| Scincosaurus Temporal range: Late Carboniferous, | |
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Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Sarcopterygii |
| Clade: | Tetrapodomorpha |
| Order: | † Nectridea |
| Family: | † Scincosauridae |
| Genus: | † Scincosaurus Frič, 1876 |
| Type species | |
| †Scincosaurus crassus Frič, 1876 | |
| Species | |
†S. crassusFrič, 1876 | |
Scincosaurus is an extinct genus of nectridean tetrapodomorphs within the family Scincosauridae. [1]
Scincosaurus crassus was first described by Bohemian paleontologist Antonín Frič in volume 1875 of "Sitzungsberichte der königlichen Böhmischen Gesellschaft der Wissenschaften in Prague", which at that time was the premiere scientific journal of Bohemia (the modern day Czech Republic). Frič's contribution to this volume was a list of Carboniferous animals he and his associates recently discovered at coal gas mines near the localities of Nýřany and Kounová. His list included short preliminary descriptions for many new genera and species of tetrapods, including Microbrachis, Branchiosaurus, Hyloplesion (at that time called Stelliosaurus), and Sparodus.Scincosaurus crassus was among the new tetrapods from Nýřany, and its short description (erroneously) considered it a robust lacertilian (lizard), possibly related to Sparodus. [2]
A much larger description was published in 1881 as part of one of Frič's personal monographs which focused entirely on the paleontology of Bohemia. Within this monograph, Frič identified Scincosaurus crassus as a nectridean and provided a comprehensive overview of the taxa's anatomy. He noticed a pair of prong-like bones near the back of the skull of one specimen, which he was convinced were examples of tabular horns. These horns, which form from the tabular bones at the rear of the skull, are characteristic of diplocaulids, and as a result Frič renamed Scincosaurus crassus to Keraterpeton crassum, a new species of the basal diplocaulid Keraterpeton. [3]
In 1895, the idea that Scincosaurus crassus was simply a species of Keraterpeton was reevaluated and subsequently refuted. While studying a specimen of Keraterpeton galvani (the type species of Keraterpeton), British paleontologist C.W. Andrews noticed that there were many differences between skulls of that species and Keraterpeton crassum (a.k.a. Scincosaurus crassus). K. galvani had fairly large eyes positioned close to each other on the skull, while K. crassum had small and widely separated eyes. The skull of K. crassum was more heavily sculptured by pits and grooves and did not possess a significant overhang of the braincase, in contrast to K. galvani. The purported tabular horns were seemingly separated from the rest of the skull by means of a ball-and-socket joint, while no such delineation existed for K. galvani, whose horns were simply rear branches of the tabular bones. As a result, he resurrected the genus Scincosaurus for "Keraterpeton" crassum, although he retained the misspelled specific name, "crassum". [4] Subsequent authors would correct this error by referring to the species as Scincosaurus crassus as Frič originally did in 1876. In 1903, German paleontologist Otto Jaekel noted that he could not find any evidence of the supposed jointed tabular horns on any Scincosaurus specimens. He supposed that Frič may have erroneously mistaken bones of the shoulder girdle (such as a scapula, or shoulder blade) for the horns. [5]
In 1909, Jaekel placed Scincosaurus within its own family, Scincosauridae. However, he did not consider scincosaurs to be part of Nectridea, which to him was restricted to the horned diplocaulids. Instead, scincosaurids were allied with the long-tailed urocordylids and snake-like ophiderpetontids in an order he called Urosauri. Urosaurs, nectrideans, and several other groups of early tetrapods were all considered to belong to the class Microsauria. Microsauria was kept separate from traditional linnean classes such as Reptilia, Mammalia, and Amphibia, due to paleontologists of the time being generally uncertain whether they were reptile-like amphibians or amphibian-like reptiles. [6] Following Jaekel's hypothesis, Robert Broom used Scincosaurus as a representative of microsaurs during his 1921 study on tetrapod ankle bones. [7]
