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Home , Castilletes Formation, Catonyx, Central American Seaway, Cocinetas Basin, Colloncuran, Friasian

[Palaeontology, 2016, pp. 1–20]

NEOGENE ASSEMBLAGES (MAMMALIA, ) OF THE (LA GUAJIRA, ): IMPLICATIONS FOR THE GREAT AMERICAN BIOTIC INTERCHANGE by ELI AMSON1,2,3,JUAND.CARRILLO2 and CARLOS JARAMILLO1 1Smithsonian Tropical Research Institute, Box 0843-03092, Balboa-Ancon, ; [email protected] 2Paläontologisches Institut und Museum der UniversitätZürich, Karl Schmid-Strasse 4, Zurich,€ CH-8006, Switzerland; [email protected] 3Current address: AG Morphologie und Formengeschichte, Bild Wissen Gestaltung – ein Interdisziplin€ares Labor & Institut fur€ Biologie, Humboldt-Universit€at, Philippstrasse, 12/13, D-10115, Berlin, Germany; [email protected]

Typescript received 19 February 2016; accepted in revised form 8 May 2016

Abstract: We describe sloth assemblages from the Cocin- probably having different feeding strategies. Being only a few etas Basin (La Guajira peninsula, Colombia), found in the hundred kilometres away from the , and Castilletes and Ware formations, located in north- a few hundred thousand older than the classically ernmost , documenting otherwise poorly recognized first main pulse of the Great American Biotic known biotas. The tentative referral of a specimen to a small interchange (GABI 1), the Ware Formation furthermore doc- megatherioid sloth, Hyperleptus?, from the early–middle uments an important fauna for the understanding of this , suggests affinities of this major event in Neogene palaeobiogeography. The for fauna with the distant Santa Cruz Formation and documents which unambiguous affinities were recovered are not closely a large latitudinal distribution for this taxon. The late Plio- related to the early immigrants found in cene Ware Formation is much more diverse, with five dis- before GABI 1. tinct taxa representing every family of ‘ground sloths’. This diversity is also remarkable at the ecological level, with sloths Key words: Cocinetas Basin, Great American Biotic Inter- spanning over two orders of magnitude of body mass and change, Neotropics, palaeobiodiversity, Pilosa, sloth.

S LOTHS (Tardigrada) are represented today by two gen- southward migration of North American taxa (Webb era that are ecologically restricted to a peculiar suspen- 1985; Cione et al. 2015). In the classical understanding, sory mode of life, and geographically restricted to the this process started with single-taxon dispersals (Wood- Neotropical region (Nowak & Paradiso 1983). However, burne 2010), involving the herald taxa sensu Webb this modern distribution is depauperate when compared (2006) as early as 20.9 Ma (Bloch et al. 2016). This was to the recent past, as their fossil record includes a wide followed by the main phases of the GABI (or pulses, range of body sizes (up to several metric tones; Farina~ GABI 1–4; sensu Woodburne 2010), occurring from 2.6– et al. 1998; Raj Pant et al. 2014), various feeding ecolo- 2.4 Ma, and involving the legion taxa sensu Webb gies (Bargo & Vizcaıno 2008), and a broad distribution (2006). These migrations have mostly been assumed to from (Stock 1942) to southernmost South Amer- have been driven by the closure of the Central Ameri- ica (and possibly Antarctica; Carlini et al. 1990; Gelfo can Seaway and the formation of the Isthmus of et al. 2015 and references therein). Their geographical Panama, the most likely route of migration. However, distribution was particularly broad during the Pleis- habitat and climatic changes probably played a much tocene, which is partly the result of a major event in more important role in migration patterns Neogene palaeobiogeography: the Great American Biotic (Bacon et al. 2016). Indeed, the timing of the formation Interchange (GABI; Wallace 1876). As South and North of the Isthmus is nowadays challenged by new geologi- America were isolated during most of the , cal data (Montes et al. 2015) and the onset of GABI by very distinct faunas populated the two landmasses palaeontological (Bloch et al. 2016) and molecular data (Simpson 1980). This isolation was ruptured by the (Bacon et al. 2015), that suggest a complex process that northward migration of South American taxa and started at the –Miocene transition.

© The Palaeontological Association doi: 10.1111/pala.12244 1 2 PALAEONTOLOGY

All four families of ‘ground sloths’ took part in all key steps of the interchange, pre- and post-GABI 1 sensu Woodburne (2010). The earliest immigrants are Thi- nobadistes () and (Megalony- chidae), which are present as herald taxa in North America by c. 9 Ma (Webb 1989). Two other herald taxa, () and ‘ chapadmalense’ (Mylodontidae; and the subsequent ; see McAfee 2009) are in North America by c. 7 and 5 Ma respectively (Woodburne 2010). Finally, subsequent sloths are involved in the main phase of GABI, including () and (Nothrotheriidae). Intensive fieldwork recently undertaken in the Cocine- tas Basin of the La Guajira peninsula of Colombia (the northernmost continental region of South America) resulted in the collection of thousands of specimens from the Jimol, Castilletes and Ware formations (Moreno et al. ° 2015). At latitude 12 S, the Cocinetas Basin stands out in FIG. 1. Geographical distribution of tardigradan specimens in delivering rich tropical South American palaeobiotas (Jar- the Cocinetas Basin. The magnified region is indicated on the amillo et al. 2015) in the most biodiverse region of the inset map by a rectangle. The cross marks the locality of the tar- world (Wallace 1876), otherwise characterized by a poor digradan specimen from the Castilletes Formation. The arrows fossil record. Moreover, the Ware Formation in particular point to the Ware Formation outcrops. Scale bar represents is critical for the understanding of the GABI (Jaramillo 5 km. Colour online. et al. 2015). Firstly, it is geographically near to the Isth- mus of Panama (only 700 km away). Secondly, it is just MATERIAL AND METHOD slightly older (c. 2.8 Ma) than GABI 1 (2.6–2.4 Ma). The Ware Formation and its tardigradan assemblage have We follow the recommendations on open nomenclature of therefore the potential to improve our understanding of Bengston (1988). For dental terminology, we follow Gaudin the dynamics of GABI in the Neotropics. (2004), that is, the mesialmost tooth is designated as the caniniform (C1 and c1 for the upper and lower respec- tively) even if its shape departs from that of a canine-like GEOLOGICAL SETTING tooth. The following (more distal) teeth are designated as molariforms (M1–4 and m1–3 for the upper four and three The Neogene of the Cocinetas Basin, includ- lower molariforms respectively). Standard measurements ing the Jimol, Castilletes and Ware formations, was were taken with digital calipers when lower than 15 cm and recently revised (Moreno et al. 2015). Of those forma- with a tape measure otherwise. In addition to standard tions, only the Castilletes and Ware formations contain digital photographs, stereophotographs were taken using a mammalian assemblages. Both crop out along the West custom-built seesaw. coast of the La Guajira peninsula (Colombia) at various A phylogenetic analysis was conducted to suggest a localities, of which one from the Castilletes Formation hypothesis regarding the affinities of one specimen (MUN and several from the Ware Formation delivered specimens STRI 36643). The data matrix of Gaudin (2004) was used, ascribed to sloths (Fig. 1). The environment of deposition pruning all non-mylodontid taxa except Bradypus and of the Castilletes Formation ranges from shallow marine Megalonyx, which are used in the present analysis as out- to fluvio-deltaic, and it has been dated as 16.7–14.2 Ma groups. Along with MUN STRI 36643, another additional (late early Miocene to early middle Miocene, upper Bur- terminal taxon, Kiyumylodon, was included. This recently digalian–, SALMA /; described mylodontine was coded based on Rinderknecht Hendy et al. 2015; Moreno et al. 2015). The base of the et al. (2007). The initial ordination of the characters of Ware Formation is dominated by fluvio-deltaic environ- Gaudin (2004) were kept. The edited data matrix is avail- ment deposits, while the top is dominated by open-ocean able in the Dryad Digital Repository (Amson et al. 2016a). shoreface and nearshore deposits. Its age ranges from 3.40 The algorithm employed was the exhaustive search (Branch to 2.78 Ma, late (Piacenzian, SALMA Chapad- and bound) of PAUP 4.0b10 (Swofford 2002). malalan/Marplatan; Hendy et al. 2015; Moreno et al. All specimens have STRI catalogue numbers and are 2015). associated with a locality number and stratigraphic data. AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 3

