F. tubocanaliculate. This set of features allows re- ary between shell units starting on the one-third ferral of specimens MPM 21543 and MPM 21544 of the inner of the eggshell thickness and some- as to the Fusioolithidae oogenus Fisuoolithus times continue to the external surface. Eggshell (see Fernández & Khosla, 2016). is composed of circular cones without clearly Comments. Late Cretaceous eggs and eggshells demarcated boundary lines; the shell units are from Patagonia, usually interpreted as cor- partially fused. The shell units are fan shaped responding to Titanosauria, have been sorted similar to the eggs of oofamily Megaloolithidae into three different oofamilies: Fusioolithidae, but it differ in the nature of the eggshell units in Faveoloolithidae, and Megalolithidae. The which they are partially fused. (Fernández and Fusioolithidae, including Fusioolithus baghensis Khosla, 2014). Fernandez & Khosla 2016, documented in the Besides, Faveoloolithidae is abundantly rep- Campanian Anacleto Formation, Auca Mahuevo, resented in Patagonia in Allen and Los Alamitos Neuquen, and Maastrichtian Allen Formation formations, Salitral Moreno, Rio Negro), and from Santa Rosa and Trapalcó (Rio Negro). distinguish for being coarse-shell eggs, with com- Fusioolithidae characterize by a dinosauroid- pactituberculated ornamentation, filiesferulitic spherulitic basic type, tubospherulitic morpho- structural morphotype, and multicaniculated type, tubocanaliculate pore system. Its ornamen- pore system. Paquiloolithus rionegrinus (Simón, tation is compactituberculate. Thins sections 2006) has been referred to this oofamily. shows that the accretion lines cross the bound- Finally, Megaloolithidae is represented 266 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Megaloolithus jabalpurensis (Fernández & of the mammillae, with no evidence of nucletion Khosla, 2014; 2016), documented in Bajo de center. These spherulites growth distally, up to la Carpa Formation, Neuquén City, and the the limit with the continuous layer, changing Campanian-Maastrichtian Allen Formation at their orientation to form compact aggregates of Santa Rosa, Trapalcó, and Salitral Moreno (Rio vertical rhombohedral crystals. These crystals Negro Province). These eggshells have a discre- gradualy change into the continuous layer. For tispherulitic morphotype, eggs are spherical to this reason, and because of indistinct bound- sub-spherical in shape with diameter variable ary, these eggshells belong to the “dinosauroid- from 140 to 160 mm. The eggshell thickness prismatic basic type” (Mikhailov, 1997). The ranges from 1.0 to 2.38mm and shows compac- continuous layer reveals more homogeneous and tituberculate ornamentation. The average node compact tabular ultrastructure. The organic core diameter is about 0.67mm with diameter rang- is not preserved. Whitin the continuous layer, ing from 0.35 to 1mm. The shell units are fan the prismatic and external zones can be distin- shaped and of variable width and shape. The lat- guished, the last one showing a more compact eral margins of shell units are non-parallel. The material. This set of features allows referral of average height/width ratio is 2.45:1. The growth specimen MPM 21551as to the Prismatoolithidae lines are moderately arched upwards, and have oofamily. tubocanaliculate pore system (pore canals are Comments. Late Cretaceous eggs and egg- straight). shells from Patagonia interpreted as belonging Features enumerated above for MPM to Theropoda are restricted to the single oo- 21543 and MPM 21544 are consistent with species Arriagadoolithus patagoniensis, from Fusioolithidae, and sharply differ from the Maastrichtian Allen Formation, Río Negro both Faveoloolithidae and Megaloolithidae. (Agnolin et al., 2012). MPM 21551 differs from Faveoloolithidae have 5mm thick eggshells, Arriagadoolithus patagoniensis in that in the while MPM 21543 and MPM 21544 are thinner, later one the shell is much thicker (about 1 mm), faveoloolithid nodes from external surface are and the outer ornamentation is much more com- smaller than fusioolithid nodes, then faveoloolit- plex (it composes of low irregular nodes, isolated his eggshells have different pore canal sytem node-like ridges, low an elongate ridges intercon- (multicanaliculated) and shell units are multi- nected each other to form a net; Agnolin et al., spherulitic (Mikhailov, 1997). On the other hand 2012). Megaloolithidae eggs have compactutuberculat- ed ornamentation, but each node at the external Mammalia Linnaeus, 1758 surface appears isolated. Shell units are sharply Genus and species indeterminate separated from each other, constituting an important diference with fusioolithid eggshells Referred material. MPM 21552, anterior cau- (Mikhailov. 1997). dal vertebra (Figure 31 A-E), and MPM 21553, mid-to-posterior caudal vertebra (Figure 31 F-K). Oofamily PRISMATOOLITHIDAE Hirsch, 1994 Both caudals were collected from locality 4. Ichnogenus and Ichnospecies indet. Description. MPM 21552 and MPM 21553 are identified as caudal vertebrae of Mammalia on Referred material. MPM 21551, five eggshells the basis of following combination of features: collected in locality 4 (Figure 30). 1) platycoelous centra; 2) presence of two lon- Description. The sculpture of the outer surface gitudinal keels on the ventral surface of cen- is nearly smooth, with some areas finely sculp- trum; 3) neural spine anteroposteriorly long tured (Figure 30C,D and F). The eggshell is 0.2 and very low; 4) postespinal fossa present; 5) through 0.3 mm thick. Observed under SEM it transverse processes aliform; 6) transverse pro- shows a prismatic structure separated into two cesses divided into anterior and posterior por- different layers: a mammillary layer (ML), 0,06 tions, separated through a medial constriction; mm thick, and a continuous layer (CL) 0.23 mm 7) transverse process with a blunt lip on both thick. The CL:ML ratio is 1:0.2. The boundary anterior and posterior ends; 8) prezygapophy- between layers is not abrupt. The mammillary seal process more extensive than the postzyga- layer exhibits a tabular structure, showing radial pophyseal one; and 9) absence of neural canal. sections with slender mammillae with straigth This set of characters is not observed in caudal limits between each mammilla. The mammillae vertebrae of other vertebrate groups, includ- are built up by spherulites rising from the base ing turtles, lizards, crocodiles and dinosaurs. Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 267

The MPM 21552 is an incomplete posterior with the haemal arches. half of centrum of a relatively large vertebra, be- The neural spine is low and feebly devel- ing robust and transversely wide (8.99 mm). The oped. Near the anterior and posterior ends, the vertebral centrum is subcircular in transverse neural spine is subdivided into two crests that section, slightly dorsoventrally depressed, and delimit the preespinal and postespinal fossae, re- becomes notably narrower at mid- length. The spectively. Prezygapophyseal processes are well posterior articular surface is platycoelous. The developed, dorsolaterally projected and located base of the transverse processes is located at cen- laterally with respect to the preespinal fossa. trum mid-height, it is anteroposteriorly extended Postzygapophyseal processes are absent. There and reaching the posterior margin of centrum. are several nutrient foramina on both sides of The neural arch is poorly preserved. The bases the neural spine; one foramen is located between of the postzygapophysial processes are located on the anterior and posterior transverse processes. the dorsolateral corner of centrum. The base of The position and shape of transverse processes the neural spine is located on the middle portion and neural spine indicate that this element