As the 20th century proceeded, Scincosaurus fell into obscurity. However, by the 1960s sources which did discuss it once again considering it a member of Nectridea outside of Microsauria. During his 1963 monograph on the advanced diplocaulid Diploceraspis , J.R. Beerbower placed Scincosaurus as a basal diplocaulid closely related to Batrachiderpeton in a subfamily he called Batrachiderpetoninae. [8] Even so, Scincosaurus was still distantly related to microsaurs, as a growing body of evidence suggested that microsaurs were not reptiles, but relatives of the nectrideans within a subgroup of amphibians called Lepospondyli. [9] [10]
In 1982, a second species of Scincosaurus was named by C. Civet: Scincosaurus spinosus. This species, which was found in Carboniferous deposits near Montceau-les-Mines in France, is well-preserved yet poorly described. [11] During their description of the urocordylid Montcellia in 1994, Jean-Michel Dutuit and D. Heyler considered that S. spinosus may not belong to Scincosaurus, but rather its French close relative Sauravus . [12] Phylogenetic studies on nectrideans conducted by Andrew Milner, Angela Milner, and Marcello Ruta have consistently found Scincosaurus to be a member of the order since 1978. One of these studies, Milner & Ruta (2009), included a large redescription and reinterpretation of Scincosaurus crassus. [1]
Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco, lepospondyls lived from the Early Carboniferous (Mississippian) to the Early Permian and were geographically restricted to what is now Europe and North America. Five major groups of lepospondyls are known: Adelospondyli; Aïstopoda; Lysorophia; Microsauria; and Nectridea. Lepospondyls have a diverse range of body forms and include species with newt-like, eel- or snake-like, and lizard-like forms. Various species were aquatic, semiaquatic, or terrestrial. None were large, and they are assumed to have lived in specialized ecological niches not taken by the more numerous temnospondyl amphibians that coexisted with them in the Paleozoic. Lepospondyli was named in 1888 by Karl Alfred von Zittel, who coined the name to include some tetrapods from the Paleozoic that shared some specific characteristics in the notochord and teeth. Lepospondyls have sometimes been considered to be either related or ancestral to modern amphibians or to Amniota. It has been suggested that the grouping is polyphyletic, with aïstopods being primitive stem-tetrapods, while recumbirostran microsaurs are primitive reptiles.
Adelospondyli is an order of elongated, presumably aquatic, Carboniferous amphibians. They have a robust skull roofed with solid bone, and orbits located towards the front of the skull. The limbs were almost certainly absent, although some historical sources reported them to be present. Despite the likely absence of limbs, adelospondyls retained a large part of the bony shoulder girdle. Adelospondyls have been assigned to a variety of groups in the past. They have traditionally been seen as members of the subclass Lepospondyli, related to other unusual early tetrapods such as "microsaurs", "nectrideans", and aïstopods. Analyses such as Ruta & Coates (2007) have offered an alternate classification scheme, arguing that adelospondyls were actually far removed from other lepospondyls, instead being stem-tetrapod stegocephalians closely related to the family Colosteidae.
Westlothiana is a genus of reptile-like tetrapod that lived about 338 million years ago during the latest part of the Viséan age of the Carboniferous. Members of the genus bore a superficial resemblance to modern-day lizards. The genus is known from a single species, Westlothiana lizziae. The type specimen was discovered in the East Kirkton Limestone at the East Kirkton Quarry, West Lothian, Scotland in 1984. This specimen was nicknamed "Lizzie the lizard" by fossil hunter Stan Wood, and this name was quickly adopted by other paleontologists and the press. When the specimen was formally named in 1990, it was given the specific name "lizziae" in homage to this nickname. However, despite its similar body shape, Westlothiana is not considered a true lizard. Westlothiana's anatomy contained a mixture of both "labyrinthodont" and reptilian features, and was originally regarded as the oldest known reptile or amniote. However, updated studies have shown that this identification is not entirely accurate. Instead of being one of the first amniotes, Westlothiana was rather a close relative of Amniota. As a result, most paleontologists since the original description place the genus within the group Reptiliomorpha, among other amniote relatives such as diadectomorphs and seymouriamorphs. Later analyses usually place the genus as the earliest diverging member of Lepospondyli, a collection of unusual tetrapods which may be close to amniotes or lissamphibians, or potentially both at the same time.
