Albanerpetontid amphibians from the Lower Cretaceous of Spain and Italy: a description and reconsideration of their systematics

Abstract

Albanerpetontids were small, terrestrial amphibians with robust limbs and tails. They are known from deposits from the Middle Jurassic (Bajocian) to the Miocene of Europe, North America and Central Asia. They can be diagnosed by a series of unique derived character states, which include an interdigitating mandibular symphysis, an atlas-axis joint analogous to that of mammals and regular polygonal sculpturing on dermal roofing bones of the skull. They remained remarkably conservative throughout their long history, but the shape of their frontals appears to diagnose genera as well as species. Previous descriptions of albanerpetontids were based on disarticulated remains. Described here in detail are two complete specimens from the Cretaceous (Berriasian) of Spain; one, particularly well-preserved specimen has traces of skin and possibly male courtship glands. A description of the albanerpetontid specimen from the Cretaceous (Albian) of Italy is also given. Previous authors have placed albanerpetontids as either true caudates or as a sister-group of caudates. This new material helps to clarify the systematic position of the group; character analyses show them to be clearly not true caudates but possibly a sister-group of salamanders plus frogs (±gymnophionans). Their relationships with Palaeozoic amphibians remains equivocal with an ancestor most likely to be found in either the microsaurs, or amphibamid or branchiosaurid temnospondyls.