AMERICAN MUSEUM Novtitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3323, 23 pp., 5 figures, 2 tables February 27, 2001 A New Carinate Bird from the Late Cretaceous of Patagonia (Argentina) JULIA A. CLARKE! AND LUIS M. CHIAPPE? ABSTRACT A new bird from the Late Cretaceous of Patagonia (Argentina), known from associated wing elements, is described and its phylogenetic position evaluated. Fossil taxa as well as representatives of species of extant birds sampled from lineages considered to be basal within the crown clade were included in a cladistic analysis of 72 characters primarily from the thoracic limb. Based on the results of the phylogenetic analysis and identification of autapo- morphies in the specimen, we name a new taxon Limenavis patagonica. Limenavis patagonica is identified as closer to the crown clade than Enantiornithes by the presence of three unambiguous synapomorphies: a fossa (sometimes with two distinguishable subparts) on the dorsal, distalmost extremity of the humerus; distal fusion of metacarpals II and III; and an extensor process on metacarpal I. It is placed closer to the crown clade than Ichthyornis, and, thus, unambiguously as a carinate (see Methods for terminology), by two further synapomorphies: the abruptly truncate contact of the dorsal trochlear surface of the ulna with the ulnar shaft and the loss of a tubercle adjacent to the tendinal groove on the distal ulna. Finally, Limenavis patagonica is diagnosed by three autapomorphies: the attach- ment of the pars ulnaris of the trochlea humeroulnaris on the proximal ulna developed as a pit-shaped fossa; the location of the pisiform process with its proximal surface at approxi- mately the same level as the proximal surface of metacarpal I; and a scar of the ligamentum collaterale ventrale of the ulna proximodistally elongate and extending down the caudal margin of the brachial impression. Limenavis patagonica is placed just outside the avian crown clade. The shortest tree with the new taxon as part of the crown clade is five steps longer than the most parsimonious topology. ' Department of Geology and Geophysics, Yale University, RO. Box 208109, New Haven, CT 06520-8109. ? Research Associate, Division of Vertebrate Zoology (Ornithology), American Museum of Natural History. As- sociate Curator and Chairman, Section of Vertebrate Paleontology, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007. AMERICAN MUSEUM NOVITATES NO. 3323 RESUMEN Se describe una nueva especie de ave del Cretacico tardio de Patagonia (Argentina), cuyo unico ejemplar se encuentra representado por elementos del miembro toracico, y se evaltia su posicion filogenética. Varios taxones fdésiles, a la vez que representantes de linajes actuales considerados de posicion basal, fueron inclufdos en un andalisis cladistico de 72 caracteres, principalmente caracteres del miembro toracico. Sobre la base de los resultados de este andlisis filogenético y la identificacién de autapomorfias en el ejemplar aqui descripto, se erige el nuevo tax6n Limenavis patagonica. Tres sinapormofias de optimizacioén no ambigua indican que Limenavis patagonica esta mas cercanamente emparentado con el “‘crown clade” (el grupo compuesto por el ancestro comun de todas las aves vivientes mas todos sus descendientes) de lo que lo estén los Enantiornithes. Estas sinapomorfias comprenden la presencia de una fosa (a veces diferenciada en dos) en la parte dorsal de la extremidad mas distal del humero, la fusi6n distal de los metacarpos II y III, y la presencia de un proceso extensor del metacarpo I. Otras dos sinapomorfias indican que Limenavis patagonica se encuentra mas cercanamente emparentado al ‘‘crown clade’’ que Ichthyornis, y que por lo tanto puede ser reconocido de forma no ambigua como un Carinatae (ver ‘“‘Methods’’ para aspectos nomenclatoriales). Estas dos sinapomorfias son el contacto abrupto entre la superficie troclear dorsal y la diafisis de la ulna, y la pérdida de un tubérculo adyacente al surco tendinal en el extremo distal de éste Ultimo hueso. Finalmente, tres