Data from: A redescription of Orovenator mayorum (Sauropsida, Diapsida) using high-resolution μCT and the consequences for early amniote phylogeny

The earliest known neodiapsid Orovenator mayorum from the early Permian of
Oklahoma is redescribed using high-resolution μCT, revealing remarkable
details of the skull anatomy. Our findings are relevant to both
palaeoecology (suggesting burrowing and nocturnality) and phylogeny.
Orovenator and other sauropsids share at least 16 character states with
varanopids, many of which were not recognised by previous studies. These
include a rounded subnarial shelf of the premaxilla, a posterodorsal
extension of the external naris, the asymmetrical bifurcation of the
anterior vomer, and a prominent dorsomedial shelf of the surangular. This
exceptional degree of similarity between Orovenator and varanopids (a
nominally synapsid clade) questions our current understanding of
relationships among early amniotes. We test this by including Orovenator
in a phylogenetic data matrix used in an earlier study to differentiate
between early diapsids and synapsids, and find a monophyletic clade of
Orovenator + varanopids within Diapsida. Recent phylogenetic research on
early amniote evolution has focused on resolving intra-clade affiliations
rather than the interrelationships of major taxonomic groups.
Nevertheless, the relative incompleteness of existing phylogenetic
character lists for early amniotes can only be remedied by detailed
cross-clade assessment. We therefore suggest that early amniote
relationships require further scrutiny before we can confidently accept or
reject our new phylogenetic hypothesis.