El escamoso de Algora y las adaptaciones evolutivas de pitonomorfos al medio marino abierto en el XXI EJIP/6th IMERP

Miembros del Grupo de Biología Evolutiva de la UNED han presentado durante el XXI EJIP/6th IMERP, el trabajo titulado “The evolutionary trend towards the fully-marine lifestyle of the mosasaurs: the case of a ‘pachyostotic’ squamate from the basal Late Cretaceous of Spain” como comunicación oral. En esta comunicación se ha presentado un estudio osteológico de la vértebra perteneciente al recientemente descrito Carentonosaurus algorensis, un lagarto escamoso acuático del Cretácico Superior más basal de Algora (Guadalajara, España). En este estudio, se ponen en contexto las características osteológicas presentes en el espécimen de Algora dentro del marco evolutivo del grupo Pythonomorpha (que incluye a los conocidos mosasaurios) y las adaptaciones adquiridas por los taxones que componen el mismo en su transición al medio marino abierto. De esta manera, se hace un recorrido analizando las adaptaciones vertebrales observadas en el linaje hasta la aparición de las formas nadadoras activas de aguas más profundas de finales del Cretácico. A continuación, os dejamos el resumen perteneciente a este trabajo:

The mosasaurs (Mosasauridae) were a clade of aquatic squamates ranging from the Turonian (early Late Cretaceous) to the Maastrichtian (lattermost Cretaceous), that probably originated in the Tethys region and that were distributed worldwide at the end of the Cretaceous. Although highly adapted to open-sea environments, mosasaurs radiated from a lineage including more basal forms, informally referred to as ‘dolichosaurs’ and ‘aigialosaurs’ (i.e., non-mosasaurid mosasaurians), that were adapted to shallow-marine and freshwater environments. A major radiation of shallow-marine mosasaurians that mainly inhabited the Mediterranean Tethys, occurred in the Cenomanian (earliest Late Cretaceous), during which an incipient adaptation of the clade to marine environments is evidenced by ‘pachyostosis’ (a non-pathological condition of bone hypertrophy). The ‘pachyostosis’ (or pachyostosis s.l) may be represented as pachyostosis s.s (increase in volume of the periosteal cortex), osteosclerosis (increase of the bone inner compactness) or pachyosteosclerosis (the combination of both conditions). ‘Pachyostotic’ mosasaurians were almost exclusively restrained to the Cenomanian, since more derived forms (i.e., the members of Mosasauridae) were already adapted to a hydrodynamic lifestyle in open-sea environments and, therefore, their osseus characteristics were extremely modified. The gradual transition towards an open-marine lifestyle is reflected in the external bone morphology and microanatomy of some primitive mosasaurian taxa. In this context, a pachyosteoclerotic vertebra of a squamate has been identified in the Cenomanian site of Algora (Guadalajara, Central Spain). The specimen from Algora shows several characters that allow its identification as a non-mosasaurid mosasaurian and, more specifically, as an undefined form closely related to Carentonosaurus mineaui, from the Cenomanian of France. The aim of this work is to discuss anatomical analysis of the vertebra from Algora including its degree of ‘pachyostosis’ within the evolutionary framework of the adaptations towards a fully marine lifestyle recognized for derived mosasaurians.