La anatomía de Spinophorosaurus en el 63rd SVPCA

Entre las comunicaciones presentadas por el Grupo de Biología Evolutiva de la UNED en la 63ª edición del Symposium of Vertebrate Palaeontology and Comparative Anatomy (SVPCA) destacaron dos comunicaciones en formato poster defendidas por Pedro Mocho sobre la anatomía del saurópodo africano Spinophorosaurus. En el primero de ellos, se discutía la presencia de espinas caudales en estos dinosaurios del Jurásico Medio. El resumen es el siguiente:

Spinophorosaurus from Middle Jurassic of Niger was firstly referred as a non-eusauropod. The systematic revision of Spinophorosaurus is in progress, and preliminary results place this taxon within Eusauropoda. One of the most peculiar features of this sauropod was to have spike-bearing osteoderms placed in the distal tail region. Indeed, this feature was used to formulate its generic name. However, herein, we provide a detailed description for these structures providing a new anatomical interpretation.

Two spine-shaped elements (HB64M) were found in association with the scapular girdle (two scapula and a coracoids in articulation) and displaced from its anatomical position. These structures present a triangular to “L-“shaped morphology in internal and external view with a convex external and a concave internal faces. The base of the “L” is expanded and bears a D-shaped cross-section. The distal end of “L” short branch has a rough articular surface in the internal side. The long branch is lenticular in cross-section and bears a longitudinal wide crest in both sides. The outer side of the “L” also bears an important rough surface.

This morphology was considered to be similar to caudal spikes found in some Chinese sauropods suggesting that they might correspond to caudal spikes osteoderms. These of elements are scarce in the sauropod record and some authors have discussed the previous interpretation. The bones have been recently prepared. Now, a full description of these elements supports its reinterpretation as clavicles. The Spinophorosaurus clavicles are thicker and bear deeper internal surface than in basal neosauropods.

En el segundo de los posters, se analizaba la variación morfológica en el cuello de Spinophorosaurus. El resumen es el siguiente:

Spinophorosaurus (Niger, Middle Jurassic) was considered a non-eusauropod with several similarities with mamenchisaurids. The systematic revision is considering a new phylogenetic position, within Eusauropoda. The exceptionally preserved axial skeleton of Spinophorosaurus is important to understand the variability of several characters along the series and it is important for the establishment of new morphological characters. Some aspects of the cervical vertebrae morphology along the cervical series are discussed as well as the laminae pattern. The laminae pattern is conservative along the cervicals, with welldefined podl, prdl, spol, sprl and short acdl and pcdl. The position and orientation of laminae are mainly controlled by morphological changes in the spine. The presence of a posteriorly projected tpol might be exclusive of Spinophorosaurus and a convergence with some euhelopodids.

Other exclusive features in Spinophorosaurus cervicals were proposed: i) anterior cervicals with accessory anterior processes on prezygapophyses; ii) triangular posterior processes on diapophyses; and iii) enlarged triangular cervical epipophyses, posteriorly directed. The former feature is more pronounced in mid-posterior cervicals bearing a striated surface for the attachment of the Mm. ascendens cervicalis and Mm. longus colli dorsalis. Epipophyses is prong-shaped (as in Jobaria and Euhelopus), and is round and stout on posterior cervicals. The triangular posterior process of diapophyses becomes prominent from middle cervical vertebrae and sometimes bears striated surface probably for Mm. intertransversarii attachment. Some of those features are present in a partial neck of a probable juvenile of Spinophrosaurus, while the absence of some characters may be attributed due ontogeny.

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Referencias:

• Mocho, P., Aberasturi, A., Ortega, F. 2015. Is Spinophorosaurus nigerensis a dinosaur with caudal spike osteoderms? 63rd Symposium for Vertebrate Palaeontology and Comparative Anatomy 24th Symposium of Palaeontological Preparation and Conservation with the Geological Curators' Group (Abstract Book), 97.
• Mocho, P., Páramo, A., Aberasturi, A., Escaso, F., Ortega, F. 2015 Morphological and laminae pattern variation along the neck of the eusauropod Spinophorosaurus nigerensis (Niger, Middle Jurassic). 63rd Symposium for Vertebrate Palaeontology and Comparative Anatomy 24th Symposium of Palaeontological Preparation and Conservation with the Geological Curators' Group (Abstract Book), 98.

Imagen:

• En la fotografía, Pedro Mocho explica uno de sus posters sobre Spinophorosaurus.