''Proxilodon'' 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 ...

recumbirostra Recumbirostra is a clade of tetrapods which lived during the Carboniferous and Permian periods. They are thought to have had a fossorial (burrowing) lifestyle and the group includes both short-bodied and long-bodied snake-like forms. At least o ...

microsaur Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been consider ...

from the Early Permian Speiser Formation of

Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to th ...

, United States. It contains a single species, ''Proxilodon bonneri'', (formerly "

Euryodus ''Euryodus'' is an extinct genus of microsaur within the family Gymnarthridae. References See also * Prehistoric amphibian * List of prehistoric amphibians This list of prehistoric amphibians is an attempt to create a comprehensive listing ...

" ''bonneri'').

History of study

There is only one known specimen of ''Proxilodon bonneri'', the former holotype of ''Euryodus bonneri'', named by Schultze & Foreman (1981). It was collected in 1976 by Brian Foreman from a roadcut site in Kansas in the lower Speiser Formation (often called the Speiser Shale) that preserves primarily aquatic vertebrates, such as the

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

'' Gnathorhiza'', the dvinosaur

temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carbo ...

'' Acroplous vorax'', the

nectridean 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 they ...

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 ...

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 ...

'', and the lysorophian '' Lysorophus tricarinatus''. The species was named after Orville Bonner, who prepared the specimen, a complete skull with the left lower jaw in articulation and associated vertebrae and a fragmentary humerus. Huttenlocker et al. (2013) identified numerous differences from other species of ''Euryodus'' and erected the new genus ''Proxilodon'', derived from a Latinized version of the Greek 'Euryodus,' which means 'broad-tooth' and which was the original taxonomic identification; 'proxilus' in Latin for broad/wide, and '-odon' refers to 'tooth.'

Anatomy

As with gymnarthrids like ''Euryodus'', ''Proxilodon'' possesses a long postorbital region and a slightly convex occiput, but it also has a much narrower skull than is typical of ''Euryodus'' and a higher premaxillary tooth count, among other features, that differentiate it from gymnarthrids at large. Other features listed in the diagnosis include a small notch in the premaxilla that articulates with the nasal, a nasal longer than it is broad (in line with the generally narrow skull), and the absence of a pineal foramen, instead being replaced by a shallow fossa. The holotype skull is typically sized for 'microsaurs,' measuring slightly less than 19 mm in length. Most of the internal anatomy is obscured by the articulation with the skull.

Relationships

A phylogenetic analysis of the position of ''Proxilodon'', and another novel taxon, ''

Huskerpeton ''Huskerpeton'' is an extinct genus of recumbirostran microsaur amphibian from the Early Permian Eskridge Formation of Nebraska, United States. It contains a single species, ''Huskerpeton englehorni''. The genus was named for the University of ...

'', by Huttenlocker et al. (2013) recovered ''Proxilodon'' as a recumbirostran microsaur within a clade formed by gymnarthrids, ostodolepids, and their relatives. Below is the topology recovered by those authors:

References

{{Taxonbar, from=Q16757765 Fossil taxa described in 2013 Cisuralian amphibians of North America Paleontology in Kansas