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Martínez & Novas: coelurosaurian from 243

Rev. Mus. Argentino Cienc. Nat., n.s. 8(2): 243-259, 2006 , ISSN 1514-5158

Aniksosaurus darwini gen. et sp. nov., a new coelurosaurian theropod from the Early of Central Patagonia,

Ruben D. MARTINEZ1 & Fernando E. NOVAS2

1Laboratorio de Paleontología de Vertebrados, Universidad Nacional de la Patagonia «San Juan Bosco», (9.000) Comodoro Rivadavia, Argentina. 2Laboratorio de Anatomia Comparada y Evolucion de los Vertebrados, Museo Argentino de Ciencias Naturales «B. Rivadavia». CONICET. Av. Angel Gallardo 470 (1405), Buenos Aires, Argentina.

Abstract: The theropod Aniksosaurus darwini gen. et sp. nov. has been recovered from the Upper Cretaceous, , of Central Patagonia. Aniksosaurus darwini gen. et sp. nov. was a small tetanurine, approximately 2 meters long. Aniksosaurus exhibits several unique traits (e.g., cranial cervical ver- tebrae with dorsoventrally deep neural arches, provided with a pair of cavities at their cranial surfaces; neural canal wide; cranial caudals with ventral sagittal keel, and transverse processes triangular-shaped in dorsal view; manual ungual phalanges robust; with extremely expanded brevis shelf; with deep notch for M. Iliotrochantericus; metatarsal and IV of pes transversely narrow). Available postcranial bones of Aniksosaurus exhibit derived features of (e.g., ilium with well developed cuppedicus fossa; femur with anterior trochanter proximally projected, almost reaching the level of the articular head; greater tro- chanter craniocaudally expanded; femoral head rectangular-shaped in cranial aspect; and fibular shaft craniocaudally narrow), as well as characteristics suggesting that the new Patagonian is more derived than some coelurosaurians such as compsognathids, , and coelurids. Comparisons with maniraptoriforms (a including , , , and ) support that Aniksosaurus is less derived than these theropods. In sum, Aniksosaurus is here considered as a Late Cretaceous survivor of a basal coelurosaurian radiation.

Key words: coelurosaurian, Late Cretaceous, Patagonia, Argentina. ______

The record of coelurosaurian theropods list of coelurosaurians a new predatory dinosaur, from South America has considerably increased Aniksosaurus darwini gen. et sp. nov., from the in the last 15 . Currently, remains of seven Bajo Barreal Formation of central named of non-avian coelurosaurians have Patagonia (Fig. 1). been recovered from different Cretaceous locali- The new taxon is known from postcranial re- ties of Argentina and Brazil. They are members mains belonging to at least to five specimens that of a variety of lineages including, among the most were recovered from a single fossil locality. The conspicuous, the compsognathid discovery was made by personnel of the Labo- asymmetrica (Naish et al., 2004), and the ratorio de Paleovertebrados of the Universidad maniraptoriform placidus Nacional de la Patagonia «San Juan Bosco» (Kellner, 1999, 2001), both from the ? (UNPSJB) in the context of the project «Los Santana Formation of NE Brazil, the vertebrados del Grupo Chubut: características y alvarezsaurids Alvarezsaurus calvoi and evolución-primera etapa», conducted by the se- puertai (Bonaparte, 1991; Novas, nior author. The new theropod was briefly de- 1996, 1997), possible oviraptorosaurs from NW scribed by Martínez & Novas (1997) who prelimi- Argentina (Frankfurt & Chiappe, 1999), derived narily interpreted it as a basal coelurosaurian maniraptorans of unknown affiliation from the resembling the Late Ornitholestes Marilia Formation (Novas et al., hermanni from (Osborn, 1917; 2005), and the dromaeosaurids Carpenter et al., 2005). argentinus (Novas & Pol, 2005), comahuensis (Novas & Puerta, 1997; Novas, Institutional abbreviations: AMNH, 2003), Buitreraptor gonzalezorum (Makovicky et American Museum of Natural History, New York; al., 2005), and possibly also Unquillosaurus MACN, Museo Argentino de Ciencias Naturales ceibali (Novas & Agnolín, 2004). We add to this «B. Rivadavia», Buenos Aires; MCZ, Museum of 244 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006

Fig. 1. Geographic location of the Estancia «Laguna Palacios», Chubut Province, central Patagonia, Argentina, where the remains of Aniksosaurus darwini gen. et sp. nov. were found.

