Kayentachelys Temporal range: Early Jurassic | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Pantestudines |
Clade: | Testudinata |
Clade: | Mesochelydia |
Genus: | † Kayentachelys Gaffney et al., 1987 |
Species: | †K. aprix |
Binomial name | |
†Kayentachelys aprix Gaffney et al., 1987 | |
Kayentachelys ("Kayenta turtle") is an extinct genus of turtle known only from the "silty facies" of the Lower Jurassic Kayenta Formation in northeastern Arizona on the lands of the Navajo Nation. [1]
The earliest mention of turtles from the Kayenta Formation in the literature is within the description of the ornithischian dinosaur Scutellosaurus by Colbert (1981). [2] These first specimens were collected during the 1970s and early 1980s by field parties from the Museum of Northern Arizona (MNA) and the Museum of Comparative Zoology (MCZ) at Harvard University. Specimens from these field excursions were used to establish the taxon Kayentachelys in 1987, and it is an MNA specimen (MNA V1558) which was designated as the holotype of the taxon. [1] During the early 1980s, addition turtle specimens from the Kayenta Formation were collected by field parties from the University of California Museum of Paleontology (UCMP), which were reported by Clark & Fastovsky (1986) prior to the naming of Kayentachelys. [3] Many additional specimens of Kayentachelys were collected by the Texas Memorial Museum (TMM; now the Texas Vertebrate Paleontology Collections [4] ) at The University of Texas at Austin between 1997 and 2000. [5] That work by the TMM remains the most recent large-scale collecting of vertebrate fossils from the Kayenta Formation in Arizona.
Kayentachelys is significant because it is the first truly abundant turtle in the fossil record, and its unique phylogenetic position documents the transition from early turtles to the common ancestor of the crown. Additionally, as of 2018, Kayentachelys is the most abundantly known vertebrate taxon from the Kayenta Formation. [5]
Kayentachelys is known from several dozen specimens preserving elements from both the cranial and postcranial skeleton. Its shell is about 20 cm (7.9 in) in length. [6]
As originally diagnosed, [1] Kayentachelys possesses pterygoid teeth and a ventrally-exposed prootic, both of which are ancestral amniote features. Ancestral turtle features of the shell include nine costal scutes and an epiplastron with a dorsal process. Derived features shared with early turtles like Proterochersis and cryptodirans include an antrum postoticum of the squamosal, a fused basipterygoid articulation, and 11 peripheral osteoderms. Gaffney et al. united Kayentachelys with cryptodiran taxa based upon featured of the palate and braincase.
Sterli and Joyce (2007) [7] emended the diagnosis of Kayentachelys using a unique combination of ancestral and derived cranial character states, including prefrontals which do not contact one another at the midline, the absence of lacrimals, frontals which contribute to the orbit, an unpaired vomer, pterygoid teeth, the absence of palatal teeth, and a retroarticular process, among many other features.
The genus Kayentachelys is monotypic, comprising only one species. The type species Kayentachelys aprix was defined based upon the holotype specimen MNA V1558 and the referred specimens MNA V1559-V1570 and MCZ 8914-8917. The specific epithet aprix (Greek: tight) refers to the fused basicranial articulation. [1]
When Kayentachelys was first described by Gaffney et al. (1987), it was classified as the oldest and earliest branching cryptodiran turtle and the sole taxon within a new clade called Kayentachelyidae. [1] Kayentachelys was noted to possess a unique combination of derived character states which united it with all cryptodiran turtles and ancestral character states which excluded it from a clade comprising all other cryptodiran taxa that the authors called Selmacryptodira. Below is a cladogram depicting the initial classification of Kayentachelys within Cryptodira by Gaffney et al. (1987):
Testudines |
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In 2007, a competing hypothesis regarding the phylogeny of Kayentachelys arose. [7] Sterli and Joyce (2007) Sterli and Joyce (2007) argued that Kayentachelys was not a member of Crytodira and instead represented an early testudinatan outside of Testudines. The placement of Kayentachelys outside of Cryptodira has been upheld by most subsequent phylogenetic analyses of early turtles. [8] [9]
Below is a cladogram depicting the phylogenetic hypothesis from Sterli and Joyce (2007):
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Kayentachelys is known only from the "silty facies" of the Kayenta Formation in northeastern Arizona. The Kayenta Formation is a stratigraphic unit within the Triassic-Jurassic Glen Canyon Group, which crops out across the Colorado Plateau. Despite extensive outcrop of the "typical facies" of the Kayenta Formation in Utah, Colorado, and northern Arizona, vertebrate fossils are rare in these regions. Vertebrate fossils from the "silty facies" of the Kayenta Formation are most abundantly known from Ward Terrace along the Adeii Eechii Cliffs southeast of Tuba City, AZ on the lands of the Navajo Nation. In particular, specimens of Kayentachelys have been recovered near an area called Gold Spring, which has recently been dated to the Pliensbachian-Toarcian ages of the Early Jurassic Epoch based upon uranium-lead ages acquired using laser ablation inductively coupled mass spectrometry. [10]