These are accessible through the STRI PaleoDatabase (http://biogeodb.stri.si.edu/jaramillo/fossildb). Specimens are deposited at the palaeontological collections of MAPUKA (MUN), Universidad del Norte, Barranquilla, Colombia. In order to estimate body mass of several specimens, we used the published regression equations of Janis (1990) (in Farina~ et al. 1998). One of these equations involves the occlusal area of first lower molariform (herein designated as c1 for Pliomegatherium lelongi, see below). This area was measured on a photograph (with scale) of the specimen with the program Fiji (Schindelin et al. 2012).

Institutional abbreviations. F:AM, Frick Collection of the Ameri- can Museum of Natural History, New York, USA; MCL, Museu de Ciencias Naturais da Pontifıcia, Universidade Catolica de , Belo Horizonte, ; MMP, Museo Municipal de Ciencias Naturales ‘Lorenzo Scaglia’, Mar del Plata, Argen- tina; MUN, Mapuka Museum, Universidad del Norte, Barran- FIG. 2. Tardigrada gen. et sp. indet. from the Ware Formation, quilla, Colombia; MUT, Museo Universitario, Tarija, ; left patella (MUN STRI 20108). A, anterior view (proximal towards STRI, Smithsonian Tropical Research Institute, ciudad de top). B, posterior view (proximal towards top). C, proximal view Panama, Panama. (anterior towards top). Scale bar represents 2 cm. Colour online.

Other abbreviations. AP, anteroposterior; CC, craniocaudal; DV, Mionothropus (De Iuliis et al. 2011). The apex is strongly tapered dorsoventral; GABI, Great American Biotic Interchange; LL, labi- (Fig. 2A, B), as in (Amson et al. 2015), but it dif- olingual; MD, mesiodistal; ML, mediolateral; PD, proximodistal. fers from that of the latter in being bent laterally. Teeth: C1/c1, upper/lower caniniform; M1–4/m1–3, upper four/ lower three teeth distal to the caniniform; ‘A’ preceding one of Remarks. We will conservatively not consider MUN STRI the former, the corresponding alveolus. 20108 to represent a taxon of its own in the diversity count, as the possibility that it represents one of the taxa SYSTEMATIC PALAEONTOLOGY recognized below cannot be excluded.

MAMMALIA Linnaeus, 1758 MYLODONTIDAE Gill, 1872 Cope, 1889 Gen. et sp. indet. TARDIGRADA Latham & Davies, 1795 Figure 3 [= PHYLLOPHAGA Owen, 1842; = FOLIVORA Delsuc et al., 2001] Gen. et sp. indet. Referred material. MUN STRI 38047, locality 470062, Ware For- Figure 2 mation.

Description. MUN STRI 38047 consists of an eroded posterior Referred material. MUN STRI 20108, locality 390022, Ware For- dentary bearing three partial molariforms here referred to as m1– mation. 3 (m2 MD length = 8.1 mm; m3 MD length = 16.5 mm; DV height at coronoid process = c. 56 mm; DV height at condyloid Description. MUN STRI 20108 consists of a left patella (maxi- process = 45.9 mm). The ontogenetic stage cannot be precisely mum PD length = 66.7 mm; maximum ML width = 53.8 mm; assessed. Based on the mesiodistal length of the last molariform, it AP depth at centre of articular facet = 22.8 mm; apex PD length is larger than the holotype of the small-sized ‘Brievabradys’ laven- (taken from distal border of articular facet) = 26.9 mm; facet tensis (Villarroel 2000; this is probably a synonym of Glos- ML width = 52.7 mm). It represents a small-sized sloth, sotheriopsis pascuali or another species of Glossotheriopsis,H.G. approaching the dimensions of for instance. The McDonald, pers. comm. 2015), and approaches the dimensions of articular surface is strongly convex mediolaterally (Fig. 2C). This a juvenile Glossotherium chapadmalense (Anaya & MacFadden indicates a strongly developed medial trochlear ridge of the 1995; mentioned therein as Glossotheridium chapadmalense, see femur. The medial portion of the articular surface is much smal- McAfee 2009). The m1 only preserves a rounded portion of distal ler than the lateral one, which is reminiscent of outer layer of the tooth (Fig. 3B). The m2–3 only preserve the lin- (Fig. 2B). The proximal side bears two grooves (Fig. 2C), as in gual half of each tooth. The outline of m2 was most likely 4 PALAEONTOLOGY

Description. MUN STRI 36643 consists of an edentulous partial horizontal ramus of the dentary (Fig. 4A, B; Ac1 MD length = 24.4 mm; Ac1 LL width = 17.8 mm; Am1 MD length = 19.7 mm; Am1 LL width = 18.2 mm; Am2 MD length = 24.6 mm; Am2 LL width = 19.5 mm; ramus DV depth between c1 and m1 = c. 54 mm). The complete alveoli of the three most mesial teeth and the mesial half of a more distal alve- olus are preserved. Based on the depth of the horizontal ramus, MUN STRI 36643 is roughly 20% smaller than Thinobadistes segnis (Webb 1989), hence much smaller than armatus (Lydekker 1894) and much larger than Glossotheriopsis pascuali (McDonald 1997) or ‘Brievabradys’ laventensis (the latter species probably being either a synonym of the former or another spe- cies of Glossotheriopsis, H. G. McDonald, pers. comm. 2015). The c1 alveolus is slightly deflected labially, as in Thinobadistes and Bolivartherium urumaquensis (Carlini et al. 2006a; Fig. 4A, B). This deflection is accompanied by a labial bulge of the den- tary, and, in occlusal view, by the presence of concavities on the labial side of the dentary directly distal and mesial to the alveo- lus of the caniniform, as is Thinobadistes. However, the mesial concavity is more marked in Thinobadistes, an almost right angle FIG. 3. Mylodontidae gen. et sp. indet. from the Ware Forma- marking the posterolateral edge of the spout. In Lestodon and tion, partial left dentary with fragmentary m1–3 (MUN STRI Lestobradys (Rinderknecht et al. 2010), the caniniform is more 36643). A, lingual view (occlusal towards top). B, occlusal view strongly deflected labially. There is no marked diastema in MUN (labial towards top). Scale bar represents 5 cm. Colour online. STRI 36643, as in Thinobadistes, Glossotherium (Owen 1842), Kiyumylodon (Rinderknecht et al. 2007), and Pseudoprepotherium subcircular. The m3 is bilobate, and the relative size of the lobes is (Hirschfeld 1985), and differing from Lestodon (in which a dia- hard to assess due to their preservation. Such a disposition is typi- stema is present). In occlusal view, the outline of the c1 alveolus cally found in mylodontids. It is noteworthy that geologically is triangular with rounded edges. It bears a low longitudinal older forms of uncertain status, such as Orophodon, also feature ridge on its lingual wall, as in Lestodon and Lestobradys. In the such a disposition (Pujos & De Iuliis 2007). latter genera, however, the alveolus projects dorsally and is The coronoid process is small and rounded dorsally (Fig. 3A). somewhat twisted medially. In MUN STRI 36643, the c1 alveo- The condyloid process has a short neck and a ventral position, lus is larger than those of m1 and m2, as in Lestodon and Thi- roughly at the level of the tooth row (diagnostic of the - nobadistes. An enlarged and triangular caniniform is considered tidae; Saint-Andre et al. 2010). The posteromedial opening of the to be diagnostic of the formed by Thinobadistes and Lesto- mandibular canal is located ventral to the anterior edge of the don (Lestodontini sensu Gaudin (2004); Lestodontinae sensu dorsal tip of the coronoid process. The smaller posterolateral Webb (1989)). However, the caniniform is relatively not as opening of the mandibular canal is located at the level of the ante- enlarged as in the latter taxa. The m1 of the specimen F:AM rior root of the coronoid process. Although eroded, the angular 102658, referred to Thinobadistes segnis (Webb 1989) is 69% as process appears regularly rounded, differing from the posteriorly large as the c1 (mesiodistal length), while in MUN STRI 36643 pointed process usually seen in mylodontids. it is 81% as large. In occlusal view, the alveoli of m1 and m2 are oval, with their Remarks. We will conservatively not consider MUN STRI main axis directed mesiolabially. A very slight longitudinal ridge 38047 to represent a taxon of its own in the diversity count, is found on the labial wall of m1 alveolus. The alveolus of m3, as the possibility that it represents a juvenile individual of although fragmentary, preserves part of a strong labial longitudi- the Lestodontini recognized below cannot be excluded. nal ridge, indicating that the tooth was lobate. A lower dentition comprising a caniniform, mesial molariforms with subcircular cross-section, and a lobate distal molariform, is a disposition typically found in some mylodontines. The cross-section of m1 MYLODONTINAE Gill, 1872 and m2 is oval in Kiyumylodon and Lestodon, but subtriangular LESTODONTINI Ameghino, 1889 sensu Gaudin (2004) in Thinobadistes (Webb 1989). Gen. et sp. nov. A large mental foramen (dorsoventral height = 11.3 mm) is Figure 4 found just anterior to the alveolus of the caniniform. MUN STRI 20424 consists of a proximal fragment of the left tibia (Fig. 4C–E; ML width = 115.2 mm; AP depth between Referred material. MUN STRI 36643, locality 470060, and tenta- condyles = 63.8 mm; length from posterior edge of lateral con- tively MUN STRI 20424, locality 390023 and MUN STRI 34353, dyle to anterior edge of medial condyle = 93.8 mm). The speci- locality 470060 (see remarks below), all Ware Formation. men is from an adult, as shown by the epiphyseal closure. AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 5