Comparative , Cambridge; MDT-PV, (these derived features are listed in the text be- Museo Desiderio Torres -Paleovertebrados, low); and, 5) there is no evidence of any other di- Sarmiento, Chubut, Argentina; MOR, Museum nosaurian taxon preserved in the quarry. However, of the Rockies, Bozeman; NMC, Canadian Mu- with the exception of the specimen (con- seum of , Ottawa; YPM, Yale Peabody Mu- sisting of an articulated right hindlimb), the ma- seum, New Haven. jority of the bones were found disarticulated, thus we avoid the identification of discrete specimens MATERIALS AND METHODS composed of more than a single bone. For this rea- son, we confer consecutive numbers to the isolated Studied specimens: The following specimens skeletal elements found in the quarry. were studied: fragilis (AMNH 5767), The fossil-bearing tuff is pure and shows no antirrhopus (AMNH 3015, MCZ indication of transport (J. C. Sciutto, pers. 4371, YPM 5205, 5206, 5236), Ornitholestes comm.). Therefore, we tentatively interpret that hermani (AMNH 619), and the taphonomic association of different individu- floresi (MACN-CH 895). als of Aniksosaurus darwini as evidence of gre- Terms of anatomical orientation: We follow garious behavior in this theropod species. terms employed in avian anatomy (Clark, 1993). Interestingly, there are some differences «Cranial» and «caudal» are used here in place of among the various long bones of Aniksosaurus, «anterior» and «posterior», respectively. that mainly concern the robustness of the hu- Systematic nomenclature: Coelurosauria in- merus, the proportion (i.e., area and depth) of the cludes extant and all theropods sharing a fossa for the insertion of the M. ischiotrocantericus more recent common ancestor with extant birds (Hutchinson, 2001) on the femur, and the relative than with Allosaurus (Holtz et al., 2004). size of the crista fibularis of . Collected material of Aniksosaurus darwini: On femur MDT-PV1/23 there are marks The material referred to this taxon was recov- of small size (3 mm wide), arranged in opposing ered from a single quarry four meters long, two rows that were probably left by a small scaveng- meters wide and one meter thick. The recovered ing . bones includes five tibiae of the right side, thus indicating that the fossil assemblage is made up, SYSTEMATIC at least, by five different specimens. We inter- pret that they belong to a single species for the DINOSAURIA Owen, 1842 following reasons: 1) all the bones correspond to Seeley, 1887 small of approximately the same size; 2) Marsh, 1881 at least some bones (e.g., femur, tibia and foot of Gauthier, 1986 the holotype specimen, MDT-PV 1/48) were pre- COELUROSAURIA Huene, 1920 served in articulation; 3) duplicate hindlimb ele- ments (e.g., femur, tibia, metatarsals, and pedal Aniksosaurus, gen. nov. phalanges) are anatomically identical to the ho- lotype; 4) available bones exhibit theropod, Etymology. From Greek aniksi, «spring», re- tetanurine and coelurosaurian synapomorphies ferring to September 21st (i.e., the beginning of Martínez & Novas: Cretaceous coelurosaurian from Patagonia 245 the spring in the Southern Hemisphere), the day gual phalanges resembling na- when the theropod was found; and Greek saurus, munhuaiquii (Martínez et al., 1999). Sauropods «». found in the same levels include remains of a species. Aniksosaurus darwini, sp. nov. diplodocimorph (Sciutto & Martínez, 1994), a Known distribution. Upper Cretaceous, Cen- nearly complete and partial cervical series tral Patagonia, South America. of a yet unnamed basal titanosaurian (Martínez, Diagnosis. As for the type and only known 1998b, 1999), remains referred to the basal species. titanosaur Andesaurus sp. (Calvo & Bonaparte, 1991; Powell et al., 1989), most of postcranial Aniksosaurus darwini, sp. nov. skeleton of the early titanosaurian Epach- (Figs. 2-13, Table 1-2) thosaurus sciuttoi (Martínez et al., 1989, 2004; Powell, 1990), and Titanosaurinae remains Holotype. MDT-PV 1/48. Articulated right (Powell, 1986; Sciutto & Martínez, 1994). A basal hindlimb including femur, , tibia and foot. igua-nodontian ornithopod, Notohypsilophodon Hypodigm. Associated material collected at comodorensis has also been described from the the site where the holotype was discovered: cer- Bajo Barreal Fm (Martínez, 1998a). vical (MDT-PV 1/14); two dorsal verte- Diagnosis. Small theropod with the following brae (1/6, 1/18); proximal caudal vertebra (1/32); autapomorphies: with the neu- mid-caudal vertebra (1/13); six indeterminate ral arch pedicels unusually deep (i.e., 2.5 times vertebrae (1/7, 1/8, 1/9, 1/15, 1/47, 1/52); three the height of the centrum); wide neural canal on indeterminate neural arches (1/21, 1/30, 1/46); cervical vertebrae; cranial caudals with ventral three left humeri (1/29, 1/37, 1/42); two right saggital keel; manual ungual phalanges robust; humeri (1/16, 1/36); left (1/17); manual un- iliac brevis shelf lateroventrally expanded; gual phalanx (1/40); three left ilia (1/24, 1/33, 1/ caudolateral surface of proximal femur with 35); right ilium (1/5); left ischium (1/41); two left strong depression and rugosities presumably for femora (1/23, 1/26); two right femora (1/3, 1/27); the attachment for M. ischiotrochantericus; three left tibiae (1/1, 1/22 , 1/34); four right tibiae metatarsal IV and its correspondent digit trans- (1/2, 1/10, 1/28, 1/44); two indeterminate meta- versely narrow. tarsi (1/4, 1/45); indeterminate phalanx (1/43); Etymology. In honor of the great naturalist and several indeterminate fragments (1/11, 1/12, Charles Darwin, who visited Patagonia in 1832- 1/19, 1/20, 1/25, 1/31, 1/38, 1/39). 1833, inspiring him to reach clearer interpreta- Locality and Horizon. Laguna Palacios ranch, tions of the of life that changed human approximately 30 km north of Buen Pasto, in thought forever. south-central Chubut Province, 280 km west of Comodoro Rivadavia, Argentina (Fig. 1). The DESCRIPTION specimens come from a level of volcanic tuff at the upper part of the Lower Member of the Bajo Aniksosaurus was a small, albeit robust Barreal Formation. The Bajo Barreal Fm. is theropod with an estimated body length of 2 widely exposed in the southeastern corner of the meters and 70 centimeters tall at the level of the Argentinian Province of Chubut, central pelvic girdle. Following methods explained by Patagonia. The age of the Bajo Barreal Forma- Heinrich et al. (1993) for estimation of body tion has recently been under dispute, although weight based on measurements from available most authors agree that it falls within the Late femora, the body weight of the preserved speci- Cretaceous. Based on palynological studies of mens ranged between 65 through 40 kilograms equivalent units, Archangelsky et al. (1994) as- (G.Casal, pers.comm.). Available specimens of signed a Late Albian-Cenomanian age to the Aniksosaurus appear to correspond to adult indi- Lower Bajo Barreal Fm. Recently obtained ra- viduals, as suggested by fusion between neural diometric Ar-Ar dating ages from tuffs and ign- arches and centra of recovered caudal vertebrae. imbrites of the Bajo Barreal Fm. provide ages between 91 and 95.8 Ma (Bridge et al., 2000), a and range of ages corresponding to Cenomanian- Five incompletely preserved vertebrae (i.e., a . This unit has yielded remains of cervical, a fragmentary dorsal, and three caudals) abelisaurid theropods (e.g., form the basis of the following description. Also, bonapartei and other abelisaurid remains; some fragmentary remains of ribs have been re- Martínez et al., 1986; Martínez et al., 1993; covered. The available cervical vertebra (Fig. Lamanna et al., 2002; Martínez et al., 2004), and 2) preserves the caudal section of the neural arch a large theropod with hypertrophied pedal un- and the vertebral centrum. It resembles cervical 246 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006

