Kraterokheirodon

Last updated

Kraterokheirodon
Temporal range: Late Triassic,
225–213  Ma
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Clade: Reptiliomorpha
Clade: Amniota
Clade: incertae sedis
Genus:† Kraterokheirodon
Irmis & Parker, 2005
Species:
†K. colberti
Binomial name
†Kraterokheirodon colberti
Irmis & Parker, 2005

Kraterokheirodon ("cupped hand tooth") is an extinct genus of enigmatic tetrapod, that was possibly an amniote, from the Late Triassic Chinle Formation of Arizona. The type and only species is K. colberti. Although it is known only from two large teeth, their shape is so unlike those of any other animal that Kraterokheirodon cannot definitively be classified under any known group of tetrapods. Its discovery also indicates that our understanding of Late Triassic tetrapod diversity is still incomplete, with Kraterokheirodon representing an otherwise unknown lineage of large tetrapod in western North America.

Contents

Description

The teeth of Kraterokheirodon are broad and relatively large—27.7 mm across at their base and approximately 19 mm high—with an arched ridge across its crown. Without associated jaws, even the orientation of the teeth are unknown, but the ridge has been interpreted as running transversely across the tooth from side-to-side, rather than front to back. The tooth crown possesses six cusps, the innermost of which is the largest (12.5 mm across) while the second cusp is the smallest (4.8 mm across). The remaining four cusps are roughly equal in size. Each cusp bears a vertical ridge that run down either side of the tooth, although the ridge of cusp II is pinched off by the ridges of cusps I and III. Cusps IV, V and VI run down the side of each tooth and are angled outwards (labially), curving slightly towards the probable back of the tooth. Likewise, the crown expands and flattens out to form a shelf on what's presumed to be the back side of the teeth. One of the two specimens (AMNH 4947) possesses a clear root, and indicates that the teeth likely had a thecodont implantation, meaning the roots were not fused to the jaw bones and were embedded in sockets. Enamel is present only on the crown of the teeth, and shows patterns of wear indicating that the teeth occluded while eating. [1]

Although very little can be determined about the appearance of Kraterokheirodon, the size of its teeth indicate that they must have belonged to a large-bodied animal. [2]

History of discovery

The first tooth of Kraterokheirodon was collected in September, 1946 by Guy E. Hazen, a member of the USGS, from St. Johns in the Apache County of Arizona. He presented the tooth to palaeontologist Edwin ("Ned") Colbert that year, who redeposited the specimen at the American Museum of Natural History with the label AMNH 4947. A second tooth, PEFO 9984, was discovered in 1984 from the Petrified Forest National Park by Lynette Gillette, just north of the Dinosaur Hill Quarry. This tooth is less complete than AMNH 4947, missing the root and half of the crown. In 1995, these teeth were presumed to belong to a "huge" traversodont cynodont by Robert A. Long and Phillip A. Murry in a review of Late Triassic vertebrates from the southwestern United States. Both teeth were under study by Colbert until his death in 2001, and the specimens subsequently went missing. [1] [3]

In 2002, casts of both teeth and the original specimen of PEFO 9984 were rediscovered in Colbert's office, however the original specimen of AMNH 4947 remains missing. The teeth were then studied by palaeontologists Randy Irmis and William Parker, who would formally name them as the new taxon Kraterokheirodon colberti in 2005. The genus name is derived from the Ancient Greek krater (cup), kheiros (hand), and odon (tooth), to refer to the superficial resemblance of the teeth's shape to a cupped hand. The species was named in honour of Edwin "Ned" Colbert. Despite being incomplete, PEFO 9984 was designated as the holotype of Kraterokheirodon due to the original specimen of AMNH 4947 being lost. [1]

Although the exact field location is unknown, AMNH 4947 was likely collected from either the top of the Bluewater Creek Member or from the base of the Blue Mesa Member of the Chinle Formation, dated to the late Carnian between 217 and 225 Ma. PEFO 9984 was collected from the middle of the younger Petrified Forest Member, which has been dated to the early or middle Norian at approximately 213 Ma. This indicates that Kraterokheirodon had a long stratigraphic range, in spite of its rarity. [1] [2] [4]

