Colorado City Formation | |
---|---|
Stratigraphic range: Late Triassic | |
Type | Formation |
Unit of | Dockum Group |
Underlies | possibly Cooper Canyon Formation |
Overlies | Camp Springs Formation |
Lithology | |
Primary | siltstone, sandstone |
Location | |
Region | Texas |
Country | United States |
The Colorado City Formation is a Late Triassic geologic formation in the Dockum Group of Texas, United States. It has previously been known as the Iatan Member, Colorado City Member [1] [2] or 'Pre-Tecovas Horizon' [3] (as it is assumed to be older than the Tecovas Formation).
The Colorado City Formation is mostly restricted to Howard and Borden counties. The formation hosts the Otis Chalk fossil sites, named after a ghost town in Howard County. Despite their importance, the Otis Chalk localities have been difficult to resolve in the stratigraphy of Triassic Texas. [4] They occupy a narrow band of sediments between the slightly older Camp Springs Formation and much younger Cretaceous deposits.
The first excavations near Otis Chalk were led by UMMP paleontologists starting in 1927, discovering the holotype of the phytosaur Brachysuchus. University of Oklahoma paleontologists followed with their own expedition in 1931. The vast majority of fossils collected from the formation were recovered during a 1939–1941 state-sponsored Works Progress Administration paleontological survey. Several sites southeast of Big Spring were particularly productive. Fossils collected by these efforts were stored at the newly opened Texas Memorial Museum in Austin. Since the 1940s, collection from the Otis Chalk area has been more limited. One notable find is a pond deposit, the Schaeffer Fish Quarry, discovered in 1967 by AMNH paleontologist Bobb Schaeffer. [3]
The Otis Chalk localities that are situated in the Colorado City Formation form the basis of the Otischalkian Land Vertebrate Faunachron (LVF), which is defined by the first appearance of Parasuchus. [5]
Color key
| Notes Uncertain or tentative taxa are in small text; |
Other archosaur fossils include remains of an unnamed silesaurid [6] and a partial femur of a theropod or herrerasaurian dinosaur referable to the Chindesaurus + Tawa clade. [7]
Archosaurs of the Colorado City Formation | ||||||
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Genus / Taxon | Species | Material | Location | Notes | Images | |
"Chatterjeea" [3] | C. elegans [3] | Vertebrae, hip bones, and femora [3] |
| Postcranial bones of an unusual bipedal archosaur related to poposaurids. [3] Later determined to be synonymous with Shuvosaurus , a shuvosaurid poposauroid initially misidentified as a theropod dinosaur. [8] | ![]() | |
Coahomasuchus | C. kahleorum [2] | Two skeletons, one of which is nearly complete [2] while the other shows adaptations for a carnivorous diet. [9] | An aetosaurine aetosaur | |||
Crocodylomorpha [10] | indet. [10] | Isolated ilium [10] |
| An unnamed basal crocodylomorph, one of the oldest from North America. [10] | ||
Desmatosuchus? | D. spurensis? | Osteoderms (scutes) and vertebrae [3] | Most Otis Chalk desmatosuchin aetosaur fossils have been referred to Longosuchus or Lucasuchus, but a few have been referred to Desmatosuchus (Episcoposaurus) haplocerus. [3] The modern valid combination for this species is Desmatosuchus spurensis. [11] | ![]() | ||
Dromomeron | D. gregorii [12] | Hindlimb bones (femora and tibiae) [12] |
| A lagerpetid avemetatarsalian | ![]() | |
Lepidus [13] | L. praecisio [13] | Partial hindlimb (tibia, fibula, astragalus) [13] |
| A possible coelophysid theropod, potentially the oldest dinosaur from North America. [13] | ![]() | |
Longosuchus | L. meadei | Skulls, osteoderms, vertebrae, other postcrania [3] [9] |
| A desmatosuchin aetosaur previously considered a species of Typothorax . | ![]() | |
Lucasuchus [3] | L. hunti [3] | Osteoderms and other referred fossils (including a possible skull) [3] [9] |
| A desmatosuchin aetosaur similar to Longosuchus [2] but most likely a distinct valid taxon. [14] | ||
Poposaurus | P. gracilis | Hip and ankle bones [3] |
| A poposaurid poposauroid | ![]() | |
