''Albanerpeton'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

-like

lissamphibian The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relatives) ...

found in North America and

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

, first appearing in

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

-aged strata. There are eight described members of the genus, and one undiagnosed species from the

Paskapoo Formation The Paskapoo Formation is a stratigraphic unit of Middle to Late Paleocene age in the Western Canada Sedimentary Basin. The Paskapoo underlies much of southwestern Alberta, and takes the name from the Blindman River (''paskapoo'' means "blind m ...

, with the most recent, ''A. ektopistikon'' being described by Carrano ''et al.''in 2022. Members of the genus had a robust head and neck which likely allowed them to actively burrow, characteristic of fossorial species, and they lived in a wide range of environments. This genus of amphibian was the last of its order, surviving until the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58southern Europe Southern Europe is the southern region of Europe. It is also known as Mediterranean Europe, as its geography is essentially marked by the Mediterranean Sea. Definitions of Southern Europe include some or all of these countries and regions: Alba ...

, and into the Early Pleistocene (

Gelasian The Gelasian is an age in the international geologic timescale or a stage in chronostratigraphy, being the earliest or lowest subdivision of the Quaternary Period/System and Pleistocene Epoch/Series. It spans the time between 2.58 Ma (million ye ...

) of northern

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

. It likely became extinct when the region developed its present Mediterranean-type climate, having preferred one that was cold and humid. The

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

of ''Albanerpeton'' has recently been questioned

History and Discovery

Albanerpeton was first described by Estes and Hoffstetter in 1976. However, the genus was re-described by Gardner in 1999 after a large collection of jaws and frontals from

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

fissure fills near La Grive-Saint-Alban in southeastern France was found. 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 Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...

, as its only salamander-like features were held in common with small, limbed, and non-

saltatorial This glossary of entomology describes terms used in the formal study of insect species by entomologists. A–C A synthetic chlorinated hydrocarbon insecticide, toxic to vertebrates. Though i ...

amphibians in general. ''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 The Albanerpetontidae are an extinct family of small amphibians, native to the Northern Hemisphere during the Mesozoic and Cenozoic. The only members of the order Allocaudata, they are thought to be allied with living amphibians belonging to Lis ...

, and genus, ''Albanerpeton'', all of which were new at the time. Seven of the eight species are restricted to the Western Interior of North America, suggesting that the evolutionary history of the genus was centered there, although the presence of a sole species in France, ''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.

Geology and palaeoenvironment

The description of ''A''. ''arthridion'' by Gardner in 1999 established a minimum age of latest Aptian for Albanerpetontidae's establishment in North America. 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. The finding and description of ''A. pannonicus'' in 2005 extended the genus’ temporal range from the middle Miocene to the early Pliocene. In 2018, Villa et al. investigated fossil

herpetofauna Herpetology (from Greek ἑρπετόν ''herpetón'', meaning "reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnophiona)) and rept ...

and the palaeoenvironment in Northern Italy's town of

Rivoli Veronese Rivoli Veronese is a little town (''comune'') in the Province of Verona, Veneto, Italy, located on the hills overlooking the right bank of the river Adige, northwest of Verona. History Rivoli Veronese is celebrated as the scene of the Battle of ...

. 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. The discovery and description of a new Albanerpetontidae species, who is closely related to genus ''Albanerpeton'', from the

Kuwajima Formation The Kuwajima Formation is an Early Cretaceous geologic formation in Japan. Its precise age is uncertain due to a lack of identifying fossils, and it was previously considered likely Valanginian to Hauterivian in age. However, it is now considered ...

in Japan, ''Shirepeton isajii'', further extends the group into Asia, though the genus ''Albanerpeton'' has still only been found in North America and Europe.

Description

Albanerpeton are distinct from

frog A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...

s, and

caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics o ...

s, forming their own family of Lissamphibia, Albanerpetontidae. Membership of species in the family is determined by diagnostic character states of the frontals and

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

ry synapomorphies, both of which can be used to further diagnose less inclusive clades in the genus. 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. The origins of these sister, snout-based clades can both be traced back to the early Late Cretaceous, and therefore antedate the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

. ''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. Diagnostic characteristics of the genus itself include characteristics of the teeth and skull.

Dentition

''Albanerpeton'' teeth are about one-third of the distance from the anterior end of the tooth row, and these are markedly larger than other nearby teeth. Additionally, the dorsal edge of the dental boundary is curved on its lingual side.

Skull

In 2013, Maddin et al. created a computer-generated tomography of a partially preserved, three-dimensional ''A. pannonicum'' neurocranium which deposited during the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Pannonian Basin, Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the ...

