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Home , Baptornis, Barun Goyot Formation, Graculavus, Hesperornis, Juncitarsus, Odontornithes

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3447, 12 pp., 3 ®gures, 2 tables June 2, 2004

New Avialan Remains and a Review of the Known Avifauna from the Late of

JULIA A. CLARKE1 AND MARK A. NORELL2

ABSTRACT

Small vertebrates have remained relatively poorly known from the Nemegt Formation, al- though it has produced abundant and well-preserved large remains. Here we report three new avialan specimens from the () of Omnogov Aimag, Mongolia. These were collected from the Nemegt Formation exposed at the locality of Khushu in the southern . All of the new ®nds are partial isolated bones with a limited number of preserved morphologies; however, they further understanding of dinosaur diversity in the Late Cretaceous of Mongolia and, speci®cally, from the Nemegt Formation. The new specimens are described and evaluated in phylogenetic analyses. These analyses indicate that all three fossils are placed as part of the . Avialan diversity of the Nemegt Formation is reviewed and brie¯y compared with that of the underlying Djadokhta and Barun Goyot Formations. These formations have been consid- ered to represent at least two distinct Late Cretaceous environments, with the Nemegt typically interpreted as representing more humid conditions. Ornithurine and enantiornithine are known from the Nemegt as well as the Djadokhta and Barun Goyot Formations, although ornithurine remains are more common in the Nemegt. No avialan known from the Djadokhta, or Barun Goyot, are also known from the Nemegt Formation and, overall, the avialan taxa from these formations do not appear more closely related to each other than to other avialans. Whether these faunal differences are best interpreted as environmental, tem- poral, or sampling/preservational should be further investigated.

1 Division of Paleontology, American Museum of Natural History; North Carolina State University and North Carolina Museum of Natural Sciences (Julia࿞[email protected]). 2 Division of Paleontology, American Museum of Natural History ([email protected]).

Copyright ᭧ American Museum of Natural History 2004 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3447

Fig. 1. Map of Mongolia indicating where the fossils were recovered, the locality of Tsaagan Khushu in the western Gobi Desert (Omongov Aimag).

