?Ascendonanus nestleri (Spindler 2017, MNC-TA1045) is specimen mistakenly referred to the genus Ascendonanus (MNC-TA0924), which is a basal archosauromorph diapsid you can see here and below.
By contrast this specimen is an iguanid squamate found in vulcanized early Permian (291mya) sediments. It is the oldest lepidosaur known and based on its phylogeny, suggests an earlier radiation of lepidosaurs that earlier presumed. Other early lepidosauriformes include Paliguana and Lacertulus from the Late Permian. Other basal iguanids and pre-iguanids, like Scandensia, Calanguban, Euposaurus and Liushusaurus are late-survivors in the Late Jurassic and Early Cretaceous. Iguana is a late-survivor of an early radiation living today.
Ascendonanus was originally described
as a tree-climbing varanopid synapsid by Spindler et al. (2018), but no lepidosauriformes were tested. The bones are difficult to see through the scaly skin. Upper temporal fenestra and other lepidosaur traits were overlooked. No other basal synapsids were arboreal, but some Iguana species are also arboreal. Spindler et al. 2018 were unaware of the synapsid/prodiapsid split that removes many former varanopids from the clade Synapsida, despite their having typical synapsid temporal fenestration. One more reason NOT to label taxa based on traits, but to only label taxa after cladistic analysis.
The holotype Ascendonanus
is a basalmost diapsid based on phylogenetic analysis. True diapsids, like Eudibamus and Petrolacosaurus, all nest within the Archosauromorpha. By convergence, all members of the clade Lepidosauriformes, including this specimen wrongly referred to Ascendonanus, also have a diapsid temporal configuration.
The image below compares all five specimens in the Ascendonanus quarry. 3x to 5x numbers represent skull length vs. occiput/acetabulum length. |
