| Doragnathus Temporal range: Early Carboniferous | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Superclass: | Tetrapoda |
| Class: | incertae sedis |
| Genus: | † Doragnathus Smithson, 1980 |
| Type species | |
| †Doragnathus woodi Smithson, 1980 | |
Doragnathus is an extinct genus of stem-tetrapod from the Early Carboniferous of Scotland. [1]
Sarcopterygii — sometimes considered synonymous with Crossopterygii — is a clade of bony fish commonly referred to as lobe-finned fish. They are characterised by prominent muscular limb buds (lobes) within their fins, which are supported by articulated appendicular skeletons. This is in contrast to the other clade of bony fish, the Actinopterygii, which have only skin-covered bony spines supporting the fins.
Jennifer Alice Clack, was an English palaeontologist and evolutionary biologist. She specialised in the early evolution of tetrapods, specifically studying the "fish to tetrapod" transition: the origin, evolutionary development and radiation of early tetrapods and their relatives among the lobe-finned fishes. She is best known for her book Gaining Ground: the Origin and Early Evolution of Tetrapods, published in 2002 and written with the layperson in mind.
"Labyrinthodontia" is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras. Traditionally considered a subclass of the class Amphibia, modern classification systems recognize that labyrinthodonts are not a formal natural group (clade) exclusive of other tetrapods. Instead, they consistute an evolutionary grade, ancestral to living tetrapods such as lissamphibians and amniotes. "Labyrinthodont"-grade vertebrates evolved from lobe-finned fishes in the Devonian, though a formal boundary between fish and amphibian is difficult to define at this point in time.
Romer's gap is an example of an apparent gap in the tetrapod fossil record used in the study of evolutionary biology. Such gaps represent periods from which excavators have not yet found relevant fossils. Romer's gap is named after paleontologist Alfred Romer, who first recognised it in 1956. Recent discoveries in Scotland are beginning to close this gap in palaeontological knowledge.
Lethiscus is the earliest known representative of the Aistopoda, a group of very specialised snake-like tetrapodomorphs known from the early Carboniferous (Mississippian).
Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs positioned close to, but outside of the clade Amniota, though some recent research has recovered them as the sister group to the traditional Synapsida within Amniota, based on inner ear anatomy and cladistic analyses. They include both large carnivorous and even larger herbivorous forms, some semi-aquatic and others fully terrestrial. The diadectomorphs seem to have originated during late Mississippian times, although they only became common after the Carboniferous rainforest collapse and flourished during the Late Pennsylvanian and Early Permian periods.
Casineria is an extinct genus of tetrapod which lived about 340-334 million years ago in the Mississippian epoch of the Carboniferous period. Its generic name, Casineria, is a latinization of Cheese Bay. The site near Edinburgh, Scotland where the holotype fossil was found. When originally described in 1999, it was identified as a transitional fossil noted for its mix of basal (amphibian-like) and advanced (reptile-like) characteristics, putting it at or very near the origin of the amniotes, the group containing all mammals, birds, modern reptiles, and other descendants of their reptile-like common ancestor. However, the sole known fossil is lacking key elements such as a skull, making exact analysis difficult. As a result, the classification of Casineria has been more controversial in analyses conducted since 1999. Other proposed affinities include a placement among the lepospondyls, seymouriamorphs, "gephyrostegids", or as a synonym of Caerorhachis, another controversial tetrapod which may have been an early temnospondyl.
Crassigyrinus is an extinct genus of carnivorous stem tetrapod from the Early Carboniferous Limestone Coal Group of Scotland and possibly Greer, West Virginia.
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.
Whatcheeriidae is an extinct family of stem-tetrapods which lived in the Mississippian sub-period, a subdivision of the Carboniferous period. It contains the genera Pederpes, Whatcheeria, and possibly Ossinodus. Fossils of a possible whatcheeriid have been found from the Red Hill locality of Pennsylvania. If these remains are from a whatcheeriid, they extend the range of the family into the Late Devonian and suggest that advanced tetrapods may have lived alongside primitive tetrapod ancestors like Hynerpeton and Densignathus. They also imply that a very long ghost lineage of whatcheeriids lived through Romer's gap, a period during the Early Carboniferous conspicuously lacking in tetrapod remains.
