| Acroplous Temporal range: Early Permian | |
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Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Order: | † Temnospondyli |
| Suborder: | † Dvinosauria |
| Family: | † Eobrachyopidae |
| Genus: | † Acroplous Hotton, 1959 |
| Type species | |
| Acroplous vorax Hotton, 1959 | |
Acroplous is an extinct genus of dvinosaurian Temnospondyli within the family Eobrachyopidae. [1]
Acroplous was described by Nicholas Hotton in 1959 for the type species, A. vorax. [2] The type locality is in Riley County, Kansas within the Speiser Shale (early Permian). The original description only described the holotype (KUVP 9822), a partially disarticulated skull with isolated, associated postcrania. The genus name comes from the Greek word for 'swimming at the top,' based on Hotton's inference of the animal as being a surface cruising animal. The species name comes from the inferred voracity of the taxon. Hotton suggested that some material from the Dunkard Group of Pennsylvania that had been previously described by Romer (1952) [3] as 'Saurerpeton obtusum' might represent an Appalachian occurrence of Acroplous. However, this material is not considered to belong to either Acroplous or to Isodectes , the senior synonym of Saurerpeton, and instead has been listed as merely Dvinosauroidea incertae sedis by Schoch & Milner (2014). [1] The type locality was reopened in 1971 by Orville Bonner and Larry Martin at the University of Kansas, which led to the discovery of additional vertebrate material, including a new specimen of Acroplous that was described by Coldiron (1978). [4] Like the holotype, this specimen also consisted of a partially disarticulated skull with isolated, associated postcrania. Coldiron also presented one of the earliest phylogenies of Dvinosauria (see also [5] [6] for discussion of relationships), but these early analyses in general were compromised by the perception of the time that brachyopoids were closely related to dvinosaurs, whereas this has not been supported by more recent cladistic analyses. [7] [8] [9] Nonetheless, these workers were correct in identifying many similarities with Isodectes, which is currently the only other eobrachyopid.
Additional material of Acroplous was discovered from another locality in the Speiser Shale about 40 miles from the type locality in Wabaunsee County, Kansas in 1976. This material was described by Foreman (1990), who also noted additional, previously undescribed material from the type locality. [10] The specimens described by Foreman were the most completely known skulls, which permitted a complete cranial reconstruction. Foreman continued the framework in which Acroplous was placed in the same family as Isodectes (Saurerpetontidae, now a junior synonym of Eobrachyopidae following synonymy of Saurerpeton with Isodectes). Most recently, Englehorn et al. (2008) described new material of Acroplous from several localities in Eskridge Formation exposures in Richardson County, Nebraska as well as another specimen from the type locality that had been collected by Hotton in the 1960s. [11] The Nebraska exposures (the "Humboldt localities") are thought to be Asselian in age and thus older than the horizons from the Speiser Shale. This description provided additional information on the skull based on the most completely known specimens and the most detailed information on the lower jaw. By 2008, the notion that dvinosaurs and brachyopoids were closely related had fallen out of favor, and thus Englehorn et al.'s phylogenetic analysis only sampled other Paleozoic taxa, in which they recovered Acroplous as closely related to Isodectes.
Acroplous is diagnosed by several autapomorphies (among dvinosaurs), including an internarial fenestra between the premaxillae; anteroposteriorly shortened postparietals; and interlocking mandibular symphyses formed by medially projecting prongs. Compared to Isodectes, it has a proportionately broader skull (wider than long), lacks an intertemporal, and has less developed lateral line grooves. Notably, the most complete specimens of Acroplous are smaller than those represented by more fragmentary or isolated cranial remains, which suggests that previous descriptions have been based on sub-adult or juvenile material. [11]
Historically, Acroplous has been placed in the same family as Isodectes (and associated junior synonyms with Saurerpeton). However, this family has sometimes been recovered as paraphyletic within the broader Dvinosauroidea. [12] [13] [14] Below is the phylogeny from Marsicano et al. (2021): [14]
| Dvinosauria |
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Dissorophidae is an extinct family of medium-sized, temnospondyl amphibians that flourished during the late Carboniferous and early Permian periods. The clade is known almost exclusively from North America.
Temnospondyli is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few species continued into the Jurassic and Cretaceous periods. Fossils have been found on every continent. 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 considered amphibians, many had characteristics, such as scales and armour-like bony plates, that distinguish them from modern amphibians (lissamphibians).
Dvinosaurs are one of several new clades of Temnospondyl amphibians named in the phylogenetic review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from the Late Carboniferous to the Early Triassic, being most common in the Permian period. Their distinguishing characteristics are a reduction of the otic notch; the loss of a flange on the rear side of the pterygoid; and 28 or more presacral vertebrae.
