Colorado City Formation

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For other uses, see Colorado Formation.
Colorado City Formation
Stratigraphic range: Late Triassic
TypeFormation
Unit ofDockum Group
Underliespossibly Cooper Canyon Formation
OverliesCamp Springs Formation
Lithology
Primarysiltstone, sandstone
Location
RegionTexas
CountryUnited 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,[1] Colorado City Member[2][3] or 'Pre-Tecovas Horizon'[4] (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.[5] They occupy a narrow band of sediments between the slightly older Camp Springs Formation and much younger Cretaceous deposits.

The first major excavations near Otis Chalk were led by UMMP paleontologists starting in 1927. Several new phytosaur species were discovered during these digs. 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.[4]

Biochronological significance

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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.[6]

Paleobiota

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Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Reptiles

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Archosaurs

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Other archosaur fossils include remains of an unnamed silesaurid[7] and a partial femur of a theropod or herrerasaurian dinosaur referable to the Chindesaurus + Tawa clade.[8]

Archosaurs of the Colorado City Formation
Genus / Taxon Species Material Location Notes Images
"Chatterjeea"[4] C. elegans[4] Vertebrae, hip bones, and femora[4]
  • Quarry 3 (TMM 31100)[4]
 Postcranial bones of an unusual bipedal archosaur related to poposaurids.[4] Later determined to be synonymous with Shuvosaurus, a shuvosaurid poposauroid initially misidentified as a theropod dinosaur.[9]
File:Shuvosaurus BW.jpg
Coahomasuchus C. kahleorum[3] Two skeletons, one of which is nearly complete[3] while the other shows adaptations for a carnivorous diet.[10] An aetosaurine aetosaur
Crocodylomorpha[11] indet.[11] Isolated ilium[11]
  • Quarry 3 (TMM 31100)[11]
 An unnamed basal crocodylomorph, one of the oldest from North America.[11]
Desmatosuchus? D. spurensis? Osteoderms (scutes) and vertebrae[4]
  • "near Otis Chalk"[4]
  • Borden County Site 1 (TMM 31213)[4]
 Most Otis Chalk desmatosuchin aetosaur fossils have been referred to Longosuchus or Lucasuchus, but a few have been referred to Desmatosuchus (Episcoposaurus) haplocerus.[4] The modern valid combination for this species is Desmatosuchus spurensis.[12]
File:Desmatosuchus spurensis flipped.jpg
Dromomeron D. gregorii[13] Hindlimb bones (femora and tibiae)[13]
  • Quarry 3 (TMM 31100)[13]
 A lagerpetid avemetatarsalian
File:Dromomeron BW.jpg
Lepidus[14] L. praecisio[14] Partial hindlimb (tibia, fibula, astragalus)[14]
  • near "site 7" (TMM 41936)[14]
 A possible coelophysid theropod, potentially the oldest dinosaur from North America.[14]
File:Lepidus praecisio.jpg
Longosuchus L. meadei Skulls, osteoderms, vertebrae, other postcrania[4][10]
  • Site 3 (TMM 31098)
  • Quarry 3 (TMM 31100)
  • Quarry 3A (TMM 31185)
  • Borden County Site 1 (TMM 31213)
 A common desmatosuchin aetosaur previously considered a species of Typothorax.
File:Longosuchus BW.jpg
Lucasuchus[4] L. hunti[4] Osteoderms and other referred fossils (including a possible skull)[4][10]
  • Quarry 3 (TMM 31100)
  • Quarry 3A (TMM 31185)
 A desmatosuchin aetosaur similar to Longosuchus[3] but most likely a distinct valid taxon.[15]
Poposaurus P. gracilis Hip and ankle bones[4]
  • "Otis Chalk"
  • Site 3 (TMM 31098)
  • Quarry 3 (TMM 31100)
 A poposaurid poposauroid
File:Poposaurus gracilis (1) flipped.jpg
P. langstoni[4] Hip bones and vertebrae[4]
  • Site/Quarry 1 (TMM 31025)
  • Quarry 3 (TMM 31100)
 A poposaurid poposauroid previously given its own genus, Lythrosuchus[4]
Postosuchus P. kirkpatricki Vertebrae and hindlimb bones[4]
  • Quarry 3 (TMM 31100)
  • Borden County Site 1 (TMM 31213)
 A rausuchid loricatan
File:Postosuchus kirkpatricki flipped.jpg

Phytosaurs

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Phytosaurs of the Colorado City Formation
Genus / Taxon Species Material Location Notes Images
Angistorhinus A. alticephalus Partial skeleton with skull[4]
  • Roy Lamb Ranch[4]
 Probable junior synonym of A. grandis.
A. grandis Several complete skulls and associated cranial and postcranial fragments[1][4][16]
  • Site 3 (TMM 31098)[4]
  • Quarry 3 (TMM 31100)[4]
  • TMM 42060[4]
  • "locality 9"[16]
 A common mystriosuchine phytosaur. Some sources refer all Otis Chalk Angistorhinus material to "Angistorhinus megalodon",[4] while most other sources support affinities with the type species Angistorhinus grandis from Wyoming.[16]
File:Angistorhinus NMMNH P-33527.jpg
Brachysuchus B. megalodon Two nearly complete skulls and postcranial fragments
  • "near Otis Chalk"[4]
 A mystriosuchine phytosaur closely related to Angistorhinus, and sometimes regarded as a species within that genus.[4]
File:Phytosaurus Exhibit Museum of Natural History.JPG
Paleorhinus "P." sawini[4] A skull[4]
  • Borden County Site 1 (TMM 31213)[4]
 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[4]
  • Site/Quarry 1 (TMM 31025)
  • Quarry 3 (TMM 31100)
  • Quarry 3A (TMM 31185)
 A common basal (non-mystriosuchine) phytosaur, sometimes considered a species of Parasuchus.
File:Paleorhinus Warsaw.jpg