FIG. 4. Lestodontini gen. et sp. nov. from the Ware Formation. A–B, edentulous partial left dentary (MUN STRI 36643); A, occlusal view (lingual towards top); B, labial view (occlusal towards top). C–E, proximal fragment of left tibia (MUN STRI 20424); C, anterior view (proximal towards top); D, proximal view (anterior towards top); E, lateral view (proximal towards top). F–G, right M4 missing part of the intraalveolar part of the tooth prism (MUN STRI 34353); F, photograph and drawing in occlusal view (lingual towards top); G, lingual view (occlusal towards top). Scale bars represent 5 cm for A–E and 1 cm for F–G. Colour online.

Based on width at proximal end, it is 81% as large as Thi- lateral condyles are found in Thinobadistes segnis and ‘a bridge of nobadistes segnis (mean of four specimens measured by Webb bone connecting the posterior margin of the two facets’ is (1989)). described in Pseudoprepotherium confusum (Hirschfeld 1985). In In proximal view (Fig. 4D), the relative size of the condyles proximal view, the tibial tuberosity barely protrudes anteriorly and their shape are reminiscent of Glossotherium robustum (Owen from the level of the medial condyle. A similar condition is found 1842) and Paramylodon harlani (Stock 1925). As in the latter two in Lestodon armatus, and differs from Thinobadistes segnis taxa, the medial condyle is not circular but oval, and its long axis (and most other sloths) in which the tuberosity is more developed is directed anterolaterally to posteromedially. A similar condition anteriorly at the level of lateral condyle. is found in Megalonyx jeffersonii (Leidy 1855). In Thinobadistes There is a well-developed crest joining the lateral condyle to segnis and Lestodon armatus, the medial condyle is not as elongate. the shaft, which forms a deep fossa on the posteriolateral side In cuvieri and bucklandi, the long axis of the distal to the proximal facet for fibula (Fig. 4E). This is also medial condyle is directed anteroposteriorly, and the condyle is found in mylodontines, such as Glossotherium robustum, but relatively smaller. The intercondylar space is narrower, especially not in scelidotheriines such as Catonyx cuvieri or Valgipes posteriorly, than in most sloths. However, rather close medial and bucklandi. 6 PALAEONTOLOGY

The proximal facet for the fibula faces posterodistally. It faces slightly more laterally in Glossotherium robustum and, conversely, it faces slightly more distally in Catonyx cuvieri. There is a well- developed facet for the cyamo-fabella as in other sloths, such as mylodontids and megatheriids. In MUN STRI 20424, this facet faces posteriorly and has a triangular outline. On the anterior side of the bone, there is a crest issuing from the tibial tuberosity that is directed mediodistally (Fig. 4C). A similar crest is found in Glossotherium robustum (Owen 1842). In Lestodon armatus, it is more distally directed (Gervais 1873). MUN STRI 34353 consists of a bilobate tooth formed by con- centric layers of orthodentine (Fig. 4F, G; MD length = 17.3 mm; Max LL width of mesial lobe = 13.7 mm; Max LL width of distal lobe = 6.5 mm). The inner nucleus of vasodentine is almost entirely missing (Fig. 4F). Only patches of cementum are pre- served at various heights along the tooth. The larger mesial lobe is compressed mostly mesiodistally, but with a diagonal direction as well, giving the tooth an asymmetrical shape in both the labiolin- gual and mesiodistal directions. The smaller distal lobe is strongly compressed labiolingually. Well-marked labial and lin- gual sulci at the level of junction between the lobes are found along the whole length of the tooth (Fig. 4G). The resulting morphology is reminiscent of the right M4 of Pleurolestodon dalenzae (Saint-Andre et al. 2010). The long and constricted distal lobe of M4 is a diagnostic feature of this species, as the other valid species of the , P. acutidens (Saint-Andre et al. 2010), lacks the strong labiolingually compression of the FIG. 5. distal lobe (Rovereto 1914). However, the distal lobe is longer Hypothesis of phylogenetic affinities of MUN STRI and less constricted in P. dalenzae than in MUN STRI 34353, 36643 among Mylodontidae. Strict consensus tree obtained with forming a ‘secondary’ rounded nucleus. The labial side of the PAUP 4.0b10 (Swofford 2002) that has a length of 550, a consis- mesial lobe forms a somewhat more acute curve in P. dalen- tency index of 0.59, and retention index of 0.55. zae than in MUN STRI 34353. In addition, the holotype of total of 18 equally parsimonious trees were obtained. P. dalenzae (MNHN-BOL V 3348) is larger (mesiodistal length 1.27 times greater). Their consensus is much less resolved than the first analy- It is noteworthy that an approaching morphology is featured sis, with the Mylodontinae, except for Pseudopre- by the most distal lower molariform (m3) of Pseudopre- potherium, forming a polytomy. The only relationship potherium confusum (Hirschfeld 1985), but the latter bears a that is resolved within the latter polytomy is the mesiolabially directed facet on its mesial lobe. Moreover, the Lestodontini, recovered as in the previous analysis com- whole vasodentine nucleus is relatively smaller in the m4 of prising MUN STRI 36643. As a result, MUN STRI 36643 P. confusum. should be considered as a Lestodontini sensu Gaudin The occlusal surface is not planar, the lingual part of the (2004). Differing from Lestodon and Thinobadistes, MUN mesial lobe being a bit less worn down than the rest of the STRI 36643 most likely represents an undescribed taxon, tooth. The lingual part of the mesial lobe bears a minute wear nov. gen et sp. but we refrain from formally erecting a new facet that mostly faces occluso-lingually. taxon, pending the discovery of more complete material. MUN STRI 20424 and MUN STRI 34353 can only be Remarks. We performed a phylogenetic analysis including safely ascribed to a medium-sized Mylodontinae gen. et sp. as the ingroup MUN STRI 36643 coded as a terminal indet. We tentatively ascribe them to the same taxon as taxon and the mylodontids included in Gaudin (2004). MUN STRI 36643, as no features appear be incompatible. Three equally parsimonious trees were recovered. Their topology is the same as the one recovered by Gaudin (2004), as their difference lies in the position of MUN SCELIDOTHERIINAE Ameghino, 1904 STRI 36643. The latter is indeed either sister-group of Gen. et sp. indet. Lestodon,orThinobadistes, or of the clade formed by the Figure 6 two latter genera (= Lestodontini), as shown by the poly- tomy of the strict consensus of these three trees (Fig. 5). In a second analysis we included the mylodontine Referred material. MUN STRI 16535, locality 390025, Ware For- Kiyumylodon, also known from an isolated mandible. A mation. AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 7

