Taxa at the Protsynapsid-Protodiapsid Split

When the ancestors of bats separated from the ancestors of birds is today’s topic.

Figure 1. Protorothyris, without a lateral temporal fenestra (in white) lies at the base of the Synapsida, large taxa like Aerosaurus and Archaeothyris  (in green) and the smaller Protodiapsida, like Archaeovenator, Mesenosaurus and Orovenator (in blue). All taxa are to scale. Yes, basal synapsids were bigger.

Figure 1. Protorothyris, without a lateral temporal fenestra (in white) lies at the base of the Synapsida, large taxa like Aerosaurus and Archaeothyris  (in green) and the smaller Protodiapsida, like Archaeovenator, Mesenosaurus and Orovenator (in blue). All taxa are to scale. Yes, basal synapsids were bigger.

Little studied or acknowledged, except here and at ReptileEvolution.com, the origin of non-lepidosaur diapsids had their origins in basalmost Synapsids, like Aerosaurus, and protosynapsids, like Protorothyris, which had no lateral temporal fenestra, according to results recovered from the large reptile tree.

Archosauriformes had their deepest origins with basal protodiapsids, traditionally considered varanopid synapsids, but that is based on their morphology, not their phylogeny. These taxa lie outside of the clade Synapsida when additional taxa are added, something that hasn’t been done in prior studies.

Lepidosaurformes had a convergent diapsid skull morphology, unrelated to archosauriforms, enailiosaurs, araeoscelids, etc.