A reassessment of the enigmatic diapsid Paliguana whitei and the early history of Lepidosauromorpha

Lepidosaurs include lizards, snakes, amphisbaenians and the tuatara,
comprising a highly speciose evolutionary radiation with widely varying
anatomical traits. Their stem-lineage originated by the late middle
Permian 259 million years ago, but its early fossil record is poorly
documented, obscuring the origins of key anatomical and functional traits
of the group. Paliguana whitei, from the Early Triassic of South
Africa, is an enigmatic fossil species with potential to provide
information on this. However, its anatomy and phylogenetic affinities
remain highly uncertain, and have been debated since its discovery more
than 100 years ago. We present microtomographic 3D imaging of the cranial
anatomy of Paliguana whitei that clarifies these
uncertainties, providing strong evidence for lepidosauromorph affinities
based on the structure of the temporal region and the implantation of
marginal dentition. Phylogenetic analysis including these new data
recovers Paliguana as the earliest
known stem-lepidosaur, within a long-lived group of
early-diverging lepidosauromorphs that persisted to at least the Middle
Jurassic. Our results provide insights into cranial evolution on the
lepidosaur stem-lineage, confirming that characteristics of pleurodont
dental implantation evolved early on the lepidosaur stem-lineage. In
contrast, key functional traits related to hearing (quadrate conch) and
feeding (streptostyly) evolved later in the lepidosaur crown-group.