INTRODUCTION lected in 2001. None of the specimens ap- Three new avialan fossils were collected pears to be from a juvenile ; muscular from the Maastrichtian (Martinson et al., scars and tubercles are well developed, the 1969) Nemegt Formation (Efremov, 1954; bone surfaces are smooth, and the proximal but see Gradzinski et al., 1977) in southern tarsals are completely fused to the tibia in Mongolia by the Mongolian Academy of IGM 100/1310. Sciences/American Museum of Natural His- The Nemegt Formation has been inter- tory (MAS/AMNH) expeditions in 2000 and preted as representing a dominantly ¯uvial 2001. The ®nds are all partial, isolated bones environment with most fossils from channel recovered from the western exposures of ®ll, point bar, and occasional overbank de- Tsaagan Khushu (Gradzinski et al., 1977), a posits laid down under more humid condi- locality in the Nemegt Basin (Omongov tions than in the underlying Djadokhta For- Aimag, Mongolia; ®g. 1). All three speci- mation (Gradzinski, 1970; Jerzykiewicz and mens were found in distinct, small, well-sort- Russell, 1991). In marked contrast to the un- ed sand lenses comparatively rich in isolated derlying Djadokhta Formation (Dashzeveg et small vertebrate elements (e.g., ®sh verte- al., 1995), the remains of small vertebrates brae, turtle plastron, and carapace frag- are rare from the Nemegt Formation, which ments). A proximal tibiotarsus (IGM 100/ has produced abundant and well-preserved 1311) described here was discovered during large dinosaur remains (OsmoÂlska, 1980; the 2000 MAS/AMNH expedition, and a dis- Barsbold, 1983). The Nemegt fauna has also tal tibiotarsus (IGM 100/1310) as well as a been described as more cosmopolitan than proximal humerus (IGM 100/1309) were col- that of the Djadokhta, having stronger af®n- 2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 3 ities to faunas from North American Late American Museum of Natural History; IGM, Cretaceous localities (Jerzykiewicz and Rus- Institute of Geology, Mongolian Academy of sell, 1991). Sciences, Ulaanbaatar. Previously described avialan remains from the Nemegt Formation include ®ve isolated DESCRIPTION OF THE NEW and incomplete bones referred to the Hes- MATERIAL perornithes (Kurochkin, 2000) and two spec- imens comprising associated forelimb ele- IGM 100/1309 is a proximal left humerus ments that are the holotypes of the enantior- (®g. 2A; table 1). The humeral head is glo- nithine Gurilynia nessovi (Kurochkin, 1999) bose but comparatively weakly expanded and proposed presbyornithid anseriform Tev- proximally and anteroposteriorly. The pneu- iornis gobiensis (Kurochkin et al., 2002). motricipital fossa is comparatively diminu- The small theropod olecranus tive, does not excavate the distal surface of (Perle et al., 1993) was also described from the ventral tubercle, and does not contain any the Nemegt Formation (at Bugin Tsav) as a pneumatic foramina. The dorsal surface of basal avialan (Perle et al., 1993); however, the ventral tubercle bears a depressed, sub- this taxon and other alvarezsaurids are now triangular scar. The bar that demarcates the most often placed phylogenetically outside dorsal edge of this fossa in Aves (crus dor- (e.g., Norell et al., 2001). The exis- sale; Baumel and Witmer, 1993) is essential- tence of specimens of ``graculavid charadri- ly absent. At the dorsal edge of the pneu- iforms'' or ``transitional shorebirds'', and motricipital fossa is a slight ridge, or raised crown clade avian taxa including presbyor- intermuscular scar. A concavity lying just nithid anseriforms, phalacrocoracids, and di- dorsal to this ridge (®g. 2A) may correspond omediids, in the Nemegt Formation has also to a feature identi®ed as the m. scapulohu- been indicated (Kurochkin, 2000: 556). meralis cranialis attachment in However, so far only one of these specimens pervetus (Ericson, 1999) that is also present has been described (Kurochkin et al., 2002) in the presbyornithid Telmabates antiquus and one isolated tarsometatarsus from the holotype (AMNH 3170). In IGM 100/1309, (Kurochkin, 2000) this scar is not bounded dorsally, while in was recently removed from the Presbyorni- Presbyornis pervetus and Telmabates antiq- thidae (Kurochkin et al., 2002). Thus, with uus this scar is bounded by a continuation of the exception of the large enantiornithine the dorsal edge (crus dorsale; Baumel and Gurilynia nessovi, all of the avialan taxa Witmer, 1993) of the pneumotricipital fossa. from the Nemegt have been considered parts A second fossa (®g. 2A) strongly under- of Ornithurae, either as relatively closely re- cuts the posterodistal edge of the humeral lated to Aves as part of Hesperornithes, or as head and is open to the capital incisure de- parts of crown clade avian lineages. veloped between the head and the well-pro- The taxonomic status of previously dis- jected ventral tubercle. Just dorsal to the hu- covered avialan fossils from the Nemegt For- meral head, a scar-marked dorsal tubercle is mation is brie¯y reviewed here, and known visible (®g. 2A). From the preserved frag- Nemegt avialan diversity is compared to that ment of the deltopectoral crest it cannot be from the underlying Djadokhta and Barun determined whether it was de¯ected anteri- Goyot Formations. Gradzinski et al. (1977) orly or dorsally. The proximoposterior sur- suggested, on the basis of faunal differences, face of the crest is concave. The lig. acro- that the Barun Goyot Formation was younger coracohumerale attachment is developed as a than the Djadokhta Formation. However, discrete fossa, rather than as a transverse more recent work has not supported this con- groove. clusion, instead implying that the Djadokhta IGM 100/1310 is a slightly abraded prox- and Barun Goyot are nearly coeval (Jerzyk- imal left tibiotarsus from an avialan approx- iewicz and Russell, 1991; Dashzeveg et al., imately the size of Gallus gallus (®g. 2B; 1995; Jerzykiewicz et al., 1993; Gao and No- table 1). Both anterior and lateral cnemial rell, 2000). crests are clearly developed. Although the INSTITUTIONAL ABBREVIATIONS: AMNH, midsection of the patellar crest and antero- 4 AMERICAN MUSEUM NOVITATES NO. 3447

