Skin Anatomy, Bone Histology and Taphonomy of a Toarcian (Lower Jurassic) Ichthyosaur (Reptilia: Ichthyopterygia) from Luxembourg, with Implications for Paleobiology

Abstract

A partial ichthyosaur skeleton from the Toarcian (Lower Jurassic) bituminous shales of the ‘Schistes Carton’ unit of southern Luxembourg is described and illustrated. In addition, associated remnant soft tissues are analyzed using a combination of imaging and molecular techniques. The fossil (MNHNL TV344) comprises scattered appendicular elements, together with a consecutive series of semi-articulated vertebrae surrounded by extensive soft-tissue remains. We conclude that TV344 represents a skeletally immature individual (possibly of the genus Stenopterygius) and that the soft parts primarily consist of fossilized skin, including the epidermis (with embedded melanophore pigment cells and melanosome organelles) and dermis. Ground sections of dorsal ribs display cortical microstructures reminiscent of lines of arrested growth (LAGs), providing an opportunity for a tentative age determination of the animal at the time of death (>3 years). It is further inferred that the exceptional preservation of TV344 was facilitated by seafloor dysoxia/anoxia with periodical intervals of oxygenation, which triggered phosphatization and the subsequent formation of a carbonate concretion.