El saurópodo Spinophorosaurus en las VI Jornadas de Salas de los Infantes

Los saurópodos han sido uno de los puntos fuertes de este congreso, y el Grupo de Biología Evolutiva de la UNED se ha sumado una vez más a las fiestas sauropoderas. Uno de los trabajos presentados en las VI Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno de Salas de los Infantes (Burgos) muestra algunos datos nuevos sobre el saurópodo del Jurásico Médio de Niger, Spinophorosaurus nigerensis. Este trabajo ha contado con la contribución de la Universidad Autónoma de Madrid, el Museo Paleontológico de Elche, el Grupo de Biología Evolutiva de la Uned y la Sociedade de História Natural (Torres Vedras, Portugal).

El abstract de la comunicación presentada en el congreso es el siguiente:

The sauropod Spinophorosaurus nigerensis was established by Remes et al. (2009) from two individuals found in sediments of Middle Jurassic of Niger and was firstly considered as a non-eusauropod sauropod. Nevertheless, those authors noted several similarities between Spinophorosaurus and some Eurasian Middle Jurassic forms, such as Shunosaurus and mamenchisaurids. Spinophorosaurus is one of the most complete basal sauropods known to date, and its phylogenetic reassessment might add important information about the early phase of eusauropod evolution and Middle Jurassic eusauropod paleobiogeography. In fact, the reassessment of the Spinophorosaurus holotype, with the availability of previous unprepared elements, is providing valuable new information about its anatomy and new data for the morphological data matrices. Spinophorosaurus was firstly considered as a sister taxon of eusauropods (Remes et al., 2009), more primitive than Shunosaurus and some Middle Jurassic Gondwanic sauropods, such Barapasaurus and Patagosaurus. Spinophorosaurus bears some primitive traits such as the absence of quadrate fossa, denticles in both tooth carinae, such as Barapasaurus, and the absence of spinodiapophyseal lamina in middle and posterior dorsal vertebrae. However, several apomorphic features within eusauropods are identified in Spinophorosaurus such as the presence of five sacral vertebrae, distally expanded dorsal neural spines or a reduced ischiatic peduncle, and the presence of “forked” chevrons with a cranial and a caudal pronounced process (Wilson, 2002; Upchurch et al., 2004). Spinophorosaurus also is particular similar with the eusauropods Mamenchisaurus or Omeisaurus. In this sense, the most surprising feature of Spinophorosaurus is the presence of camellate bone in dorsal vertebrae. This type of bone is common in titanosauriforms, but it was convergently acquired by mamenchisaurids such as Mamenchisaurus and Omeisaurus (Wedel, 2003; Mannion et al., 2013). Spinophorosaurus lacks some of the typical characters of Neosauropoda sauropods, such as dorsally bifurcated centroprezygapophyseal lamina on the dorsal vertebrae, circular proximal section of the tibia, and presence of pleurocoels in the sacral vertebrae (Wilson, 2002; Upchurch et al., 2004), so it is considered to be out of this group. This fact is congruent with the phylogenetic scenario during the Middle Jurassic. The reassessment of Spinophorosaurus provides a new codification for Wilson (2002) and Upchurch et al. (2004) data matrices. Results of maximum parsimony analyses consider Spinophorosaurus as a eusauropod, more derived than Shunosaurus and Barapasaurus, and close related with Patagosaurus and the mamenchisaurids Mamenchisaurus and Omeisaurus. Further phylogenetic approaches can provide new perspectives for understanding the evolution of several morphological traits, such as the camellate tissue in eusauropods, and to reformulate the paleobiogeographical model previously proposed.

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