Fig. 2. A. IGM 100/1309 in (left) posterior, (middle) anterior, and (right) proximal views. B. IGM 100/1310 in (left) anterolateral, (middle) medial, and (right) proximal views. C. IGM 100/1311 in (left) anterior, (middle) posterior, and (right) distal views. Anatomical abbreviations: acm, anterior cnemial crest; cap, capital incisure; dep, depression (m. scapulohumeralis cranialis attachment?); dt, dorsal 2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 5

TABLE 1 PHYLOGENETIC ANALYSES Measurements of New Mongolian Fossils (mm) To assess the phylogenetic relationships of the new specimens, they were scored for characters in the Clarke and Norell (2002) matrix, which includes 185 characters infor- mative for the 15 ingroup and two outgroup taxa. This dataset was analyzed using PAUP* 4.0b8[PPC] (Swofford, 2001). The three specimens (IGM 100/1309, IGM 100/1310, and IGM 100/1311) were included as sepa- rate terminals since they were unassociated, and there is no evidence that they represent a single taxon. Analysis settings were the same as those in Clarke and Norell (2002): all searches were branch and bound; ``amb'' in the ``Parsimony Settings'' menu was se- lected such that internal branches with a min- imum length of 0 were collapsed to form a proximal portion of the anterior cnemial crest soft polytomy; and ambiguity was distin- are abraded, it can be determined from their guished from polymorphism. The scorings intact portions that neither cnemial crest was for the new Mongolian specimens are given well projected proximally. The medial con- in appendix 1. dyle is large and ¯at, while the lateral is Inclusion of the three terminals IGM 100/ strongly convex. A tuberculated scar (®g. 1309, IGM 100/1310, and IGM 100/1311 2B) is projected medially from the midpoint yielded 316 most parsimonious trees (MPTs) of the medial edge of the tibiotarsus in prox- 392 steps in length. A strict consensus of imal view. these topologies (®g. 3) places the three new IGM 100/1311 is a distal right tibiotarsus elements in a polytomy including missing most of its medial condyle (®g. 2C; ukhaana and all taxa more closely related to table 1). The extensor groove is broad and crown clade Aves than that taxon. Thus, they well developed but is not covered distally by are all found to be part of Ornithurae (sensu an osseous bridge. The extensor retinaculum Gauthier and de Queiroz, 2001; see also dis- tubercles are developed, and the ®bular cussion in Clarke and Norell, 2002 and groove is deeply impressed and bounded me- Clarke et al., 2002). The rest of the recovered dially by a pronounced ridge (®g. 2C). There topology is the same as that in Clarke and is a slight medial de¯ection and mediolateral Norell (2002) to the extent that it is resolved. widening of the distalmost tibia. The shaft is The Mongolian specimens were then in- compressed anteroposteriorly. Posteriorly, cluded individually into further phylogenetic the surface for articulation with the tibial car- analyses. The analysis including only the hu- tilage (i.e., trochlea cartilaginis tibialis; Bau- merus (IGM 100/1309) of the three speci- mel and Witmer, 1993) extends just proximal mens produced 2 MPTs also of 392 steps. to the level of the condyles (®g. 2C, center). These two trees differ only in enantiornithine The medial and lateral edges of this posterior interrelationships. In both trees IGM 100/ surface are abraded, as is the lateral surface 1309 is placed as the sister taxon of Aves, of the lateral condyle. as part of the clade ϩ Aves.

← tubercle; exg, extensor groove; fg, ®bular groove; icg, intercondylar groove; ims, intermuscular scar; lah, lig. acrocoracohumerale attachment (``transverse groove''); lc, lateral condyle; lcm, lateral cnemial crest; mc, medial condyle; ptf 1, pneumotricipital fossa 1; ptf 2, pneumotricipital fossa 2; s, tuberculated scar; stc, articular surface for tibial cartilage; tre, extensor retinaculum tubercle. 6 AMERICAN MUSEUM NOVITATES NO. 3447

Fig. 3. Cladogram indicating the placement of the three new Mongolian specimens. The strict con- sensus cladogram of 316 most parsimonious trees (392 steps in length), from analysis of the dataset of Clarke and Norell (2002) scored for the new material (see appendix 1), placed all specimens as part of the clade Ornithurae.

