| Actinodon Temporal range: Early Permian, | |
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| Actinodon sp. at the Museum of Natural History, Autun | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Order: | † Temnospondyli |
| Family: | † Eryopidae |
| Genus: | † Actinodon Gaudry, 1866 |
| Type species | |
| †Actinodon frossardi Gaudry, 1866 | |
Actinodon is an extinct genus of eryopoidean temnospondyl within the family Eryopidae.
Actinodon was named in 1866 by French paleontologist Jean Albert Gaudry based on a holotype skull that was collected by Charles Frossard near Muse in the Autun Basin (early Permian) of France. [1] 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 in 1996. [2] 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. [3] [4] [5] Werneburg & Steyer (1999) were the most recent to redescribe material of this taxon, [6] and they referred it to the eryopoid Onchiodon as a valid species, while Schoch & Milner (2000) argued that it might be a species of the stereospondylomorph Sclerocephalus, [7] but phylogenetic analyses have not recovered A. frossardi in a clade with the type species of either genus (O. labyrinthicus, S. haeuseri), [8] [9] and Schoch & Milner (2014) maintained it separate from Onchiodon. [10]
Other species of Actinodon remain synonymized with other species: A. brevis and Euchirosaurus rochei with A. frossardi; and A. germanicus with Cheliderpeton vranyi . [11] 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 . [12] [6] 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.
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 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 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.
Below is the phylogeny of Eryopidae from Schoch (2021): [9]
| Eryopidae |
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Temnospondyli or temnospondyls is a diverse ancient order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent. A few species continued into the Jurassic and Early Cretaceous periods, but all had gone extinct by the Late Cretaceous. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including freshwater, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are amphibians, many had characteristics such as scales and armour-like bony plates that distinguish them from the modern soft-bodied lissamphibians.
Eryopidae were a group of medium to large amphibious temnospondyls, known from North America and Europe. They are defined as all eryopoids with interpterygoid vacuities that are rounded at the front; and large external nares. Not all of the genera previously included in the Eryopidae are retained under the cladistic revisions.
Zygosaurus is an extinct genus of dissorophid temnospondyl from the Middle-Late Permian of Russia. It was described in 1848 by Eduard Eichwald, making it the first dissorophid to be described and is known from a single species, Zygosaurus lucius. The location of the holotype, and only known specimen, is unknown, and although casts are reposited in several institutions, little is known about this taxon beyond qualitative aspects of the skull. The skull was estimated to be around 20 cm in length, making it one of the largest dissorophids, being only slightly smaller than Kamacops.
Eryosuchus is an extinct genus of capitosauroid temnospondyl from the Middle Triassic of northern Russia. It was a very large predator: the largest specimen known could reach up to 3.5 m (11.5 ft) in length, with a skull over 1 m long.
Sclerocephalus is an extinct genus of temnospondyl amphibian from the lowermost Permian of Germany and Czech Republic with four valid species, including the type species S. haeuseri. It is one of the most completely preserved and most abundant Palaeozoic tetrapods. Sclerocephalus was once thought to be closely related to eryopoid temnospondyls, but it is now thought to be more closely related to archegosauroids. It is the only genus in the family Sclerocephalidae.
Cheliderpeton is an extinct genus of temnospondyl amphibian. It lived during the Early Permian in what is now Europe. Fossils have been found from the Ruprechtice horizon of the Intrasudetic Basin of Bohemia in the Czech Republic, as well as the Saar-Nahe Basin of southwestern Germany. Cheliderpeton had a 16 cm skull, and reached about 65 cm in length.
Intasuchus is an extinct genus of temnospondyl amphibian from the Middle Permian of Russia. It is known from a single species, Intasuchus silvicola, which was named in 1956. Intasuchus belongs to the family Intasuchidae and is probably its sole member, although other taxa such as Syndyodosuchus and Cheliderpeton have been assigned to the family in the past. Intasuchus most likely belongs to the group Archegosauroidea, Permian relatives of the large, mostly Mesozoic temnospondyl clade Stereospondyli.
Trematosaurus is an extinct genus of trematosaurid temnospondyl amphibian found in Germany and Russia. It was first named by Hermann Burmeister in 1849 and the type species is Trematosaurus brauni.
Stereospondylomorpha is a clade of temnospondyls. It includes the superfamily Archegosauroidea and the more diverse group Stereospondyli. Stereospondylomorpha was first proposed by Yates and Warren (2000), who found Archegosauroidea and Stereospondyli to be sister taxa in their phylogenetic analysis. A similar clade is Archegosauriformes, named by Schoch and Milner (2000), which includes Stereospondyli and some Permian temnospondyls that are similar in appearance to stereospondyls, including the archegosauroids. However, according to Schoch and Milner's phylogeny, Archegosauroidea is a paraphyletic group of taxa that are successively basal to Stereospondyli, rather than a monophyletic sister taxon.
Actiobates is an extinct genus of trematopid temnospondyl that lived during the Late Carboniferous. It is known from the Garnett Quarry in Kansas.
Laccosaurus is an extinct monotypic genus of rhinesuchid temnospondyl, the type species being Laccosaurus watsoni.
Plagiosuchus is an extinct genus of plagiosaurid temnospondyl. It is known from several collections from the Middle Triassic of Germany.
Tersomius is an extinct genus of dissorophoid temnospondyl within the family Micropholidae. It is known from the early Permian of North America.
The Amphibamidae are an ancient family of dissorophoid temnospondyls known from Late Carboniferous-Early Permian strata in the United States.
Olsoniformes is a clade of dissorophoid temnospondyls, including the families Dissorophidae and Trematopidae. Most members of the clade were highly adapted to a terrestrial lifestyle. The clade was named in 2008 and is defined as the least inclusive clade containing Dissorophus multicinctus and Acheloma cumminsi but not Amphibamus grandiceps, Micromelerpeton credneri, or Apateon pedestris. Olsoniforms share various features such as a stout and low ilium and a thin cultriform process. The earliest-branching olsoniform is Palodromeus bairdi, from the Late Carboniferous of Ohio.
Parioxys is an extinct genus of temnospondyl amphibian from the Early Permian of Texas.
Acanthostomatops is an extinct genus of zatracheidid temnospondyl from the Lower Permian Döhlen Basin of Saxony.
Palatinerpeton is an extinct genus of temnospondyl amphibian. Fossils have been found in the Lauterecken-Odernheim Formation of Germany.
Korkonterpeton is a genus of temnospondyl from the Asselian of the Prosečné Formation. Its genus is named after the Celtic name for the Krkonoše Mountains of the Czech Republic and the Ancient Greek word ἑρπετόν (herpetón), which means reptile. Thus Korkonterpeton means "reptile of the Krkonoše Mountains". The type species, Korkonterpeton kalnense was described based on a partial skeleton with a large skull, which is visible in dorsal and palatal views. The postcranial skeleton is disarticulated but with well-preserved elements, including the vertebral column and the ribs.
Stenokranio is a genus of eryopid temnospondyl from the Permo-Carboniferous Remigiusberg Formation of Germany. It is represented by the type species, Stenokranio boldi, which was named for two specimens collected from the Remigiusberg quarry near Kusel, Saar–Nahe Basin, southwest Germany.