be- of the dorsal surface of neural arch. The neural longs to a mid-caudal or posterior portion of the spine is posteriory forked, bounding a narrow tail. postespinal fossa, “V”-shaped in contour. On Comments. Excepting for domestic species, com- ventral surface the centrum has two shallow lon- parative studies on caudal vertebrae in extant gitudinal keels. The combined presence of these and extinct mammals are scarce (e.g., Horovitz & keels in join with the position of transverse pro- Sánchez-Villagra, 2003). Specimens here reported cesses, indicate that this element is an anterior show transverse processes slightly laterally pro- caudal vertebra. jected, low neural spines, and poorly developed MPM 21553 is a complete caudal vertebra, ventral keels. This combination of characters is smaller (7.7 mm long and 4.3 mm of maximum shared with mammals having long and gracile transverse width) but proportionally more tails, as reported for Jeholodens, Yanoconodon, slender than MPM 21552. This vertebra is no- Agilodocodon, Henkelotherium, Akidolestes, tably elongate and dorsoventrally depressed, Eomaia, Pucadelphys, and Mayulestes, for exam- being cylindrical in gross-shape. The centrum ple (Nessov et al., 1998; Ji et al., 1999; Vázquez- is transversely wide at both anterior and poste- Molinero et al., 2001; Ji et al., 2002; Argot, 2003; rior ends, being more constricted at mid-length. Luo et al., 2007; Chen & Luo, 2013; Meng et al., Both articular surfaces are subcircular and with 2015). The morphology described above for MPM a shallow notochordal notch. Several nutrient 21552 and MPM 21553 are also present in some foramina are present on the ventral surface of living mammals with elongate tails, such as fe- centrum. Both anterior and posterior trans- lids (e.g., Panthera leo MACN 21.621), platyr- verse processes are separated by a constriction rhins (e.g., Alouatta caraya MACN 33.170), and at mid-length; they are wing-shaped, sharp and metatherians (e.g., Macropus giganteus MACN slightly laterally projected. Transverse processes 48.214). ends in blunt lips, probably representing the As far as for Mesozoic mammals from South insertion of M.ischiocaudalis and M.abductor America, caudal vertebrae have been described caudae dorsalis (Argot, 2003). The anterior lips only for Vincelestes (Rougier, 1993). Unlike MPM are ventrally projected and are longer and more 21552 and MPM 21553, in Vincelestes the caudal robust than the posterior lips. There is a small vertebrae show different proportions, being no- concave depression at the dorsal surface of the tably short and stout, with enlarged transverse transverse processes for probable attachement of processes, higher neural spines, and very large M. sacrocaudalis dorsalis (Kielan-Jaworowska & neural canals (Rougier, 1993). Gambaryan, 1994). On the ventral surface, the Some traits described above for Vincelestes transverse processes exhibit a depression, deeper have been also reported for other Mesozoic mam- than the dorsal one, probably corresponding to mals, such as Castorocauda, Fruitafossor, and the insertion of the M. sacrocaudalis ventralis Repenomamus (Hu et al., 2005; Luo & Wible, (Kielan-Jaworowska & Gambaryan, 1994). The 2005; Ji et al., 2006), as well as many Cenozoic ventral surface of centrum has two, well-devel- and Recent mammals with robusts tails (e.g, oped longitudinal keels, which extend along the Paleonodonta, Pantodonta, Xenarthra, Pholidota, anterior half of the vertebra. On the contrary, Talpa, and some rodents; Krause & Jenkins, these keels are reduced on the posterior half of 1983; Rose et al., 1992; Muizon et al., 2015). the centrum. These crests probably contacted These taxa possess robust caudal vertebrae, 268 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Figure 31. Mammalia indet, caudal vertebrae in A, F, dorsal; B, G, ventral; C, K, posterior; D, H, left lateral; E, I, right lateral; and J, anterior views. (A-E) MPM 21552 and (F-K) MPM 21553. Abbreviations: ap, anterior pit; atp, anterior transverse process; nf, nutrient foramina; nn, notochordal notch; ns, neural spine; pp, posterior pit; ptp, posterior transverse process; prsf, prespinal fossa; prz, prezygapophyseal process; ptsf, postspinal fossa; vc, vertebral centrum; vk, ventral keel. Scale bars: 10 mm. with laterally extended transverse processes, tebrae from the Chorrillo Formation belong to high neural spines, postzygapophyseal processes a meridiolestidan, need to be corroborated with present along the tail, and robust haemal arch- more anatomical evidence. es. This robust tail has been related with either swimming or digging behaviors (Ji et al., 2006). Invertebrates: Freshwater and Land MPM 21553 is a mid- to posterior caudal, Mollusks perforated by several nutrient foramina and Abundant gastropod material (mainly fos- presence of transverse processes with marked sil casts) has been collected at locality 4, cor- muscle attachments. These two features suggest responding to the base of the upper third of that the mammal from Chorrillo had a tail with Chorrillo beds. Available material consists of marked neurovascular innervation and a strong 56 specimens, found in close association with muscular development, possibly related with a isolated vertebrate remains. Mollusk specimens semi-arboreal lifestyle. belong to the freshwater families Ampullariidae, Upper Cretaceous beds from Patagonia (main- Pleuroceridae, Tateidae and Physidae, as well ly Los Alamitos and Candeleros formations, Río as to the terrestrial families Holospiridae, Negro province) yielded a variety of gondwanathe- Bulimulidae and Achatinidae. Aquatic forms rians and meridiolestidans (Bonaparte, 1986; predominate at level of families (60%), as well as 1990; 1992; 1994; 2002; Rougier et al., 2009a, number of collected specimens (80%). 2009b, 2011), including forms the size of a squir- Classification here followed corresponds to rel, such as the meridiolestidans Cronopio and the WoRMS Editorial Board (2019). For some Leonardus (Rougier et al., 2011; Chornogubsky, families, new genera and species will be de- 2011). Whether the small-sized mammalian ver- scribed elsewhere (Miquel & Brito, in press). Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 269

Subclass Caenogastropoda Cox, 1959 America (Simone, 2006), being absent from Order Architaenioglossa Haller, 1892 Patagonia. Superfamily Ampullaroidea Gray 1824 Ampullariidae Gray, 1824 Superfamily Truncatelloidea Gray, 1840 Pomacea sp. Tateidae Thiele, 1925 Potamolithus sp. Referred material. MPM 21554, four fragmentary casts (Figure 32 A). Referred material. MPM 21557, thirty-six Description. Casts globose, with short spires, fragmentary casts (Figure 31 D). and last whorl very convex and with rapid Description Casts globose, with low spire and growth. Larger specimen measures 18.1 mm of last whorl large and barely convex; one specimen maximum size and 15.1 mm of maximum width, with maximum size of 11.4 x 9.2 mm and 4.50 and 2.25 whorls. whorls. Comments. Ampullariidae has a Gondwanan Comments. Cretaceous record of Tateidae distribution, with fossil taxa from the Eocene of Forasiepi & López Armengol (1999) mentioned Africa, Asia and America (http://www.bagnilig- the presence of Potamolithus windhauseni gia.it /WMSD/ WMSDhome.htm, 2017). Extant (Parodiz, 1961) for the Los Alamitos Formation representatives are widely distributed in the (Campanian – Maastrichtian) from Río Negro Neotropical Region, with no living representa- Province, Argentina. The genus has a restricted tives in Patagonia (Castellanos & Landoni, 1995). areal distribution in South America, compre- Pomacea, in particular, has been recorded from hending the Río de la Plata basin and relict popu- the Eocene of La Pampa province (Argentina; lations in southern Argentina and Chile (Miquel, Melchor et al., 2002). Specimens here described 1998; de Lucía & Gutiérrez Gregoric, 2017). The represent the first Cretaceous worldwide record specimens here described constitute the south- for Ampullaridae, and the southern-most record ern-most record of Potamolithus. for the genus Pomacea. Superfamily Planorboidea Rafinesque, 1815 Superfamily Cerithioidea Flemming, 1822 Physidae Fitzinger, 1833 Pleuroceridae P. Fischer, 1885 Genus and species indeterminate Referred material. MPM 21558, Physa sp., one incomplete cast (Figure 32 E); MPM 215599, Referred material. MPM 21555, MPM 21556, Stenophysa sp., two incomplete casts (Figure two fragmentary casts (Figure 31, B-C). 