Pedro Mocho, investigador da Sociedade de História Natural, em plena apresentação de Spinophorosaurus
A Sociedade de História Natural de Torres Vedras apresentou-se mais uma vez nas VI Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno de Salas de los Infantes (Burgos). Um dos trabalhos apresentados foi conduzido por investigadores da SHN, Pedro Mocho, Francisco Ortega e Fernando Escasso. Este trabalho contou também com o contributo de Ainara Aberasturi, investigadora do Museo Paleontológico de Elche (MUPE). A Universidade Autónoma de Madrid e o Grupo de Biología Evolutiva da UNED foram outras instituições implicadas neste estudo.
O trabalho apresentado pretendia expor nova informação relativa a Spinophorosaurus nigerensis, um saurópode encontrado no Jurássico Médio do Niger, e um dos especímenes mais bem conservados do registo fóssil a nível mundial. O facto de ser datado do Jurássico Médio e de corresponder ao um eusaurópode basal (um grupo de saurópodes primitivos e diverso ao longo deste período), faz de Spinophorosaurus uma das mais importantes chaves para a compreensão deste grupo e da sua evolução.
Spinophorosaurus (Sauropoda), a new look inside eusauropod evolution
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.
- Mocho, P.; Ortega, F.; Aberasturi, A.; Escaso, F. 2013 Spinophorosaurus (Sauropoda), a new look inside eusauropod evolution. In: Torcida Fernández-Baldor, F.; Huerta, P. (Eds.). Abstract book of the VI International