auta- pomorfias diagnostican a Limenavis patagonica: la inserci6n de la pars ulnaris de la troclea humeroulnaris del extremo proximal de la ulna desarrollada en forma de una pequefia fossa, la presencia de un proceso pisiforme cuya superficie proximal se encuentra a mas 0 menos el mismo nivel que la superficie proximal del metacarpo I, y la forma proximodistalmente elon- gada de la insercién del ligamento colateral ventral de la ulna, que se extiende a lo largo del margen caudal de la impresi6n braquial. Los resultados del analisis cladistico indican que Limenavis patagonica se encuentra justo por fuera del “‘crown clade.” El arbol mas corto que incluye a este nuevo taxon dentro del “crown clade’’ es cinco pasos mas largo que aquél con la topologia mas parsimoniosa. INTRODUCTION tion of this specimen and discuss its taxo- nomic status and phylogenetic position. Although recent discoveries have helped PVL 4731 was collected by Jaime Powell to fill a significant morphological and phy- (Universidad de Tucuman, Argentina) in the logenetic gap between Archaeopteryx litho- mid-1980s from beds of the lower Allen For- graphica and the more derived Hesperornit- mation (Malargiie Group) exposed at the lo- hiformes and Ichthyornithiformes (Chiappe, cality Salitral Moreno in the northern Pata- 1995a; Feduccia, 1996; Padian and Chiappe, gonian Province of Rio Negro (Argentina) 1998), our knowledge of the early diversifi- (fig. 1). The poorly sorted yellowish to cation of modern bird lineages and their most greenish-gray sandstones at Salitral Moreno immediate outgroups is still limited by the have produced an array of plant remains, paucity of relevant fossils. Thus, the discov- gastropods, fish, turtles, and a variety of di- ery of a carinate bird (for terminology see nosaurs (Powell, 1986, 1987, 1992; Salgado Methods) from the Late Cretaceous of Pata- and Coria, 1993, 1996), including hadro- gonia (Chiappe, 1996a) provides an oppor- saurs, ankylosaurs, titanosaurs and theropods tunity to increase our understanding of the including the specimen herein described. origin of the avian crown clade. In fact, this The “‘Lower Member” of the Allen For- fossil is 1 of only approximately 12 speci- mation has been considered early Maastrich- mens of Mesozoic carinates, other than Jch- tian in age based on Ballent’s (1980) conclu- thyornis, to consist of more than a single el- sion that the ostracod fauna of the upper- ement (table 1). Chiappe (1996a) briefly re- most member of the Allen Formation was ported on this specimen, PVL-4731, provid- from the late Maastrichtian (Powell, 1987, ing data in support of an ornithurine 1992). A second biostratigraphic study, relationship. Here we provide a full descrip- though cited only as a personal communi- 2001 CLARKE AND CHIAPPE: LATE CRETACEOUS BIRD TABLE 1 Published Specimens Placed in Carinatae and Consisting of More than a Single Element Taxa Material Provenience Age Reference Ambiortus dementjevi (holotype)* postcranial Asia Early Cretaceous Kurochkin, 1982 Gansus yumemensis (holotype) postcranial Asia Early Cretaceous Hou & Liu, 1984 Apatornis celer (referred) postcranial N. America Late Cretaceous Marsh, 1880 Graculavidae indet. postcranial N. America Late Cretaceous Olson & Parris, 1987 Telmatornis priscus (referred) postcranial N. America Late Cretaceous Olson & Parris, 1987 Ichthyonis dispar (holotype) cranial & postcranial N. America Late Cretaceous Marsh, 1880 Ichthyornis victor (holotype) postcranial N. America Late Cretaceous Marsh, 1880 Ichthyornis spp. (multiple) postcranial N. America Late Cretaceous Marsh, 1880 Limenavis patagonica (holotype) postcranial S. America Late Cretaceous present paper “Polarornis” ? cranial & postcranial Antarctica Late Cretaceous Chatterjee, 1997 Presbyornithidae indet. postcranial Antarctica Late Cretaceous Noriega & Tambussi, 1995 «This specimen has not always been considered part of Carinatae (see Sereno and Rao, 1992). +The Mesozoic age of this specimen is considered uncertain. Precise locality data for the material is unpublished and the