Acheloma

Acheloma was named by Edward Drinker Cope in 1882 based on a partial skull with associated postcranial elements from the Arroyo Formation of Texas;{{Cite journal|last=Cope|first=E. D.|date=1882|title=Third Contribution to the History of the Vertebrata of the Permian Formation of Texas|journal=Proceedings of the American Philosophical Society|volume=20|issue=112|pages=447–461|issn=0003-049X|jstor=982692}} 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.{{cite journal|last=Polley|first=B.P.|author2=and Reisz, R.R.|year=2011|title=A new Lower Permian trematopid (Temnospondyli: Dissorophoidea) from Richards Spur, Oklahoma|journal=Zoological Journal of the Linnean Society|volume=161|issue=4|pages=789–815|doi=10.1111/j.1096-3642.2010.00668.x|doi-access=free|hdl=1807/18982|hdl-access=free}} A 2020 paper by Gee synonymized A. dunni with A. cumminsi, suggesting that ontogeny may account for the differences in specimens. {{Cite journal |last=Gee |first=Bryan M |date=2020-08-20 |title=Size matters: the effects of ontogenetic disparity on the phylogeny of Trematopidae (Amphibia: Temnospondyli) |url=https://academic.oup.com/zoolinnean/article-abstract/190/1/79/5741763?redirectedFrom=fulltext |journal=Zoological Journal of the Linnean Society |volume=190 |issue=1 |pages=79–113 |doi=10.1093/zoolinnean/zlz170 |issn=0024-4082}} 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. {{Cite journal |last1=Arias |first1=Adrian F. Osterling |last2=Mooney |first2=Ethan D. |last3=Bevitt |first3=Joseph J. |last4=Reisz |first4=Robert R. |date=2024-10-17 |title=A new trematopid from the lower Permian of Oklahoma and new insights into the genus Acheloma |journal=PLOS ONE |language=en |volume=19 |issue=10 |pages=e0309393 |doi=10.1371/journal.pone.0309393 |doi-access=free |issn=1932-6203 |pmc=11486393 |pmid=39418236|bibcode=2024PLoSO..1909393O }}

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.{{Cite book|title=Handbuch der Paläoherpetologie Part 3A2. Temnospondyli I.|last1=Schoch|first1=Rainer R.|last2=Milner|first2=Andrew R.|publisher=Verlag Dr. Friedrich Pfeil|year=2014|isbn=9783931516260|editor-last=Sues|editor-first=Hans-Dieter|location=Stuttgart|oclc=580976}} 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.{{Cite journal|last1=Gee|first1=Bryan M.|last2=Bevitt|first2=Joseph J.|last3=Reisz|first3=Robert R.|date=2019-03-12|title=A Juvenile Specimen of the Trematopid Acheloma From Richards Spur, Oklahoma and Challenges of Trematopid Ontogeny|journal=Frontiers in Earth Science|volume=7|pages=38|doi=10.3389/feart.2019.00038|issn=2296-6463|bibcode=2019FrEaS...7...38G|doi-access=free}}

Various analyses have confirmed hypotheses that Acheloma was a terrestrial temnospondyl.{{Cite journal|last1=Sanchez|first1=S.|last2=Germain|first2=D.|last3=De Ricqlès|first3=A.|last4=Abourachid|first4=A.|last5=Goussard|first5=F.|last6=Tafforeau|first6=P.|date=2010|title=Limb-bone histology of temnospondyls: implications for understanding the diversification of palaeoecologies and patterns of locomotion of Permo-Triassic tetrapods: Diversification of early tetrapod locomotion|journal=Journal of Evolutionary Biology|language=en|volume=23|issue=10|pages=2076–2090|doi=10.1111/j.1420-9101.2010.02081.x|pmid=20840306|doi-access=free}}{{Cite journal|last1=Quemeneur|first1=Sonia|last2=de Buffrénil|first2=Vivian|last3=Laurin|first3=Michel|date=2013|title=Microanatomy of the amniote femur and inference of lifestyle in limbed vertebrates: Femoral Microanatomy and Lifestyle|journal=Biological Journal of the Linnean Society|language=en|volume=109|issue=3|pages=644–655|doi=10.1111/bij.12066|doi-access=free}}

The following cladogram shows the phylogenetic position of Acheloma, from Polley & Reisz, 2011.

{{clade| style=font-size:85%;line-height:85%

|label1=Dissorophoidea

|1={{clade

|1=Sclerocephalus haeuseri

|2=Micromelerpeton credneri

|3={{clade

|1=Micropholis stowi

|2={{clade

|1=Eoscopus lockardi

|label2=Olsoniformes

|2={{clade

|1=Cacops morrisi

|label2=Trematopidae

|2={{clade

|1=Phonerpeton pricei

|2={{clade

|label1=Acheloma

|1={{clade

|1=Acheloma cumminsi

|2=Acheloma dunni }}

|2={{clade

|1=Actiobates peabodyi

|2={{clade

|1=Ecolsonia cutlerensis

|2={{clade

|1=Anconastes vesperus

|2=Tambachia trogallas }} }} }} }} }} }} }} }} }} }}

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Category:Dissorophidae

Category:Trematopidae

Category:Cisuralian temnospondyls of North America

Category:Prehistoric amphibian genera

Category:Taxa named by Edward Drinker Cope

Category:Fossil taxa described in 1882