Clarke & Chiappe, 2001

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P U B L I S H E D B Y T H E A M E R I C A N M U S E U M O F N AT U R A L H I S T O R Y CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 JULIA A. CLARKE 1 AND LUIS M. CHIAPPE 2 ABSTRACT INTRODUCTION 2 3 CLARKE AND CHIAPPE: LATE CRETACEOUS BIRD York, USA; ET East Texas State University, Texas, USA; PVL Paleontologı ´a de Verte- brados, Instituto Miguel Lillo, Tucuma ´n, Ar- gentina; USNM United States National Mu- seum, Washington D.C., USA; YPM Yale Peabody Museum, New Haven, USA. 2001

Text of Clarke & Chiappe, 2001

  • P U B L I S H E D B Y T H E A M E R I C A N M U S E U M O F N AT U R A L H I S T O RYCENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024Number 3323, 23 pp., 5 figures, 2 tables February 27, 2001

    A New Carinate Bird from the Late Cretaceous ofPatagonia (Argentina)

    JULIA A. CLARKE1 AND LUIS M. CHIAPPE2

    ABSTRACT

    A new bird from the Late Cretaceous of Patagonia (Argentina), known from associatedwing elements, is described and its phylogenetic position evaluated. Fossil taxa as well asrepresentatives of species of extant birds sampled from lineages considered to be basal withinthe crown clade were included in a cladistic analysis of 72 characters primarily from thethoracic 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 thepresence of three unambiguous synapomorphies: a fossa (sometimes with two distinguishablesubparts) on the dorsal, distalmost extremity of the humerus; distal fusion of metacarpals IIand III; and an extensor process on metacarpal I. It is placed closer to the crown clade thanIchthyornis, and, thus, unambiguously as a carinate (see Methods for terminology), by twofurther synapomorphies: the abruptly truncate contact of the dorsal trochlear surface of theulna with the ulnar shaft and the loss of a tubercle adjacent to the tendinal groove on thedistal 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 apit-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 ligamentumcollaterale ventrale of the ulna proximodistally elongate and extending down the caudal marginof the brachial impression.

    Limenavis patagonica is placed just outside the avian crown clade. The shortest tree withthe new taxon as part of the crown clade is five steps longer than the most parsimonioustopology.

    1 Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109.2 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.

  • 2 NO. 3323AMERICAN MUSEUM NOVITATES

    RESUMEN

    Se describe una nueva especie de ave del Cretacico tardo de Patagonia (Argentina), cuyounico ejemplar se encuentra representado por elementos del miembro toracico, y se evalua suposicion filogenetica. Varios taxones fosiles, a la vez que representantes de linajes actualesconsiderados de posicion basal, fueron includos en un analisis cladstico de 72 caracteres,principalmente caracteres del miembro toracico. Sobre la base de los resultados de este analisisfilogenetico y la identificacion de autapomorfas en el ejemplar aqui descripto, se erige elnuevo taxon Limenavis patagonica.

    Tres sinapormofas de optimizacion no ambigua indican que Limenavis patagonica esta mascercanamente emparentado con el crown clade (el grupo compuesto por el ancestro comunde todas las aves vivientes mas todos sus descendientes) de lo que lo estan los Enantiornithes.Estas sinapomorfas comprenden la presencia de una fosa (a veces diferenciada en dos) en laparte dorsal de la extremidad mas distal del humero, la fusion distal de los metacarpos II yIII, y la presencia de un proceso extensor del metacarpo I. Otras dos sinapomorfas indicanque Limenavis patagonica se encuentra mas cercanamente emparentado al crown clade queIchthyornis, y que por lo tanto puede ser reconocido de forma no ambigua como un Carinatae(ver Methods para aspectos nomenclatoriales). Estas dos sinapomorfas son el contactoabrupto entre la superficie troclear dorsal y la diafisis de la ulna, y la perdida de un tuberculoadyacente al surco tendinal en el extremo distal de este ultimo hueso. Finalmente, tres auta-pomorfas diagnostican a Limenavis patagonica: la insercion de la pars ulnaris de la trocleahumeroulnaris del extremo proximal de la ulna desarrollada en forma de una pequena fossa,la presencia de un proceso pisiforme cuya superficie proximal se encuentra a mas o menos elmismo nivel que la superficie proximal del metacarpo I, y la forma proximodistalmente elon-gada de la insercion del ligamento colateral ventral de la ulna, que se extiende a lo largo delmargen caudal de la impresion braquial.

    Los resultados del analisis cladstico indican que Limenavis patagonica se encuentra justopor fuera del crown clade. El arbol mas corto que incluye a este nuevo taxon dentro delcrown clade es cinco pasos mas largo que aquel con la topologa mas parsimoniosa.