stratigraphy of Seymour Island, with extensive Eocene outcrops as well as Cretaceous, has only been rigorously defined in the last 10 years, subsequent to the discovery of the specimen (Zinsmeister, personal commun.). cation (Heredia and Salgado, 1999), involv- York, USA; ET East Texas State University, ing pollen from the Allen Formation in the Texas, USA; PVL Paleontologia de Verte- area of Lago Pellegrini (roughly 75 km brados, Instituto Miguel Lillo, Tucumdén, Ar- northwest of Salitral Moreno), suggests an gentina; USNM United States National Mu- earlier, middle Campanian age (Heredia and seum, Washington D.C., USA; YPM Yale Salgado, 1999). New paleomagnetic data Peabody Museum, New Haven, USA. (Dingus et al., 2000), consistent with both of these biostratigraphic age estimations, assign METHODS AND COMPARATIVE a Campanian age to the Rio Colorado For- MATERIAL mation (Neuquén Group) which directly un- derlies the Allen Formation. Osteological and myological nomenclature The association at Salitral Moreno of had- follows Baumel and Witmer (1993) and Van- rosaurs and titanosaurs may suggest a cor- den Berge and Zweers (1993) when possible. relation of this fauna with those of the Lon- When structures were not named by these au- coche and Los Alamitos Formations (of thors, terminology from Howard (1929) or Mendoza and Rio Negro Provinces, respec- Stegmann (1978) was employed, or struc- tively). Currently, it is only from the faunas tures were named with reference to their to- of these three Formations of South American pological relations to other named osteolog- localities, that both taxa are known. The presence of carinate birds, PVL 4731 among ical features and/or relationships with muscle attachments or tendinal positions described them, in these faunas contrasts with the fauna for extant birds. English equivalents of the known from abundant localities of the just older Rio Colorado Formation. The Rio Col- Latin osteological nomenclature of all au- orado has so far produced remains of tita- thors were used. One further deviation from nosaurs, and more basal avian taxa, such as the terminology of Baumel and Witmer Patagopteryx deferrariisi and the enantior- (1993) involves the names for the metacar- nithine Neuquenornis volans (Chiappe, pals and the manual digits. We accept the 1996a) but no hadrosaurs or carinate birds. identification of the digits of the avian hand INSTITUTIONAL ABBREVIATIONS: AMNH as digits I, II, and III of the pentadactyl limb American Museum of Natural History, New (Meckel, 1821; George and Berger, 1966; + AMERICAN MUSEUM NOVITATES NO. 3323 67.38' rn| General Roca N Salitral , Moreno ; ' ‘ < é aWrtieetmrt ye Figs #1, Map of Argentina, indicating the locality of Salitral Moreno (Rio Negro Province) where the holotype of Limenavis patagonica was collected. Stegmann, 1978; Gauthier, 1986; Wagner thyornis, is currently unnamed and will be re- and Gauthier, 1999). ferred to informally as the “‘modern bird stem” ““Crown-clade birds” refers to the crown or “modern avian stem’’. group (Jefferies, 1979) called Neornithes by Several derived characters suggested that Li- Thulborn (1984) and the clade comprising the menavis is closer to the crown clade than most recent common ancestor of the Ratitae, Enantiornithes (Chiappe, 1996a). Thus, in the Tinami, and Neognathae and all of its descen- present cladistic analysis, Confuciusornis sanc- dants, called Aves by Gauthier (1986). tus and Enantiornithes were used as outgroups. “Birds” refers to the clade called Avialae by The secondarily flightless Patagopteryx defe- Gauthier (1986) or called Aves by Chiappe rrariisi and Hesperornithiformes were exclud- (1992a). “‘Avian” refers to “‘birds’’ as defined ed from the phylogenetic analysis. Either the above. The taxon name “Ornithurae”’ is used apomorphic nature or the nonpreservation of following Chiappe (1991, 1995a, 1995b) as a their wing elements made comparisons to Li- node-based name (de Queiroz and Gauthier, menavis largely untenable. In consequence, the 1992) for the most recent common ancestor