# Colorado City Formation

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Geologic formation in Texas, United States

For other uses, see [Colorado Formation](/source/Colorado_Formation_(disambiguation)).

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](/source/Late_Triassic) [geologic formation](/source/Formation_(geology)) in the [Dockum Group](/source/Dockum_Group) of [Texas](/source/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](/source/Tecovas_Formation)).

The Colorado City Formation is mostly restricted to [Howard](/source/Howard_County%2C_Texas) and [Borden](/source/Borden_County%2C_Texas) counties. The formation hosts the **Otis Chalk** fossil sites, named after a [ghost town](/source/Ghost_town) in Howard County. Despite their importance, the Otis Chalk localities have been difficult to resolve in the [stratigraphy](/source/Stratigraphy) of Triassic Texas.[5] They occupy a narrow band of sediments between the slightly older [Camp Springs Formation](/source/Camp_Springs_Formation) and much younger Cretaceous deposits.

The first major excavations near Otis Chalk were led by [UMMP](/source/UMMP) paleontologists starting in 1927. Several new phytosaur species were discovered during these digs. [University of Oklahoma](/source/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](/source/Works_Progress_Administration) paleontological survey. Several sites southeast of [Big Spring](/source/Big_Spring%2C_Texas) were particularly productive. Fossils collected by these efforts were stored at the newly opened [Texas Memorial Museum](/source/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](/source/American_Museum_of_Natural_History) paleontologist Bobb Schaeffer.[4]

## Biochronological significance

The Otis Chalk localities that are situated in the Colorado City Formation form the basis of the [Otischalkian](/source/Otischalkian) [Land Vertebrate Faunachron](/source/Land_Vertebrate_Faunachron) (LVF), which is defined by the first appearance of *Parasuchus*.[6]

## Paleobiota

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

#### Archosaurs

Other archosaur fossils include remains of an unnamed [silesaurid](/source/Silesauridae)[7] and a partial femur of a [theropod](/source/Theropoda) or [herrerasaurian](/source/Herrerasauria) [dinosaur](/source/Dinosaur) referable to the *[Chindesaurus](/source/Chindesaurus)* + *[Tawa](/source/Tawa_hallae)* 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] Coahomasuchus C. kahleorum[3] Two skeletons, one of which is nearly complete[3] while the other shows adaptations for a carnivorous diet.[10] NMMNH locality 3357[3] Quarry 3 (TMM 31100)?[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] Dromomeron D. gregorii[13] Hindlimb bones (femora and tibiae)[13] Quarry 3 (TMM 31100)[13] A lagerpetid avemetatarsalian 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] 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. 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 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

#### Phytosaurs

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] 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] 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.

#### Other reptiles

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] 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] 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] 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

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] Latiscopus[24] L. disjunctus[24] A skull[24] Site/Quarry 1 (TMM 31025)[24] A latiscopid temnospondyl[24]

### Fish

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

- [Earth sciences portal](https://en.wikipedia.org/wiki/Portal:Earth_sciences)
- [Texas portal](https://en.wikipedia.org/wiki/Portal:Texas)
- [Paleontology portal](https://en.wikipedia.org/wiki/Portal:Paleontology)

- [List of fossiliferous stratigraphic units in Texas](/source/List_of_fossiliferous_stratigraphic_units_in_Texas)

- [Paleontology in Texas](/source/Paleontology_in_Texas)

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Adapted from the Wikipedia article [Colorado City Formation](https://en.wikipedia.org/wiki/Colorado_City_Formation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Colorado_City_Formation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.