Dryptosaurus (/ˌdrɪptoʊˈsɔːrəs/ DRIP-toh-SOR-əs) is a genus of eutyrannosaurian theropod dinosaur that lived on the island continent of Appalachia approximately 67-66 million years ago during the end of the Maastrichtian age of the Late Cretaceous period. Dryptosaurus was a large, bipedal, ground-dwelling carnivore that could grow up to 7.5 metres (25 ft) long and weigh up to 756–1,500 kilograms (1,667–3,307 lb).

Although it is now largely unknown outside of academic circles, the 1897 painting of the genus by Charles R. Knight made Dryptosaurus one of the more widely known dinosaurs of its time, despite of its poor fossil record. First described by Edward Drinker Cope in 1866 and later renamed by Othniel Charles Marsh in 1877, Dryptosaurus is among the first theropod dinosaurs ever known to science.

Up until 1866, theropods from the Americas were only known from isolated teeth discovered by Ferdinand Van Hayden during Geological Survey excursions into Montana. During the summer of 1866, workers from the West Jersey Marl Company uncovered an incomplete theropod skeleton in a quarry near Barnsboro, New Jersey with sediments belonging to the Maastrichtian-aged New Egypt Formation. In August 1866, paleontologist Edward Drinker Cope was notified of the discovery and encouraged to visit the marl pit to obtain the specimen. When he arrived, he was thoroughly surprised by the skeleton's completeness and uniqueness, calling it the "finest discovery I have yet made". The skeleton was then deposited at the Academy of Natural Sciences in Philadelphia under the catalogue number ANSP 9995 and includes; skull and dentary fragments, teeth, caudal vertebrae, humeri, an incomplete manus, a partial pelvis, and nearly complete left hindlimb. However, four chevrons, a sternum, and a scapula which are now lost were also noted by Cope in addition to several sacral vertebrae which are now referred to the protostegid Pneumatoarthrus. An isolated metatarsal possibly belonging to the skeleton was found at the same locale, but this has come into question.

Cope presented his description of the specimen to the Academy on August 21, 1866, naming it a new genus and species of dinosaur, Laelaps aquilunguis. "Laelaps", which is derived from the Greek word "hurricane" or "storm wind", was also the name of a dog in Greek mythology who never failed to catch what it was hunting. The genus name was occupied by a mite and replaced by the name Dryptosaurus, "slashing reptile", by Othniel Marsh, Cope's rival in the Bone Wars, in 1877. However, Cope maintained that the name Laelaps was valid for years after, refusing to use Dryptosaurus. Also in the 1870s, a partial dentary of a theropod was unearthed from the Late Jurassic strata of the Morrison Formation outside Canon City, Colorado. Cope coined Laelaps trihedrodon, "three-hedged tooth", for the dentary in 1877, but it has since been lost. Later L. trihedrodon was moved the genus Antrodemus, now Allosaurus, based on its derivation but it is now considered a nomen dubium. Five damaged partial tooth crowns from AMNH 5780, mistakenly thought to have belonged to the L. trihedrodon holotype, share many features in common with Allosaurus and probably belong to that genus instead. However, some of the Allosaurus-like characteristics of the teeth are primitive to theropods as a whole and may have been present in other large-bodied Morrison Formation theropod species. Brusatte et al. (2011) noted that well-preserved, historic casts of most of the type material from ANSP 9995 and AMNH FARB 2438 are housed in the collections of the Natural History Museum in London (NHM OR50100). The casts show some detail that is no longer preserved on the original specimens, which have significantly degraded due to pyrite disease.

The discovery of this genus gave North American paleontologists the opportunity to observe an articulated, albeit incomplete, theropod skeleton. During the late 19th century, this genus unfortunately became a wastebasket taxon for the referral of isolated theropod elements from across North America, given that Tyrannosauroidea was not recognized as a distinct group of large theropods at the time and numerous theropod species were assigned to it (often as Lælaps or Laelaps), only to be later reclassified.

Laelaps trihedrodon was coined by Cope in 1877 for a partial dentary (now missing) from the Morrison Formation of Colorado.

Laelaps macropus was also coined by Cope for a partial leg found in the Navesink Formation that Joseph Leidy had referred earlier to the ornithomimid Coelosaurus, distinguishing it from Dryptosaurus by its longer toes. Thomas R. Holtz listed it as an indeterminate tyrannosauroid in his contribution to the second edition of the Dinosauria. In 2017, it was informally given the new generic name "Teihivenator". Earlier that year, Brownstein (2017) analyzed the material of Laelaps macropus and found that only the partial tibia could be definitely classified as that of a tyrannosauroid and that the distal metatarsal could have been from an ornithomimosaur. Brownstein also placed the pedal phalanges in Ornithimimosauria, though he did not create a lectotype for Laelaps macropus.

Some potential specimens consisting of partial teeth and femur fragments from the Tar Heel/Coachman Formation have been described in 1979 as cf. Dryptosaurus or Albertosaurus. In February 2018, based on specimens described by Baird and Horner (1979), Brownstein tentatively classified the partial teeth (USNM 7199 and ANSP 15332) as D. sp. and the partial femur fragments (ANSP 15330 and USNM 7189, the latter of which was in part a syntype of Hypsibema) as D. aquilunguis. He also referred some teeth and fragmentary postcranial material from the Marshalltown Formation to D. sp. In December 2018, he simply referred to these specimens as "material comparable to the tyrannosaur Dryptosaurus aquilunguis", not directly representing Dryptosaurus itself.