''Acheloma'' (also known as ''Trematops milleri'') is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

that lived during the

Early Permian 01 or 01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), ''01'' (Richard Müller album), 2001 * 01 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...

. The

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

is ''A. cumminsi''.

History of study

''Acheloma'' was named by

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...

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 The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...

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. A 2020 paper by Gee synonymized ''A. dunni'' with ''A. cumminsi'', suggesting that

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the ovum, egg to adult. The term can also be used to refer to t ...

may account for the differences in specimens. However, the 2024 paper from Osterling Arias et al., which established the new species ''A. cryptatheria'' from a reexamined block of Richards Spur material, resurrected the species of ''A. dunni'' based on considerations of internal skull morphology.

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 language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

shows the

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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

References

{{Taxonbar, from=Q4673596 Dissorophidae Trematopidae Cisuralian temnospondyls of North America Prehistoric amphibian genera Taxa named by Edward Drinker Cope Fossil taxa described in 1882