caudal 4 of Allosaurus (Madsen, 1976). The neu- ral spine is high, vertically oriented and rectan- gular-shaped in side view and placed on the cau- dal half of the neural arch. Deep, but narrow pre- and post-spinal cavities are present at the base of the neural spine. The prezygapophyses are short and robust. The transverse processes are trian- gular in dorsal aspect and oriented at an angle of 40º with respect to the axial plane. The centrum is amphicoelous, transversally narrow, V-shaped in cross-section, with a sharp ventral keel. An- Fig. 2. Aniksosaurus darwini gen. et sp. nov. Cer- other caudal (MDT-PV 1/13, Fig. 4) resembles cau- vical vertebra (MDT-PV 1/14) in lateral (A), and dal 19 of Allosaurus (Madsen, 1976) in the pro- dorsal (B) views. Abbreviations: ns, neural spine; portionally long and low centrum and reduction prz, prezygapophysis. and distal placement of the neural spine. The lat- ter structure is craniocaudally short and the prezygapophyses slightly surpass the cranial mar- 9 of Allosaurus (Madsen, 1976) and the first dor- gin of the centrum. The transverse processes are sal of Deinonychus (labeled as «cervico-dorsal» well developed and caudally projected, with their in Ostrom, 1969) in the height of the neural arch, bases located on the caudal half of the neural arch. bearing epipophyses of small size, a craniocau- The centrum has traces of a ventral longitudinal dally short neural spine, and presence of an ex- groove. cavation on the lateral surface of neural arch. The neural spine of this vertebra is incomplete, but Forelimb it seems to have been craniocaudally short and . This bone (Fig.5A-C) is sigmoid dorsoventrally low. Caudal to the neural spine, a in lateral view, as in Allosaurus (Madsen, 1976) large and deep postspinal cavity is present. The and Piatnitzkysaurus (Bonaparte, 1986). Unfor- postzygapophyses are robust and with late- tunately, any of the five available humeri is com- roventrally oriented and transversely wide ar- plete, so the length of the most complete humerus ticular facets. The epipophyses are represented (MDT-PV 1/16) is estimated to be around 13 cm. by small, elliptical rugosities on the dorsal face The humerus is a robust element, especially to- of the postzygapophyses. The caudal surface of wards the extremities, being subcircular in cross- the neural arch exhibits, above the neural canal, section at mid-shaft. The robustness of this bone a deep pneumatic excavation. The neural canal clearly distinguishes from the considerably more equals the diameter of the caudal centrum sur- slender and elongate humeri of Ornitholestes and face. Such features of the cervical vertebra of (Carpenter et al., 2005). Albeit the ex- Aniksosaurus differ from those of Allosaurus and tremities of the available humeri of Aniksosaurus Deinonychus, for example, in which the centrum are not entirely preserved, a «twisting» along the is transversely wider and inversely the neural longitudinal axis of shaft is apparent: as observed canal is smaller in size. The centrum looks pro- from one of its ends, the angle resulting from the portionally reduced (in transverse diameter). It intersection of both proximal and distal trans- is slightly excavated laterally and lacking of ven- verse axes is around 50o, an angling similar to tral keel. It is internally hollow, with a thin sagital that of Piatnitzkysaurus floresi (MACN-CH 865). wall dividing the centrum into two internal cavi- The deltopectoral crest is not complete on any of ties. The available cervical of Aniksosaurus dif- the available humeri, but the preserved portions fers from those of abelisauroid theropods (e.g., show that it was well developed. The crest is , ) in that the postzyga- transversely thick and cranially oriented, as pophyses are closer to the midline than in the usual in non-avian theropods. Its distal end is latter taxa (in which the neural arch is notably bulky and rounded. The lateral surface of the wider transversely), and the epipophyses are deltopectoral crest shows a weak muscle scar. The small, in contrast with the well-developed ones humeral shaft bears a large depression on its of abelisauroids. Finally, Aniksosaurus lacks the caudolateral surface for a muscle attachment. wide pneumatic cavities that are present caudal Another, but weaker, muscle scar extends diago- to the diapophysis as occurs among abelisauroid nally across the caudal face of humerus, distal to theropods (e.g., Ilokelesia). the mid-shaft. The distal end of the humerus is Three caudal vertebrae have been recov- cranially bowed; on its cranial surface there are ered. One of them (MDT-PV 1/32; Fig. 3) resembles traces of an intercondylar depression. The hu- Martínez & Novas: Cretaceous coelurosaurian from Patagonia 247

Fig. 3. Aniksosaurus darwini gen. et sp. nov. Proximal caudal vertebra in lateral (C), caudal (D), dorsal (E), and ventral (F) views. Abbreviations: k, ventral keel; ns, neural spine; prz, prezygapophysis; tp, transverse processes.

Allosaurus and Piatnitzkysaurus, but it is more robust in comparisson with that of Ornitholestes and Coelurus (Carpenter et al., 2005). The ulna of Aniksosaurus is craniocaudally expanded and has a convex medial surface. The lateral tuber- osity delimits the depression for articulation with Fig. 4. Aniksosaurus darwini gen. et sp. nov. Dis- the proximal end of . The ulnar shaft is tal caudal vertebra in lateral (A), dorsal (B) and curved (i.e., caudally convex), albeit it does not cranial (C) views. Abbreviations: ns, neural spine; form the continuous convexity as observed in poz, postzygapophysis; prz, prezygapophysis; tp, derived coelurosaurs (e.g., dromaeosaurids, transverse processes. troodontids), but a change in curvature exists on both proximal and distal ends, resembling basal tetanurans (e.g., Allosaurus, Piatnitzkysaurus). Notably, the caudal margin of the shaft is sharp, merus of Aniksosaurus is clearly distinguishable a condition resembling that of Megaraptor (No- from these of abelisauroid theropods (e.g., vas, 1998; Calvo et al., 2004), but different from , , ), in the transversely rounded caudal surface seen in which the dectopectoral crest is poorly developed most theropods (e.g., Piatnitzkysaurus, Deinony- and the humeral shaft is straight in both cranial chus, birds). The ulna thins distally, but expands and lateral views (Novas et al., 2006). again transversely and craniocaudally at its The only available ulna (MDT-PV 1/17) be- distalmost end. As a result, a planar surface ex- longs to a left forelimb. The proximal end of the tends across the cranial surface of the distal half ulna is incomplete, lacking the olecranon of the bone. The distal articular surface of the and the articular surface for the humerus. The bone is elliptical, with the longest axis trans- ulna was found no more than 25 cm away from versely oriented, in contrast with the rounded two of the available humeri (MDT-PV 1/16 and distal end of coelophysids (Colbert, 1989; Raath, 1/29). Although it is not unreasonable that these 1977), and the craniocaudally expanded articu- forelimb bones may belong to the same indi- lar surface of Allosaurus, dromaeosaurids (e.g., vidual, the ulna looks proportionally elongate MOR 660) and ornithomimids. compared to any of the available humeri: our best In this sense, the ulna of Aniksosaurus resembles estimate of the ulna to humerus length ratio is the ulna of troodontids in its transversely ex- 80%, a condition resembling that of the derived panded distal end (? NMC 12.433). Al- maniraptoran Deinonychus (Ostrom, 1969), in though the forearm is not well documented contrast to basal tetanurans in which the ulna is among basal abelisauroids, both ulna and radius shorter with respect to the humerus. The ulna of are extremely short in (e.g., Aniksosaurus seems more gracile than those of Carnotaurus, Aucasaurus), in sharp contrast to 248 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006

Fig. 5. Aniksosaurus darwini gen. et sp. nov. A-C, right humerus (MDT-PV 1/16) in cranial (A), lateral (B) and medial (C) views. D,E, manual ungual phalanx (MDT-PV 1/40) in side (D) and proxi- mal (E) views. Abbreviations: dpc, deltopectoral crest.

