OBSERVACIONES HISTOLÓGICAS DE REPTILES MARINOS (PLESIOSAURIA, MOSASAURIA) DEL CRETÁCICO SUPERIOR DE PATAGONIA Y ANTÁRTIDA

MARIANELLA TALEVI Y LEONARDO SALGADO

Plaza Huincul, Neuquén

Jornada; XXI JORNADAS ARGENTINAS DE PALEONTOLOGÍA DE VERTEBRADOS; 2005

Comisión ad hoc

During the last years, bone histology have been used to study lifestyles of extinct vertebrates. Nevertheless, paleohistological studies in Argentina are scarce, particularly that of marine reptiles. Bones of two elasmosaurid plesiosaurus (one subadult and one adult) from the Upper Cretaceous of Patagonia (Argentina) and one adult mosasaur from the Upper Cretaceous of Antarctica are histologically described in order to obtained information related to their lifestyles. This information is intended to provide a base for future comparisons with that available from other marine reptiles from other parts of the world. The bones of the subadult elasmosaurid from Pellegrini (Río Negro, Argentina), display a well developed endosteal compaction or osteosclerosis, being higher the degree of osteosclerosis in the vertebra than in the humerus or pelvic girdle. On the contrary, the bones of the adult elasmosaurid analyzed (cf. Mauisaurus from the Salinas de Trapalcó area, Río Negro), display internal vacuities leading to a lightening of the bone (osteoporotic-like bone structure). The distribution of osteosclerotic bone structure in juvenil plesiosaurs and osteoporotic-like structure in adults is similar to the one described in plesiosaurs from New Zealand, and could be related to adaptations to different aquatic environments: estuaries and shallow waters for juveniles and open seas for adults. Both situations are in agreement with paleoenvironment reconstructions of Fm. Allen and Fm. Jagüel in Lago Pellegrini and Salinas de Trapalcó respectively. In the bones of the mosasaurs from Fm. López de Bertodano, Upper Cretaceous, Isla Marambio, Antarctica), compact bone is in the inner part of the vertebra, while in the transverse process there is a high degree of osteoporotic tissue. Probably both types of bones, osteoporotic and osteosclerotic, were uneven distributed in the skeleton according to the process of inner reshaping and to the dynamic development of these reptiles.