When the proximal tibia (IGM 100/1310; for 2002). Presbyornithid anseriforms and the which only one character could be scored) putative `transitional shorebird' form family was included, 28 MPTs resulted (392 steps ``Graculavidae'', which have been reported in length), a strict consensus of which yield- from the Nemegt Formation (Kurochkin, ed the same topology as the analysis includ- 2000; Kurochkin et al., 2002), also lack this ing all three elements. Finally, when only the pneumatic foramen in the humerus. Howev- distal tibiotarsus (IGM 100/1311) was in- er, there are problems in interpreting this cluded, 18 MPTs (392 steps in length) re- character as indicative of presbyornithid or sulted. A strict consensus of these trees ``graculavid'' af®nities. As previously men- placed IGM 100/1311 in a polytomy includ- tioned, a pneumatic foramen is ancestrally ing Hesperornithes plus all taxa more closely lacking in Ornithurae (and Avialae; e.g., related to Aves than Apsaravis ukhaana. Clarke, 2002; Clarke and Norell, 2002). On the available evidence, therefore, the lack of DISCUSSION a pneumatic foramen could as easily be ple- The proximal humerus (IGM 100/1309) is siomorphically retained as apomorphically placed outside crown clade Aves by the lack acquired. of a penetrating pneumatic foramen. This The well-developed fossa excavating the foremen, although absent in a variety of taxa base of the humeral head in IGM 100/1309 nested within Aves (e.g., Ericson, 1997), op- is present in a variety of basal avian taxa timizes as ancestrally present for the crown (e.g., and extant galliforms) as well as clade (Clarke and Norell, 2002; Clarke, in extant (Baumel and Wit- 2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 7 mer, 1993), Passeriformes (Bock, 1962), and as the sister taxon of the clade Apsaravis Procellariformes (Hope, 1999). This fossa ukhaana ϩ Aves. This placement would has been used simultaneously as evidence to make it potentially outside of a clade known support referral to (Ericson, to have a homologous with that of 2000), to the form family ``Graculavidae'' Aves (see pygostyle de®nition, and apomor- (e.g., Olson and Parris, 1987; Hope, 1999), phy-based de®nition of ``Ornithurae'' in to Charadriiformes, and as an example of Gauthier and de Quieroz, 2001). However, in mosaicism uniting these taxa (e.g., Hope, new analyses (Clarke et al., 2002; in prep.) 1999). As has been repeatedly remarked including two taxa placed as basal to Apsa- (e.g., Clarke, 2000; Livezey, 2003), using ravis (Zhou and Zhang, 2001), a pygostyle characters like this fossa (often in small num- is present (Zhou and Zhang, 2001) and two bers), whose distributions have not been op- cnemial crests are apparently lacking. Based timized in analysis with appropriate taxon on these data, IGM 100/1310 is unambigu- sampling, must result in correspondingly ously part of Ornithurae (sensu Gauthier and weak systematic hypotheses. More inclusive de Quieroz, 2001). analyses of basal avian relationships, includ- The distal tibiotarsus (IGM 100/1311) is ing further well-represented fossil taxa and, placed outside of Aves by the absence of an speci®cally, better preserved exemplars of ossi®ed supratendinal bridge, which optimiz- the taxon known from IGM 100/1309, are es as ancestrally present in Aves (e.g., Clarke necessary to more completely resolve its and Norell, 2002; Clarke, 2002). Isolated el- phylogenetic placement. However, its cur- ements identi®ed as part of Hesperornithes rent, relatively unresolved placement best re- from the Nemegt Formation include a distal ¯ects the most strongly supported phyloge- portion of a tibiotarsus also from Tsagaan netic hypothesis given the data currently Khushu (Kurochkin, 2000; see also Introduc- available. The specimen is easily differenti- tion). This specimen was identi®ed as Bap- ated from both the Ambior- tornis sp. (Kurochkin, 1988) and later re- tus dementjevi (Kurochkin, 1985) and Apsa- identi®ed as ``more closely related to Para- ravis ukhaana (Norell and Clarke, 2001; '' (Kurochkin, 2000: 545). This Clarke and Norell, 2002), the two most com- distal tibiotarsus is nearly identical in mor- plete avialans known from the of phology to IGM 100/1311. It is also close in Mongolia, by the presence of the distinct fos- size. Its distal mediolateral width is given as sa excavating the posterodistal humeral head 11.7 mm (Kurochkin, 2000), compared to as well as by comparison of nearly every 12.1 mm in IGM 100/1311. Both fossils are other morphology of the proximal humerus. from individuals slightly more than one-half Phylogenetic analysis of the proximal ti- the size of advenus (e.g., AMNH biotarsus IGM 100/1310 does not resolve 5101; 19.0 mm), the only named species of whether it is a part of Aves. Relatively low Baptornis (Marsh, 1880; Martin and Tate, cnemial crests in IGM 100/1310 (even taking 1976). into account abrasion) are present, for ex- These two nearly identical specimens from ample, in both Ichthyornis and some crown Tsaagan Khushu also share anteroposterior clade lineages (e.g., Tinamidae, ). compression, a broad extensor groove, as These crests are, in contrast, comparatively well as a prominent ®bular groove. These high in Hesperornithes (Marsh, 