P. langstoni [3] | Hip bones and vertebrae [3] |
| A poposaurid poposauroid previously given its own genus, Lythrosuchus [3] | |||
Postosuchus | P. kirkpatricki | Vertebrae and hindlimb bones [3] |
| A rausuchid loricatan | ![]() |
Phytosaurs of the Colorado City Formation | ||||||
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Genus / Taxon | Species | Material | Location | Notes | Images | |
Angistorhinus | A. alticephalus | Partial skeleton with skull [3] |
| Probable junior synonym of A. grandis. | ||
A. grandis | Complete skull and associated postcrania [15] |
| A mystriosuchine phytosaur. | ![]() | ||
Brachysuchus | B. megalodon | Two nearly complete skulls and postcranial fragments |
| A mystriosuchine phytosaur closely related to Angistorhinus, and sometimes regarded as a species within that genus. [3] | ||
Paleorhinus | "P." sawini [3] | A skull [3] |
| A basal (non-mystriosuchine) phytosaur from Borden County. Probably does not form a clade with other species referred to Paleorhinus or Parasuchus. | ||
P. bransoni | Several skulls [3] |
| A basal (non-mystriosuchine) phytosaur, sometimes considered a species of Parasuchus . | ![]() |
Other reptiles of the Colorado City Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Material | Location | Notes | Images | |
Ankylosuchus [16] | A. chinlegroupensis [16] | Partial skeleton with cranial and pelvic fragments, osteoderms, vertebrae, and an indeterminate limb bone [16] |
| A doswelliid archosauriform. | ||
Doswellia | D. kaltenbachi | Vertebrae and osteoderms [3] |
| A doswelliid archosauriform. [3] | ![]() | |
Malerisaurus | M. langstoni [17] | Disarticulated skeleton [17] [18] |
| A carnivorous azendohsaurid allokotosaurian in the subfamily Malerisaurinae. Regarded as a chimera by Spielmann et al. (2006), [19] but treated as valid by other sources. [17] [18] Numerous disarticulated Malerisaurus-like fossils are also known from Quarry 1 (TMM 31025). [18] | ![]() | |
Otischalkia | O. elderae | Humeri, femora [3] |
| A dubious putative rhynchosaur, likely synonymous with Malerisaurus langstoni. [18] Supposed premaxilla fossils have been reinterpreted as metoposaurid cleithra. [18] Femora and humeri previously referred to this species likely belong to Trilophosaurus [3] or Malerisaurus [18] instead. | ||
Protecovasaurus [20] | P. lucasi [20] | Teeth [20] |
| A reptile of uncertain affinities known from serrated teeth similar to ornithischian dinosaurs. [20] | ||
Trilophosaurus | T. buettneri | Numerous skulls, braincases, and postcranial material [3] [21] | A common trilophosaurid allokotosaurian. [21] | ![]() | ||
Triopticus [22] | T. primus [22] | Partial skull [22] |
| A protopyknosian archosauriform with a reinforced skull similar to pachycephalosaurid dinosaurs. [22] |
Amphibians of the Colorado City Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Material | Location | Notes | Images | |
Anaschisma | A. browni | Numerous skulls, interclavicles, clavicles, vertebrae, and other postcranial bones [3] |
| A common metoposaurid temnospondyl, previously named under the genus Koskinonodon or Buettneria [3] | ![]() | |
Latiscopus [23] | L. disjunctus [23] | A skull [23] |
| A latiscopid temnospondyl [23] |
Fish fossils from Quarry 1 (NMMNH 860 / TMM 31025) include lungfish teeth ( Arganodus ?), coelacanth scales, "palaeoniscid" scales (aff. Turseodus ), and hybodont shark teeth and spines ( Lissodus ? or Lonchidion ?). [20]
Fish of the Colorado City Formation | ||||||
---|---|---|---|---|---|---|
Genus / Taxon | Species | Material | Location | Notes | Images | |
Cionichthys | C. greeni [24] | Articulated skulls and postcrania [24] |
| A redfieldiiform actinopterygian (ray-finned fish) | ||
Lasalichthys | L. hillsi | Skull, scale, and postcranial fragments [24] [25] | A redfieldiiform actinopterygian | |||
L. otischalkensis [25] | Numerous articulated skulls and postcrania [25] |
| A redfieldiiform actinopterygian. [25] Some specimens were previously referred to Lasalichthys (= Synorichthys) stewarti. [25] |
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.