the more conservative proportions described for Ilium. The iliac blades are broken off, except- Aniksosaurus. ing for some portions of the preacetabular wing. A manual ungual phalanx, lacking part of However, most of pubic and ischiadic peduncles, its proximal end, is preserved (MDT-PV 1/40; Fig. acetabular rim, and postacetabular wing are 5D,E). This ungual probably belongs to digit I of available, thus offering relevant information the manus, based on its remarkable curvature, about iliac anatomy. The craniolaterally exca- transverse thickness, axial symmetry, and rela- vated pubic peduncle of one of the ilia (Fig. 6) tive proportions with respect to the available demonstrates that a widely developed cuppedicus humeri and ulna. However, the ungual cannot fossa was present, and part of its external bound- be confidently assigned to the left or to the right ary ridge is represented by a horizontal crest on hand. The ungual phalanx is strongly curved in the lateral surface of the preacetabular wing. The lateral view, and looks big with respect to the presence of a cuppedicus fossa on the ilium of preserved humeri and ulna, thus suggesting that Aniksosaurus constitutes a synapomorphy of Aniksosaurus was a large-clawed . Proxi- Coelurosauria, as it is seen in most of its mem- mally, the ungual phalanx is oval in cross sec- bers (e.g, Ornitholestes, , Orni- tion. The flexor tubercle is prominent and thomimidae, Deinonychus), being absent in basal rounded in ventral view. tetanurines (e.g., Allosaurus) and abelisauroids. The acetabulum is proportionally low, with a faint Pelvic girdle and slightly laterally projecting supracetabular The pelvic girdle of Aniksosaurus is repre- crest. Thus, the acetabular roof is transversely sented by four incomplete ilia and an isolated narrow, a condition differing from that of basal ischium, but none of the pubes has been recov- Theropoda (e.g., , , ered. Allosaurus) in which the supracetabular crest is Martínez & Novas: Cretaceous coelurosaurian from Patagonia 249

Table 1. Measurements (in millimeters) of selected bones of Aniksosaurus darwini gen. et sp. nov. The asterisk (*) indicate that the bone is incomplete or deformed.

Cervical vertebra MDT-PV 1/14 Centrum height at the cranial articular surface 12 Height of the neural arch up to the spine base 23 Height of the neural canal 10 Anterior caudal vertebra MDT-PV 1/32 Centrum length 34 Centrum width 33 Centrum height 37 Total height 80 Middle caudal vertebra MDT-PV 1/13 Centrum length 40 Length of rhe neural arch 38 Total height 17* Humeri MDT-PV 1/16 MDT-PV 1/37 MDT-PV 1/29 MDT-PV 1/42 Length 110* ? ? ? Width of deltopectoral crest 26 29* ? 22 Distal width 30* ? ? ? Least shaft diameter 15 14 13 13 Ulna MDT-PV 1/17 Length 110* Proximal width 25 Least shaft diameter 10 Manual ungual phalanx MDT-PV 1/40 Length 44 Greatest width 16 Proximal height 24 Ilia MDT-PV 1/33 MDT-PV 1/24 length 165* 160* Femora MDT-PV 1/3 MDT-PV 1/23 MDT-PV 1/27 MDT-PV 1/26 Length 247 204* 204* 240* Least shaft diameter 27 21 27 29 Proximal width 60 ? ? ? Ischium MDT-PV 1/41 Preserved length 75 Probable length 160 Tibiae MDT-PV MDT-PV MDT-PV MDT-PV MDT-PV MDT-PV 1/1 1/2 1/10 1/22 1/28 1/34 length ? 245* ? 270* ? 250 least width 17 21 18 22 20 19

laterally prominent, and is similar to the more is craniocaudally elongate, and its lateral surface derived condition of coelurosaurs in which this is convex, reflecting the existence of a well devel- crest is reduced. Moreover, the supracetabular oped ventral fossa for the M. caudifemoralis brevis. crest of Aniksosaurus is less well developed than The brevis fossa expands transversely towards the in the basal maniraptoran Ornitholestes. The pu- rear, depicting a paddle-shaped contour in ventral bic peduncle of ilium is craniocaudally elongate view. The brevis fossa is bounded laterally by a and has a triangular cross-section, as is usual in prominent and markedly expanded brevis shelf, Tetanurae. The ischiadic peduncle is smaller, and which is quadrangular in lateral view (Fig. 6A). part of the antitrochanter is discernible on one of The brevis fossa is also limited by a medial shelf the ilia (MDT-PV 35). The antithrochanter is (which articulates with the sacral ribs), extend- craniocaudally convex and placed more laterally ing parallel to the brevis shelf, although it is less than the pubic peduncle. The postacetabular blade well developed than the latter structure. 250 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006

Table 2. Measurements (in millimeters) of holo- those of Tyrannosaurus and type specimen of Aniksosaurus darwini gen. et (Osmólska et al., 1972) in being craniocaudally sp. nov. The asterisk (*) indicate that the bone is expanded, constituting a derived coelurosaurian incomplete or deformed. condition different from that of Allosaurus and more basal theropods (e.g., abelisauroids, Length Least width of shaft coelophysoids) in which the greater trochanter is craniocaudally narrower. Distal to the greater Femur 204* 20 trochanter, there is a small but deep elliptical Tibia 245* 23 depression near the caudal margin of the lateral Fibula 225* 4 surface of femur, which may represents the site Mtt II 98 10 of insertion of the M. ischiotrochantericus (Fig. Mtt III 124 10 7B, istr; Hutchinson, 2001). This feature does not Mtt IV 105 9 seem as well-developed in smaller specimens. The Ph I-1 16 elliptical depression mentioned above is present, Ph I-2 15 but less marked, in Piatnitzkysaurus and prob- Ph II-1 31 ably in (Gilmore, 1920) and Tyr- Ph II-2 21 annosaurus (Osborn, 1906). Ph III-1 33 The fourth trochanter is not complete on any Ph III-2 30 of the femora, but the information taken together Ph IV-1 22 from several specimens indicates that it was not Ph IV-2 16 prominent, although it was proximodistally very Ph IV-3 15 extensive reaching the middle of the shaft. There is a marked muscular trace on the medial sur- face of the femoral shaft, immediately cranial to the fourth trochanter. This depression is deep and Ischium. This bone (MDT-PV 1/41) lacks a semicircular in contour, and corresponds to the good part of its cranial border and almost all the insertion of the M.caudifemoralis longus (e.g., distal part of the shaft. The preserved portions Hutchinson, 2001). This depression is as deep as of ischium indicate this bone was long and slen- in Allosaurus (Madsen, 1976), (Currie der, transversely flattened and slightly curved & Zhao, 1993), and (Lambe, 1914), medially. The acetabular surface is represented thus contrasting with the condition present in by a proximal emargination, being caudally adult specimens of derived coelurosaurs (e.g., bounded by an enlarged, transversely thick iliac ornithomimids, oviraptorans, dromaeosaurids) in peduncle. The rest of the preserved ischium in- which such depression is almost absent. dicates that the obturator process and pubic pe- The femoral shaft is curved in lateral view duncle (both broken) appear to have been plate- and triangular in transverse section with the like. The shaft is transversely almost flattened, apex projecting cranially. A nutrient with its external surface convex. perforates the proximal third of the shaft on its cranial surface, as in Allosaurus. A sharp and Hindlimb rugose ridge extends along the craniomedial edge Femur. Five femora have been recovered of the distal shaft, bounding the adductor fossa from the quarry, the best preserved of which is present on the medial surface of the femoral MDT-PV 1/3 (Fig.7). The femur of Aniksosaurus shaft. However, the adductor fossa is not as deep is stout, closely resembling the proportions of as in other theropods such as Allosaurus, Allosaurus (Gilmore, 1920; Madsen, 1976). The Sinraptor, Tyrannosaurus and , for femoral head is transversely elongate and example. craniomedially projected. The anterior tro- Distally, the femur is transversely wide, with chanter is wing-shaped and separated from the well-defined articular . The extensor greater trochanter by a deep cleft, which is nar- groove is weakly defined on the craniodistal sur- rower than that on the femur of Allosaurus. The face of the femur, a condition that differs from anterior trochanter is more proximally projected that of Piatnitzkysaurus, Sinraptor, Allosaurus than in Allosaurus, reaching a level slightly ven- or Tyrannosaurus in which this groove is deep. tral to the greater trochanter. The anterior tro- The tibial is transversally narrow, chanter has a marked bulge (accessory tro- proximodistally low and craniocaudally wide, chanter; Hutchinson, 2001) at the base of its cra- with a flattened distal articular surface. The fibu- nial margin, as it is seen in Tyrannosaurus, for lar condyle is conical, craniocaudally short, and example. The greater trochanter is similar to more distally projected than the tibial condyle. Martínez & Novas: Cretaceous coelurosaurian from Patagonia 251