1880; Martin morphologies are present in Baptornis ad- and Tate, 1976; Galton and Martin, 2002) venus (AMNH 5101). The proposed af®nities and Presbyornithidae (Ericson, 2000) as well of the tibiotarsus described by Kurochkin as in other crown lineages (e.g., Anatidae, (2000) as closer to than to Charadriiformes). Baptornis was supported by ``few differences Relative to the other taxa included in the between the lateral and medial condyles, no present phylogenetic analyses, it would be distal projection of the medial condyle and ambiguous whether IGM 100/1310 was part the remarkable medial position of the exten- of Ornithurae. The only character scorable sor groove'' (Kurochkin, 2000: 545). These from the fossil is missing data in Apsaravis differences from Baptornis advenus could ukhaana, and the fossil could thus be placed not be con®rmed. Instead, the extensor 8 AMERICAN MUSEUM NOVITATES NO. 3447 groove on IGM 100/1311 and the specimen sampled, and Hesperornithes are, indeed, a commented on by Kurochkin (2000) appear cosmopolitan clade dominating inland river- to have an extensor groove slightly more lat- ine and marine environments in the Late Cre- erally located than in Baptornis advenus taceous of North America and Asia (Nessov, (AMNH 5101; contra Kurochkin, 2000). 1992; Kurochkin, 2000). The relevancy of emphasizing compari- sons made to Hesperornithes is questionable, REAPPRAISAL OF AVIALAN however. It depends on how optimistic one DIVERSITY IN THE NEMEGT is that the morphologies described from the FORMATION distal tibia will be supported in analysis as synapomorphies of Hesperornithes and/or a Both ornithurine and enantiornithine birds subclade thereof. A well-sampled phylogeny are known from the Nemegt and Djadokhta/ with these characters optimized is lacking, Barun Goyot Formations, although ornithu- and several characters are already known to rine remains have been more commonly re- have a homoplastic distribution (e.g., Martin ported from the Nemegt (table 2). After the and Tate, 1976), apparently associated with isolated tarsometatarsus from the Barun Goy- a diving habitus. For instance, anteroposte- ot Formation (Kurochkin, 2000) was re- rior compression of the distal tibiotarsal shaft moved from the Presbyornithidae (Kuro- is seen in a variety of diving crown clade chkin et al., 2002) to Avialae incertae sedis, taxa including phalacrocoracids, anhingas, no species or higher taxa less inclusive than and some sphenisciforms (Simpson, 1946). Ornithurae and are known in Further, the compact bone layer in IGM 100/ both the Djadokhta/Barun Goyot Formation 1311 (or IGM 100/1310 for that matter) is and the Nemegt Formation. Previous taxo- not conspicuously thickened in comparison nomic assessment of the Nemegt ornithurines to the condition in Baptornis advenus (Kurochkin, 2000) is consistent with Jerzyk- (AMNH 5101) or Heperornis regalis iewicz and Russell's (1991) conclusion that (Marsh, 1880). the fauna from the Nemegt Formation is Tibia IGM 100/1311 from Tsaagan Khu- more similar to North American Late Cre- shu is similar to Baptornis advenus; however, taceous faunas than to Djadokhta/Barun because these similarities are either shared Goyot faunas, as Presbyornithidae, ``Gracu- with other diving taxa, have an inadequately lavidae'', and Hesperornithes are taxa which investigated distribution, or are plesiomorph- have been proposed to have cosmopolitan ic for Ornithurae, referral to this taxon is distributions and are known from the Late weak at best. We conclude simply that IGM Cretaceous and/or Early Tertiary or North 100/1311 and the other distal tibia (Kuro- America (e.g., Ericson, 2000; Marsh, 1880; chkin, 1988, 2000) from Tsaagan Khushu are Hope, 2002). non-crown clade ornithurines incertae sedis. The kind of evidentiary support for the Nessov (1992) suggested the presence of taxonomic assignments of previously de- a small, possibly ¯ighted, hesperornithine in scribed avialan material from the Nemegt the Late Cretaceous of Central Asia, and an varies markedly. The large enantiornithine array of other fragmentary material from from Gurilyn Tsav, Gurilynia nessovi (Ku- across Central Asia has been referred to taxa rochkin, 1999), is known from a proximal of Hesperornithes (Nessov and Prizemlin, humerus and proximal coracoid, and both el- 1991; Nessov and Yarkov, 1993; Kurochkin, ements preserve optimized autapomorphies 2000). The referral of this material, and the of Enantiornithes (Kurochkin, 2000; i.e., V- assumption that all non-crown clade ornithu- shaped humeral head and raised convex sur- rines with diving modi®cations are part of a face for scapular articulation on the coracoid monophyletic Hesperornithes, deserves re- [Chiappe, 1996]). However, the referral of appraisal and is, for the reasons stated above, partial, isolated cervical and thoracic verte- problematic. If, however, future analyses and brae, a tarsometatarsus, and a dentulous man- new discoveries support this conclusion, it dible to Hesperornithes (Kurochkin, 2000), would imply that Late Cretaceous ornithurine as well as the distal tibiae discussed here, diversity is low, has been remarkably well rests on the more tenuous ground that there 2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 9