Description. MUN STRI 16535 consists of a complete left ulna (see 3D model in Amson et al. 2016b). The specimen is from an adult, as shown by the epiphyseal closure (PD length = 280 mm; AP depth at coronoid process = 93.3 mm). MUN STRI 16535 is shorter than all scelidotheriines measured by McDonald (1987), which span from 313 to 476 mm. The four specimens of Sceli- dotherium leptocephalum measured by Mino-Boilini~ et al. (2014) are also longer, the smaller measuring 370 mm. It is however longer than that of Pseudoprepotherium confusum (c. 20 cm; Hirschfeld 1985). In lateral view (Fig. 6C), the posterior end of the olecranon process does not reach the level of the anterior end proximally, which is reminiscent of Glossotherium robustum (Owen 1842) and leptocephalum (Mino-Boilini~ et al. 2014) and differs from those of Catonyx tarijensis (McDonald 1987), Cato- nyx cuvieri, Valgipes bucklandi (Cartelle et al. 2009) and Paramy- lodon harlani (Stock 1925). The most reminiscent olecranon process is found in Scelidotherium leptocephalum, which also fea- tures a characteristic pointed proximal end. The anconeal process is very slightly broken, but is obviously weakly developed (Fig. 6C), which differs from Glossotherium robustum, Catonyx cuvieri and Valgipes bucklandi (Cartelle et al. 2009), and is reminiscent of Scelidotherium leptocephalum, Paramylodon harlani and Catonyx tarijensis. The radial facet is restricted to a small area continuous with the most lateral part of the humeral facet (Fig. 6A). The ulna is more elongate (depth at coronoid process/proxi- modistal length = 0.33) when compared to Glossotherium robus- tum (0.45; Owen 1842) and Paramylodon harlani (0.41; Stock 1925), and slightly stouter than Valgipes bucklandi (0.26; MCL 22464) and Pseudoprepotherium confusum (0.26; Hirschfeld 1985), its proportions being more reminiscent of those of Sceli- dotherium leptocephalum and chiliense (both 0.32; MMP 549S and MUT 1510 respectively; McDonald 1987). A generic attribution is precluded by the paucity of postcra- nial data for Neogene taxa (Mino-Boilini~ et al. 2011).

MEGATHERIOIDEA Gray, 1821 Hyperleptus? Ameghino, 1891 Figure 7

Referred material. MUN STRI 37413, locality 130024, Castilletes Formation.

Description. Bone fragment with three poorly preserved molari- forms (M2 MD length = c. 6 mm; M2 LL width = c. 10 mm; M3 MD length = 6.8 mm; M3 LL width = c. 8 mm; M4 MD length = 6.8 mm; M4 LL width = 6.2 mm). The different types of dental tissues are not discernable. There is no diastema (Fig. 7A). On the lingual side of the middle and mesial teeth,

FIG. 6. Scelidotheriinae gen. et sp. indet. from the Ware For- mation, left ulna (MUN STRI 16535). A, anterior view (proxi- mal towards top). B, posterior view (proximal towards top). C, lateral view (proximal towards top). Scale bar represents 10 cm. Colour online. 8 PALAEONTOLOGY

preserves mesial and distal ridges, a synapomorphy of megatheri- oids (Gaudin 2004). Conversely, the outline of M4 (the only one entirely preserved) is subcircular, a singular trait in sloths. The mesial half of its occlusal surface is covered by a labionlingual ridge. Although mostly broken, there was most likely a lower dis- tal ridge as well. Hyperleptus garzonianus is characterized by a rounded M4 and mesiodistally compressed M1–3(Ameghino 1891). However in Hyperleptus garzonianus the M4 is not as circular as in MUN STRI 37413, being slightly wider labiolin- gually than long mesiodistally (see measurements of Scott (1903–1904)).

Remarks. A sub-circular outline of M4 seems to be a derived trait found of Hyperleptus garzonianus. As the M4 of MUN STRI 37413 also departs from the plesiomorphic strongly elliptical condition of megatherioids, a close affinity with the latter species is likely. But the fragmen- tary nature of MUN STRI 37413 and the fact that its M4 seems even more circular than that of Hyperleptus garzo- nianus preclude a definitive attribution to this species. Hyperleptus is known from the Santa Cruz Formation (Scott 1903–1904), and is one of a number of small megatherioids of uncertain affinity, which also includes Pelecyodon, Schismotherium, Analcimorphus and Hapalops (Gaudin 2004).

MEGALONYCHIDAE Gervais, 1855 Gen. et sp. nov. Figure 8

Referred material. MUN STRI 16601, locality 390077 and MUN STRI 34226, locality 470060, both Ware Formation.