Eryosuchus is an extinct genus of capitosauroid temnospondyl amphibian 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.
Dvinosaurus is an extinct genus of amphibious temnospondyls localized to regions of western and central Russia during the middle and late Permian, approximately 265-254 million years ago. Its discovery was first noted in 1921 by Russian paleontologist Vladimir Prokhorovich Amalitskii in a posthumously published paper that documents the findings of a site in Russia's Arkhangelsk District. Its name is derived from the proximity of this site to the Northern Dvina River.
Brachyopoidea is a superfamily of temnospondyls that lived during the Mesozoic. It contains the families Brachyopidae and Chigutisauridae. The earliest records of brachyopids are from the Lower Triassic in Australia. The latest-surviving member of the superfamily is the chigutisaurid Koolasuchus from the Early Cretaceous of Australia.
Lydekkerinidae is a family of stereospondyl temnospondyls that lived in the Early Triassic period. During this time period, lydekkerinids were widely distributed, with putative remains reported from Russia, Greenland, India, South Africa, Madagascar, Australia, and Antarctica. In contrast to most other stereospondyls, lydekkerinids were relatively small-bodied. The type genus is Lydekkerina, the namesake of the family and the best-known lydekkerinid.
Eobrachyopidae is a family of dvinosaurian temnospondyls.
Trematopidae is a family of dissorophoid temnospondyl spanning the late Carboniferous to the early Permian. Together with Dissorophidae, the family forms Olsoniformes, a clade comprising the medium-large terrestrial dissorophoids. Trematopids are known from numerous localities in North America, primarily in New Mexico, Oklahoma, and Texas, and from the Bromacker quarry in Germany.
Bothriceps is an extinct genus of stereospondyl temnospondyl. It is a member of the infraorder Trematosauria and is the most basal brachyopomorph known. It is one of the only brachyopomorph that lies outside the superfamily Brachyopoidea, which includes the families Brachyopidae and Chigutisauridae. It shares several similarities to Keratobrachyops, another basal brachyopomorph, and may be closely related to or even synonymous with it.
Tersomius is an extinct genus of dissorophoid temnospondyl within the family Micropholidae. It is known from the early Permian of North America.
Micropholis is an extinct genus of dissorophoid temnospondyl. Fossils have been found from the Lystrosaurus Assemblage Zone of the Karoo Basin in South Africa and are dated to the Induan. Fossils have also been found from the lower Fremouw of Antarctica.Micropholis is the only post-Permian dissorophoid and the only dissorophoid in what is presently the southern hemisphere and what would have been termed Gondwana during the amalgamation of Pangea.
Pasawioops is an extinct genus of early Permian dissorophoid temnospondyl within the clade Amphibamiformes.
Rubeostratilia is an extinct genus of amphibamiform temnospondyl from the early Permian of Texas. It is known from a single skull. This genus was named by Hélène Bourget and Jason S. Anderson in 2011, and the type species is Rubeostratilia texensis. The genus name comes from the Latin translation of 'redbeds' in reference to the Texas redbeds that produced both the holotype and many other early Permian fossils. The specific name is for the state of Texas. The holotype and only known specimen was collected in 1941 from the Nocona Formation exposures in Clay County by a Works Projects Administration project that was transferred to the Field Museum of Natural History through an interinstitutional exchange with the Texas Memorial Museum.
Perryella is an extinct genus of dvinosaurian(?) temnospondyl from the Permian of Oklahoma.
Vigilius is an extinct genus of brachyopid temnospondyl amphibian from the Triassic of Arizona. It is known from the single type species Vigilius wellesi.
Proxilodon is an extinct genus of recumbirostran microsaur from the Early Permian Speiser Formation of Kansas, United States. It contains a single species, Proxilodon bonneri,.
The Micropholidae are an extinct family of dissorophoid euskelian temnospondyls known from Late Carboniferous to Early Triassic strata in the United States and South Africa.
Amphibamiformes is an unranked clade with Dissorophoidea created by Schoch (2018). It encompasses all of the taxa traditionally considered to be "amphibamids", branchiosaurids, and hypothetically lissamphibians under the traditional temnospondyl hypothesis of lissamphibian origins. These taxa are typically small-bodied dissorophoids and form the sister group to Olsoniformes, which comprises dissorophids and trematopids.
Procuhy is an extinct genus of dvinosaurian temnospondyl amphibian in the family Trimerorhachidae represented by the type species Procuhy nazariensis from the Early Permian of Brazil.
