Dryptosaurus is estimated to have been 7.6 metres (25 ft) long and to have weighed 1.5 to 1.7 tons, although this is based on partial remains of one individual. Like its relative Eotyrannus, Dryptosaurus seems to have had relatively long arms compared to, for example, Tyrannosaurus, and the hands are believed to have had three fingers. Each of these fingers was tipped by a talonlike 8 inch claw. These claws lend a meaning for the type species aquilunguis: eagle-clawed.
Discovery and species
In 1866, an incomplete skeleton (ANSP 9995) was found in New Jersey by quarry workers in rock belonging to the upper part of the New Egypt Formation. Paleontologist E.D. Cope described the remains, naming the creature "Lælaps" ("storm wind", after the dog in Greek mythology that never failed to catch what it was hunting). Lælaps became one of the first dinosaurs described from North America (following Hadrosaurus, Aublysodon and Trachodon). Subsequently, it was discovered that the name Lælaps had already been given to a genus of mite, and Cope's lifelong rival O.C. Marsh changed the name in 1877 to Dryptosaurus.
Diagram showing the remains after Dryptosaurus During the 19th century, numerous theropod species in North America were assigned to the genus Dryptosaurus (often as Lælaps or Laelaps), only to be reclassified. Only one potential second species is sometimes recognized today, D. macropus, known from a partial hind limb found in the Navesink Formation (probably roughly equivalent to the New Eagle Formation in time). Joseph Leidy originally referred the specimen to Coelosaurus. Cope later recognized it as a distinct species, referring to it as Lælaps macropus, differing from the specimen now known as Dryptosaurus by its longer toes. Subsequently, most scientists had concluded that it probably belonged to Coelosaurus after all, but in 2004 paleontologist Thomas R. Holtz listed it as an indeterminate tyrannosauroid, possibly referable to the genus Dryptosaurus.
Although certainly a carnivore, the paucity of known Cretaceous East Coast dinosaurs make ascertaining the specific diet of Dryptosaurus difficult. Hadrosaurids are known from the same time and place as Dryptosaurus, the island continent of Appalachia, and they may have been a prominent part of its diet. Nodosaurs were also present, although less likely to be hunted due to their armor plating.
Dryptosaurus was the only large carnivore known in eastern North America before the discovery of Appalachiosaurus in 2005. During that time Dryptosaurus was classified in a number of theropod families. Originally considered a megalosaurid by Cope, it was later assigned to its own family (Dryptosauridae) by Marsh, and later found (through phylogenetic studies of the 1990s) to be a coelurosaur, though its exact placement within that group remained uncertain. The discovery of the closely related (and more complete) Appalachiosaurus made it clear that Dryptosaurus was a primitive tyrannosauroid.
Artist's restoration The fossil material assigned to Dryptosaurus was reviewed by Ken Carpenter in 1997 in light of the many different theropods discovered since Cope's day. He felt that due to some unusual features it couldn't be placed in any existing family and warranted placement in its own family, Dryptosauridae. Dubious species Numerous species have been assigned to Dryptosaurus based on very fragmentary material, and probably belong to various other types of theropod. These include:
D. macropus (Cope, 1868) [originally Laelaps]
D. falculus (Cope, 1876) [originally Laelaps]
D. hazenianus (Cope, 1876) [originally Laelaps]
Another dubious species was Laelaps trihedrodon by Cope in 1877. Although the type specimen included a partial dentary, all material—except for a collection of five damaged partial tooth crowns (AMNH 5780)—has been lost. AMNH 5780 has many features in common with Allosaurus and is probably referable to that genus. However some of the Allosaurus-like characters of the tooth are primitive to theropods as a whole and may have been present in the less-studied or poorly preserved [Morrison Formation theropod species. Consequently the synonymization of L. trihedrodon with Allosaurus is tentative, despite its high likelihood.