Description. MUN STRI 16601 consists of a left patella repre- senting a relatively large-sized taxon (Fig. 8D–E; maximum PD length = 112.3 mm; maximum ML width = 92.7 mm; AP depth at centre of articular facet = 32.2 mm; apex PD length (taken from distal border of articular facet) = 47.8 mm; facet ML width = 86.4 mm). It is slightly smaller than the specimen of Megalonyx jeffersonii measured by Leidy (1855), but much larger than Pliomorphus mutilatus, as shown by the width of the patel- FIG. 7. Megatherioidea Hyperleptus? (MUN STRI 37413) from lar trochlea of the femur (Brandoni 2009). The tapered apex the Castilletes Formation. A, photograph and drawing in occlu- gives the patella a teardrop shape in anterior view (Fig. 8D), as sal view (labial towards top). B, lingual view (occlusal towards commonly seen in sloths. The articular facet is only very weakly top). Scale bar represents 2 cm. Colour online. convex mediolaterally (Fig. 8E), precluding the attribution to a pedolateral sloth (Mylodontidae or Megatheria) or a . the bone projects medially. Attributable to a small portion of Moreover, the lateral half of the facet is shorter proximodistally the posterior end of the palatine, this indicates that the specimen than the medial half, as in Megalonyx jeffersonii (Leidy 1855). represents upper teeth and maxilla. The occlusal surface of the However, in anterior view, the general shape differs from that of teeth does not reach the most ventral level of the bone, possibly Megalonyx jeffersonii, in that both its proximal border and apex suggesting a very immature individual or a very abrasive diet are more tapered. (Fig. 7B). Furthermore, each tooth is surrounded by a large MUN STRI 34226 consists of an ulna preserving the proximal space, which would tend to corroborate the first hypothesis. The epiphysis and part of the diaphysis (Fig. 8A–C; AP depth at M2 is poorly preserved. Its outline and that of M3, although not coronoid process = 83.0 mm; PD length from proximal end to entirely preserved, are clearly compressed mesiodistally. The M3 level of coronoid process = 62.2 mm). The specimen is from an AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 9 adult, as shown by the epiphyseal closure. The most distal part The olecranon process is directed posteroproximally, forming of the preserved diaphysis is anteroposteriorly deep, suggesting an angle of roughly 45° with the proximodistal axis of the bone that roughly at least a fifth of the diaphysis is missing. (Fig. 8A–C), as in Megalonyx jeffersonii (see for instance Leidy 1855, pls IX, X). However, it differs from the latter genus by lack- ing the strong medial inflection that affects the whole tuberosity (Fig. 8A). Indeed, the olecranon process only slightly protrudes medially in MUN STRI 34226. The presence of a small tuberosity on the medial side of the tip of the olecranon process is reminis- cent of Megalonyx jeffersonii, and Nothrotheriops shastensis as well. The articular surface for the humeral trochlea is not entirely preserved, but one can observe that it is weakly expanded laterally and posteriorly (Fig. 8A, C), a characteristic feature of Megalonyx jeffersonii, and differing from Nothrotheriops shastensis for instance. As in both latter genera, the anconeal process is weakly developed anteriorly. It appears even narrower mediolaterally than in these two genera. Although fragmentary, it can be discerned that the radial facet is continuous with the humeral facet. Intraspecific variation regarding this trait is described in Mega- lonyx jeffersonii (McDonald 1977). A large rounded pit is present distal to the radial facet. A strong crest, issued from the process for the radial notch, joins rapidly the anterior edge of the shaft. The shaft is slightly bent medially (Fig. 8A, B). Its lateral side bears a strong muscular crest issued from the posterior end and directed anterodistally.

Remarks. MUN STRI 16601 and MUN STRI 34226 were found isolated and each can be ascribed to an undescribed Megalonychidae. We conservatively ascribe both specimens to the same Megalonychidae gen. et sp. nov. in order to avoid overestimating the taxonomic diversity of the Ware Formation.

MEGATHERIA sensu Gaudin (2004) MEGATHERIIDAE Gray, 1821 MEGATHERIINAE Gray, 1821 Pliomegatherium lelongi Kraglievich, 1930 Figure 9

Referred material. MUN STRI 36685, locality 390024, and tenta- tively MUN STRI 19747, locality 390017 and MUN STRI 20446, locality 390026, all Ware Formation.

Description. MUN STRI 36685 consists of a partial mandible with c1 (mesialmost tooth, molarized in megatheriines), eroded below the level of the alveolar plane (Fig. 9A–B; maxi- mum MD length of c1 = 32.3 mm; maximum LL width of c1 = c. 36 mm; LL width at distal end = 33.8 mm; maximum MD length of alveolus of c1 = 37.4 mm). It is an adult

FIG. 8. Megalonychidae gen. et sp. nov. from the Ware Forma- tion. A–C, left ulna (MUN STRI 34226); A, anterior view (proximal towards top); B, posterior view (proximal towards top); C, lateral view (proximal towards top). D–E, left patella (MUN STRI 16601); D, anterior view (proximal towards top); E, posterior view (proxi- mal towards top). Scale bar represents 10 cm. Colour online. 10 PALAEONTOLOGY

FIG. 9. Pliomegatherium lelongi from the Ware Formation. A–B, partial mandible with c1 (MUN STRI 36685); A, photograph and drawing in occlusal view (anterior towards top); B, right lateral view (occlusal towards top). C, partial caudal (MUN STRI 19747) in dorsal view (cranial towards top). Scale bar represents 5 cm. Colour online. AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 11

TABLE 1. Body size estimations for the two size extremes of the tardigradan assemblage of the Ware Formation. Measurements (cm/cm2) Prediction (kg)

MUN STRI 36685 c1 length (FLML) log mass = log FLML * 3.263 + 1.337 3.23 996 c1 width (FLMW) log mass = log FLMW * 2.909 + 2.03 3.60 4449 c1 area (FLMA) log mass = log FLMA * 1.553 + 1.701 10.042 1806 Mean of predictions 2417 MUN STRI 12924 Occipital height (OCH) log mass = log OCH * 2.783 À 0.42 5.37 41

The equations are based on Janis (1990) (in Farina~ et al. 1998). First lower (FLM) corresponds to c1 in Pliomegatherium lelongi (MUN STRI 36685). individual, as indicated by the thorough closure of the symph- 1861; Pujos & Salas 2004). In Megalonyx, the transverse pro- ysis, and the very short distance between the labial side of c1 cesses are also strongly oriented laterocaudally, but they are alveolus and lateral side of horizontal ramus (De Iuliis 1996). more dorsoventrally flattened. In , the transverse Based on the tooth dimensions, it is a medium-sized megath- processes are either oriented only laterally or laterocranially (e.g. eriine, similar to the holotype of Pliomegatherium lelongi Glyptotherium texanum, Gillette & Ray 1981). (Brandoni 2006), and smaller than Pyramiodontherium brevi- MUN STRI 20446 consists of a centrum of caudal vertebra rostrum (Carlini et al. 2002; and, by extension, also smaller (CC length of centrum = 57.9 mm; DV height of centrum at than Megatheriops rectidens, see Pujos et al. 2013). The cross- cranial side = 56.2 mm; ML of centrum at caudal side = section of c1 is trapezoidal, with the mesial side slightly nar- c. 71 mm; maximum ML width (one side doubled) = 170 mm). rower labiolingually than the distal side (Fig. 9A). This is The cross-section of the centrum is slightly flattened dorsoven- characteristic of Pliomegatherium lelongi (Brandoni 2006), and trally, indicating proximity to the cranial region of the series. differs from the mesiolabially constricted teeth of early The cranial and caudal facets of the centrum are only slightly megatheriines such as Megathericulus, and square cross-section oblique to each other (i.e. the cranial is set slightly dorsal to the of the teeth of americanum, Eremotherium lauril- caudal). The four hypophyseal processes and their facets for the lardi and Eremotherium eomigrans. The dorsal edge of the pre- haemal arches are well developed. served portion of the spout is not preserved (Fig. 9B), which prevents us from precisely assessing the relative development of the ventral bulge of the dentary (diagnostic within the Megatheri- Remarks. Pliomegatherium lelongi is otherwise recorded in inae subfamily; De Iuliis 1996). The posterior end of the symph- the ‘conglomerado osıfero’, Ituzaingo Formation, Entre ysis is preserved (Fig. 9A). It forms a partially closed notch Rıos Province, (upper Miocene – Pliocene; Bran- (c. 80°). This is reminiscent of Pliomegatherium lelongi (Brandoni doni 2006). Pliomegatherium sp. is also reported in the 2006) and Eremotherium laurillardi, and differs from the more ‘Barrancas de San Gregorio’, San Jose member of Raigon open symphysis of Megathericulus patagonicus, and more closed Formation (Perea et al. 2013), San Jose Department, Uru- one of Megatherium americanum. It is located approximately at guay (Mones 1988). These localities are at a latitude of the level of the mid-mesiodistal length of c1, roughly as in Ere- c. 32–34°S, and are c. 5000–5500 km from the localities of motherium laurillardi, Pliomegatherium lelongi and Pyramiodon- the Ware Formation. The geographical range of P. lelongi is therium bergi (Brandoni 2006), but differs from Megathericulus hence drastically expanded, with specimens being found patagonicus, Eomegatherium andinum, and Anisodontherium halmyronomumin, in which it is more anterior (Pujos et al. 2013; across the northern two-thirds of South America. The Tejada-Lara et al. 2015). In adult Megatherium americanum,itis broad geographical distribution seems to be common in more posterior (De Iuliis 1996). the subfamily, as exemplified by the Panamerican Eremoth- MUN STRI 19747 consists of a centrum with a transverse erium laurillardi (Cartelle & De Iuliis 1995). Based on the process from a caudal vertebra (Fig. 9C; CC length of cen- dimensions of the c1 of MUN STRI 36685, the body mass trum = 59.8 mm; DV height of centrum at cranial side = 57.3 of this individual is estimated to be between c. 1000 and mm; ML of centrum at caudal side = 77.6 mm). The dimen- 4400 kg, with a mean value of 2400 kg (Table 1). This is sions would fit a medium-sized Megatheriinae, such as the sev- consistent with the 2500 kg estimate given for another enth caudal vertebra of Megatherium urbinai. The cross-sectional medium-sized megatheriine, Pyramiodontherium scillatoy- shape of the centrum is slightly flattened dorsoventrally, indicat- anei (De Iuliis et al. 2004). ing proximity to the cranial region of the series. The cranial and MUN STRI 19747 and MUN STRI 20446 can only be caudal facets of the centrum are only slightly oblique. The trans- verse process is oriented laterocaudally, forming an angle of safely ascribed to Megatheriinae indet. and Xenarthra roughly 40° with the sagittal plane. It ends with a globular indet., respectively. But, given the similar morphology tuberosity that is located caudal to the level of the centrum. and dimensions of the centra, and the fact that no fea- Moreover, the body of the transverse process is triangular in tures appear to be incompatible, we tentatively ascribe cross-section. Such a condition is found in Megatherium (Owen them to the same taxon as MUN STRI 36685. 12 PALAEONTOLOGY