32F). Description. Casts with whorls of uniform Description. Sinistral gastropods, ovoid to fu- growth, with last whorl well-developed; sutures soid, with little to well-developed spire, and with delineated by an angular rim; one specimen with last whorl prominent. One of the specimens re- maximum size of 31.5 x 17.3 mm and 6 whorls. In ferred as to Physa sp. has a maximum size of 8.9 another specimen, whorls are slightly convex, of x 5.5 mm and1.5 whorls. Specimen referred as to regular growth, and suture marked with a quite Stenophysa sp. attains a maximum size of 13.7 x strong shoulder; one specimen with maximum 7.5 mm and 4 whorls. size of 20.1 x 11.6 mm and 5 whorls. Comments. Physidae are pulmonate gastro- Comments. Pleuroceridae is known from the pods, historically classified in a confused way Lower Cretaceous (Goniobasis multicarinata (Taylor, 2003). This family has an almost world- Russell, 1932) from Alberta, Canada (Henderson, wide distribution, with no living representatives 1935). The genus Paleanculosa Parodiz, 1969 Patagonia. has been recorded from Paleocene beds of South Genus Physa has been reported from differ- America, including P. bullia Ihering, 1907, P. mac- ent Upper Cretaceous localities of North America rochilinoides Doello Jurado, 1927, P. rionegrina (White, 1877; Taylor, 2003; Russell, 1935) and Parodiz, 1969, and Paleoanculosa sp. (Parodiz, South America (Cabrera et al., 2018; Mezzalira, 1969). Some taxa related with Pleuroceridae 1974; Ghilardi et al., 2011). For Patagonia, the were also described from the Cenomanian Mata species Physa doeringi Doello Jurado, 1927, and Amarilla Formation (Pyrgulifera Meek, 1872; Physa wichmanni Parodiz, 1961, have been de- Santa Cruz Province; Griffin & Varela, 2012). scribed for the Maastrichtian-Danian Jagüel Extant representatives of Pleuroceridae in- Formation (Río Negro province; Salvador et al., habit aquatic systems in warm regions of South 2018). Thus, discovery of specimens of Physa in 270 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 the Campanian - Maastrichtian Chorrillo beds Description. General aspect “bulimoid”, simi- expands to the south the paleobiogeographic lar to the extant genus Bulimulus Leach, 1814, distribution of the genus. Regarding Stenophysa Bostryx Troschel, 1847, and Naesiotus Albers, Martens, 1898, the specimens collected from the 1850, of medium size, with several whorls that Chorrillo Formation represent the first world- increase its size gradually; one specimen with wide Cretaceous records for this genus. maximum size of 23.3 x 16.0 mm and other ones with maximum size of 13.9 x 7.6 mm, with 6 and Superfamily Achatinoidea Swainson, 1840 8.5 whorls, respectively. ?Achatinidae Swainson, 1840 Comments. This is a family with extant rel- ?Subulininae P. Fischer & Crosse, 1877 ict populations in Patagonia (Breure, 1979). Some Cretaceous Bulimulidae recorded from Referred material. MPM 21560, MPM 21561, South America include: Bulimulus klappenbachi two fragmentary casts and shells (Figure 32 (Parodiz, 1969) from the Queguay Formation G-H). (Uruguay, Late Cretaceous) (Cabrera et al., 2018; Description. Fragments with general appear- Veroslavsky et al., 2019); others, more modern, ance of “Subulinidae”, one of them large, with are Thaumasthus patagonicus Parodiz, 1946 axial sculpture, and another specimen medium (Eocene), Paleobulimulus eocenicus Parodiz, and smooth. The former with maximum size of 1949 from the Eocene-Miocene of Chubut 14.4 x 8.9 mm and 2 whorls; the latter with maxi- (Argentina), and Bostryx sp. and Bulimulus mum size of 16.2 x 11.0 mm and 2 whorls. sp. from the Eocene of La Pampa (Argentina) Comments. Subulininae is recorded from the (Melchor et al., 2002; Salvador et al., 2018). upper Paleocene of the Americas (Zilch, 1959) Bostryx sp. aff. Bostryx jujuyensis (Holmberg, and the Eocene of China (Pan, 1977). In South 1900) as Bulimulus aff. jujuyensis was mentioned America, the subulinine genus Neobeliscus from early Late Miocene of Catamarca (Miquel, Pilsbry, 1896 is recorded from the Miocene 1995; Salvador et al., 2018).The specimens here Pebas Formation (Brazil). Extant subulinines reported constitute the first record for the family inhabit South America (Simone & Mezzalira, for the Cretaceous of Patagonia. 1994; Salvador et al., 2018), being absent from Patagonia. The specimens collected from the Marine invertebrates Chorrillo Formation may represent the first re- Fossil marine invertebrates are represented cords for the subfamily for the Cretaceous world- by a few taxa that were collected from locality wide. 5. Rock samples (MPM 21565; MPM 21566) contain different bivalve species. Preliminary deter- Urocoptoidea Pilsbry, 1898 minations encompass bivalves of diverse clades, Holospiridae Pilsbry, 1946 including ostreids of the genera Gryphaeostrea Holospira sp. (species similar to G. callophyla Ihering, 1903) and Cubitostrea (species similar to C. ameghinoi Referred material. MPM 21562, one fragmen- Ihering, 1902), pectinids related with the Danian tary cast (Figure 32 I). species “Chlamys” salamanca Ihering, 1902, and Description. Columnar shape, with numerous an indeterminate Mytilidae (D. Pérez, B.Santelli, whorls, which rapidly reaches a large size and and M.Álvarez, pers. comm.). then progresses more slowly; available specimen attains a maximum size of 18.5 x 8.5 mm and 10 Plants - Fossil woods whorls. Comments. This record constitutes the first one Pinidae Cronquist, Takht & Zimmerm. 1966 of Holospira for South America, also constitut- ?Podocarpaceae Endlicher 1847 ing the oldest known record for the entire family Fossil genus Podocarpoxylon Gothan 1904 worldwide. Type species Podocarpoxylon juniperoides Gothan, in Gagel (1904) Superfamily Orthalicoidea Martens, 1860 Podocarpoxylon dusenii Kraüsel 1924 Bulimulidae Tryon, 1867 Genus and species indeterminate Referred material. MPM 21568, fragmentary wood from locality 1 (Figure 33). Referred material. MPM 21563, MPM 21564, Description. Growth ring boundaries distinct. five fragmentary casts (Figure 32 J-K). Latewood consisting of c.6 tracheids with re- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 271