Despite the inferred large body size and long stratigraphic range of Kraterokheirodon, there are as yet no known isolated body fossils that could potentially be attributed to this species. This is in spite almost a century of geological and palaeontological study of the Chinle Formation, and indicates that the faunal diversity of the Late Triassic is still incompletely understood, including unknown species of large tetrapods like Kraterokheirodon, even in well sampled locations such as western North America. [1] [2]

Classification

Although only known by its teeth, Kraterokheirodon was compared to the teeth of other Triassic vertebrate groups to try and determine its relationships, as teeth can be diagnostic to vertebrate lineages. However, the unique structure of its teeth does not match those seen in any other known fossils. The presence of thecodont roots in particular, present in both Archosauriformes and synapsids, supports an amniote affinity for Kraterokheirodon, and they likewise do not match any similar teeth known from lungfish or actinopterygian fish, as well as those of temnospondyl amphibians. [1]

Within Amniota, multiple lineages have multicusped teeth like Kraterokheirodon, including early archosauromorphs, crocodylomorphs, dinosaurs and pterosaurs, although they only show vague similarities to Kraterokheirodon. Superficially, Kraterokheirodon most closely resembles the lower postcanine teeth of traversodont cynodonts, including a ridge with vertical cusps and a posterior shelf at their base. However, in addition to being much larger than any known traversodont cynodont, Kraterokheirodon also possesses more cusps than any traversodont tooth (6 compared to 2 or 3), and they are arranged parallel to each other in traversodonts unlike the curving row of cusps in Kraterokheirodon. Furthermore, traversodonts possess enamel on the posterior shelf, which Kraterokheirodon lacks. [1]

Due to these differences, as well as the possibility that the features similar to traversodonts could be convergently evolved, rather than shared homologous structures, Irmis and Parker referred Kraterokheirodon to Amniota incertae sedis and suggested it belonged to an as yet unrecognised clade of tetrapods. [1]

Related Research Articles

<span class="mw-page-title-main">Aetosaur</span> Extinct order of heavily armoured reptiles

Aetosaurs are heavily armored reptiles belonging to the extinct order Aetosauria. They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs more closely related to crocodilians than to birds and other dinosaurs. All known aetosaurs are restricted to the Late Triassic, and in some strata from this time they are among the most abundant fossil vertebrates. They have small heads, upturned snouts, erect limbs, and a body ornamented with four rows of plate-like osteoderms. Aetosaur fossil remains are known from Europe, North and South America, parts of Africa, and India. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve as important Late Triassic tetrapod index fossils. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site in which they are found.

<i>Camposaurus</i> Extinct genus of dinosaurs

Camposaurus is a coelophysid dinosaur genus from the Norian stage of the Late Triassic period of North America. The pertinent fossil remains date back to the early to middle Norian stage, and is widely regarded as the oldest known neotheropod.

<i>Crosbysaurus</i> Genus of reptiles

Crosbysaurus is a genus of extinct archosauromorph that lived in the Late Triassic of Arizona, New Mexico, North Carolina, Texas, and Utah. It is known from the Chinle Formation and Dockum Group rock units from the southwestern United States. The type species is C. harrisae, and the only known material includes teeth. 11 specimens are known, each including a single tooth.

Lucianosaurus is an extinct genus of amniote of unknown affinities, known only from teeth. Initially described as a basal ornithischian dinosaur, subsequently reclassified as a member of the clade Archosauriformes of uncertain phylogenetic placement and later, taking into account the similarity of its teeth to the teeth of traversodontid cynodonts such as Dadadon, as an amniote of uncertain affinities.

