''Arizonerpeton'' 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 ...
of
nectridea
Nectridea is the name of an extinct order of lepospondyl tetrapods from the Carboniferous and Permian periods, including animals such as '' Diplocaulus''. In appearance, they would have resembled modern newts or aquatic salamanders, although the ...
n
lepospondyl
Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco (''Diplocaulus minumus''), lepospondyls lived from the Early Carboniferous ( Mississippian) to the Early Per ...
. It contains a single species, ''Arizonerpeton wellsi''. It lived in what is now the
Swisshelm Mountains
The Swisshelm Mountains are a small mountain range adjacent to the southwest corner of the Chiricahua Mountains of eastern Cochise County, Arizona. They are separated from the Pedrogosa Mountains to the southeast, the Chiricahuas to the northea ...
of modern-day
Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
, United States.
This locality belongs to the Black Prince Limestone Formation, which is dated to the middle
Pennsylvanian sub-period of the
Carboniferous period.
Description
''Arizonerpeton'' is known exclusively from a collection of unusual
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
e collected by Robert Wells, the namesake of its
specific name. These vertebrae can be designated as belonging to the order Nectridea, a collection of long-tailed
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
s (
amphibians in the broad sense) also including the famous "boomerang-headed" ''
Diplocaulus
''Diplocaulus'' (meaning "double caul") is an extinct genus of lepospondyl amphibians which lived from the Late Carboniferous to the Late Permian of North America and Africa. ''Diplocaulus'' is by far the largest and best-known of the lepospond ...
''. Like other nectrideans, ''Arizonerpeton's'' vertebrae had a single main body (a pleurocentrum) fused to a plate-like neural spine jutting out of the top. The flared rims of the front and rear surfaces of the pleurocentum possesses small structures which would have formed
tongue-and-groove
Tongue and groove is a method of fitting similar objects together, edge to edge, used mainly with wood, in flooring, parquetry, panelling, and similar constructions. Tongue and groove joints allow two flat pieces to be joined strongly together t ...
articulations with other vertebrae. The "tongue" projected forward from the front rim while the "groove" was present between two projections on the rear rim. The only definitive feature classifying this genus as a nectridean lies in the fact that there are also two pairs of joint plates (
zygapophyses) on each end of the vertebrae. The vertebrae are amphicoelous (hourglass-shaped) from the side, but not strongly so, and are covered in small pits. On the side of each vertebra, an extension known as a transverse process juts out perpendicularly, although also occasionally with a very slight upward angle.
The most unusual feature of these vertebrae lie in the fact that the neural spines are bifurcated. This means that a tall gap is present between the front and rear portions of each neural spine, effectively making it seem like there are two neural spines joined at the base. Vertebrae which are believed to have been part of the sacral (hip) region have shorter neural spines than those of the back, and are sightly titled backwards.
Less extreme neural spine bifurcation is also known in the early
diplocaulid ''
Diceratosaurus'' and some specimens of the
urocordylid ''
Ctenerpeton'', two other nectrideans. In addition, the pitted vertebrae are somewhat similar to those of diplocaulids. However, the deep neural spine bifurcation and "tongue-and-groove" articulations possessed by ''Arizonerpeton'' are unknown in any other nectridean groups. As a result, ''Arizonerpeton'' is usually treated as a member of Nectridea ''
incertae sedis
' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...
''.
See also
*
Prehistoric amphibian
This list of prehistoric amphibians is an attempt to create a comprehensive listing of all genera from the fossil record that have ever been considered to be amphibians, excluding purely vernacular terms. The list includes all commonly accepted g ...
*
List of prehistoric amphibians
This list of prehistoric amphibians is an attempt to create a comprehensive listing of all Genus, genera from the fossil record that have ever been considered to be amphibians, excluding purely vernacular terms. The list includes all commonly accep ...
References
Holospondyls
Prehistoric amphibians of North America
{{Lepospondyli-stub