Fig. 6. Aniksosaurus darwini gen. et sp. nov. Left ilium in lateral (A) and ventral (B) views. Abbre- viations: ac, acetabulum; bf, brevis fossa; bs, brevis shelf; cuf, fossa cuppedicus; isp, ischiadic pe- duncle; pup, pubic peduncle.

The ectocondylar tuberosity, although incomplete sharp, longitudinally extensive and laterally di- in all the femora, is triangular in cross-section, rected flange, restricted to the proximal third of being proximodistally high and transversely nar- the tibia, being intermediate in lateral outgrowth row. Between the ectocondylar tuber and the between the robust and conspicuous one of tibial condyle there is a deep, wide, and triangu- Allosaurus and the less marked of Deinonychus. lar popliteal fossa, with a weak circular depres- A foramen is present on the lateral face of the sion in its proximal portion. The shape of this shaft, distal to the fibular crest. The tibial shaft fossa and the presence of the circular depression is almost straight in lateral view, but slightly at its proximal portion are similar to the condi- curved (i.e., laterally convex) in cranial aspect. tion in Allosaurus. The fibular condyle is Most of the cranial surface of the shaft is flat- proximodistally high, approximately the same tened, and along its outer side there is a distinct height caudally as the ectocondylar tuberosity. facet for articulation with the fibula. The fibular The lateral surface of the fibular condyle has a crest is connected with the outer malleolus of number of well-marked striations similar to those distal tibia through a sharp lateral margin. in Allosaurus. Distally, the end of the tibia is moderately Tibia. Seven tibiae are available. The tibia is expanded transversely and it is not flared medi- long and slender, and based on the holotype speci- ally and laterally to the degree observed in men (MDT-PV 1/50; Fig.8), it is longer (by ap- Allosaurus, for example. The distal end is proximately 20%) than the respective femur. craniocaudally compressed and triangular in dis- However, the tibia of Aniksosaurus is notably tal view. The depression for reception of the as- more robust and proportionally shorter than in cending proccess of astragalus is craniocaudally Coelurus (Carpenter et al., 2005), in which this shallow and describes a proximodistally high and bone is slender and considerably more elongate transversely wide subtriangular contour, indica- respect to femur length. The cnemial crest of the tive that this part of the astragalus (not pre- tibia of Aniksosaurus looks prominent, but its served) was scale-like and well developed. incomplete state in all of the available tibiae pre- Aniksosaurus differs from Allosaurus in that the cludes comparisons of its development (e.g., de- flange that abuts against the proximal edge of gree of cranial and proximal projection) to other the ascending proccess of astragalus is almost theropods. The fibular crest is represented by a absent. Moreover, the internal border of the ar- 252 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006

Fig. 7. Aniksosaurus darwini gen. et sp. nov. Right femur in cranial (A), lateral (B), caudal (C) and medial (D) views. Abbreviations: at, anterior trochanter; cfb, insertion of M. caudifemoralis brevis; ec, ectocondylar tuberosity; fc, fibular condyle; 4t, fourth trochanter; gt, greater trochanter; istr, insertion of M.ischiotrochantericus; tc, tibial condyle.

ticular facet for reception of the ascending as- to that of coelurosaurian theropods (e.g., tragalar process approaches the medial edge of Coelurus, Gallimimus; Rauhut, 2003). Its proxi- the inner malleolus more closely than in mal region is craniocaudally expanded and me- Allosaurus, indicating that the ascending process dially excavated, but state of preservation avoids of astragalus in Aniksosaurus was transversely to estimate its depth and extension. Unlike other wider than in basal theropods (e.g., Allosaurus, theropods, a «biceps tubercle» (i.e., the site of Sinraptor). insertion of the M. iliofibularis) is not obvious. The lateral malleolus of the distal tibia is The distal expansion of the fibula for articula- more prominent than the medial one, and exhib- tion with the tarsus is reduced, also indicating a its a transversely convex cranial facet for articu- reduced fibular facet on both calcaneum and as- lation with the distal extremity of fibula. In dis- tragalus. tal view, the tibia depicts a subtriangular con- Metatarsals and phalanges. A well-pre- tour, with concave both cranial and caudal mar- served, articulated right foot is available (MDT- gins and the outer malleolus curved and projected PV 1/51; Fig. 9). The proximal and distal ends of caudally. metatarsals I, III and IV are slightly eroded, and Fibula. Only the right fibula (MDT-PV 1/49) the ungual phalanx of digit 2 and the three dis- of the holotype has been preserved. It is proxi- tal phalanges of digit 3 are not preserved. The mally incomplete and its shaft is somewhat de- foot is approximately symmetrical, with metatar- formed. It is a very long and thin bone, much sal III being the longest and metatarsals II and more slender than in Allosaurus, being similar IV virtually equal in length. Metatarsal III Martínez & Novas: Cretaceous coelurosaurian from Patagonia 253

