Supporting information for phylogenetic analysis and imaging of Agriodontosaurus

The Lepidosauria is the most species-rich group of land-dwelling
vertebrates. The group includes around 12,000 species of lizards and
snakes (Squamata) and one species of Rhynchocephalia, the tuatara
Sphenodon punctatus from New Zealand. Squamates owe their success to their
generally small size, but also to their highly mobile skull that enables
them to manipulate large prey. These key features of lizard and snake
skulls are not seen in Sphenodon, which makes it important to understand
the nature of their common ancestor. Lepidosaurs originated in the
Triassic 252–201 million years ago, but confusion has arisen because of
incomplete fossils, many of which are generalized lepidosauromorphs,
neither squamates nor rhynchocephalians. Here we report a reasonably
complete skull and skeleton of a definitive rhynchocephalian from the
Middle Triassic (Anisian) Helsby Sandstone Formation of Devon, UK that is
around 3–7 million years older than the oldest currently known lepidosaur.
The new species shows, as predicted, a non-mobile skull but an open lower
temporal bar and no large palatine teeth, and it seems to have been a
specialized feeder on insects. This specimen helps us understand the
initial diversification of Lepidosauria as part of the Triassic
Revolution, when modern-style terrestrial ecosystems emerged.