TABLE 2 Comparison of Avialan Remains from the Nemegt and Djadokhta/Barun Goyot Formations

are characters in each of these fragmentary Mesozoic age; Kurochkin et al., 2002: 2). specimens that will, once investigated, opti- Teviornis gobiensis is known from associat- mize as synapomorphies of Hesperornithes ed, well-preserved wing elements. It was or a subclade thereof. We suggest this ma- identi®ed as an anseriform based on the ``ab- terial be currently considered Ornithurae in- sence of craniocaudal curvature of corpus of certae sedis. carpometacarpus (os metacarpale minus) rel- Teviornis gobiensis is the only described ative to os metacarpale majus'' (Kurochkin Nemegt specimen referred to the avian et al., 2002: 4), a character from Livezey crown clade (Kurochkin et al., 2002; Pres- (1997). However, lack of a bowed metacarpal byornithidae: ). Because of this III is primitive for Avialae (e.g., Clarke and proposed systematic position, Teviornis is Norell, 2002) and is also plesiomorphically relevant to the debate concerning fossil evi- retained within Ornithurae. Not only is this dence for Cretaceous avian divergences (al- morphology present in nonavian ornithurines though there appears to have been confusion (e.g., Ichthyornis; Marsh, 1880), a straight initially surrounding the holotype specimen's metacarpus is present in basal parts of Gal- 10 AMERICAN MUSEUM NOVITATES NO. 3447 liformes (e.g., Paraortigoides messelensis, Luis Chiappe for helpful comments on the placed as the sister taxon of Galliformes manuscript. Tom Stidham also provided use- (Mayr, 2000) and Palaeognathae (e.g., Lith- ful information about anseriform morpholo- ornis; Houde, 1988), two themselves gy and called our attention to aspects of the placed as two of the deepest divergences structure of Hesperornithes long bones. The within the avian crown. Therefore, although Frick Fund of the Section of Vertebrate Pa- relative to the set of extant taxa studied by leontology, American Museum of Natural Livezey (1997), the absence of a curved History, supported this work. metacarpal III would be a synapomorphy of Anseriformes; with broader taxon sampling REFERENCES (especially of other Mesozoic and early Ter- Barsbold, R. 1983. Carnivorous of the tiary taxa), the resultant optimization of this Cretaceous of Mongolia. Trudy Sovmstnoi Sov- character (as plesiomorphic for Aves) does etsko-Mongol'skoi Paleontologicheskoi Ekspe- not provide evidence for the referral of Tev- ditsii 19: 1±120. iornis to Anseriformes. Baumel, J.J., and L.M. Witmer. 1993. Osteologia. Teviornis gobiensis was also referred to In J.J. Baumel, A.S. King, J.E. Breazile, H.E. Presbyornithidae on the basis of three char- Evans, and J.C. Vanden Berge (editors), Hand- acters from Ericson (2000; Kurochkin et al., book of avian anatomy: nomina anatomica av- ium, 2nd ed. Publications of the Nuttall Orni- 2002), although only one (i.e., the posterod- thological Club 23: 45±132. istal extension of the dorsal edge of the car- Bock, W.J. 1962. The pneumatic fossa of the hu- pal trochlea) has been included in any anal- merus in the Passeres. Auk 79: 425±443. ysis (Ericson, 1997; and is also present in Chiappe, L.M. 1996. Late Cretaceous birds of Anhimidae). Another of these suggested southern South America: anatomy and system- presbyornithid autapomorphies, a small in- atics of Enantiornithes and defer- terosseus dorsalis canal (Ericson, 2000; Ku- rariisi.MuÈnchner Geowissenschaftliche Ab- rochkin et al., 2002), is also present, for ex- handlungen (A) 30: 203±244. ample, in Psittaciformes, Charadriiformes Chiappe, L.M., M.A. Norell, and J. Clark. 