Figure 32. Gastropoda. A, Ampullariidae. Pomacea sp. MPM 21554. B, Pleuroceridae. Genus et species indet. MPM 21555. C, Pleuroceridae. Genus et species indet. MPM 21556. D, Tateidae. Potamolithus sp. MPM 21557. E, Physidae. Physa sp. MPM 21558. F, Stenophysa sp. MPM 21559. G, Achatinidae. Genus et species indet.MPM 21560. H, Achatinidae. Genus et species indet. MPM 21561. I, Holospiridae. Holospira sp. MPM 21562. J, Bulimulidae. Genus et species indet. MPM 21563. K, Bulimulidae. Genus et species indet. MPM 21564. Scale bars 0.5 cm in A-C, I and J. Scale bars 2 mm in D-H and K. 272 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 duced radial diameter. Transition from early- matosum (Pujana et al., 2014). Podocarpoxylon wood to latewood gradual. Earlywood tracheid garciae Del Fueyo (1998) from the Campanian- tangential diameter 24.8 +/- 7 (16.9–46.5) μm. Maastrichtian Allen Formation has axial paren- Latewood tracheids thin walled. Intercellular chyma, a feature not recorded in the specimens spaces rare to absent. Tangential pits and axial here studied. Podocarpoxylon mazzoni (Petriella) parenchyma not observed. Müller-Stoll & Schultze-Motel, an ubiquitous Rays homogeneous, parenchymatous, with taxon found in Campanian–Maastrichtian to cells 20+/-4(11.7–28.5) μm in vertical diameter. Paleocene units of northern Patagonia differs Horizontal and end walls of ray parenchyma cells from this species by having uniseriate to triseri- smooth. Rays very low to medium, 3+/-2 (1–9) ate pits in radial walls, partially biseriate (and cells high, uniseriate and with a frequency of locally triseriate) very tall rays, and septa-like 4+/-1(2–6) rays per mm. structures (see Vera et al., 2019, and references Tracheid radial pitting uniseriate (Si = 1), abi- therein). etinean, with Cp = 7%. Radial pits circular to Affinities. Many species of Podocarpoxylon have oval 12.5+/-1.1 (9.6–14.1) μm in vertical diam- been recognized from regions where no conclu- eter. Cross-field pitting podocarpoid, 1 (rarely 2) sive Podocarpaceae remains were identified, sup- pits per cross field. When 2 pits are present, they porting the fact that this type of wood cannot be are arranged vertically. Cross-field pits 8.3+/-1 conclusively referred to Podocarpaceae (see dis- .3(6.8–11.1) μm in vertical diameter. Pits oval, cussion in Pujana & Ruiz, 2017). Nevertheless, oblique, with narrow areola. given that gymnosperm pollen grains record- Comments. Kraüsel (1924) erected this species ed in this unit, are essentially represented by for specimens recovered at Santa Cruz Province, Podocarpaceae (see below), the fossil woods are Argentina. Following his description, this taxon tentatively referred to this family. is characterized by: lack of axial parenchyma, cross-fields with one (or rarely 2) pits, uniseriate Palynology pitting of the radial walls of the tracheids, and Well-preserved palynological assemblag- uniseriate (rarely biseriate) rays 1–20 cells tall. es were obtained for the first time from the The material here studied falls within the de- Chorrillo Formation. Two palynological samples scribed features by Kraüsel for this taxon. Rays (MPM 21570, 21571; Figure 34) were recov- described by Kraüsel (1924) seem to be taller ered from locality 3 and yielded palynofloras than our materials, but this feature may show with a moderate specific diversity. Eighteen instraspecific variation (Carlquist, 1988; Poole et spore species, 7 gymnosperm pollen grains al., 2001). Provenance data of the original speci- and 4 angiosperm pollen grains were identi- men of this taxon is unclear, and Kraüsel (1924) fied. The assemblage is characterized by the states that it was found near the La Leona River. presence of spores related with different ferns Coordinates provided by this author suggest that (Polypodiopsida), such as Gleicheniaceae it was found at the northern margin of the Lago (Clavifera triplex (Bolkhovitina) Bolkhovitina Argentino, near La Leona river mouth. The age 1966 and Gleicheniidites senonicus Ross 1949), of this taxon is currently regarded as Cenozoic, Osmundaceae (Baculatisporites comaumen- as originally pointed by Kraüsel (“Tertiär”), giv- sis (Cookson) Potonie 1956, Baculatisporites en its unclear stratigraphic provenance. kachaikensis Archangelsky & Llorens 2005) Podocarpoxylon aparenchymatosum Gothan and Polypodiaceae (Tuberculatosporites parvus from the Eocene (and probably the Paleocene) of Archangelsky 1972). It is also recorded the fam- Antarctica (Pujana et al., 2014; Pujana & Ruiz, ily Dicksoniaceae (Trilites fasolae Archangelsky 2017) shares with the material here studied the 1972, Trilites sp. cf. T. parvallatus Krutzsch 1959 absence of axial parenchyma, but rays are taller and Trilites sp. cf. T. tuberculiformis Cookson (9(1–17)). Furthermore, cross-fields typically 1947), and particularly Cyatheacidites annulatus have 2 pits, reaching up to 5, whereas the speci- Cookson ex Potonie 1956, with affinities with ex- mens here studied have only one (or rarely 2 pits). tant genus Lophosoria C. Presl. Other fern spores Podocarpoxylon fildesense Zhang & Wang from cannot be related to any particular family, such the Paleocene of Antarctica has slightly taller as Concavissimisporites sp., Laevigatosporites rays, and cross-fields typically have 1-2 pits, but ovatus Wilson & Webster 1946 and Leptolepidites up to 4 pits per cross fields were reported (Zhang sp. cf. L. major Couper 1953, and representa- & Wang, 1994; Poole et al., 2001; Pujana & Ruiz, tives of the genus Cyathidites Couper. Within 2017), and may be synonym of P. aparenchy- the latter, three species are identified, namely: Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 273

Figure 33. Podocarpoxylon dusenii Kraüsel 1924. A, (MPM 21568) Growth ring in a transverse section (TS). Bar: 20 μm. B, (MPM 21568) Detail of growth ring (TS). Bar: 20 μm. C, (MPM 21567) Spaced uniseriate radial pitting and cross fields (LRS). Bar: 50 μm. D, (MPM 21567) Spaced uniseriate radial pitting and cross fields (LRS). Bar: 20 μm. E, F, (MPM 21567) Cross fields with 1 or 2 podocarpoid pits (LRS). Bar: 20 μm. G, (MPM 21567) Uniseriate rays (LTS). Bar: 20 μm. H, (MPM 21567) Detail of uniseriate rays (LTS). Scale bar: 50 μm

Cyathidites australis Couper 1953, C. minor with Tricolpites sp. (of unknown affinities), be- Couper 1953 and C. rafaeli Burger 1980, all psi- ing all these species scarce in the assemblages late triangular spores related to Cyatheaceae, recovered from Chorrillo Formation. Dicksoniaceae, Dipteridaceae, or Matoniaceae. Lycopodiopsida are recorded with spores refer- DISCUSSION able to Selaginellales (Ceratosporites equalis Cookson & Dettmann 1958 and Foveosporites 1. Dinosaur assemblages canalis Balme 1957) and Lycopodiales Retitriletes 1.1. Vertebrate assemblage yielded by austroclavatidites (Cookson) Doring et al., in Chorrillo and Dorotea Formations Krutzsch 1963). Marcelo Leppe (e.g., Leppe et al., 2014; Vogt et Gymnosperm pollen grains are less diverse al., 2014; Manriquez et al., 2019) has conducted than spores, and are represented by taxa related successful explorations in the Las Chinas River to Podocarpaceae (Microcachryidites antarcti- Valley (NE from the Torres del Paine National cus Cookson 1947, Phyllocladidites mawsonii Park, Magallanes Region, Ultima Esperanza Cookson 1947 ex Couper 1953, Podocarpidites Province, Chile). This locality is approximately ellipticus Cookson 1947, P. sp. cf. P. herbstii 4.2 km southeast from the border to Argentina Burger 1966, P. sp., and Trichotomosulcites sub- (Figure 1). Leppe and crew reported semi-ar- granulatus Couper 1953) and pteridosperms ticulated skeletons of dinosaurs at levels of the (Vitreisporites signatus Leschik 1955). Dorotea Formation. Dinosaur remains include Similarly, the angiosperm pollen grains indeterminate titanosaurs, ornithischians, and show a low diversity, being Peninsulapollis gilli also abundant hadrosaur remains (e.g., Leppe et (Cookson) Dettmann and Jarzen 1988 the only al. 2014, Jujihara et al., 2014; Soto Acuña et al., angiosperm abundant in the studied palyno- 2014; Vogt et al., 2014; Manriquez et al., 2019). flora (at least representing 90% from the total In Las Chinas River Valley, Leppe et al. (2014) angiosperm pollen grains). This species is re- distinguished three stratigraphic sections for the lated to Proteaceae, probably with Beauprea- Dorotea Formation: the lower Casa Las Chinas, like forms (Dettman & Jarzen, 1988). Other the middle Saurópodo, and the upper El Puesto taxa include Clavatipollenites sp. (related to the section. The Saurópodo stratgraphic section Chloranthaceae), Tricolpites reticulatus Cookson shows abundance of titanosaur remains, and 1947 ex Couper 1953 (related to Gunnera), along may be partially equivalent to the lower and mid- 274 