of ingroup was assembled to sample Carinatae. the Hesperornithiformes and modern birds plus Ingroup taxa included Limenavis patagonica, all of its descendants. “Carinatae”’ is used for Ichthyornis, Lithornis, and 11 species of extant the most recent common ancestor of Ichthyor- birds including representatives of 8 traditional nithiformes and modern birds plus all its de- ‘“‘orders’’. Broader anatomical comparisons scendants (Chiappe, 1995a). The stem-based with many more extant species were undertak- counterpart to the node-based name for the en. These comparisons formed the basis for crown clade (de Queiroz and Gauthier, 1992), references to traditional ‘“‘orders’’ made in the including all modern birds as well as all extinct Anatomical Description. taxa more closely related to them than to Jch- Representatives of two extant palaeognath 2001 CLARKE AND CHIAPPE: LATE CRETACEOUS BIRD 5 taxa (Rheidae and Tinamidae) and of four (e.g., Sibley and Ahlquist, 1990), Charadriifor- neognath taxa (Anhimidae, Anatidae, Craci- mes (e.g., Chu, 1995), Gruiformes (here only dae, and Phasianidae) that have been consid- Rallidae and Gruidae) (e.g., Sibley and Ahl- ered to represent the earliest divergences in quist, 1990; Livezey, 1997), and the living Pa- modern birds (e.g., Cracraft, 1988; Sibley laeognathae (e.g., Lee et al., 1998) is well sup- and Ahlquist, 1990; Groth and Barrow- ported by a broad array of molecular, morpho- clough, 1999) were also included. Species of logical, and ethological data. If these assump- some taxa (Columbidae, Gruidae, Rallidae, tions of monophyly are shown to be ill justified Burhinidae and Scolopacidae) which have by subsequent analyses, the results of this anal- been alternatively considered to be basal di- ysis would also need to be problematized. That verences of the crown clade (e.g., Olson Galliformes and Anseriformes are most closely 1985), or relatively basal divergences of sub- related to each other, and that the monophyletic sequent neognath diversification (e.g., Cra- clade that they are part of is sister taxon to the craft, 1988; Sibley and Ahlquist, 1990; Eric- rest of Neognathae are well supported by ex- son, 1997; Groth and Barrowclough, 1999) tensive molecular (Groth and Barrowclough were also included. 1999; van Tuinen et al., 2000) and morpholog- The two species of Anseriformes, Galli- ical data (Cracraft, 1988; Livezey, 1997b). formes and Charadriiformes included were Constraining for a monophyletic Galloanseres chosen to sample basal and later divergences did not affect the phylogenetic placement of within these clades. These taxa were chosen Limenavis relative to the base of the crown following previous phylogenetic hypotheses clade. for these clades (e.g., Sibley and Ahlquist, In the matrix (see appendix 2), states of un- £090: Chu L995. hivezey, 19974. TO97B). certain homology were indicated with an “‘N’’, Given the historically controversial compo- to distinguish this ambiguity from character sition of Gruiformes (e.g., Olson, 1985; Eric- states that were not preserved in fossil taxa, son, 1997; Livezey, 1998), two species of the which were coded as ”’?”. Computationally, most often included taxa (i.e., Gruidae and these two entries are treated the same. Char- Rallidae) were chosen. Columbiformes was acters were not summarily rejected if a state represented by one species. For extant mod- could not be assessed in a taxon. In these few ern birds, individual species rather than su- cases, these states were scored as “N’”’. It has praspecific terminals were preferred while been suggested that the inclusion of more char- composite terminals were used for the fossil acters, even if with an attendant increase in taxa (Enantiornithes, [chthyornis and Lithor- missing data (though obviously not to excess), nis) in light of unavoidable issues of missing generally improves the accuracy of phyloge- data (Wilkinson, 1995). netic analyses (Weins, 1998). The data matrix consisted of 11 multistate Comparative material included in the phy- characters (8 ordered, or additive) and 61 bi- logenetic analysis: Tinamus guttatus (AMNH nary characters for a total of 72 characters. 