NOTHROTHERIIDAE Ameghino, 1920 3D model in Amson et al. (2016b); ML width at postorbital con- NOTHROTHERIINAE Ameghino, 1920 striction = 54.5 mm; ML width at mastoid processes = 82.0 mm; cf. Nothrotherium Lydekker, 1889 ML width at root of zygomatic process of squamosal = 95.1 mm; = Figures 10, 11 maximum ML width of occipital condyles 56.5 mm; occipital height = 53.7 mm; maximum ML width of foramen mag- num = 30.0 mm; maximum DV height of foramen magnum = Referred material. MUN STRI 12924, locality 390024, Ware For- c. 28 mm). Two foramina are present at the posterior edge of the mation. basioccipital, which indicate the incomplete ossification and hence immaturity of the specimen. Moreover, some of the sutures appear Description. MUN STRI 12924 consists of a fragmentary basicra- thoroughly closed (e.g. interfrontals, interparietals), while others are nium, with the posterior portion of the skull roof (Fig. 10; see not (e.g. supraoccipital-exoccipital). A subadult stage is hence

FIG. 10. Cf. Nothrotherium from the Ware Formation, partial basicranium (MUN STRI 12924), general views (photograph and drawing). A, dorsal view (right lateral towards top). B, left lateral view (dorsal towards top). C, occipital view (dorsal towards top). Abbreviations: ape., anterior process of entotympanic; coa., canal for the occipital artery; eoc., external occipital crest; exc., exoccipital crest; f., foramen; frag., fragment; nc., nuchal crest; oc., occipital condyle; Occ., occipital bone; p., process; sf., stylomastoid foramen. Scale bars represent 5 cm. Colour online. AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 13

AB C

FIG. 11. Cf. Nothrotherium from the Ware Formation, partial basicranium (MUN STRI 12924), close-up of the left auditory region in ventral view (anterior towards top). A–B, left and right stereophotographs. C, same view as B but labelled. Abbreviations: ant. cr. fr., anterior crus fragment; ant. p. ent., anterior process of entotympanic; Bo., basioccipital; Bs., basisphenoid; car. f. + mlf., carotid fora- men and medial lacerate foramen; ent. p. ali., entoglenoid process of alisphenoid; exo. cr., exoccipital crest; f., foramen; gl., Glaserian fissure; mast. p., mastoid process; pet. fr., petrosal fragment; p., process; post. p. ent., posterior process of entotympanic; th., tympa- nohyoid; sm., superficies meatus; ssp., scar of suture for pterygoid bulla; sth. fos., stylohyal fossa; stylo. f., stylomastoid foramen; su. int. car. art., sulcus for internal carotid artery. Scale bar represents 2 cm. Colour online.