2001. (Stegmann, 1978), and, within Anseriformes, A new skull of minuta (Aves: En- antiornithes) from the Cretaceous of the Gobi in taxa other than the Presbyornithidae (Stid- Desert. American Museum Novitates 3346: 1± ham, personal commun.). The optimization 35. of this character has also not been investi- Clarke, J.A. 2000. Setting limits on phylogenetic gated in any analyses (e.g., Ericson, 1997; inference from isolated elements. Vertebrata Livezey, 1997). In addition, no synapomor- PalAsiatica 38(suppl.): 9±10. phies of Aves, Neognathae or Galloanseres Clarke, J.A. 2002. The morphology and system- are described for, or appear preserved in, the atic position of Ichthyornis Marsh and the phy- holotype of Teviornis gobiensis to support its logenetic relationships of basal Ornithurae. proposed position nested within Anserifor- Ph.D. dissertation, Yale University, New Ha- mes. ven, CT, 532 pp. Clarke, J.A., and M.A. Norell. 2002. The mor- In sum, our knowledge of Mongolian Late phology and phylogenetic position of Apsaravis Cretaceous avialans and the fauna of the Ne- ukhaana from the Late Cretaceous of Mongo- megt Formation are augmented by recent de- lia. American Museum Novitates 3387: 1±46. scriptive work and the ®nds described here. Clarke, J.A., Z. Zhou, and F. Zhang. 2002. An However, new and better preserved material ornithurine from the Early Cretaceous of China. will allow a more complete assessment of Journal of Vertebrate Paleontology 22: 45A. their phylogenetic and biogeographic impli- Dashzeveg D., M.J. Novacek, M.A. Norell, J.M. cations. Clark, L.M. Chiappe, A. Davidson, M.C. Mc- Kenna, L. Dingus, C. Swisher, and A. Perle. 1995. Unusual preservation in a new vertebrate ACKNOWLEDGMENTS assemblage from the Late Cretaceous of Mon- golia. Nature 374: 446±449. We thank Mick Ellison for photographing Efremov, I.A., 1954. Palaeontological research in the specimens and for preparing ®gure 2, Ev- the Mongolian People's Republic: results of the geny Kurochkin for access to specimens and expeditions of 1946, 1948, and 1949. Trudy discussion of Mongolian fossil birds, and Mongol'skoi Komissii AN SSSR 59: 3±32. 2004 CLARKE AND NORELL: NEW AVIALAN FOSSILS FROM MONGOLIA 11

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APPENDIX 1 Characters scored for the new specimens (IGM IGM 100/1309 (humerus): 106:1, 107:1, 108:1, 100/1309, IGM 100/1310, IGM 100/1311). Num- 109:0, 110:0, 111:1,112:?, 114:1, 118:0. bers correspond to the characters and the charac- IGM 100/1310 (proximal tibiotarsus): (127): 178: ter states listed in appendix 2 of Clarke and Norell 1. (2002; i.e., 106:2 refers to state 2 of character 106 IGM 100/1311 (distal tibiotarsus): 177:2; 180:1, of Clarke and Norell [2002]). 181:1, 182:1, 183:0, 184:0, 185:2, 186:1, 187:1.