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Noqvitates PUBLISHED by the AMERICAN MUSEUM of NATURAL HISTORY CENTRAL PARK WEST at 79TH STREET, NEW YORK, N.Y AMERICAN MUSEUM Noqvitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 3083, 27 pp., 13 figures, 4 tables December 27, 1993 Enantiornithine (Aves) Tarsometatarsi from the Cretaceous Lecho Formation of Northwestern Argentina LUIS M. CHIAPPE1 ABSTRACT Enantiornithine tarsometatarsi from the Maas- metatarsal II forms a sharp edge (convergent with trichtian Lecho Formation at the locality of El those of L. bretincola). Brete (northwestern Argentina) are described to- The relationships among these three species, and gether with their associated material. Three new their interrelationships with respect to other Late species, namely Yungavolucris brevipedalis, Lec- Cretaceous enantiornithine taxa, are explored. A tavis bretincola, and Soroavisaurus australis, are character analysis based on tarsometatarsal fea- recognized. Y. brevipedalis is distinguished by hav- tures is presented. This analysis supports the hy- ing a short and broad tarsometatarsus with a pul- pothesis that Soroavisaurus australis is the sister leylike trochlea of metatarsal II, and equally long group of a clade formed by Avisaurus archibaldi metatarsals III and IV with the distal end of the and a new form from the Two Medicine Forma- former laterally curved. The long and slender tar- tion of Montana. This clade is in turn the sister sometatarsus of L. bretincola is characterized, group of Neuquenornis volans. These four taxa among other features, for bearing a hypotarsus de- compose the monophyletic taxon Avisauridae. In veloped primarily over the metatarsal II. In turn, the present analysis, the relationships among Lec- S. australis exhibits a long and narrow fenestra tavis bretincola, Yungavolucris brevipedalis, and between the proximal halves ofmetatarsals III and Avisauridae remain unresolved. IV, and the plantar surface ofthe proximal half of RESUMEN Se describen los tarsometatarsos, y material aso- nuevas especies: Yungavolucris brevipedalis, Lec- ciado, de Enantiornithes del Maastrichtiano de la - tavis bretincola, y Soroavisaurus australis. Y. bre- Formacion Lecho en la localidad de El Brete (no- vipedalis se distingue por poseer un tarsometatarso roeste de Argentina). Se reconocen y nombran tres corto y ancho, la tr6clea del metatarso II en forma ' Frick Research Fellow, Department of Vertebrate Paleontology, American Museum of Natural History. Copyright C American Museum of Natural History 1993 ISSN 0003-0082 / Price $3.60 2 AMERICAN MUSEUM NOVITATES NO. 3083 de polea, los metatarsos III y IV de longitud equi- otros Enantiornithes del Cretacico tardio. Se pre- valente, y el extremo distal del metatarso III cur- senta un analisis de caracteres basado en caracteres vado lateralmente. El delgado y largo tarsometa- del tarsometatarso. Este an'alisis sustenta la hi- tarso de L. bretincola se caracteriza, entre otros potesis que Soroavisaurus australis es el grupo her- rasgos, por poseer un hipotarso desarrollado prin- mano de un clado formado por Avisaurus archi- cipalmente sobre el metatarso II. A su vez, S. aus- baldi y una nueva forma de la Formacion Two tralis exhibe una larga y angosta fenestra entre las Medicine de Montana. Este clado es a su vez el mitades proximales de los metatarso III y IV, y la grupo hermano de Neuquenornis volans. Estos superficie plantar de la mitad proximal del me- cuatro taxones comprenden el taxon monofiletico tatarso II formando un borde filoso (convergente Avisauridae. El presente an'alisis no resuelve las con aquel de L. bretincola). relaciones entre Lectavis bretincola, Yungavolucris Se exploran las relaciones filogeneticas entre es- brevipedalis y Avisauridae. tas tres especies, y sus relaciones con respecto a INTRODUCTION The Enantiornithes is a Cretaceous group limb elements is known (contra Walker, of volant birds originally recognized by 1981). Walker (1981) on the basis of the large as- In this paper the enantiornithine tarso- semblage of bones from the Maastrichtian metatarsi from El Brete, and the material as- Lecho Formation at the locality of El Brete sociated with them, are described. Three new (southern Province of Salta, northwestern species are recognized and their phylogenetic Argentina) (fig. 1). In this paper Walker il- relationships analyzed. The rest ofthe El Brete lustrated several bones from El Brete, in- collection will be described elsewhere. cluding the three types oftarsometatarsi here described, and briefly remarked on the pe- INSTITUTIONAL ABBREVIATIONS culiar anatomy of the group. After the erec- tion of the AMNH American Museum of Natural History Enantiornithes, several authors GI Geological Institute, Mongolian Academy of assigned previously described forms (Martin, Sciences, Ulaan Baatar 