21.7.14

Sobre la validez de una tortuga egipcia en la 15 edición del congreso Gondwana


Como ya se ha comentado, durante la pasada semana se celebró en Madrid el congreso internacional Gondwana 15. Continuamos con alguno de los trabajos sobre paleontología de vertebrados defendidos en dicha reunión. El resumen del trabajo “Finding the supposedly lost holotype and only known specimen of the podocnemidid Stereogenys libyca, a turtle from the early Oligocene of Egypt” es el siguiente:

The shell-based species Stereogenys libyca (Pleurodira, Podocnemididae) was described by Andrews (1903) from one specimen collected during his 1902 expedition to the Fayum Depression (Egypt). It comes from early Oligocene levels. That nearly complete shell is the only specimen so far robustly attributed to this taxon. Andrews (1903) described it and published a figure consisting of three drawings: much of the dorsal and ventral views, and the right lateral view. He reproduced the same figure in another paper in 1906, but no photograph of this specimen was ever published. Discussions by other authors, in subsequent papers, are based on the data provided in the two mentioned works. Recently, Gaffney et al. (2011) conducted a detailed review and update of knowledge of Podocnemididae. They indicated that the current whereabouts of the holotype of Stereogenys libyca was unknown, not having been identified in the Cairo Geological Museum (Egypt), where it should have been held from the 1960s. Therefore, Gaffney et al. (2011) figured and discussed Stereogenys libyca solely of the basis of the works of Andrews (1903, 1906).

The holotype of Stereogenys libyca has now been located. It is presented here, being recognized as one of the best preserved shells from the Fayum Depression. Its study allows me to assess the validity of the interpretation of the morphology of the plates and scutes proposed by Andrews. Furthermore, the anatomy of the visceral region, both of the carapace and of the plastron, can be analyzed. Other skeletal elements, such as the pelvis, are studied here for the first time. The new study of this specimen, performed over 110 years after its original description, greatly improves knowledge of this taxon. Because of holotype was not available to them, Gaffney et al. (2011) could not confirm the validity of Stereogenys libyca or recognize it as a junior synonym of Stereogenys cromeri (another taxon of the Fayum Depression, defined by Andrews in 1901). Its recovery, together with those of several partial shells attributable to Stereogenys also from the Fayum Depression, should allow me to test whether there are separate species, or to recognize them as included in the range of variation of a single taxon.
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Más información:
  • Referencia: Pérez-García, A. 2014. Finding the supposedly lost holotype and only known specimen of the podocnemidid Stereogenys libyca, a turtle from the early Oligocene of Egypt. In: Pankhurst, R.J., Castiñeiras, P., Sánchez Martínez, S. (Eds.). Abstract Book of Gondwana 15, North meets South: 136.
  • Imagen: El supuestamente desaparecido holotipo.