Kayentachelys was initially interpreted as an aquatic turtle, based upon the sharp tapered edges of the low-domed shell and the lack of both limb armor and sculpturing on the carapace. [1]
Kayentachelys is one component of a diverse assemblage of vertebrate taxa preserved within the Kayenta Formation. Kayentachelys lived alongside hybodontoid chondrichthyans; the early anuran Prosalirus ; the gymnophionan Eocaecilia ; sphenodontid diapsids; several species of crocodylomorph, including Kayentasuchus , Eopneumatosuchus , Protosuchus , and the goniopholidid Calsoyasuchus ; the pterosaur Rhamphinion ; the sauropodomorph dinosaur Sarahsaurus ; the theropod dinosaurs Dilophosaurus and "Syntarsus" kayentakatae ; the ornithischian dinosaur Scutellosaurus; the tritylodontid synapsids Oligokyphus , Dinnebitodon , and Kayentatherium ; the mammaliaform synapsid Dinnetherium; and several other yet-unnamed taxa. [5]
The paleoenvironment of the Kayenta Formation in which Kayentachelys lived has been reconstructed as a floodplain drained by low-energy, sediment-rich streams. [3] The presence of aquatic and moisture-reliant taxa including Kayentachelys, Prosalirus , and Eocaecilia indicates that water was likely abundant. This abundance of water is also supported by the presence of mudstones within "silty facies" the Kayenta Formation on Ward Terrace. Petrified wood is common in the Kayenta Formation on Ward Terrace, suggesting abundant gymnosperm plantlife.
Oligokyphus is an extinct genus of herbivorous tritylodontid cynodont known from the Late Triassic to Early Jurassic of Europe, Asia and North America.
Echinodon is a genus of heterodontosaurid dinosaur that lived during the earliest Cretaceous of southern England and possibly western France in the Berriasian epoch. The first specimens were jaw bones named Echinodon becklesii by Sir Richard Owen in 1861, and since their original description only additional teeth have been discovered. The specific name honours collector Samuel Beckles who discovered the material of Echinodon and many other taxa from across England, while the genus name translates as "prickly tooth" in reference to the dental anatomy of the taxon.
Scutellosaurus is a genus of thyreophoran ornithischian dinosaur that lived approximately 196 million years ago during the early part of the Jurassic Period in what is now Arizona, USA. It is classified in Thyreophora, the armoured dinosaurs; its closest relatives may have been Emausaurus and Scelidosaurus, another armored dinosaur which was mainly a quadrupedal dinosaur, unlike bipedal Scutellosaurus. It is one of the earliest representatives of the armored dinosaurs and the basalmost form discovered to date. Scutellosaurus was a small, lightly-built, ground-dwelling herbivore, that could grow up to an estimated 1.3 metres (4.3 ft) long.
The Glen Canyon Group is a geologic group of formations that is spread across the U.S. states of Nevada, Utah, northern Arizona, north west New Mexico and western Colorado. It is called the Glen Canyon Sandstone in the Green River Basin of Colorado and Utah.
Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic. Its fossils have been found in Mecklenburg-Vorpommern, northern Germany. Emausaurus is the only known Toarcian thyreophoran, as well as the only dinosaur from the zone of the same age with a formal name.
The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Traditionally has been suggested as Sinemurian-Pliensbachian, but more recent dating of detrital zircons has yielded a depositional age of 183.7 ± 2.7 Ma, thus a Pliensbachian-Toarcian age is more likely. A previous depth work recovered a solid "Carixian" age from measurements done in the Tenney Canyon. More recent works have provided varied datations for the layers, with samples from Colorado and Arizona suggesting 197.0±1.5-195.2±5.5 Ma, while the topmost section is likely Toarcian or close in age, maybe even recovering terrestrial deposits coeval with the Toarcian Oceanic Anoxic Event. This last age asignation also correlated the Toarcian Vulcanism on the west Cordilleran Magmatic Arc, as the number of grains from this event correlate with the silt content in the sandstones of the upper layers.
Protostegidae is a family of extinct marine turtles that lived during the Cretaceous period. The family includes some of the largest sea turtles that ever existed. The largest, Archelon, had a head one metre (39 in) long. Like most sea turtles, they had flattened bodies and flippers for front appendages; protostegids had minimal shells like leatherback turtles of modern times.
Calsoyasuchus is a genus of crocodylomorph that lived in the Early Jurassic. Its fossilized remains were found in the Sinemurian-Pliensbachian-age Kayenta Formation on Navajo Nation land in Coconino County, Arizona, United States. Formally described as C. valliceps, it is known from a single incomplete skull which is unusually derived for such an early crocodile relative. This genus was described in 2002 by Ronald Tykoski and colleagues; the specific name means "valley head" and refers to a deep groove along the midline of the nasal bones and frontal bones. It has often been interpreted as the earliest diverging member of Goniopholididae, but other studies have recovered it in various other positions.