17991); Pterocnemia pennata (AMNH This matrix was analyzed using the phyloge- 12892); Gallus gallus (AMNH 18553); Crax netic software PAUP* 4.0b1 (ppc) (Swofford, globulosa (AMNH 4935); Chauna_ torquata 1998). Due to the limited number of taxa, the (AMNH 3616); Anas platyrhynchos (AMNH ‘branch and bound”’ search algorithm could be 5847); Grus grus (AMNH 1265); Rallus lon- used, an algorithm guaranteeing that all short- girostris (AMNH 5629); Numenius phaeopus est trees were found (Hendy and Penny, 1982). (AMNH 3696); Burhinus capensis (AMNH The present dataset was assembled to provide 3595); Columba livia (AMNH 2002); [chthy- the best estimate of the phylogenetic position ornis dispar (YPM_ 1450); I. victor (YPM of Limenavis patagonica possible without un- 1452), and /. spp., material not formally re- dertaking a comprehensive analysis of basal ferred to a species and awaiting a revision of crown-clade relationships. Thus, the option Ichthyornis (YPM. 1738, YPM 1775, YPM provided by PAUP* of applying topological 1740, YPM 1462, YPM 1460, YPM 1453, constraints was used to require traditional “‘or- YPM 1447, YPM 1441, YPM 1724, YPM ders’’ of modern birds to be monophyletic. The 1726, USNM 11641); LZ. antecessor (USNM monophyly of Anseriformes and Galliformes 22820); Lithornis plebius (USNM 336534, 6 AMERICAN MUSEUM NOVITATES NO. 3323 AMNH 21902); L. promiscuus (USNM 1996a). PVL 4731 consists of a portion of 336535, USNM 424072, AMNH 21903); Lit- the shaft and distal end of the humerus; prox- hornis celetius (USNM 290554, YPM-PU imal and distal ends of the ulna; proximal 23485, YPM-PU 23484, YPM-PU 23483, end of the radius; proximal and distal ends YPM-PU 16961); Enantiornis leali (PVL of the carpometacarpus; ventral ramus (crus 4035, PVL 4020, PVL 4023, PVL 4181) and longus) of the ulnare; radiale; most of the several other isolated enantiornithine speci- proximal phalanx of digit IH including the mens [PVL 4054, PVL 4059, PVL 4023, PVL distal end; and several indeterminate frag- 4267, PVL 4265, PVL 4697, PVL 4025, PVL ments. The material is generally unabraded 4032-2 (see Walker, 1981, and Chiappe and but crushed. The radius is cemented to the Walker, in press); and a cast of Sinornis san- humerus, partially obscuring its cranial sur- tensis, (see Sereno and Rao, 1992)]; and a face. The proximal carpometacarpus distal to large collection of specimens of Confuciusor- the carpal trochlea of the incorporated sem- ilunate carpal is covered by the attached dis- nis sanctus (see Chiappe et al., 1999). Though the identification of certain remains tal end of the ulna, and the ventral surface is partially obscured by the fragment of the ul- referred to Ichthyornis has been problematized nare. The radiale is preserved roughly in ar- recently (Clarke, 1999), the material cited in ticulation with the carpal trochlea. the description, and scored for Jchthyornis in ETyMoLoGcy: Limen, Latin for “‘thresh- the analysis, is considered safely referred to hold,” avis, Latin for bird, and patagonica, that taxon. Most of the thoracic limb (humerus, from the provenience of the specimen from ulna, radius, distal carpometacarpus) are well northern Patagonia, for the window it offers preserved in the holotype of the type species into the origin of the radiation of the avian of Ichthyornis, I. dispar (YPM 1450). The crown clade. proximal end of the carpometacarpus and LOCALITY AND HORIZON: Salitral Moreno, proximal phalanx of the second manual digit 20 km south of General Roca, Province of were scored for [chthyornis from other referred Rio Negro, Argentina (fig. 1); Allen Forma- material by comparing the elements represent- tion, Upper Cretaceous (Campanian—Maas- ed in YPM 1450 to corresponding elements in trichtian; Powell, 1987; Heredia and Salgado, the other associated specimens or isolated ma- 1999). terial (in the case of the carpometacarpus). The DIAGNOsIS: Carinate bird with the attach- other cranial and postcranial characters were