Eucritta is an extinct genus of stem-tetrapod from the Viséan epoch in the Carboniferous period of Scotland. The name of the type and only species, E. melanolimnetes is a homage to the 1954 horror film Creature from the Black Lagoon.
Keraterpeton is an extinct genus of "nectridean" tetrapodomorphs, previously included within the monotypic Keraterpedontidae family, from the Carboniferous period of Europe and North America ; it is the oldest known member of the family Diplocaulidae.
Diplocaulus is an extinct genus of lepospondyl amphibians which lived from the Late Carboniferous to the Late Permian of North America and Africa. Diplocaulus is by far the largest and best-known of the lepospondyls, characterized by a distinctive boomerang-shaped skull. Remains attributed to Diplocaulus have been found from the Late Permian of Morocco and represent the youngest-known occurrence of a lepospondyl.
Nectridea is the name of an extinct order of lepospondyl tetrapods from the Carboniferous and Permian periods, including animals such as Diplocaulus. In appearance, they would have resembled modern newts or aquatic salamanders, although they are not close relatives of modern amphibians. They were characterized by long, flattened tails to aid in swimming, as well as numerous features of the vertebrae.
Diplovertebron is an extinct genus of embolomere that lived in the Late Carboniferous period (Moscovian), about 310 million years ago. Diplovertebron was a medium-sized animal, around 50 cm in length. Members of the genus inhabited European Carboniferous swamps in what is now the Czech Republic. They were closely related to larger swamp-dwelling tetrapods like Proterogyrinus and Anthracosaurus. However, Diplovertebron were much smaller than these large, crocodile-like creatures. Known from a single species, Diplovertebron punctatum, this genus has had a complicated history closely tied to Gephyrostegus, another genus of small, reptile-like amphibians.
Spathicephalus is an extinct genus of stem tetrapods that lived during the middle of the Carboniferous Period. The genus includes two species: the type species S. mirus from Scotland, which is known from two mostly complete skulls and other cranial material, and the species S. pereger from Nova Scotia, which is known from a single fragment of the skull table. Based on the S. mirus material, the appearance of Spathicephalus is unlike that of any other early tetrapod, with a flattened, square-shaped skull and jaws lined with hundreds of very small chisel-like teeth. However, Spathicephalus shares several anatomical features with a family of stem tetrapods called Baphetidae, leading most paleontologists who have studied the genus to place it within a larger group called Baphetoidea, often as part of its own monotypic family Spathicephalidae. Spathicephalus is thought to have fed on aquatic invertebrates through a combination of suction feeding and filter feeding.
Actinodon is an extinct genus of eryopoidean temnospondyl within the family Eryopidae.
Acherontiscus is an extinct genus of stegocephalians that lived in the Early Carboniferous of Scotland. The type and only species is Acherontiscus caledoniae, named by paleontologist Robert Carroll in 1969. Members of this genus have an unusual combination of features which makes their placement within amphibian-grade tetrapods uncertain. They possess multi-bone vertebrae similar to those of embolomeres, but also a skull similar to lepospondyls. The only known specimen of Acherontiscus possessed an elongated body similar to that of a snake or eel. No limbs were preserved, and evidence for their presence in close relatives of Acherontiscus is dubious at best. Phylogenetic analyses created by Marcello Ruta and other paleontologists in the 2000s indicate that Acherontiscus is part of Adelospondyli, closely related to other snake-like animals such as Adelogyrinus and Dolichopareias. Adelospondyls are traditionally placed within the group Lepospondyli due to their fused vertebrae. Some analyses published since 2007 have argued that adelospondyls such as Acherontiscus may not actually be lepospondyls, instead being close relatives or members of the family Colosteidae. This would indicate that they evolved prior to the split between the tetrapod lineage that leads to reptiles (Reptiliomorpha) and the one that leads to modern amphibians (Batrachomorpha). Members of this genus were probably aquatic animals that were able to swim using snake-like movements.