Testudinata is the group of all tetrapods with a true turtle shell. It includes both modern turtles (Testudines) and many of their extinct, shelled relatives (stem-turtles), though excluding Odontochelys and Eorhynchochelys, which are placed in the more inclusive Pantestudines.
Kayentasuchus is a genus of sphenosuchian, a type of basal crocodylomorph, the clade that comprises the crocodilians and their closest kin. It is known from a single skeleton found in rocks of the Sinemurian-Pliensbachian-age Lower Jurassic Kayenta Formation, northeastern Arizona.
Condorchelys was a genus of stem turtle from Early Jurassic Cañadon Asfalto Formation of Argentina. Condorchelys represents the oldest Jurassic-aged Turtle from South America, with only one species described, Condorchelys antiqua.
Kayentavenator is a genus of small carnivorous tetanuran dinosaur that lived during the Early Jurassic Period; fossils were recovered from the Kayenta Formation of northeastern Arizona and were described in 2010.
Dinnebitodon is an extinct genus of advanced herbivorous cynodonts of the early Jurassic period. It has only been found in the Kayenta Formation in northeastern Arizona. It closely resembles the related genus Kayentatherium from the same formation. It is set apart by differences in the dentition, while resembling in most other respects.
Sarahsaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic period in what is now northeastern Arizona, United States.
Pegomastax is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic of South Africa. The only known specimen was discovered in a 1966–1967 expedition in Transkei District of Cape Province, but was not described until 2012 when Paul Sereno named it as the new taxon Pegomastax africana. The genus name is derived from the Greek for "strong jaw", and the species name describes the provenance of Africa; it was originally spelled africanus, was corrected to africana to align with the gender of the genus name.
Megapnosaurus is an extinct genus of coelophysid theropod dinosaur that lived approximately 188 million years ago during the early part of the Jurassic Period in what is now Africa. The species was a small to medium-sized, lightly built, ground-dwelling, bipedal carnivore, that could grow up to 2.2 m (7.2 ft) long and weigh up to 13 kg (29 lb). It was originally given the genus name Syntarsus, but that name was later determined to be preoccupied by a beetle. The species was subsequently given a new genus name, Megapnosaurus, by Ivie, Ślipiński & Węgrzynowicz in 2001. Some studies have classified it as a species within the genus Coelophysis, but this interpretation has been challenged by more subsequent studies and the genus Megapnosaurus is now considered valid.
Coelophysis? kayentakatae is an extinct species of neotheropod dinosaur that lived approximately 200–196 million years ago during the early part of the Jurassic Period in what is now the southwestern United States. It was originally named Syntarsus kayentakatae, but the genus Syntarsus was found to be preoccupied by a Colydiine beetle, so it was moved to the genus Megapnosaurus, and then to Coelophysis. A recent reassessment suggests that this species may require a new genus name.
Laquintasaura is a genus of Venezuelan ornithischian dinosaur containing only the type species Laquintasaura venezuelae. The species was the first dinosaur to have been identified from Venezuela. It is known from extensive remains, all from a singular bonebed locality which has been sampled for specimen blocks over the course of several expeditions, largely led by Marcelo R Sánchez-Villagra. A small, very primitive animal, it is known for its distinct dental anatomy and for being one of the earliest and most primitive ornithischians in the fossil record. Taxonomic uncertainty has led to conflicting theories that it is either as the base of Ornithischia or at the base of the subgroup Thyreophora. In either model, its dating to around 200 million years ago, at the start of the Jurassic, existence in equatorial latitudes, and primitive nature make it a key view into early ornithischian evolution. It's thought that Laquintasaura would've lived in groups and had a possible omnivorous diet, living on a seasonal alluvial plain and being preyed about by the contemporary Tachiraptor.
Meiolaniformes is an extinct clade of stem-group turtles, defined as all taxa more closely related to Meiolania than to Cryptodira and Pleurodira. It is known from the Early Cretaceous to the Holocene of Australia, Oceania and South America. Some Eurasian taxa have been suggested to be part of the group, but this is disputed.
Mesochelydia is a clade within Pantestudines, more inclusive than Perichelydia, but less than Testudinata. The clade is known from the Early Jurassic to the Present, and contains all Jurassic representatives of Testudinata aside from Australochelys. The ancestral condition for Mesochelydia is thought to be aquatic, as opposed to terrestrial for Testudinata. They are distinguished from more basal testudinatans by the presence of the following characters: strap like pectoral girdle, supramarginals absent, reduced posterior entoplastral process, eleven pairs of peripherals, elongate processus interfenestralis, paired basioccipital tubercles, fully formed cavum tympani and antrum postoticum, single vomer, confluent external nares, lacrimals and supratemporals absent.