ment of the pars ulnaris of the trochlea hu- scored from YPM 1450 with the exception of meroulnaris on the proximal ulna developed the quadrate (from YPM 1775) and the prox- as a pit-shaped fossa, the location of the pi- imal coracoid (from YPM 1452). However siform process with its proximal surface at both of these specimens have elements directly approximately the same level as the proximal overlapping those of YPM 1450 and are con- surface of metacarpal I, and the scar of the sidered safely referable to Ichthyornis. In con- ligamentum collaterale ventrale of the ulna trast, the single tarsometatarsal character in- proximodistally elongate, extending down cluded in the analysis was not scored for Ich- the caudal margin of the brachial impression thyornis because all referred elements available (23:1). These autapomorphies, along with the are isolated and their identification as Ichthy- presence of three other characters with re- ornis is considered tentative. stricted distributions: (1) a well-developed tendinal groove on the ulnare, (2) the deep SYSTEMATIC PALEONTOLOGY infratrochlear fossa of the carpometacarpus, and (3) the presence of three fossae on the REPTILIA proximal surface of the dorsal supracondylar THEROPODA AVIALAE (AVES SENSU CHIAPPE, 1995b) process of the humerus, provide a unique CARINATAE suite of characters diagnosing Limenavis pa- tagonica. Limenavis patagonica (new taxon) HOLOTYPE: Limenavis patagonica, includ- ANATOMICAL DESCRIPTION ing associated distal portions of a right wing The humerus is crushed craniocaudally. given brief reference in Chiappe (1992b, However, most of its morphology is still 2001 CLARKE AND CHIAPPE: LATE CRETACEOUS BIRD 7 readily discernible (fig. 2A). The dorsal and to this larger fossa on the craniodorsal edge ventral condyles are clearly developed on the of the humeral shaft. The more ventral of cranial surface. The dorsal condyle is orient- these forms a short groove. A similar group- ed primarily in the long axis of the humerus ing of three fossae occurs in Lithornis cele- and angling toward the ventral surface. The tius (YPM-PU 23485), Ichthyornis dispar, ovoid ventral condyle is oriented dorsoven- Ichthyornis spp. (e.g., YPM 1738, YPM trally at the distal edge of the humerus. In 1447), and Ichthyornis antecessor (fig. 3). Confuciusornis sanctus, Enantiornithes, Pa- These fossae are especially prominently de- tagopteryx deferrariisi, Ichthyornis dispar, veloped in the latter taxon and one specimen and modern birds the condyles are similarly of Ichthyornis sp. (YPM 1447) although they developed cranially (Chiappe, 1996b) and a are present in all Jchthyornis humeri. Brod- ventrally angled, elongate dorsal condyle is korb (1963) described comparable pits on the present. In enantiornithines, however, the dorsal supracondylar tubercle of the Late ventral condyle developed as a straplike Cretaceous bird, Torotix clemensi, and con- ridge as opposed to the hemispherical form sidered them peculiarities of the specimen. it has in the other listed taxa. The two proximal fossae were not observed The measure of the long axis of the dorsal in any crown-clade taxa examined, though condyle is more than the same measure of the single large fossa is present in some ex- the ventral condyle as in Confusiusornis tant taxa (e.g., Tinamidae) (fig. 3F). sanctus, Ichthyornis dispar, Ichthyornis spp. The distal end of the dorsal surface of the (YPM 1738, YPM 1447), and neognaths. humerus of Limenavis patagonica bears two The angle (declination) between the dorsal faint fossae (fig. 2A, C). These fossae are humeral margin and the long axis of the dor- observed in varying degrees of development sal condyle is relatively high compared to in all crown-clade birds considered as well most taxa of the crown clade. It is roughly as in Ichthyornis dispar and Ichthyornis an- 45° in Limenavis, whereas within the crown tecessor. They are have been identified as the clade, as well as in Confuciusornis sanctus origins of the m. extensor digitorum com- and Ichthyornis dispar, it more closely