Fig. 8. Aniksosaurus darwini gen. et sp. nov. Right tibia (MDT-PV 1/50) in lateral (A), cranial (B), medial (C), caudal (D) and distal (E) views. Abbreviations: ast, astragalar depression; cf, crista fibularis; cn, cnemial crest; ic, inner condyle of proximal tibia; im, inner malleolus; om, outer malleolus. roughly represents 50% of tibial length (ratio view, becoming transversely broader towards the based on measurements of the holotype speci- distal end. It is mediolaterally compressed along men). The metatarsals are proportionally robust the proximal half, but subtriangular in cross-sec- and subcylindrical in cross-section. In general, tion distally. It is sigmoid (i.e., caudal convexity) the foot of Aniksosaurus looks more robust than in side view. The distal articulation is partially in Ornitholestes (Carpenter et al., 2005), espe- damaged, but it is documented the presence of a cially the pedal phalanges which in the later deep medial ligament pit. Metatarsal III is taxon are longer and more slender than in the straight in cranial view and its shaft becomes Patagonian taxon. The same observation also transversely broader towards its distal extrem- applies for Coelurus (Carpenter et al., 2005) ity. Its proximal end is craniocaudally expanded, which exhibits very elongate metatarsals, even thus forming triangular surfaces for the articu- more than in Ornitholestes. lation with the proximal extremities of both A fragment of metatarsal I has been pre- metatarsal II and IV. As seen in proximal aspect, served attached to the caudolateral half of the countour of metatarsal III is tear-shaped, metatarsal II. Metatarsal I exhibits a ginglymoid being transversely wider cranially than caudally. distal articulation with a deep wide lateral liga- However, this metatarsal apparently lacks the ment pit. Metatarsal II is straight in cranial «hour-glass» shape present among basal teta- 254 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006

