# Cloverly Formation

The Cloverly Formation is a geological formation of Early and Late Cretaceous age (Valanginian to Cenomanian stage) that is present in parts of Montana, Wyoming, Colorado and Utah in the western United States. It was named for a post office on the eastern side of the Bighorn Basin in Wyoming by N.H. Darton in 1904. The sedimentary rocks of formation were deposited in floodplain environments and contain vertebrate fossils, including a diverse assemblage of dinosaur remains. In 1973, the Cloverly Formation Site was designated as a National Natural Landmark by the National Park Service.

## Stratigraphy

The Cloverly Formation rests disconformably on the Morrison Formation and is conformably overlain by the Thermopolis Shale. It is subdivided into a variety of members, depending on the location. In the Bighorn Basin along the Montana-Wyoming border, Moberly (1960) divided the Cloverly into the following three members:
* The Pryor Conglomerate lies at the base and contains abundant black chert. It is named from thick beds exposed on the west side of the Pryor Mountains.
* The Little Sheep Member lies in the middle and is composed of pale-purple, gray to almost white, bentonitic mudstone.
* The uppermost unit is the Himes Member, which contains some coarse-grained channel sandstone deposits, but consists primarily of brightly multicolored (variegated) mudstones.
In contrast, Ostrom (1970) divided the formation into four units, which he named Units IV-VII:
* Unit IV equates to the Pryor Conglomerate of Moberly and consists of a conglomerate or conglomeratic sandstone.
* Unit V, overlaying Unit IV, consists of a lower grey-to-purple claystone with abundant fist-sized chalcedony and barite concretions; the unit is highly bentonitic and contains occasional channel sands.
* Unit VI is a discontinuous "salt and pepper" cross-stratified channel sandstone with occasional conglomerate, considered by Moberly to be part of the Himes Member.
* Unit VII, the uppermost, is a maroon to orange claystone with occasional highly rounded and polished pebbles of silica.

## Age

A stratigraphic revision of the Cloverly Formation using new uranium lead dates reinterpret the formation as spanning the Valanginian-Cenomanian stages of the Cretaceous period. The individual ages of the members are listed below:
* Pryor Conglomerate; 140-130 Ma (Valanginian-Hauterivian)
* Little Sheep Member; 130-124 Ma (marine section) (Hauterivian-Barremian) and 124-109 Ma (terrestrial section) (Barremian-Albian)
* Himes Member; 109-98 Ma (Albian-Cenomanian)

## Depositional environment

The sediments of the Cloverly Formation were deposited in alluvial and floodplain environments. The basal conglomerates probably represent braided river deposits, while the sandstones were deposited in fluvial channels. The mudstones that contain most of the fossils represent overbank, lacustrine, and pedogenic deposits.

## Vertebrate fauna

Animals recovered include the dinosaurs Deinonychus, Microvenator, Tenontosaurus, Zephyrosaurus and Sauropelta as well as fragmentary remains of Titanosaurs, Ankylosaurs and Ornithomimids. As well, two genera of turtle Naomichelys and Glyptops and the lungfish Ceratodus. Dinosaur eggs have been found in Montana.
References for data: Ostrom 1970; Cifelli et al. 1998; Cifelli 1999; Nydam and Cifelli 2002. Possible goniopholidid remains are known from the formation.

### Dinosaurs
#### Ornithischians
##### Ankylosaurs

Ankylosaurs reported from the Cloverly Formation :
| Genus | Species | State | Stratigraphic position | Material | Notes | Images |
| Sauropelta | S. edwardsorum | Montana Wyoming | | Known from "several articulated skeletons" and common armor plates. Only one partial skull is known. | Articulated skeletons are often encased in carbonate caliche deposits that require acid to be removed safely. | Sauropelta |
| Tatankacephalus | T. cooneyorum | Montana | Cloverly VII | Partial cranium, rib fragments, and osteoderms. | Originally described as an ankylosaurid but has since been reclassified as a nodosaurid. | Sauropelta |

##### Ceratopsians

Ceratopsians reported from the Cloverly Formation :
| Genus | Species | State | Stratigraphic position | Material | Notes | Images |
| Aquilops | A. americanus | Montana | Cloverly VII; Himes Member | | A basal neoceratopsian. | Aquilops |

##### Ornithopods

Ornithopods reported from the Cloverly Formation :
| Genus | Species | State | Stratigraphic position | Material | Notes | Images |
| Tenontosaurus | T. tilleti | Montana Wyoming | | Its remains are the most common of any dinosaur of the formation. | Juvenile remains are sometimes found together, suggesting that young Tenontosaurus lived in sibling groups. Deinonychus teeth are sometimes associated with Tenontosaurus, suggesting a predator-prey relationship between the two. | Tenontosaurus Zephyrosaurus |
| Zephyrosaurus | Z. schaffi | Montana | Himes Member | Its remains are "very rare." | An orodromine ornithopod. | Tenontosaurus Zephyrosaurus |