ap- munis and the m. extensor carpi ulnaris proximates 30°. In enantiornithines, it ap- (Brodkorb, 1963; McKitrick, 1991). proaches 75° to 80°. Proximal to the ventral condyle, on the The area where the brachial fossa (when cranioventral surface of the humerus, there is present) is developed is largely destroyed by a well-developed, pit-shaped fossa. A small crushing and obscured by the location of the and incompletely preserved facet, or flat, an- attached fragment of the radius. No distinct gling bone surface, lies dorsally adjacent and fossa is discernible. However, close to the slightly distal to this fossa. These two fea- proximal end of the radial fragment and tures are identified respectively as the attach- slightly dorsal to it, there is a small area of ment of the m. pronator superficialis and lig. differently textured bone. The brachial fossa collaterale ventrale (m. pronator brevis and in Ichthyornis dispar and Ichthyornis spp. anterior articular ligament, respectively, sen- (YPM 1738, YPM 1447), as well as in some su Howard, 1929). The attachment of the m. crown-clade taxa, is also often not developed pronator superficialis is developed as a small as a fossa, but as a scar. pit-shaped fossa in enantiornithines, /chthy- The dorsal supracondylar tubercle of the ornis dispar and Ichthyornis spp. (YPM humerus is well developed, though not as the 1738, YPM 1447), as well as within the avi- pointed process seen in Charadriiformes and an crown-clade. While located on the ventral Passeriformes (Baumel and Witmer, 1993). humeral surface in enantiornithines and some Further, although the process is of similar crown-clade taxa, it is developed obliquely proportion to that of other crown-clade birds cranioventrally in J. dispar and other taxa of (e.g., Tinamidae), it is more cranially rather the crown. than dorsally projected. A shallow circular The flexor process of the humerus is short, fossa is located on the dorsal supracondylar extending less distally than either of the con- tubercle and opens proximally (fig. 2A). Two dyles. The ventral epicondylar surface may smaller fossae lie adjacent and just proximal bear two faint tendinal impressions. How- 8 AMERICAN MUSEUM NOVITATES NO. 3323 Fig. 2. Limenavis patagonica, holotype (PVL 4731). Right distal humerus attached proximal end of the radius in A, cranial; B, caudal; C, distal views. Right ulna D, ventral; E, dorsal; and F, proximal views. (Casts were used in photographs). bim bicipital impression; bit bicipital tubercle; bri brachial impression; dea dorsal cotyla; dco dorsal condyle; ddf dorsal distal fossae; dst dorsal supracondylar tubercle; hut attachment humeroulnar trochlea; imb impression of m. brachialis; lev attachment lig. collaterale ventrale; ole olecranon; psa m. pronator superficialis attachment; rad radius; vea ventral cotyla; vco ventral condyle; vdf ventral distal fossae. ever, this area is incompletely preserved. The described above are present in both enan- flexor process is short (as defined above) in tiornthines and Confuciusornis sanctus as Confuciusornis sanctus, I. dispar, and Ich- well as within the avian crown. In enantior- thyornis spp. (YPM 1447, YPM 1738), as nithines, however, these fossae are positioned well as in some taxa of the crown clade. In more ventrally and are aligned proximodis- enantiornithines, the whole ventrodistal hu- tally rather than craniocaudally. meral margin angles farther distally than e1- The morphology of the olecranon fossa ther of the condyles. The two distal fossae could not be determined as the caudal surface 2001 CLARKE AND CHIAPPE: LATE CRETACEOUS BIRD 9 ddf Fig. 2. Continued. of the humerus is severely crushed (fig. 2B). determine and its excavation is exaggerated It is, however, not strongly developed. There by breakage. is no evidence of grooves for the m. scapu- Just caudal and proximal to the area of the lotriceps or the m. scapulohumeralis. In J. ulnar brachial impression lies a _w ell-pre- dispar, the groove for the m. scapulotriceps served, flat, triangular area of textured bone is