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 dle levels that shed the many titanosaur remains radimetric dating shows that the Mata Amarilla of the Chorrillo beds. In Las Chinas site the El Formation is Cenomanian in age (approxima- Puesto section sheds at its base Nothofagus leaf tely 97my; Varela et al., 2012), Cerro Fortaleza imprints, followed upward by levels with abun- Formation is Campanian (around 76.2Ma, based dant hadrosaur remains, and plesiosaur and on studies by Sickman et al., 2018), and upper mosasaur bones at the top of the section. The terms of the Dorotea is Maastrichtian (as suppor- El Puesto is considered here equivalent with the ted by radiometric dating and paleontological upper portion of the Chorrillo Formation, on the evidence; Manriquez et al., 2019). Explorations Argentine side, which shed the basal iguanodon- carried on in SW Santa Cruz province by the se- tian Isasicursor associated with the mosasaur nior author since 1998, have produced different teeth. dinosaur species from these beds: Mata Amarilla, Current information about tetrapod taxo- in proximities of the Sheuen River, afforded car- nomic diversity in both Chorrillo and Dorotea in- charodontosaurid remains (Novas et al., 1999) cludes turtles, ophidians, colossosaurian titano- which are congruent with a Cenomanian age saurs, basal iguanodontians, hadrosaurids, meg- obtained by radiometric studies (Varela et al., araptorids, abelisauroids, basal paravians, basal 2012). The Cerro Fortaleza beds, at Cerro de Los neornithes, and mammals. Integrative studies Hornos fossil site, shed different dinosaur taxa on both sides of the Argentina-Chile border will (i.e., Talenkauen, Orkoraptor, Puertasaurus, eventually result in considerable increase in Dreadnoughtus; Novas et al., 2004, 2005, 2008; knowledge of this Maastrichtian ecosystem from Lacovara et al., 2014) which resemble forms from the southern tip of South America. the Neuquina Basin (i.e., Macrogryphosaurus, Megaraptor, Futalognkosaurus) recorded in the 1.2. Dinosaur-bearing beds from southern Turonian Portezuelo Formation (Calvo et al., Patagonia 2007). The age based on paleovertebradological Dinosaur-bearing beds of Upper Cretaceous fossil content does not fit with the radiometric age crop out in the SW corner of Santa Cruz pro- ages obtained by Sickman et al. (2018) which su- vince, comprising the vicinities of Viedma Lake pport a Campanian age for the Cerro Fortaleza (to the north) up to Argentino Lake (to the south), Formation. Besides, the upper third of the as well as along La Leona River, the water course Dorotea Formation yielded abundant hadrosau- connecting both lakes. These dinosaur-bearing rid material (Jujihara et al., 2014; Soto Acuña beds extend south, crossing the international bor- et al., 2014), as it also occurs in Maastrichtian der with Chile, including (from north to south) localities from NW and Central Patagonia (e.g., Mata Amarilla, Cerro Fortaleza, Chorrillo and Bonaparte et al., 1984; Gasparini et al., 2015; Dorotea. The stratigraphic correlations among Brett-Surman, 1979; Becerra et al., 2018). The these continental beds have been, and still are, Chorrillo beds apparently corresponds to an a theme of intense debate among geologists (see, age (i.e., late Campanian-early Maastrichtian), Varela et al., 2012; Sickman et al., 2018). Available intermediate between the Campanian Cerro

Figure 34 (next page). Palynology. A, Baculatisporites comaumensis (Cookson) Potonie 1956, MPM 21571-2:M62/1; B, Baculatisporites kachaikensis Archangelsky & Llorens 2005, MPM 21571-2:R48/1; C, Ceratosporites equalis Cookson & Dettmann 1958, MPM 21571-3:S40/0; D, Concavissimisporites sp., MPM 21571-3:H27/0; E Clavifera triplex (Bolkhovitina) Bolkhovitina 1966, MPM 21571-5:R42/3; F, Cyatheacidites annulatus Cookson ex Potonie 1956, MPM 21571-4:Z48/2; G, Cyathidites australis Couper 1953, MPM 21571-3:X55/4; H, Cyathidites minor Couper 1953, MPM 21570-6:T24/4; I, Cyathidites rafaeli Burger 1980, MPM 21570-6:D55/4; J, Foveosporites canalis Balme 1957, MPM 21571-6:C42/3; K, Gleicheniidites senonicus Ross 1949, MPM 21571-6:Y24/0; L, Laevigatosporites ovatus Wilson & Webster 1946, MPM 21571-6:C32/3; M, Retitriletes austroclavatidites (Cookson) Doring et al. in Krutzsch 1963, MPM 21571-4:Q41/0; N, Trilites fasolae Archangelsky 1972, MPM 21571-1:D36/1; O, Leptolepidites sp. cf. L. major Couper 1953, MPM 21571-2:O24/1; P, Trilites sp. cf. T. tuberculiformis Cookson 1947, MPM 21571-5:R57/0; Q, Trilites sp. cf. T parvallatus Krutzsch 1959, MPM 21571-2:X58/2; R, Tuberculatosporites parvus Archangelsky 1972, MPM 21571-6:O48/0; S, Microcachryidites antarcticus Cookson 1947, MPM 21571- 3:Y36/0; T, Podocarpidites sp. cf. P.ellipticus Cookson 1947, MPM 21571-3:S19/4; U, Podocarpidites sp. cf. P. herbstii Burger 1966, MPM 21571-2:B55/1; V, Podocarpidites sp., MPM 21571-2:H55/4; W, Phyllocladidites mawsonii Cookson 1947 ex Couper 1953, MPM 21571-1:Q63/4; X, Trichotomosulcites subgranulatus Couper 1953, MPM 21571-8:V31/0; Y, Vitreisporites signatus Leschik 1955, MPM 21571-8:J39/2; Z, Clavatipollenites sp., MPM 21571-7:V47/0; AA, Peninsulapollis gilli (Cookson) Dettmann & Jarzen 1988, MPM 21571-3:P31/6; BB, Peninsulapollis gilli (Cookson) Dettmann & Jarzen 1988, MPM 21571-7:L27/4; CC, Tricolpites reticulatus Cookson 1947 ex Couper 1953, MPM 21571-7:L48/3; DD, Tricolpites sp., MPM 21571-7:J28/3. Scale bar: 10 µm. Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 275

Fortaleza and the upper Maastrichtian Calafate the upper Maastrichtian hadrosaurid-bearing formations. levels of the Dorotea Formation. The sequence Summing up, we identify a succession of at is capped by marine beds (i.e., Calafate, Monte least four different dinosaur assemblages from Chico, and upper terms of Dorotea formations) beds exposed in the SW corner of Santa Cruz: the which yielded remains of plesiosaurs and mosa- oldest ones corresponding to the Cenomanian saurs (Bonaparte et al., 2002; Leppe et al., 2014; Mata Amarilla Formation, the Campanian Cerro Vogt et al., 2014; Novas et al., 2016; Soto Acuña Fortaleza Formation, the upper Campanian – et al., 2016). lower Maastrichtian Chorrillo Formation, and Such biostratigraphic succession has to be 276 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 taken as a tentative one, and new paleontological Antarctica, in contrast with the Late Cretaceous discoveries (dinosaurs in particular) are needed from Brazil and northwestern Argentina, were to confirm or correct these interpretations. An enantiornithines are the only known birds so far important topic requiring consideration con- (see discussion in Agnolin, 2017). In spite that the cerns with the taxonomic distinctions that may fossil record of Mesozoic birds in the Southern exist between vertebrate faunas documented in Hemisphere is still relatively poor, the discovery the Chorrillo Formation with respect to the un- of a variety of neornithine-related birds indicates derlying Cerro Fortaleza beds. Both units share that southern Gondwana constituted a cradle for the same inclusive clades (i.e., Titanosauridae, the early evolution of extant bird clades (Ericson Elasmaria, Megaraptoridae), although some et al., 2001; Cracraft, 2001; Agnolin et al., 2016). generic distinctions exist among titanosauri- 1.3.c. Concerning sauropod dinosaurs, the ans and elasmarians: the Chorrillo beds yield- Maastrichtian record of the clade in the Austral ed Nullotitan and Isasicursor, while Cerro basin is still meagre. Together with the Chilean Fortaleza Formation yielded the titanosaurids records (Manriquez et al., 2019), Nullotitan Puertasaurus and Dreadnoghthus, and the elas- represents one of southernmost records of marian Talenkauen. Titanosauria for South America. The presence of large-sized forms in both Chorrillo and 1.3. Paleobiogeographic comments