Jade B. Atkins, Peter Sourges, Nadia B. FrÃbisch, Robert R. Reisz & Hillary C. Maddin (2020)
Late ontogeny in the small Early Permian amphibamiform dissorophoid Pasawioops mayi.
Journal of Vertebrate Paleontology Article: e1772800
Ontogenetic series are rarely preserved in the fossil record, but when present they provide valuable insight into life history, developmental, and evolutionary patterns in extinct taxa. Here, we describe an intact, three-dimensionally preserved skull of Pasawioops mayi (Amphibamiformes, Micropholidae), which has not been fully described previously. Together with the holotype, also an intact skull, these two specimens of Pasawioops are interpreted as part of an ontogenetic series. The two specimens differ in traits that are thought to change during ontogeny in temnospondyls, including elongation of the postorbital region, transformation of the palatal dentition from small groups of denticles to significantly larger teeth, and a posteriorly shifting lower jaw articulation. We survey previously described amphibamiform taxa and use the ontogenetic data derived from Pasawioops to identify other potential ontogenetic series (e.g., Eoscopus). Additionally, we briefly compare amphibamiform ontogenetic series to known ontogenetic data of olsoniform and micromelerpetontid dissorophoids, and other early tetrapod lineages, to determine the extent to which ontogeny may or may not be conserved across these lineages. Several aspects of the ontogeny of Pasawioops are found to be present in lissamphibians and Amphibamiformes (i.e., branchiosaurids and amphibamids), revealing that some ontogeny-dependent traits are highly conserved within this group, whereas others are more broadly conserved across other tetrapod lineages.