    INTRODUCTION

    Although recent discoveries have helpedto fill a significant morphological and phy-logenetic gap between Archaeopteryx litho-graphica and the more derived Hesperornit-hiformes and Ichthyornithiformes (Chiappe,1995a; Feduccia, 1996; Padian and Chiappe,1998), our knowledge of the early diversifi-cation of modern bird lineages and their mostimmediate outgroups is still limited by thepaucity of relevant fossils. Thus, the discov-ery of a carinate bird (for terminology seeMethods) from the Late Cretaceous of Pata-gonia (Chiappe, 1996a) provides an oppor-tunity to increase our understanding of theorigin of the avian crown clade. In fact, thisfossil is 1 of only approximately 12 speci-mens of Mesozoic carinates, other than Ich-thyornis, to consist of more than a single el-ement (table 1). Chiappe (1996a) briefly re-ported on this specimen, PVL-4731, provid-ing data in support of an ornithurinerelationship. Here we provide a full descrip-

    tion of this specimen and discuss its taxo-nomic status and phylogenetic position.

    PVL 4731 was collected by Jaime Powell(Universidad de Tucuman, Argentina) in themid-1980s from beds of the lower Allen For-mation (Malargue Group) exposed at the lo-cality Salitral Moreno in the northern Pata-gonian Province of Ro Negro (Argentina)(fig. 1). The poorly sorted yellowish togreenish-gray sandstones at Salitral Morenohave produced an array of plant remains,gastropods, fish, turtles, and a variety of di-nosaurs (Powell, 1986, 1987, 1992; Salgadoand Coria, 1993, 1996), including hadro-saurs, ankylosaurs, titanosaurs and theropodsincluding the specimen herein described.

    The Lower Member of the Allen For-mation has been considered early Maastrich-tian in age based on Ballents (1980) conclu-sion that the ostracod fauna of the upper-most member of the Allen Formation wasfrom the late Maastrichtian (Powell, 1987,1992). A second biostratigraphic study,though cited only as a personal communi-

  • 2001 3CLARKE AND CHIAPPE: LATE CRETACEOUS BIRD

    TABLE 1Published Specimens Placed in Carinatae and Consisting of More than a Single Element

    cation (Heredia and Salgado, 1999), involv-ing pollen from the Allen Formation in thearea of Lago Pellegrini (roughly 75 kmnorthwest of Salitral Moreno), suggests anearlier, middle Campanian age (Heredia andSalgado, 1999). New paleomagnetic data(Dingus et al., 2000), consistent with both ofthese biostratigraphic age estimations, assigna Campanian age to the Ro Colorado For-mation (Neuquen Group) which directly un-derlies the Allen Formation.

    The association at Salitral Moreno of had-rosaurs and titanosaurs may suggest a cor-relation of this fauna with those of the Lon-coche and Los Alamitos Formations (ofMendoza and Ro Negro Provinces, respec-tively). Currently, it is only from the faunasof these three Formations of South Americanlocalities, that both taxa are known. Thepresence of carinate birds, PVL 4731 amongthem, in these faunas contrasts with the faunaknown from abundant localities of the justolder Ro Colorado Formation. The Ro Col-orado has so far produced remains of tita-nosaurs, and more basal avian taxa, such asPatagopteryx deferrariisi and the enantior-nithine Neuquenornis volans (Chiappe,1996a) but no hadrosaurs or carinate birds.

    INSTITUTIONAL ABBREVIATIONS: AMNHAmerican Museum of Natural History, New

    York, USA; ET East Texas State University,Texas, USA; PVL Paleontologa de Verte-brados, Instituto Miguel Lillo, Tucuman, Ar-gentina; USNM United States National Mu-seum, Washington D.C., USA; YPM YalePeabody Museum, New Haven, USA.

    METHODS AND COMPARATIVEMATERIAL

    Osteological and myological nomenclaturefollows Baumel and Witmer (1993) and Van-den Berge and Zweers (1993) when possible.When structures were not named by these au-thors, terminology from Howard (1929) orStegmann (1978) was employed, or struc-tures were named with reference to their to-pological relations to other named osteolog-ical features and/or relationships with muscleattachments or tendinal positions describedfor extant birds. English equivalents of theLatin osteological nomenclature of all au-thors were used. One further deviation fromthe terminology of Baumel and Witmer(1993) involves the names for the metacar-pals and the manual digits. We accept theidentification of the digits of the avian handas digits I, II, and III of the pentadactyl limb(Meckel, 1821; George and Berger, 1966;

  • 4 NO. 3323AMERICAN MUSEUM NOVITATES

    Fig. 1. Map of Argentina, indicating the locality of Salitral Moreno (Ro Negro Province) wherethe holotype of Limenavis patagonica was collected.

    Stegmann, 1978; Gauthier, 1986; Wagnerand Gauthier, 1999).

    Crown-clade birds refers to the crowngroup (Jefferies, 1979) called Neornithes byThulborn (1984) and the clade comprising themost recent common ancestor of the Ratitae,Tinami, and Neognathae and all of its descen-dants, called Aves by Gaut