Biological implications of the bone microstructure of a new elasmosaurid (Sauropterygia, Plesiosauroidea) from the uppermost Cretaceous of Patagonia

ABSTRACT

The aim of present contribution is to describe the osteohistology of an articulated skeleton of an unnamed elasmosaurid coming from Santa Cruz province, Argentina, and recovered in late Cretaceous beds of Calafate Formation (Maastrichtian). Histological analysis indicates that the specimen reached somatic and sexual maturity. The specimen exhibits a unique combination of histological features that suggest complex palaeobiological and palaeocological implications. One remarkable aspect of the specimen is the presence of an external fundamental system (EFS) in the gastralia, a feature only cursorily described for plesiosaurs. Occurrence of EFS indicates a somatic maturation for the specimen. The transverse section of the phalanx and vertebral apophysis are osteoporotic, whereas those of the dorsal rib and gastralia show two layers of thick pachyostosic cortical tissue surrounding osteoporotic bone. This contradicts previous hypotheses that proposed that in elasmosaurids, the juveniles (characterised by osteoporotic histology) inhabited coastal waters and migrated to the open sea after reaching adulthood after an ontogenetic shift in bone density.

KEYWORDS:

• Elasmosaurid
• bone histology
• microanatomy
• Late Cretaceous
• ontogeny
• osteosclerosis
• pachyostosis
• patagonia

Acknowledgments

We especially thank Mirta González and Vicky Sánchez (Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’) for their assistance in the use of the petrographic microscope. We thank the partners of the LACEV (Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’), specially thanks to Mauro Aranciaga Rolando, Gabriel Lio, Ana Moreno, Matias Motta, Gonzalo Muñoz, Nicolas Chimento, Sebastián Rozadilla, Santiago Miner, Gaston Lo Coco Mauricio Cerroni, Gerardo Álvarez and Marcelo Isasi for their comments and discussion. We thank Emily Jane Wickenhauser for the revision of the English in the present manuscript. We would like to thank the two reviewers for their comments and discussions which greatly improved the manuscript. We thank ‘Cruz del Sur’ transport company, for moving fossils from Santa Cruz to Buenos Aires. Special thanks to Oscar Canto and Carla Almazán (Secretaría de Cultura de Santa Cruz) for continued support. The research presented here was funded from ANCyT PICT 58 and Conicet PIP 5153 (to FEN), and Spotila Foundation (to KL).

Disclosure statement

No potential conflict of interest was reported by the author(s).