on di- Dorotea coincides with that of the underlying nosaur faunas Cerro Fortaleza beds, from which very large ti- The following preliminary paleobiogeo- tanosaurs have been collected (Puertasaurus, graphic interpretations emerge from compar- Dreadnoughthus; Novas et al., 2005; Lacovara ing Maastrichtian dinosaur faunas from the et al., 2014). This faunal component contrasts Austral Basin with those from other regions of with the smaller-sized saltasaurines and mid-to Gondwana: large-sized aeolosaurines documented in lower 1.3.a. Theropod records here reported include latitudes of Gondwana (e.g., northern of Santa the southernmost records for unenlagiid para- Cruz, Neuquén, Río Negro, and Salta provinces vians and noasaurid abelisauroids. In addition, of Argentina, and São Paulo and Minas Gerais at least three different megaraptorid specimens states of Brazil; Powell, 2003; Casal et al., 2007; were found, indicating that this theropod clade Santucci & Arruda-Campos, 2011). was relatively abundant during the deposition Besides, the abundance of titanosaur speci- of the Chorrillo Formation. The set of megarap- mens in southern Patagonia contrasts with the torid specimens described in the present paper infrequent records of these herbivores in the constitutes evidence for their survival into the Antarctic Peninsula (Novas, 2009; Cerda et al., Maastrichtian. This information counters pre- 2011). However, such distinction may be related vious interpretations (Novas et al., 2013) pro- with the marine-influenced paleoenvironments posing megaraptorids went extinct before the that dominated the Antarctic Peninsula during Campanian, and that abelisaurids were dominant the Late Cretaceous. In agreement with this, in Campanian-Maastrichtian theropod faunas titanosaurid bones are abundant in the conti- (Novas, 2009). Recurrent discovery of megarap- nental deposits of the lower and middle thirds torid remains in the Chorrillo beds, alongside of the Chorrillo Formation, contrasting with the with the paucity in abelisauroid remains, sharp- virtual absence of sauropods from the marine-in- ly contrast with the Campanian-Maastrichtian fluenced upper third of the unit, were ornithopod theropod assemblages from northern Patagonia, remains are recorded in association with mosa- Madagascar and India, in which abelisauroids saur remains. are common and megaraptorids virtually absent. Sauropod bones have been reported from Las Interestingly, theropod assemblages from the Chinas River Valley (Manriquez et al., 2019). southern end of the continent resembles the ear- Although such discovery still awaits formal de- ly Late Cretaceous record from Australia, were scription, available information shows the com- carnivorous dinosaur assemblages were domi- mon presence of large titanosaurs in both Dorotea nated by megaraptorids , whereas abelisaurids and Chorrillo formations. Whether the remains seem absent (Benson et al., 2012; Novas et al., of these animals from Chile and Argentina be- 2013; Poropat et al., 2019). long to a same titanosaur species needs to be 1.3.b. Regarding the presence of possible neorni- confirmed. Previous contributions considered thine birds in the Chorrillo Formation, this clade that gigantic titanosaurs were restricted to mid- has been recorded in northern Patagonia and Cretaceous times (pre-Campanian-Maastrich- Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 277 tian; Salgado and Bonaparte, 2007; Carballido nental gastropods from South America were et al., 2017), but recent research indicates that barely represented by some specimens of the giant forms, such as Antarctosaurus, survived up families Pleuroceridae (Early Cretaceous), to the Campanian-Maastrichtian time interval Physidae (Early Cretaceous), Bulimulidae (Garcia and Salgado, 2013). Nullotitan confirms (Late Cretaceous) and “Endodontidae” (Late the survival of gigantic colossosaurian sauropods Cretaceous) (Salvador et al., 2018) (see Table up to the latest Cretaceous. 1). Pleuroceridae and Bulimulidae were unk- Although knowledge on Maastrichtian di- nown from Mesozoic beds, and their respective nosaur faunas from the southern tip of South fossil records were restricted to the Cenozoic of America is just at the beginning, available infor- Patagonia (Parodiz, 1969). Discoveries here re- mation indicates that no small-sized sauropods ported from the Chorrillo Formation allow mo- (e.g., saltasaurines) have been found so far nei- difying this situation with the documentation ther in Chorrillo nor in Dorotea beds, in contrast of the first Mesozoic remains of Ampullariidae with their abundant record in northwestern and Holospiridae for South America, and con- Argentina and northern Patagonia. Such dis- firming the presence of Tateidae, Physidae and tinction, in join with the taxonomic differences Bulimulidae in the South American Mesozoic. noted above for Theropoda, suggest the influence Further, such discoveries constitute the souther- of environmental controls in paleobiogeographic nmost records for these families. Holospiridae distribution of Patagonian dinosaurs. is recorded for the first time in South America. 1.3.d. In respect to ornithischians, documenta- Notably, almost all families exhibit features co- tion of the basal iguanodontian Isasicursor, con- rresponding to new genera and species, which stitutes a novelty of the present report, because it will be studied elsewhere (Miquel and Brito, in conforms the first Maastrichtian elasmarian for press). southern Patagonia. Basal iguanodontian diver- Holospiridae is a group that currently lives sity during Campanian-Maastrichtian time span in Central and North America, with numerous in Southern Patagonia and Antarctic Peninsula genera and species, with fossil records from the (see Rozadilla et al., 2016) agrees with the idea Paleocene of USA (Zilch, 1960). Excepting this expressed by Brown et al. (2011) indicating that group, the remaining families have been recor- basal ornithopods increased in diversity from ded in South America, some with numerous taxa, the Campanian through the late Maastrichtian. as Bulimulidae and Subulininae (Breure, 1979; Alongside basal iguanodontians, hadrosaurids Schileyko, 1999). Bulimulidae has a distribu- are commonly found in Maastrichtian localities tion restricted to Australasian and Neotropical in NW and central Patagonia, as well as in the realms (Solem, 1981). In Argentina, specimens upper section of the Dorotea Formation, where of Bulimulidae are currently dispersed mainly in they have been commonly recorded (Jujihara et the north and center of the country, even in high al., 2014; Soto Acuña et al., 2014). altitudes in the Andes mountains (Breure, 1979). The Chorrillo Formation vertebrate as- The Achatinidae Subulininae is recorded in wet semblage has some similarities with those tropical climates (Fernández, 1973; Schileyko, from the Late Cretaceous of Australia and 1999). Antarctica, including the common presence of Besides, Ampullariidae, Pleuroceridae, Chelidae, Calyptocephalellidae, Elasmaria, and Tateidae and Physidae are abundant in rivers Megaraptoridae, together with the absence or and lakes and can live in estuary environments scarcity of saltasaurine and aeolosaurine titano- of low salinity (e.g., Rio de la Plata, Argentina; saurs and abelisaurid theropods, dinosaur clades Castellanos & Landoni, 1995). Holospiridae, which are frequently documented in NW and Achatinidae and Bulimulidae would show the central Patagonia. Such differences in faunal existence of areas with different tree formations, composition need to be investigated in depth to as well as habitats and microhabitats favorable elucidate if they mirror different paleoenviron- for the development of gastropods, and some dry- mental conditions in southern Patagonia. humid climate seasonality.