Boii is an extinct genus of microsaur within the family Tuditanidae. It was found in Carboniferous coal from mines near the community of Kounov in the Czech Republic. The only remains of the genus consist of a crushed skull, shoulder girdle bones, and scales, which were similar to microsaurian elements originally referred to Asaphestera. Boii can be characterized by its heavily sculptured skull, thin ventral plate of the clavicles, and a larger number of fangs on the roof of the mouth. For many years the type and only known species, Boii crassidens, was considered to be a species of Sparodus, until 1966 when Robert Carroll assigned it to its own genus.
Batropetes is an extinct genus of brachystelechid recumbirostran "microsaur". Batropetes lived during the Sakmarian stage of the Early Permian. Fossils attributable to the type species B. fritschi have been collected from the town of Freital in Saxony, Germany, near the city of Dresden. Additional material has been found from the Saar-Nahe Basin in southwestern Germany and has been assigned to three additional species: B. niederkirchensis, B. palatinus, and B. appelensis.
Odonterpeton is an extinct genus of "microsaur" from the Late Carboniferous of Ohio, containing the lone species Odonterpeton triangulare. It is known from a single partial skeleton preserving the skull, forelimbs, and the front part of the torso. The specimen was found in the abandoned Diamond Coal Mine of Linton, Ohio, a fossiliferous coal deposit dated to the late Moscovian stage, about 310 million years ago.
Rhynchonkos is an extinct genus of rhynchonkid microsaur. Originally known as Goniorhynchus, it was renamed in 1981 because the name had already been given to another genus; the family, likewise, was originally named Goniorhynchidae but renamed in 1988. The type and only known species is R. stovalli, found from the Early Permian Fairmont Shale in Cleveland County, Oklahoma. Rhynchonkos shares many similarities with Eocaecilia, an early caecilian from the Early Jurassic of Arizona. Similarities between Rhynchonkos and Eocaecilia have been taken as evidence that caecilians are descendants of microsaurs. However, such a relationship is no longer widely accepted.
Hyloplesion is an extinct genus of microbrachomorph microsaur. It is the type and only genus within the family Hyloplesiontidae. Fossils have been found from the Czech Republic near the towns of Plzeň, Nýřany, and Třemošná, and date back to the Middle Pennsylvanian. The type species is H. longicostatum, named in 1883. Two species belonging to different genera, Seeleya pusilla and Orthocosta microscopica, have been synonymized with H. longicostatum and are thought to represent very immature individuals.
Altenglanerpeton is an extinct genus of microsaur tetrapod from the Late Carboniferous or Early Permian of Germany. Altenglanerpeton was named in 2012 after the Altenglan Formation in which it was found. The type and only species is A. schroederi.
The Urocordylidae are an extinct family of nectridean lepospondyl amphibians. Urocordylids lived during the Late Carboniferous and Early Permian in what is now Europe and North America and are characterized by their very long, paddle-like tails. In life, they were probably newt-like and aquatic.
Ductilodon is an extinct genus of nectridean tetrapodomorphs in the family Diplocaulidae. The type and only species Ductilodon pruitti was named in 1999 from the Early Permian of Kansas. Distinguishing features of Ductilodon include horns that project backward from the skull and an arched row of teeth on the palate. Ductilodon is most closely related to the diplocaulids Diplocaulus and Diploceraspis.
Hylerpeton is an extinct genus of microsaurian tetrapods belonging to the family Gymnarthridae from the late Carboniferous period.
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