metatarsal III describes a slight longitudinal ridge between the aforementioned concavities. Such construction of metatarsal III differs from that of Allosaurus (Madsen, 1976). In contrast, the metatarsal III of Aniksosaurus resembles (albeit it is not identical to) the condition present among derived coelurosaurians (e.g., Neuquenraptor). Finally, in contrast to Allo- saurus, Megaraptor, and , in which the caudal surface of distal articulation is strongly excavated and bounded by a pair of lon- gitudinal ridges, in Aniksosaurus this surface is almost flat. The distal articulation of metatar- sal III has a wide cranial excavation for extensor ligament, as well as deep collateral ligament pits. Metatarsal IV is nearly straight in cranial view. In proximal view it has a subtriangular outline with a caudomedial projection for articu- lation with metatarsal III, that is similar to but less developed than those present in Piat- nitzkysaurus, Sinraptor, Allosaurus and Orni- tholestes. The caudal surface of metatarsal IV is almost flat, especially over its proximal two thirds. The distal half of the medial face of the shaft is marked by a diagonal groove directed caudodistally. The distal third of the bone thins transversely, roughly representing half the trans- verse width of metatarsal III. This condition dif- fers from the other tetanurans (e.g., Allosaurus, Sinraptor, Gallimimus, Ornitholestes, Deinony- chus, Sinornithoides) in which the distal end of metatarsal IV is unreduced. Pedal phalanges. The proximal phalanges Fig. 9. Aniksosaurus darwini gen. et sp. nov. Right are longer than the distal phalanges. All of the foot in cranial view. Abbreviations: 1-4, digits 1 proximal phalanges have their distal ends slightly to 4; I-IV, metatarsals I to IV. craniocaudally and transversely expanded. Ven- trally the phalanges are quite flat, more than in Allosaurus, Sinraptor or Deinonychus. The un- nurans (e.g., Piatnitzkysaurus, Sinraptor, Allo- gual phalanx of digit 1 is subtriangular and saurus, Ornitholestes, ). The cra- lateromedially compressed with a lateral groove. nial surface of metatarsal III is transversely con- There is no groove on the medial surface. vex on its proximally third, becoming flat on the rest of the bone. The medial and lateral surfaces CHARACTER ANALYSIS of metatarsal III are nearly flat, but the medial surface for articulation with metatarsal II is Aniksosaurus distinguishes from other slightly grooved longitudinally, thus sharply dis- theropods by the following combination of fea- tinguishing from the caudal surface of metatar- tures: sal III. Moreover, the medial facet for metatarsal 1) Caudal cervicals with elevated neu- II exhibits a well defined distal margin, thus ral arch pedicles. The base of the neural arch clearly separating from the medial surface of dis- in the caudal cervical vertebrae is not dorsoven- tal ginglymoid. The caudal surface of metatarsal trally higher than the vertebral centrum in II is almost flat, except for its distal third, which , Allosaurus, Tyrannosauridae, is slightly notched both medially and laterally. Gallimimus, Ornitholestes and Deinonychus. In Such medial and lateral concavities create the Aniksosaurus, however, the base of the neural room for the distal articulations of metatarsals arch is 2.5 times the height of the centrum. II and IV, respectively, when the metatarsals are 2) Wide neural canal on caudal cervical articulated. As a result, the caudal surface of vertebrae. In Aniksosaurus the neural canal is Martínez & Novas: Cretaceous coelurosaurian from Patagonia 255 wide and elliptical, with a vertical longest axis of nal boundary of the brevis fossa. In ventral view the ellipse being dorsoventrally oriented. The the brevis fossa is rectangular-shaped, even in neural canal is proportionally small in relation Ceratosaurus (Gilmore, 1920) and abelisaurids to the vertebral centrum and the base of the neu- (e.g., Carnotaurus; Bonaparte et al., 1990) in ral arch in Sinraptor, Allosaurus, Gallimimus. which the brevis shelf is well developed. Moder- and Deinonychus, for example. The neural canal ately expanded brevis shelves are documented in is also large in Coelurus (Carpenter et al., 2005) , Piatnitzkysaurus, Allosaurus, and Avimimus (Kurzanov, 1987) although it is Sinraptor, and basal coelurosaurs such as Orni- not elliptical but square. Wheter this feature of tholestes, Tyrannosaurus and (in Aniksosaurus was related with allometric some derived maniraptorans, such as the dro- changes during ontogeny remains unknown. maeosaurid Deinonychus, a wing-like brevis shelf 3) Cranial caudals with saggital ventral is absent on the caudolateral portion of the ilium; keel. There is a longitudinal ventral groove on Novas, 1996). Aniksosaurus clearly distinguishes the cranial caudal centra of many theropods: from theropods mentioned above in that the cau- Dilophosaurus, Ceratosaurus, Carnotaurus, dal half of brevis shelf is strongly projected out- , Piatnitzkysaurus, Sinraptor, side, thus resulting in a fan-shaped expansion in Allosaurus, Gallimimus, Ornitholestes, Coelurus, ventral view. Interestingly, the condition de- Deinonychus and Alvarezsauridae (Bonaparte, scribed for Aniksosaurus is reminiscent of that 1991; Bonaparte et al., 1990; Britt, 1991; Carpen- in the alvarezsaurid Shuuvuia deserti (Chiappe ter et al., 2005; Currie & Zhao, 1993; Madsen, et al., 2002) as well as the flightless Cretaceous 1976; Novas 1997; Osmólska et al, 1972; Ostrom, Patagopteryx deferrarisi (Alvarenga & Bona- 1969). In this context, the single saggital keel parte, 1992). present in the proximal caudals of Aniksosaurus 6) Caudolateral surface of proximal fe- is tentatively interpreted as an autapomorphic mur with strong depression and rugosities feature of this taxon, pending on more informa- presumably for the attachment for M. tion about the distribution of this character ischiotrochantericus. On the caudolateral sur- within Tetanurae. face of proximal femur, Aniksosaurus has a strong 4) Robust manual unguals. In most thero- semilunar bulge, delimiting a well-marked de- pods, the manual ungual phalanges are strongly pression on some femora, which presumably compressed transversely. The height to width served for the attachment of the M. ischiotro- ratio of the articular surface of the manual un- chantericus (Hutchinson, 2001). On the contrary, gual phalanges is 1.54 for , 1.58 for such depression is absent in ceratosaurians (e.g., Dilophosaurus, 1.6 for Sinraptor, 1.83 for Ceratosaurus, Carnotaurus, Xenotarsosaurus), Allosaurus and 2.34 for Deinonychus (Maleev, basal tetanurans (e.g., Piatnitzkysaurus, Allo- 1955; Welles, 1984; Currie & Zhao, 1993; Gilmore, saurus), and coelurosaurians (e.g., Tyrannosau- 1920; Ostrom, 1969). Conversely, the ratio in rus, Gallimimus, Deinonychus). Aniksosaurus is 1.1, thus demonstrating the pres- 7) Metatarsal IV and its digit transver- ence of manual unguals of heavy construction, sely narrow. In most theropods, the distal end which look large when compared with any of the of the metatarsal IV is less expanded transversely preserved long bones (e.g., humeri, ulna, femora, than those of metatarsals II and III. Neverthe- tibiae) of this taxon. In contrast, the manus of less, the distal reduction of metatarsal IV is much Coelurus (Carpenter et al., 2005) and Tanyco- more marked in Aniksosaurus than in other lagreus (Carpenter et al., 2005) are delicate and theropods. The ratio of the distal width of meta- slender, in sharp contrast with the robust con- tarsal III with respect to the distal width of meta- struction of the manus of Aniksosaurus inferred tarsal IV is 1.57 in Dilophosaurus, 1.37 in Allo- on the basis of its ponderous ungual. The robust saurus, 1.16 in Sinraptor, 0.85 in Gallimimus, condition of the ungual phalanges of Anikso- and 1.14 in Deinonychus (Welles, 1984; Gilmore, saurus remembers some ornithomimids and 1920; Currie & Zhao, 1993; Osmólska et al, 1972; alvarezsaurids, in which the height to width ra- Ostrom, 1969). In Aniksosaurus, the ratio is 2.14. tio is lower than 1.5 (P. Makovicky, pers. comm). In congruence with the reduction of metatarsal However, manual unguals of these two derived IV, its correspondent digit is also constricted coelurosaurians are not trenchant and transversely, but without loss of phalanges: pha- curved as in Aniksosaurus. lanx 2 of digit 4 in Aniksosaurus has a transverse 5) Brevis shelf of the ilium extremely width of 9 mm, representing 75% of the thick- expanded and projected lateroventrally. In ness of phalanx 2 of digit 2 (12 mm) and slightly theropods, the brevis shelf is a well developed less than 70% of phalanx 2 of digit 3 (13 mm). In ridge oriented ventrolaterally, serving as exter- contrast, digit 4 is equal or subequal to digit 2 in 256 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006 transverse width in Dilophosaurus, Allosaurus rosauria. For example, a transversely wide and Deinonychus. Digit 4 is lateromedially cuppedicus fossa, an anterior trochanter placed thicker than digit 2 in Sinraptor and Gallimimus. level with the greater trochanter, a reduced Digit 4 is also thicker than digit 3 in the troo- fourth trochanter, a poorly developed adductor dontid (Osmólska, 1987). The condi- fossa on the distal femur, and a reduced fibula tion described above for Aniksosaurus resembles are features shared by compsognathids, coelurids, that of ceratosaurians (e.g., Ceratosaurus, abe- ornithomimids, tyrannosaurids and paravians. In lisauroids), in which metatarsal III and its digit this context, the narrowing of metatarsal IV and