2. Terrestrial and freshwater mollusks 3. Paleobotany and palynology Until relatively recently, the records of 3.1. Comparisons with other Maastrichtian Mesozoic land snails were almost restricted palynological assemblages from Patagonia. to North America and Europe (Solem, 1979). In spite that present palynological report is pre- In contrast, the Cretaceous records of conti- liminary, and the collected samples are meagre, 278 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019

Table 1. Records of mollusks according to time and geographical area. ?Achatinidae is excluded because of the doubtful taxonomic location of the described fragments.

CRETACEOUS PALEOGENE RECENT RECENT

South America South America South America Patagonia Ampullariidae X X X --- Pleuroceridae X X X --- Tateidae X X X X Physidae X X X --- Holospiridae X ------Bulimulidae X X X X some interesting comparisons and conclusions Formation, when compared with the ones pres- are exposed as follows. ent in the underlying Cerro Cazador Formation. Povilauskas et al. (2008) reported palyno- Although Nothofagidites is still present in Monte floras from the La Irene Formation (at Calafate Chico Formation, an increase in diversity of hill, southwestern Santa Cruz Province), which angiosperm families with tropical or subtropi- underlies the Chorrillo Formation. The palyno- cal distribution is recorded (Povilauskas, 2013). logical assemblages from La Irene Formation The Danian Cerro Dorotea Formation share many species with those here studied, (Povilauskas, 2017) contains a less diverse pa- among them the presence of Peninsulapollis lynoflora, sharing with the assemblages of gillii. Furthermore, both Chorrillo and Irene Chorrillo beds the presence of Peninsulapollis Formations lack Nothofagidites. Angiosperms gilli, Cyatheacidites annulatus, and few other in the La Irene Formation show higher diver- taxa. Noteworthy, this unit contains pollen re- sity than the one recorded in the assemblages ferable to Bombacaceae, of tropical or subtropi- here studied, including Arecipites minutiscabra- cal distribution, along with Nothofagidites and tus Mc. Intyre 1968, Liliacidites cf. variegatus Proteaceae. Couper 1960, Longapertites sp., Proteacidites sp. Assemblages from the Dorotea Formation and Spinozonocolpites hialinus Archangelsky reported from Cerro Guido and other localities & Zamaloa 1986 (Povilauskas et al., 2008), cur- (Leppe et al., 2012) contain no stratigraphically rently absent from samples got in Chorrillo significant taxa. Some taxa, as Baculatisporites Formation. kachaikensis, Gleichenites senonicus and Povilauskas (2016) reported diverse palyno- Cyathidites minor are shared with the Chorrillo logical assemblages obtained from the Cerro Formation. Noteworthy, although five angio- Cazador Formation (upper Campanian-lower sperms pollen grains are reported from the Maastrichtian) from outcrops near Rio Turbio Dorotea Formation, none of those is shared with (southwest Santa Cruz Province) and from the the palynoflora here studied. Monte Grande Hill near the limit with Chile. In summary, the palynofloras recovered from These palynofloras share some species with Chorrillo Formation share many taxa with units those here studied, such as Trilites fasolae, from southern Argentine Patagonia, includ- Cyatheacidites annulatus and Peninsulapollis ing many species of spores and gymnosperm gilli. The angiosperm pollen grains are more pollen grains, including Peninsulapollis gilli. diverse than the palynofloras here studied, and Furthermore, the absence of Nothofagidites the genus Nothofagidites is recorded in low in the Chorrillo beds is shared with La Irene proportions in the Cerro Cazador Formation. Formation. One remarkable difference with Noteworthy, palynofloras from Cerro Cazador most of these palynofloras is the absence of pol- Formation lack subtropical to tropical families. len grains related with subtropical to tropical The overlying Monte Chico Formation (upper taxa, a feature shared with the Cerro Cazador Maastrichtian–Danian) studied by Povilauskas Formation. However, the poor representation (2011, 2012, 2013, 2017) at the same localities, of angiosperm pollen grains on the palynofloras share several taxa with the Chorrillo Formation of Chorrillo Formation may be a preservation assemblages, including the marker taxon issue making comparisons less reliable. Future Peninsulapollis gilli. A floristic replacement detailed studies based on a larger sample num- seems apparent in the assemblages of Monte Chico ber would allow more detailed comparisons. Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 279

3.2. Paleoclimatological implications. The ture of tropical (e.g., Arecales, Bombacaceae, palynoflora recovered from Chorrillo Formation Casuarinaceae, Aquillafoliaceae, Olacaceae) and contains some taxa that, using modern analogs, austral (e.g., Nothofagaceae, Proteaceae) ele- may provide information regarding the paleocli- ments, suggesting cool-temperate to warm climate where these plants grew. Peninsulapollis matic conditions. However, assemblages from is allied to Proteaceae related with Beauprea, northern Patagonia (e.g., Allen, Lefipán, Paso del a genus that nowadays grow in temperate to Sapo, Puntudo Chico, and Lago Colhué Huapí cold environments (Quattrochio & Ruiz, 1999). Formations) show a tendency towards a warmer The abundant and diverse ferns, along with climate respect to the southern ones, having subordinate Chloranthaceae, may have grown yielded abundant palms (e.g., Spinizonocolpites in the understory, associated with ponds, small Muller 1868, Longapertites Van Hoeken streams or rivers just landward of the shoreline. Klinkenberg 1964, Palmoxylon Schenk 1882), en- Cyatheacidites annulatus is an indicative of ferns cephalartoid cycads (e.g., Wintucycas Martínez et similar to the large fern Lophosoria quadripin- al., 2012, Brunoa Artabe et al., 2004, Wordsellia nata, that lives in cloud forest in the tropics and Artabe et al., 2004; see Martínez et al., 2018), in cool, wet regions further south (Hill et al., and pollen grains of tropical-subtropical fa- 2001). It grows in a variety of habitats and read- milies (e.g. Bombacacidites sp., Ilexpollenites ily colonizes disturbed areas (Tryon & Tryon, sp., Haloragacidites harrisii (Couper) Harris 1982). Cantrill (1998) compiled and analyzed the in Mildenhall & Harris, Anacolosidites diffu- distribution of this species, suggesting this fern sa Archangelsky 1973). Proteaceae (e.g., grows in temperate to tropical climates. Finally, Peninsulapollis gilli, Proteacidites sp., the arboreal stratum was essentially composed Triatriopollenites spp.) and Podocarpaceae by Podocarpaceae, a conifer family almost en- (Podocarpidites sp., Phyllocladidites mawsonii tirely restricted to rainforest or wet montane en- Cookson 1947 ex Couper 1953) are recorded vironments (Hill & Brodribb, 1999). in variable proportions in these assemblages. In summary, presence of these taxa suggests Nothofagaceae, on the other hand, are almost ab- cool and humid climatic conditions during the sent from these assemblages, being recorded in deposition of the Chorrillo Formation. The pre- very small proportions in the Lefipán Formation sence of well-developed growth rings in the fossil (Barreda et al., 2012). Available information in- woods (see above) suggests periods of arrested dicates that Maastrichtian floras from Patagonia growth. were influenced by climatic conditions depending 3.3. Palaeobiogeographical implications. on latitude, a fact that should be extrapolated to From a paleophytogeographical point of view, the vertebrate associations, as