''Tersomius'' 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 n ...

of dissorophoid

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 Carb ...

within the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Micropholidae. It is known from the early

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...

of North America (Oklahoma and Texas).

History of study

''Tersomius'' was first named in 1910 by American paleontologist E.C. Case based on a partial skull collected from the Archer City Formation of Texas. The type species is ''T. texensis'', in reference to its geographic provenance. The brief original description was supplemented by a lengthier redescription of the holotype and description of new material by Carroll (1964). At least two of these specimens do not belong to any species of ''Tersomius'' and were reassigned by Maddin et al. (2013), which has led some authors to consider it as a potential "

wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically define ...

." Material referred to ''Tersomius'' cf. ''texensis'' was reported from the early Permian South Grandfield locality in Oklahoma by Daly (1973). A second species of ''Tersomius'', ''T. mosesi,'' was named by Olson (1970) for Amos Moses, the property owner of the land in Oklahoma where the material was collected from. There are several dozen reported specimens for ''T. mosesi'', but almost all of them are in poor condition and the osteology of this species remains poorly understood. Olson differentiated it from ''T. texensis'' mostly on the basis of notably fewer marginal teeth in the jaw. A third species of ''Tersomius'', ''T. dolesensis'', was named by Anderson & Bolt (2013) from the Richards Spur locality in Oklahoma. It is differentiated from all other amphibamiforms by the presence of enlarged teeth along the palatine ramus of the vomer and is distinguished from ''T. texensis'' by a posteriorly restricted postorbital and a posteriorly extensive jugal.

Anatomy

The most recent revision of the genus is that of Schoch & Milner (2014), who list a combination of seven features and two plesiomorphies: (1) nearly circular outline of skull with curved maxilla; (2) prefrontal and postfrontal separated; (3) preorbital region equal to skull table in length; (4) internarial fenestra present; (5) teeth variably monocuspid and bicuspid; (6) vomer with both medial and lateral fangs; (7) palatine lacking denticles; (8) long supratemporal; (9) postparietal longer than tabular. Most of these features are not unique to ''Tersomius'' (the combination being unique), as evidenced by the diagnosis of Anderson & Bolt (2013), who list an elongate tabular and a medial curvature of the maxillary arcade at the position of the quadrate (shared with ''

Doleserpeton ''Doleserpeton'' is an extinct, monospecific genus of dissorophoidean temnospondyl within the family Amphibamidae that lived during the Upper Permian, 285 million years ago. ''Doleserpeton'' is represented by a single species, ''Doleserpeton ann ...

'', ''T. texensis'', and '' Micropholis'') as diagnostic. The poor understanding of ''T. mosesi'' often leads it to be excluded in discussion or diagnosing of the genus.

Relationships

Like other amphibamiforms that were described early in the 20th century, ''Tersomius'' has sometimes been listed as a

dissorophid Dissorophidae is an extinct family of medium-sized, temnospondyl amphibians that flourished during the late Carboniferous and early Permian periods. The clade is known almost exclusively from North America. History of study Dissorophidae is a ...

, but this was often the result of a lack of distinction between amphibamiforms and dissorophids for much of the 20th century. Its position within Amphibamiformes (the traditional Amphibamidae) is well-supported by modern computer-assisted phylogenetic analyses. ''Tersomius texensis'' is usually utilized as the representative of the genus in most analyses in which it is recovered as being closely related to ''Micropholis'' and ''Pasawioops'', forming the Micropholidae. Below is a phylogeny of dissorophoids from Schoch (2018): The placement of ''Tersomius dolesensis'' within ''Tersomius'' remains somewhat disputed because it is not recovered as the sister taxon of ''T. texensis'' in recent analyses by Anderson & Bolt (2013; the original description) and Maddin et al. (2013). In the former, ''T. texensis'' was excluded from the analysis, and ''T. dolesensis'' was recovered as the sister taxon to '' Plemmyradytes''. In the latter, both species of ''Tersomius'' were included and were not resolved as sister taxa. Below is the result of the analysis of Maddin et al. (2013):

References

{{Taxonbar, from=Q7705223 Amphibamids Dissorophids Prehistoric amphibian genera Taxa named by Ermine Cowles Case Fossil taxa described in 1910 Permian amphibians of North America

History of study

Anatomy

Relationships

See also

References