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, bentoniticmudstone.
The uppermost unit is theHimes 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:
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.
References for data: Ostrom 1970; Cifelli et al. 1998; Cifelli 1999; Nydam and Cifelli 2002. Possible goniopholidid remains are known from the formation.
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.
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.
A partial skeleton consisting of 18 caudal vertebrae and associated material, including an isolated neural arch, tooth, chevron, and distal section of a metacarpal.
A partial skeleton consists of a dorsal vertebral centrum, caudal vertebral neural arch, right and left pubes, right femur, proximal right fibula, and several fragments.
A dromaeosaur. Tenontosaurus remains have been recovered in association with Deinonychus teeth, suggesting a predator-prey relationship between the two.
Burton, D., Greenhalgh, B.W., Britt, B.B., Kowallis, B.J., Elliott, W.S., and Barrick, R. 2006. New radiometric ages from the Cedar Mountain Formation, Utah and the Cloverly Formation, Wyoming: implications for contained dinosaur faunas. Geological Society of America Abstracts with Programs 38(7): 52.
Chen, Z.-Q. and Lubin, S. 1997. A fission track study of the terrigenous sedimentary sequences of the Morrison and Cloverly Formations in northeastern Bighorn Basin, Wyoming. The Mountain Geologist 34:51-62.
Cifelli, R.L. 1999. Tribosphenic mammal from the North American Early Cretaceous. Nature 401:363-366.
Cifelli, R.L., Wible, J.R., and Jenkins, F.A. 1998. Triconodont mammals from the Cloverly Formation (Lower Cretaceous), Montana and Wyoming. Journal of Vertebrate Paleontology 18: 237-241.
Horner, John R. Dinosaurs Under the Big Sky (Cloverly Formation). Mountain Press Publishing Company. pp. 93–100. ISBN 0-87842-445-8.
Nydam, R.L., and Cifelli, R.L. 2002. Lizards from the Lower Cretaceous (Aptian-Albian) Antlers and Cloverly Formations. Journal of Vertebrate Paleontology 22: 286-298.
Ostrom, J. H. 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana. Peabody Museum Bulletin 35:1-234
Varricchio, D. J. 2001. Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana. pp. 42–57 in D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life. Indiana University Press, Indianapolis, Indiana.
Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.