Lance Formation

The Lance (Creek) Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas. The Lance Formation is Late Maastrichtian in age (Lancian land mammal age), and shares much fauna with the Hell Creek Formation of Montana and North Dakota, the Frenchman Formation of southwest Saskatchewan, and the lower part of the Scollard Formation of Alberta.

Description
The Lance Formation occurs in the uppermost local rock unit of the Cretaceous, which was deposited in the Maastrichtian (some 70.6 to 65.5 million years ago). The formation varies in thickness from about 90m (300 feet) in North Dakota, to almost 600m (2,000 feet) in parts of Wyoming.

At least tens of thousands of Late Cretaceous vertebrate remains have been recovered from the Lance Formation. Fossils ranging from microscopic elements to extensive bonebeds, with nearly complete, sometimes articulated dinosaur skeletons, have been found.

Paleontology
The Lance Formation was laid down by streams, on a coastal plain along the edge of the Western Interior Seaway. The climate was subtropical; there was no cold season and probably ample precipitation Most of the animals known from the formation are freshwater animals, and some are exclusively freshwater forms (for instance, frogs and salamanders). However, marine fossils are also found in the formation, suggesting that the sea was nearby. The bird fauna is mainly comprised of orders still existing today.

Birds and Theropods
Theropoda
 * Chirostenotes pergracilis (Caenagnathidae)
 * Ceramornis (Aves: Charadriiformes?)
 * "Cimolopteryx" (Aves: Charadriiformes)
 * Dromaeosaurus (Dromaeosauridae)
 * Graculavus (Aves)
 * Lonchodytes (Aves: Neoaves)
 *  Palintropus (Aves: Galliformes?)
 * Potamornis (Aves)
 * Ornithomimus velox (Ornithomimidae)
 * Ricardoestesia (Dromaeosauridae)
 * Troodon (Troodontidae)
 * Tyrannosaurus (Tyrannosauridae)
 * UCMP 143274 (Caenagnathidae?)

Other vertebrates
Other land vertebrates include pterosaurs (e.g. cf. Azhdarcho), crocodiles, champsosaurs, lizards, snakes, turtles, frogs and salamanders.

Remains of fishes and mammals have also been found in the Lance Formation.