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REVISIÓN OSTEOLOGICA, ANÁLISIS FILOGENÉTICO Y PALEOECOLOGÍA DE PROTEROCHAMPSIDAE (REPTILIA - ARCOSAURIFOMES)

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REVISIÓN OSTEOLOGICA, ANÁLISIS FILOGENÉTICO Y PALEOECOLOGÍA DE PROTEROCHAMPSIDAE (REPTILIA - ARCOSAURIFOMES) UNIVERSIDAD NACIONAL DE CUYO PROBIOL REVISIÓN OSTEOLOGICA, ANÁLISIS FILOGENÉTICO y PALEOECOLOGÍA DE PROTEROCHAMPSIDAE (REPTILIA - ARCOSAURIFOMES) MARÍA JIMENA TROTTEYN Tesis Doctoral Directora: Julia Brenda Desojo Instituto y Museo de Ciencias Naturales Universidad Nacional de San Juan CONICET A mis padres que me apoyaron incondicionalmente…. A mi abuela Coya que me apoya y me acompaña siempre…. ¿Por qué la tierra es mi casa? ¿Por qué la noche es oscura? ¿Por qué la luna es blancura que engorda como adelgaza? ¿Por qué una estrella se enlaza con otra, como un dibujo? Y ¿por qué el escaramujo es de la rosa y del mar? Yo vivo de preguntar, saber no puede ser lujo Silvio Rodriguez RESUMEN Históricamente los proterochámpsidos han sido considerados parte del clado Arcosauriformes, entidad tradicionalmente monofilética que incluye especies desde el Pérmico Tardío a la actualidad, los “Proterosuchidae”, Erythrosuchidae, Euparkeria capensis Broom y Archosauria. Los proterochámpsidos se distinguen del resto de los arcosauriformes por un cráneo muy deprimido, transversalmente expandido en el extremo posterior, hocico angosto y alargado longitudinalmente, narinas ubicadas sobre la línea media, ausencia del hueso postfrontal y presencia de un pie asimétrico. La familia Proterochampsidae se compone de cinco géneros triásicos registrados exclusivamente en Argentina y Brasil. En esta familia se incluyen las especies argentinas provenientes de la Formación Ischigualasto (Triásico Superior), Cuenca Ischigualasto-Villa Unión, Proterochampsa barrionuevoi Reig (PVSJ 77; PVSJ 606) y una nueva especie del género Chanaresuchus (PVSJ 567). Estos ejemplares se estudian detalladamente, siendo la primera descripción de los neurocráneos de ambas especies, así como la primer descripción de material poscraneano de Proterochampsa barrionuevoi. Con la información obtenida se realiza un análisis filogenético que incluye los proterochámpsidos diferenciados específicamente. Mediante este análisis se soporta la monofilia de los proterochámpsidos, la cual se sostiene con la sinapomorfía referida a la ausencia de dentículos en ambos lados de los dientes. También se presentan las siguientes relaciones internas del taxón: ((Chanaresuchus sp. nov. + C. bonapartei) + Gualosuchus reigi )+ (P. nodosa + P. barrionuevoi)) y se propone una nueva definición de la Familia Proterochampsidae. En el marco filogenéticamente controlado obtenido se I proponen medidas de masa para los ejemplares estudiados y se infiere que los mismos debieron presentar la capacidad el estado de cinesis craneana Competente parcialmente cinético, rasgo compartido con algunos dinosaurios predadores. Tanto el análisis filogenético como el estudio paleoecológico realizado se verán complementados por futuros trabajos dirigidos a dilucidar la microanatomía, paleohistología, microestructura dentaria, así como la morfología de la cavidad encefálica en desarrollo. II CAPÍTULO 1 Introducción Los proterochámpsidos son un grupo de arcosauriformes cuadrúpedos procedentes del Triásico Medio Tardío de América del Sur. Los arcosauriformes han sido considerados por numerosos autores como un grupo natural que incluye Proterosuchidae, Erythrosuchidae, Euparkeria capensis Broom 1913, y Archosauria (Gauthier, 1986; Gauthier et al., 1989; Sereno, 1991; Parrish, 1993; Brochu, 2001) (Anexo 1-Figura 1). Durante los años ‘60 y ‘70 los proterochámpsidos fueron asignados a diferentes clados y algunos taxones se relacionaron con los primeros cocodrilos (Reig, 1959, 1970; Sill, 1967) o con los fitosaurios (Walker, 1968). En 1967 Sill erigió la familia Proterochampsidae y describió por primera vez restos de un ejemplar proveniente de la Formación Ischigualasto (Cuenca Ischigualasto-Villa Unión) referido a Proterochampsa barrionuevoi, los que consistían en cráneo, vértebras y costillas cervicales. Posteriromente, Romer en 1971 describió dos nuevos taxones provenientes de la misma cuenca, pero de la Formación Chañares: Chanaresuchus bonapartei Romer, 1971 y Gualosuchus reigi Romer, 1971. Estos nuevos hallazgos llevaron a Romer (1971) y Bonaparte (1971) a descartar las hipótesis que relacionaban a los proterochámpsidos con los cocodrilos o fitosaurios. Ese mismo año Romer (1971) incluyó en la familia Proterochampsidae a los taxones previamente mencionados, arreglo que fue aceptado en los estudios sistemáticos subsecuentes (Benton y Clark, 1988; Sereno, 1991). Así mismo, Romer (1971) y Bonaparte (1971) consideraron a Proterochampsa barrionuevoi más cercanamente relacionado a los taxones provenientes de la Formación Chañares que a la especie brasilera Cerritosaurus binsfeldi Price, 1946. Con