Anguimorph lizards from the lower Eocene (MP 10–11) of the Cos locality, Phosphorites du Quercy, France, and the early evolution of Glyptosaurinae in Europe

Abstract

ABSTRACT Squamate faunas from the lower Eocene of Europe are rare. A newly discovered lower Eocene (MP 10–11) Cos locality in southwestern France has yielded an assemblage of anguimorph lizards that sheds light on the early evolution of this group. Among them is a new glyptosaurine lizard Sullivania gallica gen. et sp. nov., based on frontal material with a unique pattern and distribution of polygonal osteoderms that is distinct from that of the middle and late Eocene Placosaurus from France. It slightly resembles the stratigraphically older glyptosaurine Gaultia silvaticus from the earliest Eocene of North America, but differs from it in several aspects. Although fossils of some members of Glyptosaurinae (sensu this paper; Glyptosaurini in previous taxonomies—Glyptosaurinae is returned to the family level originally proposed by Marsh) have been documented rarely from the middle and mainly from the late Eocene of Europe, they are virtually unknown from the lower Eocene. One isolated osteoderm is referred only to Anguioidea indet. This specimen resembles osteoderms seen in Anguinae, provided that the absence of tuberclulate ornamentation is not caused by abrasion. Varanoids are represented by an isolated frontal referred to Palaeovaranidae indet. It possesses a complex ornamentation composed of mounds on the dorsal surface. A maxilla is identified as an indeterminate varanoid based on the plicidentine infolding along the bases of the preserved teeth. Although incomplete, this Cos lizard assemblage is an important and rare discovery that provides a glimpse into the ecosystems and paleobiodiversity of the lower Eocene in western Europe.