''Acheloma'' (also known as ''Trematops milleri'') 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 ...

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 ...

that lived during the Early Permian. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

is ''A. cumminsi''.

History of study

''Acheloma'' was named by Edward Drinker Cope in 1882 based on a partial skull with associated postcranial elements from the Arroyo Formation of Texas; the specimen is currently reposited at the American Museum of Natural History in New York. Subsequent discoveries of large trematopids from the Arroyo Formation were named as different species of ''Trematops'' (''T. milleri, T. willistoni''), but these have since been synonymized with ''Acheloma cumminsi''. ''Trematops stonei'' from the Washington Formation of Ohio and ''Trematops thomasi'' from Oklahoma have also been synonymized with ''A. cumminsi''. A second species of ''Acheloma'' was described by Polley & Reisz (2011) from the Richards Spur locality in Oklahoma.

Anatomy

Schoch & Milner (2014) provide nine characters in their diagnosis of ''Acheloma'': (1) toothed crest on the vomer extending medial to the internal naris; (2) constricted otic notch with nearly horizontal ventral margin; (3) preorbital region twice as long as the skull table; (4) naris twice as long as the orbit; (5) posterior skull table wide and posterolaterally expanded; (6) skull margin widens at level of and posterior to orbit; (7) palatine and ectopterygoid with tall fangs; (8) large intervomerine fenestra; and (9) choana elongate and curved with a Y-shaped contour. ''Acheloma cumminsi'' and ''A. dunni'' are distinguished by the purported absence of lateral exposures of the palatine (LEP) and the ectopterygoid (LEE) in ''A. cumminsi'', but these exposures were subsequently identified following re-examination of the holotype of this taxon.

Ecology

Various analyses have confirmed hypotheses that ''Acheloma'' was a terrestrial temnospondyl.

Phylogeny

The following

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 ...

shows the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

position of ''Acheloma'', from Polley & Reisz, 2011.

References

Dissorophids Trematopids Cisuralian temnospondyls of North America Prehistoric amphibian genera Taxa named by Edward Drinker Cope Fossil taxa described in 1882 {{Permian-animal-stub