''Actinodon'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

eryopoidea Eryopoidea are a taxon of late Carboniferous and Permian temnospondyli amphibians, known from North America and Europe. Carroll includes no fewer than ten families, but Yates and Warren replace this with a cladistic approach and include three fa ...

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

within the

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

Eryopidae Eryopidae were a group of medium to large amphibious temnospondyli, known from North America and Europe. They are defined as all eryopoids with interpterygoid vacuities (spaces in the interpterygoid bone) that are rounded at the front; and larg ...

History of study

''Actinodon'' was named in 1866 by French paleontologist

Jean Albert Gaudry Jean Albert Gaudry (16 September 1827 – 27 November 1908) was a French geologist and palaeontologist. He was born at St Germain-en-Laye, and was educated at the Catholic Collège Stanislas de Paris. He was a notable proponent of theistic evo ...

based on a holotype skull that was collected by Charles Frossard near

Muse In ancient Greek religion and mythology, the Muses ( grc, Μοῦσαι, Moûsai, el, Μούσες, Múses) are the inspirational goddesses of literature, science, and the arts. They were considered the source of the knowledge embodied in the ...

in the Autun Basin (

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 (Son of Dave album), ''01'' (Son of Dave album), 2000 * 01 (Urban ...

) of

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

. The status and relationship of the taxon was long problematic because the holotype was thought to be lost, until it was rediscovered in the collections of the

Museum d'Histoire Naturelle The French National Museum of Natural History, known in French as the ' (abbreviation MNHN), is the national natural history museum of France and a ' of higher education part of Sorbonne Universities. The main museum, with four galleries, is loc ...

in 1996. In the intervening 130 years, a variety of specimens were described by other workers, some of which were attributed to other species or only to the genus level. Werneburg & Steyer (1999) were the most recent to redescribe material of this taxon, and they referred it to the eryopoid ''

Onchiodon ''Onchiodon'' is an extinct genus of temnospondyl. It is primarily known from the Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million yea ...

'' as a valid species, while Schoch & Milner (2000) argued that it might be a species of the stereospondylomorph ''Sclerocephalus'', but phylogenetic analyses have not recovered ''A. frossardi'' in a clade with the type species of either genus (''O. labyrinthicus'', ''S. haeuseri''), and Schoch & Milner (2014) maintained it separate from ''Onchiodon''. Other species of ''Actinodon'' remain synonymized with other species: ''A. brevis'' and ''Euchirosaurus rochei'' with ''A. frossardi''; and ''A. germanicus'' with '' Cheliderpeton vranyi''. Several other species have been previously placed in ''Actinodon'' after being named in other genera, but have since been restored to their original genera or placed elsewhere: '' Glanochthon latirostris'' and '' Lysipterygium risinense''. In the present concept, ''A. frossardi'' is the only species within the genus, and material of this taxon is only known from the early Permian of France.

Anatomy

''Actinodon'' has a similar skull profile to stereospondylomorphs like ''Sclerocephalus'', but like other eryopoids, it has a proportionately shorter and wider posterior skull table; a longer prefrontal with a pointed anterior end; and a sutured basicranial articulation. Within eryopoids, the anatomy is indeed very similar to ''Onchiodon'', and the continued separation of these genera by Schoch & Milner (2014) is based on a disagreement over the interpretation of two features purportedly shared between them, a wide

choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...

and palatal fangs only on the palatine and ectopterygoid, that Werneburg & Steyer (1999) identified. Schoch & Milner argued that the choana is actually slit-like, and that the size and number of teeth is more variable. Some of this also stems from perceptions over the

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

of ''Onchiodon'', of which there are several valid species. Material of ''Actinodon'' tends to be smaller than that of many other eryopoids, which may account for some of the more proportional differences.

Relationships

Below is the phylogeny of Eryopidae from Schoch (2021):

References

{{Taxonbar, from=Q41150306 Eryopids Prehistoric amphibian genera Permian temnospondyls of Europe