Spinosuchus is an extinct genus of trilophosaurid allokotosaur from the Late Triassic of Texas, southern United States. It has been assigned to a variety of groups over its history, from coelophysid dinosaur to pseudosuchian to uncertain theropod dinosaur and to Proterosuchidae. This uncertainty is not unusual, given that it was only known from a poorly preserved, wall-mounted, partial vertebral column of an animal that lived in a time of diverse, poorly known reptile groups. However, newly collected material and recent phylogenetic studies of early archosauromorphs suggest that it represents an advanced trilophosaurid very closely related to Trilophosaurus.
Aetosaurus is an extinct genus of pseudosuchian reptile belonging to the order Aetosauria. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: A. ferratus, the type species from Germany and Italy; A. crassicauda from Germany; and A. arcuatus from eastern North America. Additional specimens referred to Aetosaurus have been found in the Chinle Group of the southwestern United States, and the Fleming Fjord Formation of Greenland. Specimens of Aetosaurus occur in Norian-age strata.
Stagonolepis is an extinct genus of stagonolepidid aetosaur known from the Late Triassic Hassberge Formation of Germany, the Drawno Beds of Poland, and the Lossiemouth Sandstone of Scotland. Supposed fossils from North and South America have been placed into their own genera, Calyptosuchus and Aetosauroides, respectively.
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.
Aetosauroides is an extinct genus of aetosaur from the Late Triassic of South America. It is one of four aetosaurs known from South America, the others being Neoaetosauroides, Chilenosuchus and Aetobarbakinoides. Three species have been named: the type species A. scagliai, A. subsulcatus and A. inhamandensis. Fossils have been found in the Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina and the Santa Maria Formation in the Paraná Basin in southeastern Brazil. The strata date to the late Carnian and early Norian stages, making Aetosauroides one of the oldest aetosaurs.
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The Tecovas Formation is a geological formation in the Texas panhandle and eastern New Mexico. It is one of several formations encompassed by the Late Triassic Dockum Group.
The Cooper Canyon Formation is a geological formation of Norian age in Texas and New Mexico. It is one of several formations encompassed by the Dockum Group.
Coahomasuchus is an extinct genus of aetosaurine aetosaur. Remains of the genus have been found from deposits in Texas and North Carolina that date to the Otischalkian faunachron of the Late Triassic. It was small for an aetosaur, being less than 1.5 metres long. The dorsal plates are distinctively flat and unflexed, and have a faint sub-parallel to radial ornamentation. The genus lacked spines or keels on these plates, features seen in many other aetosaurs. Coahomasuchus was very similar in appearance to the closely related Aetosaurus.
Euscolosuchus is an extinct genus of suchian archosaurs from the Late Triassic of Virginia. It is probably an aetosauriform, as the sister taxon to Acaenasuchus and a relative of aetosaurs.
Sterling Nesbitt is an American paleontologist best known for his work on the origin and early evolutionary patterns of archosaurs. He is currently an associate professor at Virginia Tech in the Department of Geosciences.
Lucasuchus is an extinct genus of aetosaur. Fossils have been found from the Bull Canyon Formation of the Dockum Group outcropping in the Revuelto Creek locality in Quay County, New Mexico. All specimens date back to the Norian stage of the Late Triassic. The genus was named in 1995 after the American paleontologist Spencer G. Lucas.
Paratypothorax is an extinct genus of aetosaur, known from a single species, Paratypothorax andressorum. It was a broadly distributed member of the group found in Germany, North America, and possibly parts of Gondwana. The best specimens come from Germany, though for more than a century they were mistakenly considered phytosaur armor. Paratypothorax was a large and wide-bodied typothoracine aetosaur, as well as the namesake of the tribe Paratypothoracisini.
Parrishia is an extinct genus of sphenosuchian crocodylomorph known from the Late Triassic Chinle, Dockum, and Santa Rosa Formations in Arizona and New Mexico.
Tecovasuchus is an extinct genus of aetosaur. It is known primarily from osteoderms found from the Tecovas Formation in Texas, which is Late Triassic in age, dating back to the lower Norian. Material is also known from several other localities of the Chinle Group in New Mexico and Arizona, such as older Carnian outcrops and younger Rhaetian outcrops. Specimens of Tecovasuchus have been collected from the Tecovas Formation, the Bluewater Creek Formation, and the Los Esteros Member of the Santa Rosa Formation.
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