TheAlbanerpetontidae (also spelledAlbanerpetidae andAlbanerpetonidae) are anextinct family of smallamphibians, native to the Northern Hemisphere during theMesozoic andCenozoic. The only members of the orderAllocaudata, they are thought to be allied with living amphibians belonging toLissamphibia. Despite a superficially salamander-like bodyform, their anatomy is strongly divergent from modern amphibians in numerous aspects. The fossil record of albanerpetontids spans over 160 million years from theMiddle Jurassic to the beginning of thePleistocene, about 2.13–2 million years ago.
The earliest specimen of an albanerpetontid to be discovered was that ofCeltedens megacephalus from theEarly Cretaceous (Albian)Pietraroja Plattenkalk of Italy, described byOronzio Gabriele Costa in 1864, and originally placed in the genusTriton, ajunior synonym of the salamander genusTriturus.[1] Jaw elements of albanerpetontids from the Cretaceous of North America were assigned to the salamander genusProsiren byRichard Estes in 1969, erecting the familyProsirenidae to accommodate the genus.[2]Prosiren was originally described by Coleman J. Goin andWalter Auffenberg in 1958, based on vertebrae found in Cretaceous aged deposits in Texas.[3]Albanerpeton, thetype genus of the family was first named by Estes andRobert Hoffstetter in 1976 for the species ofA. inexpectatum described from a large number of jaws and frontal bones from aMiocene aged fissure fill deposit nearSaint-Alban-de-Roche in France, and was initially classified as a salamander, and placed in the familyProsirenidae alongsideProsiren due to the morphological similarity with the jaw fragments attributed toProsiren by Estes (1969).[4] Richard Fox and Bruce Naylor in 1982 realised thatAlbanerpeton was not a salamander, noting that the holotype vertebra ofProsiren was different to those of albanerpetontids, concluding thatAlbanerpeton was "well isolated from salamanders" and that it "seems no nearerphyletically to any other known amphibians, fromDevonian to Recent" erecting the family Albanerpetontidae and the order Allocaudata to accommodate it.[5]
Bones of the only articulated albanerpetontid skull,Yaksha peretti, vomer not shown
Albanerpetontids were small (several cm to several tens of centimetres in length) and superficially lizard-like. The skin of albanerpetontids was embedded with bony, fish-like scales. The forelimbs only had fourdigits, while retaining five digits on the hindlimbs. The morphology of the complete three-dimensionally preserved skull ofYaksha peretti suggests that albanerpetontids hadballistic tongues akin to those ofchameleons andplethodontid salamanders, as evidenced by the presence of an elongated rod shaped bone in the jaw cavity, dubbed thehyoid entoglossal process, which in life was embedded within the tongue. Analogous bones exists in chameleons and plethodontids, which allow rapid propulsion of the tongue.[6] A hyoid entoglossal process is also known fromCeltedens megacephalus, suggesting that the presence of a ballistic tongue is characteristic for the group.[7][6] Distinguishingapomorphic traits characteristic of albanerpetontids include a complexmortise and tenon–like joint connecting thedentary bones at the front of the jaw, teeth which are non-pedicellate and slightly tricuspid (bearing threecusps), thefrontal bones of the skull display raised polygonal sculpturing, and three anteriorcervical components form an 'atlas–axis' complex, similar to that ofamniotes.[8]
The morphology of albanerpetontids suggests that they were sit-and-wait terrestrial predators and fed on invertebrates, similar to living plethodontids. The fact that the skull of the juvenile paratype ofYaksha was around 1/4 of the size of the adult suggests that albanerpetontids grew by direct development and did not have ametamorphic larval stage.[6] It has been suggested that albanerpetontids absorbed oxygen entirely through the skin viacutaneous respiration and lacked lungs like plethodontid salamanders, due to the length of the hyoid entoglossal process, which may have made normal breathing difficult.[6] This proposal is supported by the internalvascularisation and lack ofSharpey's fibres in the frontal bones.[9] Albanerpetontids are associated with both wet and dry environments, but it is unclear how tolerant they were of dry habitats, and they may have been confined to wet microhabitats in dry areas.[10] Some authors have suggested that they were likelyfossorial, using their heads to burrow, but this has been questioned by other authors.[11]
The distribution of albanerpetontids is largely confined toEurasia andNorth America, with remains also known from Morocco in North Africa.[12][13] The first albanerpetontids are known from the westernPalearctic (Europe and North Africa) in theMiddle Jurassic (Bathonian ~168–166 million years ago), with the oldest records of the group in North America and Asia dating to theEarly Cretaceous. The last known remains of albanerpetontids in North America are from thePaskapoo Formation in Canada, dating to thePaleocene. All otherCenozoic members of the family, belonging to the genusAlbanerpeton, are known from Europe andAnatolia, from theOligocene onwards (there is no fossil record of albanerpetontids during theEocene) until their final appearance in Northern Italy during the Early Pleistocene, around 2.13-2 million years ago.[13][14][15][8] Another possible late record is known from northern Spain, dating to around 2.2-2.6 million years ago.[16]
Albanerpetontids were long thought to be salamanders because of their small size and generalized body plans.[17] However, these features are now thought to be ancestral for lissamphibians and not indicative of close relationships between the two groups.[18] Albanerpetontids share with living lissamphibians anatlanto-occipital joint with two cotyles, a four fingered forelimb (manus), ectochordal (spoon shaped with open centra) vertebrae with cylindrical centra, ribs that do not encircle the body, and a salamander-likequadrate–squamosal articulation, but are distinguished from the three living groups of lissamphibians by their possession ofkeratinized claw sheaths and their retention of skull bones lost in other lissamphibians, includingepipterygoids,supraoccipitals and largepalatines, as well as the absence of pedicellate teeth or a wideparasphenoid cultriform process.[6] Albanerpetontids are now recognized as a distinctclade of lissamphibians separate from the three living orders of amphibians –Anura (frogs),Caudata (salamanders), andGymnophiona (caecilians). Many studies show them as more closely related to frogs and salamanders than to caecilians,[19] butbootstrap andBayesian analyses show that this result is not robust and that they could also be sister-group of theLissamphibia,[20] or as most closely related to caecillians.[21] The presence of epipterygoids and a separate supraoccipital at least argues against a position withinBatrachia.[8] A phylogenetic analysis in 2020 among lissamphibian relationships using multiple methods found no consensus for the position of Albanerpetontidae in relation to other lissamphibians, but they were always placed closer to lissamphibians than to other extinct groups of amphibians, such aslepospondyls andtemnospondyls.[6]
^O. G. Costa. 1864.Paleontologia del Regno di Napoli. Parte III [Paleontology of the Kingdom of Naples. Part III]. Atti dell'Accademia Pontaniana8:1–192
^R. Estes and R. Hoffstetter. 1976. Les urodèles du Miocène de La Grive-Saint-Alban (Isère, France) [The urodeles from the Miocene of La Grive-Saint-Alban (Isère, France)].Bulletin du Muséum National d'Histoire Naturelle, Sciences de la Terre57:297–343
^Fox, Richard C.; Naylor, Bruce G. (1982-01-01). "A reconsideration of the relationships of the fossil amphibian Albanerpeton".Canadian Journal of Earth Sciences.19 (1):118–128.Bibcode:1982CaJES..19..118F.doi:10.1139/e82-009.ISSN0008-4077.