el advenimiento de la sistemática filogenética, Sereno y Arcucci (1990) y Sereno (1991) propusieron a los M. J. Trotteyn Revisión osteológica, análisis filogenético y paleoecología de Proterochampsidae (Reptilia - Archosaurifomes) 1 proterochámpsidos como el grupo hermano de Archosauria (Anexo 1-Figura 2 A), propuesta soportada por análisis filogenéticos posteriores (e.g., Parrish, 1993; Juul, 1994; Brusatte et al., 2008) (Anexo 1-Figura 1 y 2). En una reciente contribución Dilkes y Sues (2009) redescriben al controvertido taxón Doswellia kaltenbachi Weems, 1980 del Triásico Tardío de América del Norte e incluyen en su análisis filogenético a los pocos conocidos arcosauriformes provenientes de China: Yonghesuchus sangbiensis Wu et al., 2001 y Turfanosuchus dabanensis Young, 1973. En este aporte Dilkes y Sues (2009) consideran a los proterochámpsidos como el grupo hermano de Doswellia, estando este clado más cercanamente realcionado con Archosauria (Anexo 1-Figura 2 B). Sin embargo, Ezcurra et al. (2010 a) en el marco de la descripción del arcosauriforme Koilamasuchus gonzalezdiaz Ezcurra et al, 2010, proveniente de la Formacion El Tranquilo (Cuenca Cuyana), proponen una ubicación más basal para Chanaresuchus, siendo el clado compuesto por Vancleavea + Doswellia el grupo hermano de Archosauria (Anexo 1-Figura 2 C). La composición de la Familia Proterochampsidae ha tenido numerosas interpretaciones según diferentes autores a lo largo del tiempo, estando para Gauthier (1984) conformada por Cerritosaurus binsfeldi Price, 1946, Chanaresuchus bonapartei Romer, 1971, Gualosuchus reigi Romer, 1971 y Proterochampsa Reig, 1959. Según Barberena (1982), Proterochampsidae se compone de cinco especies agrupadas en cuatro géneros: Proterochampsa barrionuevoi (Reig, 1959); Proterochampsa nodosa (Barberena, 1982); Chanaresuchus bonapartei (Romer, 1971) y Gualosuchus reigi (Romer, 1971). Esta familia se encuentra incluida en el infraorden Proterochampsia (sensu Barberena, 1982) junto a la familia Cerritosauridae, conformada por una única especie: Cerritosaurus binsfeldi (Price, 1946). Posteriormente, en concordancia con Barberena (1982), Sereno (1990) propone que en Proterochampsidae no debería incluir a Cerritosaurus. En un trabajo conjunto, este ultimo autor (Sereno y Arcucci, 1991) incluyen M. J. Trotteyn Revisión osteológica, análisis filogenético y paleoecología de Proterochampsidae (Reptilia - Archosaurifomes) 2 en esta agrupación a Tropidosuchus reigi Arcucci, 1990. Esta última combinación de taxones que componen la familia Proterochampsidae es la más ampliamente aceptada; sin embargo su definición nunca fue sustentada en un contexto filogenético que incluya a todas las especies de proterochámpsidos. En esta tesis se seguirá la propuesta de Barberena (1982) para la familia Proterochampsidae y se evaluará su monofilia en un marco filogenético que la sustente. Los proterochámpsidos son formas endémicas de América del Sur, registradas en sedimentos contientales del Triásico de Brasil y Argentina (Price, 1946; Sill, 1967; Romer, 1971; Barberena, 1982; Arcucci, 1990; Dornelles, 1995). Las especies argentinas comprenden a Chanaresuchus bonapartei; Tropidosuchus romeri; y Gualosuchus reigi, provenientes de la Formación Chañares (Triásico Medio); y Proterochampsa barrionuevoi, así como una nueva especie asignada previamente al género Chanaresuchus (Sill et al, 1994) procedentes de la Formación Ischigualasto (Triásico Superior). Los proterochámpsidos provenientes de Brasil corresponden a Proterochampsa nodosa, procedente de la Formación Santa María (Triásico Superior) y un ejemplar asignado tentativamente al clado Chanaresuchus/Gualosuchus, del cual no han podido darse mayores precisiones taxonómicas (Hsiou et al, 2002). Las características que distinguen a los proterochámpsidos del resto de los arcosauriformes son la pérdida del posfrontal en el cráneo y la presencia de un pie asimétrico (Gauthier, 1984). Además, presentan el cráneo predominantemente achatado dorso-ventralmente; lateralmente expandido en el extremo posterior, hocico angosto y alargado longitudinalmente y narinas ubicadas sobre la línea media. Los dientes son finos, largos y curvados hacia atrás. Las fenestras anterorbitarias son relativamente grandes y las supratemporales pequeñas (Sill, 1967). Los autores que han revisado los miembros posteriores de estos arcosauriformes coinciden en que los mismos poseen un tarso primitivo de tipo crurotarsal asimétrico (Arcucci, 1989 a). Funcionalmente eran formas M. J. Trotteyn Revisión osteológica, análisis filogenético y paleoecología de Proterochampsidae (Reptilia - Archosaurifomes) 3 cuadrúpedas, y se postula que su modo de vida varía entre acuático y semiacuático (Bonaparte, 1971; Romer, 1971, 1972; Arcucci, 1989 b, 1990; Sereno y Arcucci, 1990; Sereno, 1991). Las descripciones realizadas sobre material neurocraneano son abundantes entre los arcosauriformes
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