Other reptiles

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Other reptiles of the Colorado City Formation
Genus Species Material Location Notes Images
Ankylosuchus[17] A. chinlegroupensis[17] Partial skeleton with cranial and pelvic fragments, osteoderms, vertebrae, and an indeterminate limb bone[17]
  • NMMNH locality 3101[17]
 A doswelliid archosauriform.
Doswellia D. kaltenbachi Vertebrae and osteoderms[4]
  • Site/Quarry 1 (TMM 31025)
  • Site 3 (TMM 31098)
 A doswelliid archosauriform.[4]
File:Doswellia kaltenbachi life restoration.png
Malerisaurus M. langstoni[18] Disarticulated skeleton[18][19]
  • Quarry 2 (TMM 31099)[18]
 A carnivorous azendohsaurid allokotosaurian in the subfamily Malerisaurinae. Regarded as a chimera by Spielmann et al. (2006),[20] but treated as valid by other sources.[18][19] Numerous disarticulated Malerisaurus-like fossils are also known from Quarry 1 (TMM 31025).[19]
File:Malerisaurus BW.jpg
Otischalkia O. elderae Humeri, femora[4]
  • Site/Quarry 1 (TMM 31025)
  • Quarry 3A (TMM 31185)
 A dubious putative rhynchosaur, likely synonymous with Malerisaurus langstoni.[19] Supposed premaxilla fossils have been reinterpreted as metoposaurid cleithra.[19] Femora and humeri previously referred to this species likely belong to Trilophosaurus[4] or Malerisaurus[19] instead.
Protecovasaurus[21] P. lucasi[21] Teeth[21]
  • Quarry 1 (NMMNH 860)[21]
 A reptile of uncertain affinities known from serrated teeth similar to ornithischian dinosaurs.[21]
Trilophosaurus T. buettneri Numerous skulls, braincases, and postcranial material[4][22]
  • Site/Quarry 1 (TMM 31025)
  • Quarry 2 (TMM 31099)[22]
  • Quarry 3 (TMM 31100)
  • Quarry 3A (TMM 31185)[22]
  • Borden County Site 1 (TMM 31213)
 A common trilophosaurid allokotosaurian.[22]
File:Trilophosaurus buettneri (flipped).jpg
Triopticus[23] T. primus[23] Partial skull[23]
  • Quarry 3 (TMM 31100)[23]
 A protopyknosian archosauriform with a reinforced skull similar to pachycephalosaurid dinosaurs.[23]

Amphibians

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Amphibians of the Colorado City Formation
Genus Species Material Location Notes Images
Anaschisma A. browni Numerous skulls, interclavicles, clavicles, vertebrae, and other postcranial bones[4]
  • Site/Quarry 1 (TMM 31025)
  • Site 3 (TMM 31098)
  • Quarry 2 (TMM 31099)
  • Quarry 3 (TMM 31100)
  • Quarry 3A (TMM 31185)
  • Borden County Site 3 (TMM 41921)
 A common metoposaurid temnospondyl, previously named under the genus Koskinonodon or Buettneria[4]
File:Buettneria.jpg
Latiscopus[24] L. disjunctus[24] A skull[24]
  • Site/Quarry 1 (TMM 31025)[24]
 A latiscopid temnospondyl[24]

Fish

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Fish fossils from Quarry 1 (NMMNH 860 / TMM 31025) include lungfish teeth (Arganodus?[1]), coelacanth scales, "palaeoniscid" scales (aff. Turseodus[1]), and hybodont shark teeth and spines (Lissodus?[1] or Lonchidion?).[21]

Fish of the Colorado City Formation
Genus / Taxon Species Material Location Notes Images
Cionichthys C. greeni[25] Articulated skulls and postcrania[25]
  • Schaeffer Fish Quarry[25]
 A redfieldiiform actinopterygian (ray-finned fish)
Lasalichthys L. hillsi Skull, scale, and postcranial fragments[25][26] A redfieldiiform actinopterygian
L. otischalkensis[26] Numerous articulated skulls and postcrania[26]
  • Schaeffer Fish Quarry[26]
 A redfieldiiform actinopterygian.[26] Some specimens were previously referred to Lasalichthys (= Synorichthys) stewarti.[26]

See also

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References

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  5. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  6. ^ Lucas, S. G., Hunt, A. P., Heckert, A. B., and Spielmann, J. A., (2007) Global Triassic tetrapod biostratigraphy and biochronology: 2007 status: New Mexico Museum of Natural History and Science Bulletin, v. 41 (The Global Triassic), p. 229- 240.
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  8. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  9. ^ Nesbitt, S. (2007). "The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa." Bulletin of the American Museum of Natural History, 302: 84 pp. http://digitallibrary.amnh.org/dspace/handle/2246/5840
  10. ^ a b c d Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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