Pederpes is an extinct genus of early Carboniferous tetrapod, dating from 348 to 347.6 Ma in the Tournaisian age. Pederpes contains one species, P. finneyae, 1 m long.
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.
Caerorhachis is an extinct genus of early tetrapod from the Early Carboniferous of Scotland, probably from the Serpukhovian stage. Its placement within Tetrapoda is uncertain, but it is generally regarded as a primitive member of the group. The type species C. bairdi was named in 1977.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. Tetrapods are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals. While most species today are terrestrial, little evidence supports the idea that any of the earliest tetrapods could move about on land, as their limbs could not have held their midsections off the ground and the known trackways do not indicate they dragged their bellies around. Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water. The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear. They are areas of active research and debate among palaeontologists at present.
The Ballagan Formation is a geologic formation in Scotland and England. It preserves fossils dating back to the early part of the Carboniferous period. Its name comes from the "Ballagan Beds" of Ballagan Glen, near Strathblane, which has a good example of this geological formation.
Aytonerpeton is an extinct genus of stem-tetrapod from the Ballagan Formation of Scotland. It was one of five new genera of early limbed vertebrates from the Ballagan Formation described by Clack et al. in 2016. These vertebrates were among the only known in the world from a period of time known as Romer's gap. Romer's gap, which spans most of the Mississippian age of the Carboniferous, is characterized by a comparative rarity of tetrapod and stem-tetrapod fossils compared to the periods of time directly older and younger than it. However, Aytonerpeton and other Ballagan stem-tetrapods help to close in this gap in the vertebrate fossil record.
Diploradus is an extinct genus of four-limbed stem-tetrapod from the Mississippian (mid-Tournaisian) of Scotland. It contains a single species, Diploradus austiumensis, based on an incomplete skull and jaw fragments from the Ballagan Formation at Burnmouth. The most complete part of the specimen, the lower jaw, was about 3.0 cm in length and possessed several rows of small, numerous teeth. It likely represents a juvenile animal. Diploradus was described in a 2016 study which was devised to fill in the tetrapod and stem-tetrapod faunas of Romer's gap, an interval of the early Carboniferous with few vertebrate fossils. It was one of five new genera named in this study, along with Aytonerpeton, Koilops, Ossirarus, and Perittodus.
Koilops is an extinct genus of four-limbed stem-tetrapod from the Mississippian (mid-Tournaisian) of Scotland. It contains a single species, Koilops herma, based on a mold of an 8.0 cm -long skull from the Ballagan Formation. A phylogenetic analysis in its original description places Koilops as a close relative of Tulerpeton and colosteids. Koilops was described in a 2016 study which was devised to fill in the tetrapod and stem-tetrapod faunas of Romer's gap, an interval of the early Carboniferous with few vertebrate fossils. It was one of five new genera named in this study, along with Aytonerpeton, Diploradus, Ossirarus, and Perittodus.
Ossirarus is an extinct genus of four-limbed stem-tetrapod from the Mississippian (mid-Tournaisian) of Scotland. It contains a single species, Ossirarus kierani, based on disarticulated skull and postcranial bones from the Ballagan Formation at Burnmouth. It would have had a large, pointed tabular horn and several minor traits shared with Devonian stem-tetrapods. Ossirarus was described in a 2016 study which was devised to fill in the tetrapod and stem-tetrapod faunas of Romer's gap, an interval of the early Carboniferous with few vertebrate fossils. It was one of five new genera named in this study, along with Aytonerpeton, Diploradus, Koilops, and Perittodus.
Perittodus is an extinct genus of four-limbed stem-tetrapod from the Mississippian (mid-Tournaisian) of Scotland. It contains a single species, Perittodus apsconditus, based on disarticulated skull and postcranial bones from the Ballagan Formation. The lower jaw of the holotype specimen was about 6.8 cm in length and had a pattern of dentition similar to the Devonian taxon Ymeria. Perittodus was described in a 2016 study which was devised to fill in the tetrapod and stem-tetrapod faunas of Romer's gap, an interval of the early Carboniferous with few vertebrate fossils. It was one of five new genera named in this study, along with Aytonerpeton, Diploradus, Koilops, and Ossirarus.
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