<i>Acaenasuchus</i> Genus of reptiles

Acaenasuchus is an extinct genus of pseudosuchian, endemic to what would be presently be known as Arizona during the Late Triassic, specifically during the Carnian and Norian stages of the Triassic. Acaenasuchus had a stratigraphic range of approximately 11.5 million years. Acaenasuchus is further categorized as one of the type fauna that belong to the Adamanian LVF, based on the fauna of the Blue Mesa Member of the Chinle Petrified Forest Formation of Arizona, where Acaenasuchus was initially discovered.

<i>Prozostrodon</i> Extinct genus of cynodonts

Prozostrodon is an extinct genus of probainognathian cynodonts that was closely related to the ancestors of mammals. The remains were found in Brazil and are dated to the Carnian age of the Late Triassic. The holotype has an estimated skull length of 6.7 centimetres (2.6 in), indicating that the whole animal may have been the size of a cat. The teeth were typical of advanced cynodonts, and the animal was probably a carnivore hunting reptiles and other small prey.

Redondasaurus is an extinct genus of phytosaur from the Late Triassic of the southwestern United States. It was named by Hunt & Lucas in 1993, and contains two species, R. gregorii and R. bermani. It is the youngest and most evolutionarily-advanced of the phytosaurs.

<i>Progalesaurus</i> Extinct genus of cynodonts

Progalesaurus is an extinct genus of galesaurid cynodont from the early Triassic. Progalesaurus is known from a single fossil of the species Progalesaurus lootsbergensis, found in the Lystrosaurus Assemblage Zone of the Balfour Formation. Close relatives of Progalesaurus, other galesaurids, include Galesaurus and Cynosaurus. Galesaurids appeared just before the Permian-Triassic extinction event, and disappeared from the fossil record in the Middle-Triassic.

<i>Leptosuchus</i> Extinct genus of reptiles

Leptosuchus is an extinct genus of leptosuchomorph phytosaur with a complex taxonomical history. Fossils have been found from the Dockum Group and lower Chinle Formation outcropping in Texas, New Mexico, and Arizona, USA, and date back to the Carnian stage of the Late Triassic.

<i>Machaeroprosopus</i> Extinct genus of reptiles

Machaeroprosopus is an extinct genus of mystriosuchin leptosuchomorph phytosaur from the Late Triassic of the southwestern United States. M. validus, once thought to be the type species of Machaeroprosopus, was named in 1916 on the basis of three complete skulls from Chinle Formation, Arizona. The skulls have been lost since the 1950s, and a line drawing in the original 1916 description is the only visual record of the specimen. Another species, M. andersoni, was named in 1922 from New Mexico, and the species M. adamanensis, M. gregorii, M. lithodendrorum, M. tenuis, and M. zunii were named in 1930. Most species have been reassigned to the genera Smilosuchus, Rutiodon, or Phytosaurus. Until recently, M. validus was considered to be the only species that has not been reassigned. Thus, Machaeroprosopus was considered to be a nomen dubium or "doubtful name" because of the lack of diagnostic specimens that can support its distinction from other phytosaur genera. However, a taxonomic revision of Machaeroprosopus, conducted by Parker et al. in 2013, revealed that UW 3807, the holotype of M. validus, is not the holotype of Machaeroprosopus, while the species Machaeroprosopus buceros, Machaeroprosopus being a replacement name, with a fixed type species, for Metarhinus, is the combinatio nova of the type species of the genu: Belodon buceros. Therefore, the name Pseudopalatus must be considered a junior synonym of Machaeroprosopus, and all species of the former must be reassigned to the latter. This revised taxonomy was already accepted in several studies, including Stocker and Butler (2013). Stocker and Butler (2013) also treated M. andersoni as a valid species, and not a junior synonym of Machaeroprosopus buceros as was previously suggested by Long and Murry (1995).

Parrishia is an extinct genus of sphenosuchian crocodylomorph known from the Late Triassic Chinle, Dockum, and Santa Rosa Formations in Arizona and New Mexico.