indicated above. region under study (i.e., southern Patagonia) cons- The palynological assemblages here studied tituted part of an intermixed/transitional floral may be, a priori, comparable with the ones at province that extended in between two main pro- Cerro Cazador Formation, mostly by the absence vinces (Herngreen & Chlonova, 1981; Herngreen of tropical or subtropical elements. However, for et al., 1996; Vajda & Bercovici, 2014): the Palmae the time being, it is difficult to establish if the ab- province, ranging from the paleoequator up to sence of these elements is reflecting a character- northern Argentina and Chile, and characteri- istic of the flora or a preservation artifact, since zed by the presence of palm pollen grains repre- only two samples have been studied. Future senting 10-50% of the palynological assemblages; works on the megafloristic and palynological as- and the Proteacidites/Nothofagidites province, semblages of the Chorrillo Formation may shed well recorded in Antarctica. The Maastrichtian light on the relationships between this ecosystem palynological assemblage recorded in La Irene, and others recorded in coeval units. Chorrillo, Cerro Cazador and Monte Chico formations belongs to a transitional floral provin- CONCLUDING REMARKS ce, having neither Proteacidites/Nothofagidites nor palms as dominant elements (Herngreen & Present contribution includes the first de- Chlonova, 1981; Herngreen et al., 1996; Vajda & tailed description of fossil vertebrates, inver- Bercovici, 2014). tebrates, plants and polen from the Chorrillo The late Campanian to Maastrichtian fossil Formation. Previous reports of its fossil content plant record (both palynological and megafloris- consisted on brief mentions confirming the pres- tic) recovered from Patagonia (including those ence of dinosaur bones and fragmentary plant from southern Lago Argentino) reveals a mix- remains. Now, the taxonomic diversity is con- 280 Revista del Museo Argentino de Ciencias Naturales, n. s. 21(2), 2019 siderably expanded with the description of dif- nomic composition, paleogeographic evolution ferent members of a Maastrichtian continental of North America shows marine flooding dur- biota, including gastropods of a variety of aquatic ing Campanian times, being in regressive phase and terrestrial families, and different groups of during the Maastrichtian. This is different from vertebrates including fishes, anurans, turtles, Patagonia, in which the latter stage coincides with snakes, mosasaurs, titanosaurids, elasmarians, the maximum transgression persisting onto the megaraptorids, neognathans, and mammals. early Cenozoic. Maastrichtian vertebrate faunas Palynological assemblage from Chorrillo beds associated with littoral environments have been includes fern spores and both gymnosperm extensively documented in northern and central and angiosperm pollen. Although less diverse Patagonia (Casamiquela, 1978; Gasparini et al., than other Maastrichtian units, the palynologi- 2015), and evidence gained in recent years in cal content may increase with better sampled Chorrillo and Dorotea Formations demonstrates rock levels. Main novelties afforded by Chorrillo that such faunal assemblage, but with some dis- Formation include the remains of small verte- tinctions, extended up to the southern extreme brates (especially birds and mammals), the sur- of South America. Present contribution includes vival of large titanosaurs and elasmarian into the first detailed description of fossil verte- the Maastrichtian, and the documentation of brates, invertebrates, plants and palynomorphs a wide diversely of continental gastropods, the from the Chorrillo Formation. Vertebrate and Cretaceous record of which remained virtually plant assemblages are similar to those of other unknown from this region of Patagonia. southern Gondwana landmasses, including other Maastrichtian vertebrate faunas associated Santa Cruz localities, Antarctica, and Australia. with litoral environments have been extensively Further, in contrast with northern Patagonia documented in northern and central Patagonia and Chubut province, abelisaurid theropods and (e.g., Casamiquela, 1978; Gasparini et al., 2015), relatively small sauropods of the aeolosaurine and evidence gained in recent years from both and saltasaurine clades, are totally absent in lat- Chorrillo and Dorotea formations, demonstrate est Cretaceous Santa Cruz provinces. Further, in that such faunal assemblage extended, with some contrast to northern Patagonia, basal ornitho- distinctions, up to the southern extreme of South pods are abundant in the Austral basin. America. This conforms a sharp distinction with respect to North America, where marine flood- ACKNOWLEDGEMENTS ing occurred at its maximum stage during Campanian times, being followed by a regressive Thanks to Coleman Burke (New York), for phase during the late Maastrichtian (see Roberts his encouragement and financial assistance to & Kirschbaum, 1995). This is different from carry on field exploration. Facundo Echeverría Patagonia, in which the maximum transgression and his wife Daphne Fraser (La Anita farm) of- occurred during the late Maastrichtian and per- fered their valuable geographic knowledge of sisted into the early Tertiary (see Malumián & these territories, allowing us an easy access to Náñez, 2011). The paleoecological effects of such fossil sites with our 4x4 vehicles. Special thanks paleoenvironmental distinctions between South to Federico Braun for allowing access to his prop- and North America need to be investigated in erty. The following people gave formidable logis- more detail. tic support: Julian Foster (Patagonia Profunda; A better knowledge of floristic and faunis- El Calafate), Marisa and Luis Calleja (Centro tic Maastrichtian record from southern South de Interpretación Histórica; El Calafate), Paz America will eventually contribute in future dis- Fiorito (Kaulen Hostería, El Chaltén), and Anahí cussions about mass extinction occurred at Pallone (Aguisac). Cruz del Sur for transporting K-Pg boundary, which are mostly based on fossil specimens to Buenos Aires. Oscar Canto Maastrichtian fossil record from the northern and Carla Almazán (Secretaría de Cultura) for hemisphere. supporting our projects and explorations in Discussions about dinosaur mass extinction Santa Cruz. Participants of the exploration car- are mostly based on Maastrichtian fossil record ried on in January 2019 were: M.Isasi, M. Motta, from North America. South America, and other S. Rozadilla, F. Brisson, and A. Vega. Participants Gondwanan regions, are overlooked from these of the exploration carried on in March 2019 were: discussions, due to unavailability of dinosaur re- M. Isasi, M. Motta, F. Agnolín, M. Cerroni and F. mains corresponding to latest Maastrichtian age. Novas. Special thanks to the geologists F. Nullo, Aside from sharp distinctions in dinosaur taxo- F. Varela, and D. Moyano Paz for their valuable Novas et al.: Paleontology of the Chorrillo Formation at Santa Cruz province 281 comments on stratigraphy and regional geol- Cretaceous of Patagonia (Argentina). Geodiversitas ogy at Santa Cruz province. Daniel Pérez, Belen 22(2): 247-253. Santelli, and Maximiliano Álvarez are acknowl- Albino, A.M. 2010. Morfología vertebral de Boa cons- edged for taxonomical idenitification of marine trictor (Serpentes: Boidae) y la validez del gene- ro Mioceno Pseudoepicrates Auffenberg, 1923. invertebrates. Special thanks to the reviewers Ameghiniana 48(1): 53-62. 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Doi: 10.22179/REVMACN.21.655

Recibido: 20-IX-2019 Aceptado: 27-XI-2019