. The structure of this specimen is in line with what is known of older ''Albanerpeton'' neurocrania, and therefore a good reference for what the neurocranium of the whole genus is like. Features of the reconstructed skull consist of a robust, box-like unit composed of coossification of the parasphenoid, otic capsules, and occipital elements with no trace of fusion or sutural points of contact among these components. Additionally, the anterior three-quarters of the dorsal surface is open, but the furthest posterior portion,

tectum synoticum The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', "m ...

, is fused. The ventral surface of ''Albanerpeton'' neurocrania are fully ossified, solid bone. The neurocranium of ''Albanerpeton'' is in contact dorsally with paired parietals, forming the roof of the brain cavity while contacting laterally with the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

. Overall, the robust construct of ''Albanerpeton's'' neurocranium is consistent with the theory that the genus was fossorial in nature, as the thickened and strengthened skull would have lent itself to burrowing. ''Albanerpeton'' have ossified antotic pillars which sit in front of the otic capsules. Additionally, there are a pair of small, robust bony pedestals that are located ventrolaterally in front of the otic capsules, which likely served to brace the neurocranium against the

palatal The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...

region and suspensorium. In Albanerpeton, the otic capsules themselves are moderately inflated with large, rhomboid-shaped fenestra vestibulli present on both capsules. These

fenestra A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...

can be used to imply the presence of middle ear ossicles in ''Albanerpeton''. ''Albanerpeton'' had well-developed semicircular canals with a modestly developed ventral auditory region as well.

Classification

Current accepted species: Genus ''Albanerpeton'' Estes & Hoffstetter 1976 * ''Albanerpeton arthridion'' Fox & Naylor 1982 Early Cretaceous, United States * ''Albanerpeton ektopistikon'' Carrano ''et al.'' 2022 Early Cretaceous, North America * Clade "Gracile-snouted" ** ''Albanerpeton gracilis'' Gardner 2000 Late Cretaceous, North America ** ''Albanerpeton cifellii'' Gardner 1999 Late Cretaceous, United States ** ''Albanerpeton galaktion'' Fox & Naylor 1982 Late Cretaceous, North America * Clade "Robust-snouted" ** ''Albanerpeton nexuosus'' Estes 1981 Late Cretaceous, North America ** ''Albanerpeton pannonicus'' Venczel & Gardner 2005 Latest Miocene-Early Pleistocene Hungary, Italy ** ''Albanerpeton inexpectatum'' Estes & Hoffstetter 1976 Early Oligocene-Late Miocene, Europe 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. Many remains attributed to ''Albanerpeton'' from the Late Cretaceous of Europe, such as those from the Maastrichtian aged Densuş-Ciula Formation,

Sânpetru Formation The Sânpetru Formation is an early Maastrichtian geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. It is located in Romania, ne ...

and Sard Formation of Romania and the Maastrichtian aged

Tremp Formation The Tremp Formation ( es, Formación de Tremp, ca, Formació de Tremp), alternatively described as Tremp Group ( es, Grupo Tremp), is a geological Formation (geology), formation in the comarca Pallars Jussà, Lleida Province, Lleida, Spain. Th ...

of Spain, are probably only diagnostic to family level.

Cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

from Venczel and Gardner (2005): In 2020 it was found that ''Albanerpeton'' is paraphyletic with respect to ''

Shirerpeton ''Shirerpeton'' is an extinct genus of albanerpetontid amphibian from the Early Cretaceous Kuwajima Formation, which is located in Japan.Fujita, M. (2003). "Geological age and correlation of the vertebrate-bearing horizons in the Tetori Group ...

'' and ''

Yaksha The yakshas ( sa, यक्ष ; pi, yakkha, i=yes) are a broad class of nature-spirits, usually benevolent, but sometimes mischievous or capricious, connected with water, fertility, trees, the forest, treasure and wilderness. They appear in ...

,'' and it has been suggested that ''Albanerpeton'' be restricted to the Cenozoic species, with the Cretaceous species being given separate genera. Cladogram from Daza et al. (2020) Finally, with the description of ''Albanerpeton ektopistikon'' by Carrano ''et al.'' (2022), based on the data matrix from the 2018 description of ''Shirepeton isajii,'' also recovered ''Albanerpeton'' as a paraphiletic genus'','' further separated than in Daza ''et al.,'' (2020). Instead of restricting ''Albanerpeton,'' they suggested to include ''Shirerpeton'' and ''Wesserpeton'' into the genus, turning their type species into ''A. isajii'' and ''A. evansae'', respectively. Cladogram from Carrano ''et al.'' (2022):