Reassessment of the morphology and taxonomic status of the varanid lizard Saniwa orsmaelensis from the early Eocene of Northwest Europe

Saniwa is an extinct genus of varanid lizard from the Eocene of North America and Europe. It is the sister taxon to the crown-group Varanus. Up to now, only one poorly known species is recognized from Europe, Saniwa orsmaelensis from the earliest Eocene of Dormaal, Belgium. This species originally named by Louis Dollo nearly a century ago, is the earliest varanid of Europe. Unfortunately, the material was limited to vertebrae with only preliminary description and no figure provided, except for one dorsal vertebra that later has been designated as the lectotype. Here we describe and illustrate new fossil specimens collected from Dormaal and other early Eocene localities of the Paris Basin, France, including dentary and maxilla fragments as well as skull material, allowing to reassess the validity of the European taxon. These fossils allow further comparisons with the type-species, Saniwa ensidens, from the late early Eocene Bridger and Green River formations of Wyoming and to propose a new diagnosis for S. orsmaelensis. The occurrence of S. orsmaelensis is restricted to the early Eocene of Northwest Europe and its geographic origin is unresolved because the earliest record of Saniwa in North America is also from the earliest Eocene. The brief presence of varanid lizards in the European Paleogene could result from two major climatic events. At the Paleocene Eocene Thermal Maximum, large biotic interchanges occurred in the northern hemisphere allowing new dispersals into Europe. However, at the end of the Eocene, thermophilic lizards disappeared due to cooler conditions. Another hypothesis for their disappearance could be the competition that occurred with other anguimorph lizards. Grant Information: This abstract is a contribution to the Belspo Brain network project BR/121/A3/PalEurAfrica funded by the Belgian Science Policy Office.

Abstract of an Oral Presentation or a Poster, International Redaction Board, RBINS Collection(s)

Paleontology