Theropod Toe Bone
Hell Creek Formation
Wibaux County, Montana
Cretaceous 68-65 mya
Specimen approx. size: 2" x 0.75"
Theropods are characterized by hollow bones and three toes and claws on each limb. All known theropods are bipedal. Theropods are generally classed as a group of saurischian, or "reptile-hipped" dinosaurs. They were ancestrally carnivorous, although a number of theropod groups evolved to become herbivorous and omnivorous. Theropods first appeared during the late Triassic and included all the large terrestrial carnivores from the early Jurassic until at least the close of the Cretaceous. In the Jurassic, birds evolved from a group of specialized theropods, and are today represented by over 10,000 living species.
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana.
The Hell Creek Formation occurs in Montana and portions of North Dakota, South Dakota, and Wyoming.
Strata in Hell Creek a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian, the last part of the Cretaceous period, by fluvial activity in fluctuating river channels and deltas and very occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The climate was mild, and the presence of crocodilians suggests a sub-tropical climate, with no prolonged annual cold. The famous iridium-enriched K–T boundary, which separates the Cretaceous from the Cenozoic, occurs as a discontinuous but distinct thin marker bedding within the Formation, near its uppermost strata.