Virtual reconstruction and morphometric analysis of the vertebral column of the stem sirenian Pezosiren portelli (Tethytheria, Pan-Sirenia, Prorastomidae)

Abstract

In this study, we virtually reconstruct the vertebral column of Pezosiren portelli , a four-limbed stem sirenian (Pan-Sirenia, Prorastomidae) from the Eocene of Jamaica. We used three-dimensional models of various vertebrae obtained through surface scanning of fossil remains and we applied several algorithms for virtual repair, including retrodeformation of distorted vertebrae or mirroring missing processes from their bilateral counterparts. To quantify the regional morphology of P. portelli , we digitized a set of homologous landmarks, following a standardized protocol retrieved from previous morphometric studies on the evolution of the mammalian backbone. The results reveal a cervical region with relatively long spinous processes, as well as a thoracic region subdivided into prediaphragmatic and postdiaphragmatic regions with an unspecialised lumbar region. Both aspects reveal anatomical traits typical of terrestrial mammals, suggesting that P. portelli may exhibit a mosaic evolutionary pattern, showing postcranial traits typical of terrestrial taxa but also early aquatic adaptations found in its cranial skeleton. Finally, we briefly discuss the implications of morphometric analyses of the P. portelli vertebral column for understanding the evolution of axial features in other secondarily aquatic tethytherians.

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