1983) as well as new taxa (Molnar, 1986; Nes- LH Universidad Aut6noma, Madrid sov and Jarkov, 1989; Chiappe, 1991a) to MACN Museo Argentino de Ciencias Naturales, Bue- this clade. To date, enantiornithine birds are nos Aires recorded in the Lower Cretaceous of Austra- MOR Museum of the Rockies, Bozeman lia (Molnar, 1986) and Spain (Sanz et al., in MUCPv Museo de Ciencias Naturales, Universidad press), and the Upper Cretaceous of South Nacional del Comahue, Neuquen America (Walker, 1981; Chiappe, 1991a, PU Princeton University, Princeton 1991b), North America (Martin, 1983; PVL Fundaci6n-Instituto Miguel Lillo, Tucumatn Chiappe, 1992a; Varricchio and in QM Queensland Museum, South Brisbane Chiappe, UCMP Museum of Paleontology, University of Cal- press), and Asia (Martin, 1983; Nessov, 1984; ifornia, Berkeley Nessov and Jarkov, 1989). Furthermore, a YPM Yale Peabody Museum, New Haven. putative member of this clade was recently discovered in the Lower Cretaceous ofChina (Zhou et al., 1992). LOCALITY AND GEOLOGICAL SETTING The discovery of the Enantiornithes The material described here was found in strongly influenced subsequent interpretation a small quarry (approximately 8 m wide) of of early avian evolution. Nevertheless, their the middle section of the Lecho Formation most significant evidence, the large assem- in the Estancia El Brete, in the southern tip blage of bones from El Brete, still remains ofthe Argentine province ofSalta (fig. 1). The mostly unstudied. Interpretation of the El Estancia El Brete is located within the dry, Brete enantiornithines is complex due to the forested, hilly landscape of the southern part poor association among the different speci- of the phytogeographic province of the Yun- mens. Few bones were found in articulation, ga. The first excavations ofthis quarry started and no association between hind and fore- in 1975, when a crew ofthe Fundacion-Insti- l1993 CHIAPPE: CRETACEOUS TARSOMETATARSI 3 65O21' 65'20'W £~~0.5kmN EX Subgroup Santa Barbara Subgroup Balbuena lEL BR EN E; | Subgroup Pirgua Fig. 1. Map indicating the locations of the different subgroups of the Salta Group in the lands of the Estancia El Brete and the quarry (black circle) of the Lecho Formation in where the specimens were found. The label "El Brete" shows the farm houses of the Estancia. tuto Miguel Lillo (Tucuman, Argentina) dis- coastal plain, with abundant vegetation and covered the fossiliferous locality, which was ponds. The age of the Lecho Formation is reported by Bonaparte et al. (1977). generally regarded as Maastrichtian on the The Lecho Formation is part ofthe Upper basis ofits fauna (Bonaparte et al., 1977) and Cretaceous Balbuena Subgroup (Salta Group), stratigraphic relationships (Go6mez Omil et a near-border stratigraphical unit of the An- al., 1989). dean sedimentary basin (Bonaparte et al., 1977; Bonaparte and Powell, 1980). Recent MATERIALS AND METHODS stratigraphical studies defined the Lecho For- Anatomical nomenclature follows Baumel mation as those clastic lithofacies ofthe Bal- et al. (1979), using the English equivalents of buena Subgroup deposited in subaerial, flu- the Latin terminology. In regard to the tax- vial, and eolian environments (Gomez Omil onomic names here applied, the term Aves et al., 1989). Lithologically, the Lecho For- is used in reference to a group including all mation consists of mainly reddish, fine to taxa descended from the most recent com- medium, with an occasional coarse, sand- mon ancestor ofArchaeopteryx lithographica stone (Bonaparte et al., 1977). and modem birds. It is relevant to mention, The avian assemblage from El Brete comes however, that this application has been re- from fine-grained sandstones. The vertebrate cently challenged by new theoretical asser- fauna associated with the avian remains is tions restricting the name of widely known composed of several specimens of the ar- taxa to the crown group (De Queiroz and mored titanosaurid Saltasaurus loricatus, the Gauthier, 1990, 1992). Under this new in- small nonavian theropod Noasaurus leali, and terpretation, the taxon name Avialae (Gau- indeterminate nonavian theropod teeth thier, 1986) replaces Aves, and the latter sub- (Bonaparte and Powell, 1980). stitutes the taxon name Neomithes of the Bonaparte et al. (1977) suggested that the classical avian taxonomy. paleoenvironment of the Lecho Formation The three species erected in this paper are in the area ofEl Brete was a fluvial-lacustrine based on incomplete material, which is still 4 AMERICAN MUSEUM NOVITATES NO. 3083 sufficiently diagnostic. It should be noted that group for analyzing the enantiomithine in- these are not the first enantiomithine species terrelationships. M. olecranus (see Perle et named from El Brete. Walker (1981) applied al., 1993b for nomenclatural
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