From the Late Cretaceous of Patagonia

Home , Alvarezsauridae, Alvarezsaurus, Patagonykus

AMEGHINIANA (Rev. Asoc. Paleontol. Argent.) - 40 (1): 119-122. Buenos Aires, 30-03-2003 ISSN0002-7014

NOTA PALEONTOLÓGICA

A new specimen of Patagonykus puertai (Theropoda: Alvarezsauridae) from the Late Cretaceous of Patagonia

Luis M. CHIAPPE1and Rodolfo A. CORIA2

Introduction Systematic paleontology

With their short and robust forelimbs, highly ki- THEROPODA netic skulls, and a host of unique skeletal features, COELUROSAURIA alvarezsaurids are highly specialized Mesozoic ALVAREZSAURIDAEBonaparte, 1991 coelurosaurian theropods known from the Late Cretaceous of Asia, North, and South America Genus PatagonykusNovas, 1997a (Chiappe et al., 2002). Despite abundant and well- preserved material from the Gobi Desert of Patagonykussp. cf. P. puertaiNovas, 1997a Mongolia, the phylogenetic relationships of al- Figures 1 and 2 varezsaurids have remained unclear (Chiappe et Material. MCF-PVPH-102 (Museo Carmen Funes, al., 2002; Novas and Pol, 2002; Suzuki et al., 2002). Paleontología de Vertebrados; Plaza Huincul, The most basal alvarezsaurids are from South Neuquén, Argentina), an articulated phalanx 1 and 2 America and are limited to just two taxa from the (ungual) of the left manual digit I. Patagonian province of Neuquén (Argentina), Geographical provenance and geological horizon. Alvarezsaurus calvoi (Bonaparte, 1991) and Northern shore of Los Barriales lake, approximately Patagokykus puertai (Novas, 1997a), which although 80 km north Plaza Huincul. Because the specimen poorly represented are important because they was not collected by professionals, no precise strati- have been consistently interpreted as the most ple- graphic information is available; nonetheless, only siomorphic members of the group (Novas, 1996; the Late Cretaceous Neuquén Group outcrops in this Chiappe et al., 1998). area. Also, considering that the holotype specimen of Here we report on a second specimen of Patagonykus puertaiwas found in beds attributed to Patagonykus, which we assign to the species P. puer- the Portezuelo Member of Río Neuquén Formation taifrom the Late Cretaceous of Neuquén Province, (Novas, 1997a), we provisionally referred the proce- Argentina. Although known from just a single man- dence of MCF-PVPH-102 to that unit. Although ab- ual digit, this specimen provides new information re- solute dating of age is not currently available, this garding the peculiar alvarezsaurid hand, and thus formation has been regarded as Turonian (Novas, helps us towards a better understanding of the phy- 1997b). logenetic relationships of the group. Description. Phalanx 1 of MCF-PVPH-102 is almost Abbreviations:MCF-PVPH, Museo Carmen Funes, complete, missing only a portion of the lateral, hook- Paleontología de Vertebrados, Plaza Huincul, like ventroproximal process described for Patago- Neuquén, Argentina; MPD, Mongolian Paleontolo- nykus puertai(Novas, 1997a (figure 1). Only the prox- gical Center, Ulaanbataar, Mongolia. imal half of phalanx 2 is preserved (figure 2). MCF-PVPH-102 is close in size to the holotype of Patagonykus puertai(MCF-PVPH-37), although clear- ly more robust. In dorsal view, major differences in- clude the shape and depth of the extensor fossa of 1Natural History Museum of Los Angeles County, 900 Exposition phalanx 2, that is placed proximal to the distal end Blvd., Los Angeles, CA 90007, EE. UU. (figure 1.B). This element is deeper and more subcir- 2Dirección Provincial de Cultura - Museo Carmen Funes, Av. Córdoba 55, 8318 Plaza Huincul, Neuquén, Argentina. cular than the corresponding subtriangular fossa of [email protected] the holotype (figure 1.A). The subcircular and subtri- ©Asociación Paleontológica Argentina AMGHB2-0002-7014/03$00.00+.50 L \1. Ch1:ppe an.i R .\ C,

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,rnLrrlal otrtlint's i,i tltest,strriact,s ir.rrallel those of ciistirrctrishcd irr N,lCIr-PVI'H-37 (figure 1C). Thr. d llit' llr'ror lLrss,te \r,rn in brrth \lCl, PVIrH l0l arrtl t.rl uurglvnrr-rs of MCF-PVPIJ-102 is dorsoventrar \l( Ir-l'\'PI I-37. I'nrrinral to the fleror. loss,t, irr vcn- Iriglrcr than th..rt of MCIr-PVI'H-37,,1 condition tl tr,ri vit,rr', phalartr 2 ol N4( l;-I']\rl,H-.1 02 br:ars.'r pair ()f renders thc ginglvmr.rs of tl'rc lle\v speciltterl nt( tllt'I io1'.1111,na app11r.l6hing tht nr.rrgirrs of thc pl-rii- t1u.r11r.rngr-r1.u tharl tl-re rcct;rngr-r1ar or-rtiine of t 'l larrr itiuLrrt, 1.1)). ht,sc for.tnrir.tcl cirr, 1l()r€ proxir-ncll- holott pe (figr-rre l.H-C). lr lL,ratt'tl than tl'rr' i-rr.ilr' (nretlial) i(u.lnL.rr that can bct The proximal articr-rlar snrface of the Lrnuual pl

