The first evidence of iguanians and scincoids from the lower Eocene of the Cos locality (Phosphorites du Quercy, France)

Abstract

Terrestrial ecosystems in Europe, but almost everywhere, changed significantly during the Cenozoic due to global climatic changes. The importance of their better understanding is magnified by present global climate change, which includes sea-level rise, as well as expansion in the distribution of thermophilic taxa, including parasites that cause serious infectious diseases. Squamates (lizards and snakes) are the largest and most successful group of living reptiles. They are globally distributed in different habitats and have a history dating back over 200 million years. The distribution, richness, and diversity of squamates is highly dependent on climatic conditions, and climate change has a marked impact on their life history. Thus, lizards are excellent indicators of past temperatures and precipitation. The appearance of many groups conceived to be thermophilic at high latitudes indicates that the tropics were much more expanded during the Eocene. We here describe pleurodontan iguanian (potentially Geiseltaliellus), scincoid and Squamata remains from Cos locality (France), one of the oldest sites of Phosphorites du Quercy. The age of the Cos deposit has been proposed to fit the MP 1011 interval (late Ypresian). Thus, it either corresponds to the end of the Early Eocene Climatic Optimum (EECO) or slightly postdates it. In the last few years, our knowledge of early Eocene lizard faunas has increased substantially. This allows better comparison of the faunas and their changes due to temperature changes and migrations. Records are still very sketchy in European localities, but the overall picture is somewhat clearer. A small but visible drop in lizard diversity appears to be present in localities from MP 89, relative to those from MP 7, whereas at MP 10, the diversity slightly increased. This appears to correlate well with observed changes in temperature.