inferred for this specimen. The size of the specimen falls within developed as in typicum, Nothrotherium the range of the adult specimens of Nothrotherium maquinense maquinense and Nothrotheriops shastensis. measured by Cartelle & Fonseca (1983), and is slightly larger than Anterior to the carotid foramen, and medial to the Glaserian Mionothropus cartellei (De Iuliis et al. 2011) and Pronothrotherium fissure, the bone has an irregular surface and displays a broken typicum (Patterson et al. 1992). ridge (Fig. 11). Medial to it, and just anterior to the basioccipi- Only a dorsal portion of the posterior half of the frontals is pre- tal tuber, the basisphenoid shows a rugose surface. This region served (Fig. 10A, B). There is no sagittal crest (diagnostic of the most likely represents the location of the posterior part of the Nothrotheriidae; De Iuliis et al. 2011), but this could be due to ossified pterygoid bulla, which presumably would not have been the immaturity of the specimen. The frontoparietal suture is at the thoroughly sutured yet to the basiphenoid in this immature level of the root of the zygomatic process of the squamosal. Part of specimen. An ossified pterygoid bulla is present in Nothrother- the alisphenoid is present on both sides. It contacts the parietal ium maquinense and Nothrotheriops shastensis. (diagnostic of the Nothrotheriinae except Mionothropus cartellei, The ectotympanic is missing on both sides, except maybe for De Iuliis et al. 2011). The temporal line joins the dorsal edge of a small portion of the anterior crus on the left side. The ento- the zygomatic process of the squamosal posteriorly, as in tympanic is well preserved on both sides. Anterolateral and pos- Mionothropus cartellei, Nothrotherium maquinense and Nothrothe- teromedial portions can be distinguished, as described in riops shastensis, but not in Pronothrotherium typicum (De Iuliis Pronothrotherium typicum (Patterson et al. 1992) and Mionothro- et al. 2011). The parietals are globose and posteriorly depressed pus cartellei (De Iuliis et al. 2011). The posteromedial portion is (diagnostic of Nothrotherium maquinense, Paula Couto 1971). much smaller than the anterolateral one, differing in that regard The root of the zygoma is directed anteriorly (diagnostic of from Pronothrotherium typicum (Patterson et al. 1992). A similar the Nothrotheriinae; De Iuliis et al. 2011). Lateral to it, there is disposition is found in Nothrotherium maquinense (MCL 21703), a bulge (diagnostic of the Nothrotheriinae except Mionothropus but in this species the posteromedial portion seems more dorsally cartellei, De Iuliis et al. 2011), although it does not appear as elevated. In MUN STRI 12924, the anterolateral portion forms a 14 PALAEONTOLOGY ventrally expanded crest-like process. It is sigmoidal in ventral important modification to its faunal composition. The view. This process appears to be particularly vertical, not being specimen previously referred to Megatheriidae (MUN inclined medially. The posterior end of the entotympanic forms STRI 16777; Moreno et al. 2015), the only sloth formerly the medial part of the stylohyoid fossa. The junction between the recognized in the formation, is actually an astrapothere. posteromedial and anterolateral portions of the entotympanic is However, the Castilletes Formation does contain a marked by a shallow sulcus, presumably accommodating, as in tardigrade, as MUN STRI 37413 represents a small Mionothropus cartellei, the internal carotid artery. The jugular foramen (or posterior lacerate foramen) is large, extending poste- megatherioid. Tentatively referred to Hyperleptus?, this riorly up to the level of the hypoglossal foramen (diagnostic of record could be consistent with the geological age of the the Nothrotheriidae; De Iuliis et al. 2011). Both of these foram- Formation as it is otherwise known from the Santacrucian ina somewhat share the same excavation and are located espe- fauna. A sparassodont from the Castilletes formation, cially close to one another, which is very reminiscent of padillai (Suarez et al. 2015), also suggests affini- Nothrotherium maquinense and Nothrotheriops shastensis, and dif- ties with the Santacrucian fauna. On the other hand, fers from the more separate foramina of Mionothropus cartellei crocodilian taxa of the Castilletes Formation are otherwise and Pronothrotherium typicum. Posteromedial to these foramina, known from and faunas (Moreno- there is a globular paracondylar process, very reminiscent of Bernal et al. 2016). This emphasizes the importance of Nothrotherium maquinense, and differing from the more elongate the detailed description of the rest of the mammalian process of Nothrotheriops shastensis. The stylomastoid foramen is fauna from the Castilletes Formation. found at the dorsal end of a sulcus formed laterally by the mas- toid process and medially by a well-developed ridge extending from the nuchal crest (possibly the exoccipital crest sensu Gaudin 1995). This sulcus, terminating dorsally by a foramen, may repre- Diversity of the tardigradan assemblage of the Ware sent a widely exposed canal for the occipital artery, a synapomor- Formation phy of the Nothrotheriidae (Gaudin 1995). A groove also leading dorsally to the mastoid foramen is described in odon- A greater taxonomic diversity in the lower latitudes is a trigonus and Schismotherium fractum (Patterson et al. 1992). global pattern broadly found today among eukaryotes Most of the preserved articular surface of the stylohyoid fossa is (Hillebrand 2004), and it is the result of a long and com- formed by the posterodorsal side of the entotympanic. The rest plex history, as shown in particular for the Neotropics of the preserved articular surface is a narrow strip, presumably (Jaramillo et al. 2006). Recent studies have shown how formed by the tympanohyoid, as in Mionothropus cartellei for Neotropical Miocene formations can preserve hyper- instance (De Iuliis et al. 2011). diverse assemblages (for crocodilians, see The occipital condyles are sessile (Fig. 10C; diagnostic of the Nothrotheriidae; De Iuliis et al. 2011). They have a peculiar (ab- Scheyer et al. 2013; Salas-Gismondi et al. 2015). However, normal?) morphology, being marked at mid-height by a medio- taxonomic richness of fossil tropical assemblages is still laterally oriented depression. There is a distinct external occipital severely underestimated (Carrillo et al. 2015). The Ware crest, developed to an extent very similar to that of a juvenile Formation gives an important insight into the otherwise specimen of Nothrotherium maquinense (MCL 1020). The nuchal poorly documented diversity at low latitudes during the crest, however, is inconspicuous. Pliocene. The conservative diversity count for the tardi- gradan assemblage of the Ware Formation is of five Remarks. Nothrotherium is represented by the distinct taxa. Each of the four families of ‘ground sloths’ N. maquinense and N. escrivanense, which are restricted to (Mylodontidae, Megatheriidae, Nothrotheriidae and Brazilian localities. While we provisionally ascribe MUN Megalonychidae) is represented. When compared with STRI 12924 to cf. Nothrotherium due to the fragmentary assemblages from other Pliocene Neotropical formations nature and immaturity of the specimen, it is likely to rep- (Table 2), the Ware assemblage has a rather diverse tardi- resent a closely related new taxon. Based on the occipital gradan composition. The San Gregorio Formation is a height of this specimen, the body mass of the individual is geographically nearby formation that records a roughly estimated to be c. 41 kg (Table 1). We estimate this speci- synchronous continental fauna, and yet only one sloth men to be subadult, and consider it unlikely that this indi- has been reported (Vucetich et al. 2010), most likely due vidual would have reached 100 kg at maturity. to taphonomic and/or sampling biases. When compared to older formations, the Ware Formation’s tardigradan diversity is equalled by the Urumaco Formation (late DISCUSSION Miocene; where the taxa might not have been coeval, Carlini et al. 2006a) and surpassed by the better-known Mammalian assemblage of the Castilletes Formation Laventan fauna. An example of an extensively sampled Pliocene formation that is found at higher latitudes is the Although not the main focus of the present contribution, Monte Hermoso Formation. Although it records five the Castilletes Formation is discussed here because of an species in three families, only two to three species are AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 15

TABLE 2. Comparison of the sloth diversity in Neotropical and Temperate Pliocene formations. Epoch Formation Latitude (°S) Environment Taxonomic References diversity Species (families)

Neotropical formations Late Pliocene Ware 11.8 Fluvio-deltaic 5 (1) Moreno et al. 2015; present study San Gregorio 11.3 Alluvial fans 1 (1) Vucetich et al. 2010 Early Pliocene Codore 11.3 Fluvio-deltaic with 3 (3) Carlini et al. 2006a, b marine inundation Temperate formations Pliocene Uquıa À23 to À24 Fluvial 5 (3)* Reguero et al. 2007 Corral Quemado À27 – 1 (1) Reguero et al. 2007 Inchasi À19.7 Fluvial 3 (2) Anaya & MacFadden 1995 Monte Hermoso À39 Fluvial 5 (3)* Tomassini et al. 2013 / Andalhuala À27 – 3 (2) Reguero & Candela 2011

*Taxa most likely not coeval. found in the same facies (Tomassini et al. 2013), making niche partitioning was previously argued to explain the it roughly half as diverse as the Ware Formation. When high diversity of Neotropical crocodilian communities compared to other temperate Pliocene assemblages (Scheyer et al. 2013; Salas-Gismondi et al. 2015). (Table 2), a similar conclusion can be drawn, except for the Uquıa Formation. The astonishing 22 species of sloth of the Late Miocene Ituzaingo Formation (‘Conglomerado Ware Formation and GABI osıfero, mesopotamian’) has to be taken with caution, as a recent and unfinished taxonomic revision (every family Sloths are main elements in the American Biotic Inter- except the Mylodontidae) has revealed a lower diversity change, as they are present in North America as early as than previously reported (Brandoni 2013). c. 9 Ma (Hemphillian; Woodburne 2010), and as they Another aspect of the diversity of the sloths of the take part in the main pulses of GABI migration. Addi- Ware Formation dwells in their ecologies. With a body tionally, it was recently emphasized how the Ware Forma- mass estimated to be c. 2400 kg, Pliomegatherium lelongi tion can enlighten our understanding of the GABI, with is a megaherbivore sensu Owen-Smith (1987). While the the example of the carnivoran procyonid Chapalmalania closely related Megatherium americanum is reconstructed sp., found in Ware, which is suggestive that procyonids, as a selective feeder (Bargo & Vizcaıno 2008), broad geo- North American immigrants, dispersed into South Amer- graphical distribution is common in the subfamily, which ica in two separate events (Forasiepi et al. 2014). is usually considered to be indicative of generalist habits. All four families of ‘ground sloths’ that participated in In contrast, the specimen ascribed to cf. Nothrotherium is GABI (Mylodontidae, Megatheriidae, Nothrotheriidae, a small-sized sloth weighing roughly 41 kg. Although not Megalonychidae) were present in the Ware formation. A much can be argued about the ecology of the latter, the taxon closely related to Ware’s Pliomegatherium lelongi range of two orders of magnitude in body size featured (MUN STRI 36685), the megatheriine Eremotherium,is by this tardigradan assemblage suggests that disparate eco- found in North America c. 2.6 Ma (Woodburne, 2010). logical niches were occupied. In addition to intermediate This taxon is widespread in both South and North Amer- body size, the other sloths recovered feature other feeding ica while its sister taxa, Megatherium, is restricted to South ecologies. Based on the morphology of its close relatives, America. The relationships of P. lelongi to both Mega- Lestodon and Thinobadistes, Lestodontini gen. et sp nov. therium and Eremotherium are unresolved, and therefore, was most likely wide-muzzled. This is argued to correlate it is not possible to assess whether the P. lelongi clade with another feeding ecology, namely bulk-feeding (Bargo participated in GABI. Megatheriinae are also represented & Vizcaıno 2008; Czerwonogora et al. 2011). Furthermore, in northern South America by Proeremotherium and Scelidotheriinae gen. et sp. indet. was most likely as nar- Urumaquia (Carlini et al. 2006b, 2008), but the recovered row-muzzled as Scelidotherium leptocephalum, which has elements of those taxa do not include a mandible or lower been interpreted as a mixed or selective-feeder with possi- teeth that would have allowed a comparison with MUN ble uprooting habits (Bargo & Vizcaıno 2008). Similarly, STRI 36685. 16 PALAEONTOLOGY