absent or extremely faintly developed, as that in extant birds marks the insertion of the appears the condition in Confuciusornis san- lig. collaterale ventrale (fig. 2A). In Lime- tus, enantiornithines as well as the living pa- navis patagonica, this attachment surface ex- laeognath birds. It is clearly indicated in tends along the caudal edge of the brachial most extant neognath birds. impression and up the caudoventral surface The dorsal surface of the ulna is crushed, toward the olecranon. It terminates approxi- while the ventral surface is relatively undis- mately at the level of the lip of the ventral torted (figs. 2D-—F). The olecranon and the cotyla where there is a distinctive circular pit cotylae are well developed. The impression in the approximate location of the insertion of the m. brachialis is also present with an of the pars ulnaris of the trochlea humeroul- excavated lip bounding it caudally. The cra- naris in extant birds, a ligament that positions nial margin of this impression is difficult to the m. flexor carpi ulnaris (Benz and Zusi, 10 AMERICAN MUSEUM NOVITATES NO. 3323 J Fig. 3: Fossae associated with the dorsal supracondylar tubercle in A, [chthyornis antecessor; B, Ichthyornis sp. (YPM 1447); C, Ichthyornis dispar; D, Lithornis celetius, YPM-PU 23485; E, Limenavis patagonica; F, Tinamus guttatus; G, Crax globulosa; H, Rallus longirostris; 1, Burhinus capensis. J, Inset with details of fossae in Lithornis celetius (right) and Limenavis patagonica (left). 1982; Baumel and Raikow, 1993). The de- Distally, the dorsal condyle of the ulna is velopment of this attachment as a circular pit developed as a semilunate ridge (fig. 4A). Its in Limenavis patagonica is distinct from the dorsal surface bears a tendinal pit and groove poorly defined depression observed in (sensu Howard, 1929) close to the cranial crown-clade taxa. margin, a condition very similar to that of The olecranon arises directly from the dorsal Ichthyornis dispar, Ichthyornis spp. (YPM edge of the ventral cotyla, with the excavation 1740, YPM 1462, YPM 1460) and seen in of this cotyla extending three-quarters of the crown-clade birds. The tendinal groove lies way up the ventral surface of the process (fig. distal to the pit and roughly parallel with the 2D). The caudal contact between the ventral edge of the shaft. The pit is somewhat oblong cotyla and the olecranon appears concave in and angles caudally toward the proximal end proximal view (fig. 2F). The ventral cotyla is of the ulna. In enantiornithines, at least one slightly concave and larger than the flat to tendinal impression is present. slightly convex dorsal cotyla. On the caudal surface of the ulna, the sem- In Limenavis, as in Ichthyornis dispar, the ilunate ridge of the dorsal condyle appears dorsal cotyla of the ulna does not appear to truncated distally (fig. 4A). In Ichthyornis project cranially (fig. 2E). In contrast, a well- dispar, Ichthyornis spp. (e.g., YPM 1740, developed process of the dorsal cotyla is pre- YPM 1462), enantiornithines, and some taxa sent in Patagopteryx deferrariisi (Chiappe, of the crown clade this ridge slopes smoothly 1996b) and within the crown clade, where it into the ulnar shaft. The morphology of the forms a rounded flange. A weak ridge ex- ventral condyle is obscured by the carpo- tends distally from the cranial edge of the metacarpus and a fragment of the ulnare (fig. dorsal cotyla and borders the radial depres- 4B). The distal trochlear ridge of the dorsal sion. It terminates close to a small fossa, pos- condyle appears longer transversely across sibly marking the insertion of the m. biceps the width of the ulnar shaft than it is in its brachii. This fossa lies in the same position extent down the caudal margin. In at least as the bicipital tubercle, the insertion of this some enantiornithines (e.g., PVL 4020, PVL muscle in extant birds. The morphology of 4032-2) the reverse is true, while in [chthy- the radial depression could not be deter- ornis dispar and Ichthyornis spp. (YPM mined. 1453, YPM 1740, YPM 1462) these dimen-