\\l[L,]ll\l\\.\ +(l (.i ), li-rtrl A new specimen of PatagonyhLs 727 lanx of MCF-PVPH-102 matches the quadrangular outline of the first phalanx and bears well-developed facets. Dorsal ard ventral mid-projections oppose the articular surface (figure 2.C). Deep lateral grooves emarginate the sides of this phalanx and open ven- traily into distinct notches (figure 2.A), whose topo- Iogic relationships are comparable to the pair of ventral foramina present in the alvarezsaurids Morttnulktts oleliinus (Perle et n\.,7994) and SlruutLr.Lia tleserti (MPD 100/120) from the Late Cretaceous of the Gobi Desert (\Iongolia). Just proximal to each of these notches, promir-rent upturned tubercles project sideways fron-L the r-entral margin of the claw (figure 2.B). Ventroprorrrnalir- and across the surface between the latter ventral notches, the ungual phalanx of MCF-P\/PH-101 is essentiallv flat. Distal to these notches, the ventral surface of the ungual phalanx bears a short, centra-1 ridge that defines oval depressions laterallv (figure 2.8). A similar configuration is present in the onlr-knotr-n manual ungual phalanx of Alunrezsattrr$ c0!L'L-i i\ovas, 1996). Although we con- sider this ridge and its adjacent depressions (which likely serr.ed as the attachment of the powerful flex- or ligaments of maar-ral digit I) homologous with the flexor tubercle of other dinosaurian manual claws, this keeled n-Lorphologr- is nevertheless unique to Alunrezsnttrus csk,oi ar.d PotogotttlktLs puertai. Distal to this central ridge, the r.entral surface of the claw is transversell, convex, n,ith a distinct 8-shaped cross- section that constriction is formed by the lateral grooves. Such a morphology closely resembles what can be seen in the small fragment of the ungual phalanx of the first digit of the holotype of Patagonyktts puertni.

Discussion Figure 2. Patagonykus cf P. puertai,MCF-PVPH-102. Ungual phalanx of digit I in left lateral (A), ventral (B), and ventroproximal (C) Although MCF-PVPH-102 does exhibit some dif- views. Abbreviations: cr, median crest; lg, lateral groove; vn, ven- ferences with respect to MCF-PVPH-37, we have re- troproximal notch. Palcgonykus cf P. puertai, MCF-PVPH-102. ferred this new specimen to Patagonyktts puertai be- Falange ungual del digito I en ttista lateral izquierda (A), ztentral (B), y (C). cause of the quantitative nature of observed differ- trentroproximal Abreztiaturas: cr, cresta medial; lg, surco lateral; ztn, e s co t a d tr a tt en t r opr o xim al. ences and because of the iack of information regard- ing morphological variation within alvarezsaurid siomorphic condition for basal alvarezsaurids (and species (including sexual dimorphism). hence an alvarezsaurid synapomorphy) rather than a Despite its fragmentary nature, MCF-PVPH-1O2 synapomorphy of a clade formed by these two basal cloes contribute anatomical information allowing for taxa. The latter hypothesis would require the inde- the assessment of a number of other character states. pendent origin of several derived character states For example, the presence of a central keel in the that have been proposed to unite all alvarezsaurids proximoventral surface of the ungual of manual dig- other than Alztarezsaurus (Novas, 7997a; Chiappe ef it I of MCF-PVPH-102 demonstrates that this condi- aI.,7998). One of these synapomorphies appears to be tion is shared by both AlanrezsaurLLs ccrlztoi and the presence of a pair of notches or foramina on the Pntnrortrlkus puertoi, thus casting doubts on the au- proximoventral surface of the ungual of manual dig- tapomorphic status of this condition as proposed by it I, a condition previously known for Mononykus ole- Novas (7997) for Alttarezsnurt$ cah)oi. Although this crlnlts and Shtrcwtia deserti and now documented for derived character state has not yet been included in P nt ngonyktrs (MCF-PVPH-1 02). any ciadistic analysis, it is likely to represent the ple- The new specimen also sheds light on character