Nothrotheriops is recorded in North America during the raises the question of why Scelidotheriinae was not Pleistocene (c. 1.4 Ma, Woodburne 2010). However, coe- involved in GABI. The specialized niche possibly associated val Nothrotherium species, which share diagnostic features with derived muzzle shape is most likely a contributing fac- with the specimen from Ware, are restricted to Brazil. tor (McDonald 2005). Scelidotheriines are indeed charac- Therefore, it seems that Ware’s Nothrotherium is a mem- terized by long and narrow premaxillae, also acquired, ber of the South American Nothrotherium that did not although under other modalities, in non-migrant members participate in GABI. of other subfamilies such as Megatherium and Mylodon. Two other sloths of the Formation, Megalonychidae gen. et sp. nov. and Lestodontini gen. et sp. nov. (Mylodonti- dae), have ambiguous affinities. Megalonychidae represents CONCLUSIONS one of the earliest ‘’ families to migrate to North America (c. 9 Ma) and includes the early immi- The Cocinetas Basin comprises two units that record con- grants Pliometanastes, and subsequently Megalonyx and tinental Neogene biotas, the Castilletes and Ware forma- Meizonyx (Woodburne 2010). The Megalonychidae gen. et tions. Both delivered rich mammalian assemblages sp. nov. of Ware is reminiscent of Megalonyx (and by including tardigradan taxa. Sloths are represented in the extension Pliometanastes, of which the postcranium is early–middle Miocene Castilletes Formation by one frag- hardly distinguishable; McDonald & Naples 2007), but also mentary specimen. Referred to a small-sized megatheri- features clear differences. A comparison with Meizonyx is oid, this record could suggest affinities with the distant impossible due to the incompatibility of the elements Santacrucian fauna. recovered. At this point, it is not possible to assess if the The sloths from the late Pliocene Ware Formation are Megalonychidae gen. et sp. nov. of Ware is more closely represented by 12 specimens that belong to 5 taxa from related to North American or South American megalony- the 4 families of ‘ground sloths’. Their body sizes span chids, as South American large-sized megalonychids are over two orders of magnitude, and they most likely still poorly documented (e.g. Megalonychops primigenius, featured various feeding strategies, documenting a highly known by a fragmentary humerus from the Ituzaingo For- diverse assemblage of sloths from the Neotropics. mation, late Miocene of Argentina; Brandoni 2013). Although geographically close to the Isthmus of Panama, Lestodontini gen. et sp. nov. belongs to Mylodontinae, and temporally preceding GABI 1 by only 0.2–0.4 my, the a subfamily of Mylodontidae that includes Thinobadistes, sloths for which unambiguous affinities were recovered one of the earliest migrants to North America c. 9Ma are not closely related to the early immigrants found in (Woodburne 2010). The subfamily continued taking North America before the first main pulse of the Great part in GABI with the late Pliocene – American Biotic interchange. Paramylodon harlani (and a specimen of ‘Glossotherium chapadmalense’; McAfee 2009). Unfortunately, Ware’s Acknowledgements. Our gratitude goes to all the other members Lestodontini gen. et sp. nov. is not complete enough to of the field campaigns, and in particular to J. W. Moreno-Bernal provide synapomorphies that could have discriminated (STRI), who found several of the specimens presented here. The constant help of L. Londono~ (STRI) is also acknowledged. We between South and North American affinities. As empha- thank C. Montes (Universidad de los Andes) and J. Escobar sized by the phylogenetic analysis (see above), Lestodon- (Universidad del Norte) for welcoming EA to the collections tini gen. et sp. nov. is found within a clade with under their care. M. R. Sanchez-Villagra is greatly acknowledged unresolved relationships with both the early immigrant for helping to conceive the study and improve the manuscript. Thinobadistes and Lestodon, known from the Pleistocene H. G. McDonald (Museum Management Program, National of temperate South American. Lestodontinae is also rep- Park Service) and A. A. Carlini (Museo de la Plata) are thanked resented in northern South America by Bolivartherium for their useful insights. B. Schubert (East Tennessee State (Urumaco and Codore formations; Carlini et al. 2006a). University) is acknowledged for providing pictures of Megalonyx’ A subfamily of Mylodontidae, the Scelidotheriinae, did caudal series. R. K. McAfee and an anonymous reviewer are not take part in GABI (Mino-Boilini~ et al. 2014) but has warmly thanked for the improvement they brought to the been found in Ware. This subfamily had a wide distribu- manuscript. EA was granted a short-term postdoctoral fellowship of the Smithsonian Tropical Research Institute, and was subse- tion during the Pliocene and Pleistocene being recorded in quently funded by the Foundation. JC multiple localities (from À20 to À39°, Paleobiology Data- was supported by Swiss National Fund SNF 31003A-149605 to base and the related references included therein: Rusconi M. R. Sanchez-Villagra. The Smithsonian Institution, the 1954; MacFadden et al. 1993; Rodrıguez-Brizuela & Tauber National Geographic Society, the Anders Foundation, Gregory 2006; Reguero & Candela 2011). The non-migrating sceli- D. and Jennifer Walston Johnson, Universidad del Norte, the dotheriine contrasts with other taxa in Ware, whose rela- Lab of M. R. Sanchez-Villagra at the Pal€aontologisches Institut tives took part in GABI (Woodburne 2010). The record of und Museum der Universit€at Zurich,€ and the National Science Ware, in the vicinity of the Isthmus of Panama, further Foundation (Grant EAR 0957679) also helped to support this AMSON ET AL.: NEOGENE SLOTHS FROM THE COCINETAS BASIN 17

work. Thanks to Carlos Rosero for managing all the logistics in A. 2015. Biological evidence supports an early and complex the field. Thanks to the communities of Warpana, Patajau, Aule- emergence of the Isthmus of Panama. Proceedings of the chit, Nazareth, Wososopo, Sillamana, Paraguachon, La Flor de la National Academy of Sciences, 112, 6110–6115. Guajira, and Ipapura. Thanks to the Colombian National Police -MOLNAR, P., ANTONELLI, A., CRAWFORD, A. (Castilletes base) and the Colombian Army (La Flor de la J., MONTES, C. and VALLEJO-PAREJA, M. C. 2016. Guajira and Cerro de la Teta). We express special thanks to our glaciation and the Great American Biotic Inter- drivers, Grillo, Lalo and Medardo. change. Geology, 44, 375–378. BARGO, M. S. and VIZCAINO, S. F. 2008. Paleobiology of Pleistocene ground sloths (Xenarthra, Tardigrada): biome- DATA ARCHIVING STATEMENT chanics, morphogeometry and ecomorphology applied to the masticatory apparatus. 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