#### Saurischians

Theropod eggshell fragments are known from the formation. Unidentifiable ornithomimid remains are present and most commonly represented by toe bones. Indeterminate allosauroid remains are known from the formation. Remains identified by John Ostrom as Ornithomimus are suspected by Jack Horner to be of a new ornithomimid genus. Possible remains of a microraptorian, a troodontid, and a basal tyrannosauroid similar to Moros have also been found here as well.
| 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. |

##### Sauropods

Sauropods reported from the Cloverly Formation :
| Genus | Species | State | Stratigraphic position | Material | Notes | Images |
| Rugocaudia | R. cooneyi | Montana | Cloverly VII; Himes Member | | | Sauroposeidon |
| Sauroposeidon | S. proteles | Wyoming | Cloverly VII; Himes Member | | | Sauroposeidon |

##### Theropods

Theropods reported from the Cloverly Formation :
| Genus | Species | State | Stratigraphic position | Material | Notes | Images |
| Acrocanthosaurus | A. atokensis | Wyoming | Cloverly VII; Himes Member | | A carcharodontosaurid. | Acrocanthosaurus Deinonychus Microvenator |
| Deinonychus | D. antirrhopus | Montana Wyoming | | Its remains are "very rare." | A dromaeosaur. Tenontosaurus remains have been recovered in association with Deinonychus teeth, suggesting a predator-prey relationship between the two. | Acrocanthosaurus Deinonychus Microvenator |
| Microvenator | M. celer | Montana Wyoming | Himes Member | Its remains are "extremely rare." Known only from a "[p]artial skeleton with partial skull." The specimen lacks feet and is catalogued as AMNH 3041. | The type specimen AMNH 3041 was recovered by Barnum Brown from Cloverly strata in Montana in 1933. | Acrocanthosaurus Deinonychus Microvenator |
| Ornithomimus | O. velox | Montana Wyoming | | | Later found to be indeterminate ornithomimid remains. | Acrocanthosaurus Deinonychus Microvenator |

### Mammals

Mammals reported from the Cloverly Formation :
| Genus | Species | Notes | Images |
| Astroconodon | A. sp. | Previously referred as "Cloverly triconodont" | Gobiconodon |
| cf. Atokatheridium | Indeterminate | | Gobiconodon |
| Bryceomys | B. sp. | | Gobiconodon |
| Corviconodon | C. montanensis | | Gobiconodon |
| Gobiconodon | G. ostromi | | Gobiconodon |
| Janumys | J. sp. | | Gobiconodon |
| Montanalestes | M. keeblerorum | | Gobiconodon |
| cf. Oklatheridium | Indeterminate | | Gobiconodon |
| cf. Paracimexomys | Indeterminate | | Gobiconodon |
| Spalacotheriidae | Indeterminate | | Gobiconodon |

### Crocodyliforms

Crocodyliforms reported from the Cloverly Formation :
| Genus | Species |
| cf. Atoposauridae | Indeterminate |
| cf. Bernissartidae | Indeterminate |
| cf. Goniopholididae | Indeterminate| |
| cf. Pholidosauridae | Indeterminate |

### Turtles

Turtles reported from the Cloverly Formation :
| Genus | Species |
| Cryptodira | Indeterminate |
| "Glyptops" | "G". pervicax |
| Naomichelys | N. speciosa |
| Testudinata | Indeterminate |

### Lepidosaurs

Lepidosaurs reported from the Cloverly Formation :
| Genus | Species | Notes |
| Paramacellodus | P. keebleri | |
| Paramacellodidae? | Indeterminate | |
| Ptilotodon | P. wilsoni | Also known from the Antlers Formation |
| Teiidae | Indeterminate | |

### Amphibians

Amphibians reported from the Cloverly Formation :
| Genus | Species | Images |
| Albanerpeton | A. ektopistikon | Albanerpeton |
| Anura | Indeterminate | Albanerpeton |
| Batrachosauroididae | Indeterminate | Albanerpeton |
| cf. Scapherpetontidae | Indeterminate | Albanerpeton |
| cf. Scotiophryne | Indeterminate | Albanerpeton |

### Bony fish

Osteichthyes reported from the Cloverly Formation :
| Genus | Species | Images |
| Ceratodus | C. frazieri | Ceratodus |
| Ceratodus | C. nirumbee | Ceratodus |
| aff. Lepidotes | Indeterminate | Ceratodus |
| aff. Pycnodontidae | Indeterminate | Ceratodus |
| Vidalamiinae | Indeterminate | Ceratodus |

### Cartilaginous fish

Chondrichthyes reported from the Cloverly Formation :
| Genus | Species |
| Egertonodus | E. sp. |
| Hybodus | H. parvidens |
| Lonchidion | L. sp. |
| Parvodus | P. sp. |
| Pseudohypolophus | P. sp. |