AMEGHTNIANA 40 (1), 2003 122 L.M. Chiappe and R.A. Coria states previously used by Sereno (1999, 2001) to sup- script. To F. Novas and L. Witmer for their review and useful sug- port a sister-group relationship between alvarezsau- gestions. This research was funded by the Fundación Antorchas (Buenos Aires, Argentina). rids and ornithomimid coelurosaurians. One of these synapomorphies involves the ventral surface of the unguals. At the time of Sereno’s publication, informa- Bibliography tion on alvarezsaurid manual unguals was limited to Bonaparte, J. F. 1991. Los vertebrados fósiles de la Formación Río digit I. A more recently described specimen of Colorado de Neuquén y cercanías, Cretácico Superior, Shuvuuia desertiChiappeet al. provides the only avail- Argentina. Revista del Museo Argentino de Ciencias Naturales able information on the ungual phalanges of digits II “Bernardino Rivadavia” Paleontología4: 17-123. and III of the alvarezsaurid hand (Suzuki et al., 2002). Chiappe, L. M., Norell, M. A. and Clark, J. M. 1998. The skull of a new relative of the stem-group bird Mononykus. Nature392: Sereno (1999, 2001) proposed the presence of flattened 275-278. and broad ventral surfaces of the manual unguals, as Chiappe, L. M., Norell, M. A. and Clark, J. M. 2002. The opposed to the plesiomorphic condition of these sur- Cretaceous, short-armed Alvarezsauridae: Mononykusand its faces being narrow and rounded, as a synapomorphy kin. In L. M. Chiappe and L. Witmer (eds.), Mesozoic Birds: Above the Heads of Dinosaurs, University of California Press, of alvarezsaurids and ornithomimids. However, and Berkeley, pp. 31-61. as pointed out by Suzuki et al. (2002), this character Novas, F.E. 1996. Alvarezsauridae, Cretaceous basal birds from state should be restricted to manual digit I since the Patagonia and Mongolia. Proceedings of the Gondwanan di- new specimen of Shuvuuia desertishows the condition nosaur symposium, Memoirs of the Queensland Museum39:675- 702, of the ungual phalanges of digits II and III to be ple- Novas, F. E. 1997a. Anatomy of Patagonykus puertai(Theropoda, siomorphic. Further, MCF-PVPH-102 shows that Avialae, Alvarezsauridae, from the Late Cretaceous of while the ungual phalanx of manual digit I of more Patagonia. Journal of Vertebrate Paleontology17: 137-166. advanced alvarezsaurids (Shuvuuia desertiand Novas, F.E. 1997b. South American dinosaurs. In: P.J. Currie and K. Padian (eds.), Encyclopedia of dinosaurs, Academic Press, Mononykus olecranus) have broad and flattened sur- New York, pp. 678-689. faces, that of the more basal Patagonykus puertaiap- Novas, F. E. and Pol, D. 2002. Alvarezsaurid relationships recon- proaches more the plesiomorphic condition, an obser- sidered. In: L. M. Chiappe and L. Witmer (eds.), Mesozoic Birds: vation also suggested by the more fragmentary claw Above the Heads of Dinosaurs, University of California Press, Berkeley, pp. 121-125. of the holotype specimen. MCF-PVPH-102 also casts Perle, A., Chiappe, L. M., Barsbold, R., Clark, J. M. and Norell, M. some doubt on the validity of another synapomorphy A. 1994. Skeletal morphology of Mononykus olecranus proposed by Sereno (1999) to support an al- (Theropoda: Avialae) from the Late Cretaceous of Mongolia. varezsaurid-ornithomimid relationship. This consid- American Museum Novitates3105: 1-29. Sereno, P. C. 1999. The evolution of dinosaurs. Science284: 2137- ers the distal displacement of the flexor tubercle of the 2147. manual phalanges to be the derived character state Sereno, P. C. 2001. Alvarezsaurids: Birds or ornithomimosaurs? shared by these two clades. The area for the attach- In: J. Gauthier and L. F. Gall (eds.), New Perspectives on the ment of the flexor ligaments, however, is poorly de- Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom, New veloped (i.e., weakly projected ventrally) in the un- Haven, Peabody Museum of Natural History, pp. 69-98. gual phalanges of the alvarezsaurid hand (Novas, Suzuki, S., Chiappe, L. M., Dyke, G., Watabe, M., Barsbold, R. and 1997a; Suzuki et al., 2002), in contrast with the bul- Tsogtbaatar, K. 2002. A new specimen of Shuvuuia deserti bous and much better developed flexor tubercles of Chiappe et al., 1998 from the Mongolian Late Cretaceous with a discussion of the relationships of alvarezsaurids to other ornithomimids. The morphology of MCF-PVPH-102 theropod dinosaurs. Contributions in Science494: 1-17. confirms that the flexor ligaments of the unguals of digit I of basal alvarezsaurids are attached to low keels flanked by deep depressions. Further, these ar- eas are not as distally displaced as the flexor tubercles of the ungual phalanges of ornithomimids, which are often emplaced at the mid-point of the claw. The phylogenetic relationships of alvarezsaurids to other theropods continue to be controversial. Discoveries of fossils representing basal alvarezsaurids, such as MCF-PVPH-102, may provide the necessary information to clarify the historical relationships of the group.

Acknowledgements

We are grateful to R. Meir and W. Evans for image production Recibido: 14 de junio de 2002. and to P. Currie and G. Dyke for comments to the original manu- Aceptado:3 de octubre de 2002.

AMEGHINIANA40 (1), 2003