is transversely wider than metatarsals II and IV its digit documented in the coelurosaurian and their digits, condition that may have evolved Aniksosaurus is better interpreted as convergen- convergently in Aniksosaurus and ceratosau- tly evolved also in ceratosaurian theropods. rians. Elucidation of the phylogenetic position of Aniksosaurus among Coelurosauria is difficult to DISCUSSION assert, mainly due to the lack of preservation of important portions of the skeleton, including the Aniksosaurus was discovered in the same for- skull, manual bones and tarsus. At least, avail- mation were several remains of abelisauroid able information supports that the new Pata- theropods have been found (e.g., Xenotarsosaurus gonian taxon is not a member of the Manirap- bonapartei, as well as an isolated and toriformes (sensu Holtz, 2000), a coelurosaurian vertebrae referred to Abelisauridae indet.; Mar- subclade including Ornithomimosauria, Tyra- tínez et al., 1986, 2004; Lammana et al., 2002). nnosauridae, Oviraptorosauria, Alvarezsauridae Although it is appropriate to ask if Aniksosaurus and Paraves, because the Patagonian taxon re- is a member of this group of , we did tains the following plesiomorphies: distal tibia not identify abelisauroid synapomorphies in any with astragalar surface proportionally low, and of the preserved elements of Aniksosaurus (ex- insertion of the M. caudifemoralis longus exten- cepting for the narrow proportions of metatar- sive and deep. sal IV and its digit). Moreover, comparisons with Aniksosaurus exhibits limb bones that re- well known taxa of such as semble the robust proportions seen in the basal Carnotaurus (Bonaparte et al., 1990) and Masia- tetanuran Allosaurus, for example, rather than kasaurus (Carrano et al., 2002) clearly demon- the gracile and elongate ones of most coe- strate important distinctions with Aniksosaurus, lurosaurians (e.g., Ornitholestes, Coelurus, Tany- including: 1) humerus with well defined delto- colagreus, ornithomimosaurians, ovirapto- pectoral crest (different from the atrophied one rosaurians, paravians). Although the phyloge- of abelisauroids), 2) manual unguals stoutly con- netic significance of such limb bone proportions structed (being distinct from the slender and re- in theropod dinosaurs requires further explora- duced manual unguals of abelisauroids), 3) ilium tion, the robustness of Aniksosaurus may sup- with well developed cuppedicus fossa (which is port its basal position among coelurosaurians. absent among abelisauroid theropods), 4) femur Assuming that Aniksosaurus is a basal coelu- with proximally projected anterior trochanter, rosaur, it is required to examine briefly its rela- almost reaching the level of the articular head tionships with other representatives: Anikso- (contrasting with the less well projected anterior saurus resembles the compsognathid Sinosau- trochanter present among abelisauroids), 5) ropteryx (Currie & Chen, 2001) and the bizarre greater trochanter craniocaudally expanded (dif- coelurosaur (De Klerk et al., ferent from the craniocaudally narrow one 2000), in the robust construction of the humerus plesiomorphically retained by abelisauroids), 6) and manual unguals, although other basal femoral head rectangular in cranial aspect (in tetanurans (as for example, Allosaurus, Piat- contrast with abelisauroids in which the femoral nitzkysaurus, Torvosaurus) also exhibit propor- head is bulbous and craniomedially oriented), 7) tionally shortened humeri and manual unguals of trochanteric shelf represented by a faint rugos- ponderous construction. Moreover, no distinctive ity (different from the prominent ridge that is features of are identified in the characteristic of abelisauroids), and 8) fibular Patagonian taxon, thus reference of Aniksosaurus shaft craniocaudally narrow (instead of the wider to this coelurosaurian clade is untenable. Besides, shaft retained in abelisauroids). no unique features are shared by Aniksosaurus The anatomical characteristics enumerated with Ornitholestes and (including above not only justify the allocation of Anikso- Coelurus and Tanycolaegrus). saurus outside of Abelisauroidea, but also sup- Some features of Aniksosaurus look highly port the referral of Aniksosaurus within Coelu- derived for a basal coelurosaurian, including a Martínez & Novas: Cretaceous coelurosaurian from Patagonia 257 strongly reduced supracetabular crest (a condi- the following persons and institutions: Prof. tion that is shared with tyrannosaurids, Adriana Maure, Lic. Juan C.Sciutto, Mr. oviraptorosaurians and paravians), and absence Alejandro Goicoechea, Government of the city of of a medial adductor fossa on the distal femur Sarmiento, and Regimiento de Infantería 25 sta- (derived condition shared with oviraptorosau- tioned in Sarmiento. Financial support for this rians, alvarezsaurids and paravians). However, project was received from CONICET and Agencia the remaining available bones of Aniksosaurus Nacional de Promoción Científica y Técnica (to do not exhibit synapomorphies of paravians or FEN). tyrannosaurids, so the condition mentioned above for the supracetabular crest and distal fe- BIBLIOGRAPHY mur may represent independent acquisitions with respect to derived coelurosaurians. Alvarenga, H. M. F. & J. F. Bonaparte. 1992. A new In proximal view it is observed that metatar- flightless land bird from the Cretaceous of sal III of Aniksosaurus is not constricted (i.e., Patagonia. In K. E. Campbell (ed.), Pap.Avian hourglass shaped) as in the basal tetanurans Paleo.Honoring Pierce Brodkorb. Nat. Hist. Mus. Los Angeles County, Sci. Ser. 36: 51-64. Sinraptor (Currie & Zhao, 1993) and Allosaurus Archangelsky, S., E. S. Bellosi, G. A. Jalfin & C. Perrot. (Gilmore, 1920) and the basal coelurosaurians 1994. Palynology and alluvial facies from the mid- Ornitholestes and Tanycolagreus (Carpenter et Cretaceous of Patagonia, subsurface of San Jorge al., 2005). In contrast, the proximal extremity of Basin, Argentina. Cret. Res. 15: 127-142. metatarsal III of Aniksosaurus lacks the Bonaparte, J. F. 1986. Les dinosaures (Carnosaures, caudomedial hook that wraps metatarsal II cau- Allosauridés, Sauropodes, Cetiosauridés) du dally. Although Aniksosaurus seems more derived Jurassique Moyen de Cerro Cóndor (Chubut, Ar- than some basal coelurosaurians (e.g., Orni- gentine). Ann. Paléont. 72: 247-289. - 1991. Los vertebrados fósiles de la Fm. Río Colo- tholestes, Tanycolagreus; Carpenter et al., 2005) rado, de la ciudad de Neuquén y cercanías, with regard to the construction of the proximal Cretácico Superior, Argentina. Rev. Mus. Arg. metatarsus, it does not show, however, the de- Cienc. Nat. «B. Rivadavia» 4: 17-123. rived pattern of arctometatarsalian theropods Bonaparte, J. F., F. E. Novas & R. Coria. 1990. (e.g., ornithomimids, tyrannosaurids, elmisaurids Carnotaurus sastrei Bonaparte, the horned, lightly and troodontids; Holtz, 1994). In particular, built carnosaur from the Middle Cretaceous of Aniksosaurus is less derived than dromaeo- Patagonia. Contr. Sci. 416: 1-42. saurids (e.g., Deinonychus; Ostrom, 1969) in Bridge, J. S., G. A. Jalfin & S. M. Georgieff. 2000. Ge- ometry, lithofacies, and spatial distribution of Cre- which metatarsal III is proximally compressed taceous fluvial sandstone bodies, San Jorge Basin, and the facets for articulation with metatarsal II Argentina: Outcrop analog for the hydrocarbon- and IV are parallel and perpendicular with re- bearing Chubut Group. Jour. Sed. Res. 70: 341-359. spect to the transverse plane. Britt, B. 1991. Theropods of In sum, available information indicates that (, ), , Aniksosaurus occupies a basal position within with emphasis on the osteology of Torvosaurus Coelurosauria, looking more derived than tanneri. Brigham Young Univ., Geol. Stud. 37: 1- compsognathids, coelurids and Ornitholestes, al- 72. Calvo, J. O. & J. F. Bonaparte.1991. Andesaurus though less derived than . In delgadoi gen. et sp. nov. (Saurischia, ), this context, the new South American taxon is dinosaurio Titanosauridae de la Formación Río relevant, because it may represent a Late Creta- Limay (Albiano-Cenomaniano), Neuquén, Argen- ceous survivor of a poorly documented basal tina. Ameghiniana 28: 303-310. coelurosaurian radiation. Calvo, J. O., J. D. Porfiri, C. Veralli, F. E. Novas & F. Poblete. 2004. Phylogenetic status of Megaraptor namunhauiquii Novas based on a new specimen ACKNOWLEDGMENTS from Neuquén, Patagonia, Argentina. Ameghi- niana 41: 565-576. Peter Macovicky made enlighting observa- Carpenter, K., C. Miles & K. Cloward. 2005. New small tions that improved the quality of the present theropod from the Upper Jurassic Morrison For- paper. Thanks also to Leonardo Salgado for his mation of . In Carpenter, K. (ed.). The clever observations and suggestions. Matthew Carnivorous Dinosaurs. Indiana University Press, Lamanna for his assistance with editing, format- pp. 23-48. ting, and English grammar. Sergio Archangelsky Carpenter, K., C. Miles , J. H. Ostrom & K. Cloward. 2005. Redescription of the small maniraptoran for editorial assistance. Gabriel Casal for techni- theropods Ornitholestes and Coelurus from the cal preparation of the material. Marcelo Luna for Upper Jurassic Morrison Formation of Wyoming. photographs and additional preparation of the In Carpenter, K. (ed.). The Carnivorous Dinosaurs. specimen. We wish to express our gratitude to Indiana University Press, pp. 49-71. 258 Revista del Museo Argentino de Ciencias Naturales, n. s. 8 (2), 2006

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Recibido: 24-VIII-2006 Aceptado: 7-XI-2006