Uatchitodon is an extinct genus of Late Triassic reptile known only from isolated teeth. Based on the structure of the teeth, Uatchitodon was probably a carnivorous archosauromorph. Folded grooves on the teeth indicate that the animal was likely venomous, with the grooves being channels for salivary venom. The teeth are similar to those of living venomous squamates such as Heloderma and venomous snakes. Uatchitodon is the earliest known venomous reptile.

Pravusuchus is an extinct genus of leptosuchomorph parasuchid phytosaur known from the Late Triassic of Arizona, United States. It contains a single species, Pravusuchus hortus, which is known from three specimens. These specimens were previously referred to Smilosuchus or to Leptosuchus, but Pravusuchus's autapomorphy, its phylogenetic position as well as a trait shared with mystriosuchins, justified the erection of a new taxon for the material.

Arctotraversodon is an extinct genus of traversodontid cynodonts from the Late Triassic of Canada. Fossils first described from the Wolfville Formation in Nova Scotia in 1984 represented the first known traversodontid from North America. The type and only species is A. plemmyridon and is represented by teeth and several dentary bones.

Boreogomphodon is an extinct genus of traversodontid cynodonts from the Late Triassic of the eastern United States. Fossils have been found from the Turkey Branch Formation in Virginia.

Plinthogomphodon is an extinct genus of traversodontid cynodonts from the Late Triassic of the eastern United States. Fossils have been found from the Deep River basin of North Carolina, part of the larger Newark Supergroup. It is known from a single eroded snout. The type and only species is P. herpetairus.

<i>Cricodon</i> Extinct genus of cynodonts

Cricodon is an extinct genus of trirachodontid cynodonts that lived during the Early Triassic and Middle Triassic periods of Africa. A. W. Crompton named Cricodon based on the ring-like arrangement of the cuspules on the crown of a typical postcanine tooth. The epithet of the type species, C. metabolus, indicates the change in structure of certain postcanines resulting from replacement.

Tikitherium is an extinct genus of mammaliaforms from the Late Triassic. It is thought to be an insectivore and a close relative to Docodonta. Tikitherium refers to Tiki, the village located near the Tiki Formation where the specimen was found, and therium is Greek for “Beast”. The species was named copei in honor of Edward Drinker Cope for his pioneering discoveries towards understanding mammalian molars.

Kataigidodon is an extinct genus of eucynodont cynodont therapsid that was discovered in the Chinle Formation of Arizona. It is a monotypic genus, with only type species Kataigidodon venetus known.

<i>Santacruzgnathus</i> Extinct genus of cynodonts

Santacruzgnathus is an extinct genus of small cynodonts from the Late Triassic (Carnian) Santacruzodon Assemblage Zone of Brazil. It contains one species, S. abdalai. Santacruzgnathus is known from a single partial lower jaw with four postcanine teeth, only one of which is well-preserved. Some features of the specimen, including the slender shape of the jaw and the incipiently double-rooted teeth, indicate that the animal was an early member of Prozostrodontia, a group that includes mammals and their close relatives.

References

  1. 1 2 3 4 5 6 7 8 Irmis, R. B.; Parker, W. G. (2005). "Unusual tetrapod teeth from the Upper Triassic Chinle Formation, Arizona, USA" (PDF). Canadian Journal of Earth Sciences . 42 (7): 1339–1345. Bibcode:2005CaJES..42.1339I. doi:10.1139/e05-031. S2CID   46418796.
  2. 1 2 3 Parker, William G. (September 10, 2009). "Enigmatic Triassic Taxa - Kraterokheirodon colberti". Chinleana. Retrieved 2020-04-29.
  3. ↑ Long, R. A.; Murry, P. A. (1995). "Late Triassic (Carnian and Norian) tetrapods from the southwestern United States". New Mexico Museum of Natural History and Science Bulletin. 4: 1–254.
  4. ↑ Heckert, A. B.; Lucas, S. G. (2006). "Micro-and small vertebrate biostratigraphy and biochronology of the Upper Triassic Chinle Group, southwestern USA". New Mexico Museum of Natural History and Science Bulletin. 37: 94–104.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.