A new late Cretaceous squamate from Patagonia sheds light on Gondwanan diversity.

The fossil record of Mesozoic terrestrial squamates is very poor in the Southern Hemisphere. Currently recognised species represent less than 6% of the number described for Laurasian landmasses. Here, we describe the most complete Late Cretaceous terrestrial squamate known from South America. The specimen was collected in the Maastrichtian Allen Formation of northern Patagonia (Río Negro Province, Argentina) and represents a single individual that preserves a partial skull, vertebrae, and appendicular bones. The skeleton shows a unique combination of character states that allow erecting the new genus and species Paleoteius lakui. Morphological phylogenetic analyses recovered Paleoteius lakui as a Scincomorpha more closely related to Xantusiidae than to other species. When a molecular backbone is applied to those analyses, Paleoteius lakui is found outside Scincomorpha, but within a clade composed of Jurassic to Palaeogene species found as non-crown scincomorphans in previous studies. The affinities of Paleoteius lakui either as a stem-xantusiid or as a more early-diverging clade indicate the presence of a yet unrecognised lineage of squamates in South America. Paleoteius lakui is related to Laurasian forms with a probable cosmopolitan ancestry during the Jurassic-earliest Cretaceous. The new finding helps fill the still poorly known record of Mesozoic Gondwanan squamates.