Albanerpeton

Albanerpeton was first described by Estes and Hoffstetter. However, the genus was re-described by Gardner in 1999 after a large collection of jaws and frontals from Miocene fissure fills near La Grive-Saint-Alban in southeastern France was found.[5] When the type species was originally described, it was considered to be a salamander, despite possessing no known features that were otherwise restricted to Urodela, as its only salamander-like features were held in common with small, limbed, and non-saltatorial amphibians in general.[6] A. inexpectatum had many unique characteristics, distinct from salamanders and other amphibians (such as its feeding apparatus, dermal bones of the skull, and anterior cervical vertebrae) that Fox and Naylor suggested it be classified in its own order, Allocaudata, family, Albanerpetontidae, and genus, Albanerpeton, all of which were new at the time.[6] Six of the seven species are restricted to the Western Interior of North America, suggesting that the evolutionary history of the genus was centered there,[7] although the presence of a sole species in France,[5] A. inexpectatum, suggests a Tertiary dispersal of an unknown species from North America into Europe. Albanerpeton jaws and frontals are the most commonly recovered Albanerpeton bones found at dig sites, but these bones exhibit many characteristics that are taxonomically and phylogenetically informative for the genus and individual species within it.[5]

The description of A. arthridion by Gardner in 1999 established a minimum age of latest Aptian for Albanerpetontidae’s establishment in North America.[8] A later paper by Gardner in the same year, in which he described A. cifelli, helped fill missing information in the genus’ record during the Cretaceous period.[9]  The finding and description of A. pannonicus in 2005 extended the genus’ temporal range from the middle Miocene to the early Pliocene.[1]

In 2018, Villa et al. investigated fossil herpetofauna and the palaeoenvironment in Northern Italy’s town of Rivoli Veronese. The investigation supported the hypothesis that Albanerpeton favored a moist environment, and confirmed the former presence of a humid, forested landscape on Po Plain’s northern side in the Gelasian, supporting the genus’ preference for humid environmental conditions, and also further extended the genus’ temporal range to the Gelasian period.[2] The discovery and description of a new Albanerpetontidae species, who is closely related to genus Albanerpeton, from the Kuwajima Formation in Japan, Shirepeton isajii, further extends the group into Asia, though the genus Albanerpeton has still only been found in North America and Europe.[3]

Albanerpeton are distinct from frogs, salamanders, and caecilians, forming their own family of Lissamphibia, Albanerpetontidae. Membership of species in the family is determined by diagnostic character states of the frontals and premaxillary synapomorphies, both of which can be used to further diagnose less inclusive clades in the genus.[10] These less inclusive clades are the gracile-snouted clade and robust-snouted clade, made up of three and four species respectively though only three of the robust-snouted clade have been fully described. The gracile-snouted clade is defined by a triangular to slit-shaped suprapalatal pit. The robust-snouted clade is defined by a robust premaxillae, a short pars dorsalis that is sutured dorsally with the nasal, a short premaxillary lateral process on the maxilla, and an internasal process on frontals that are both narrow and similar to spines.[10] The origins of these sister, snout-based clades can both be traced back to the early Late Cretaceous, and therefore antedate the Campanian.[10] A. arthridion is interpreted as the most primitive species of Albanerpeton, being quite small. Its small size forms the basis for the hypothesis that reduced body size is derived, and was developed at least twice within the genus.[8] Diagnostic characteristics of the genus itself include characteristics of the teeth and skull.

The genus Albanerpeton is part of the family Albanerpetontidae which is part of the order Allocaudata within superorder Batrachia and class Amphibia. Members of genus Albanerpeton are considered to be Lissamphibia who are distinct in character from frogs, salamanders, and caecilians. In 2018, a closely related species, named Shirepeton isajii, was discovered and described in the Kuwajima Formation of Japan. While it is closely related to members of Albanerpeton, it does not fall within the clade.[3] Many remains attributed to Albanerpeton from the Late Cretaceous of Europe, such as those from the Maastrichtian aged Densuş-Ciula Formation, Sânpetru Formation and Sard Formation of Romania and the Maastrichtian aged Tremp Formation of Spain, are probably only diagnostic to family level.[12]

Cladogram from Venczel and Gardner (2005):[1]

In 2020 it was found that Albanerpeton is paraphyletic with respect to Shirerpeton and Yaksha, and it has been suggested that Albanerpeton be restricted to the Cenozoic species, with the Cretaceous species being given separate genera.[4]

Cladogram from Daza et al (2020)