Dryptosaurus ( ; meaning "tearing lizard") is a genus of theropod dinosaur that lived in the present-day East Coast of the United States during the Late Cretaceous period. The type, and only, species, D. aquilunguis was described by Edward Drinker Cope in 1866 as Laelaps aquilunguis, however the genus name was preoccupied by a mite. As a result, Cope's rival in the Bone Wars, Othniel Marsh, replaced the genus name with Dryptosaurus. Dryptosaurus is known from a single, fragmentary skeleton including parts of the mandible (lower jaw), limbs, and vertebrae. These fossils were unearthed by fertilizer miners in New Jersey in rock layers of the New Egypt Formation. This formation dates to the late Maastrichtian stage of the Late Cretaceous, around 67 to 66 million years ago. Several other fragmentary remains have been assigned to Dryptosaurus, however their referral is uncertain.
Like other tyrannosaurs, Dryptosaurus was a bipedal carnivore with a long tail and elongated skull. Unlike other tyrannosaurs like Tyrannosaurus and Tarbosaurus, Dryptosaurus possessed large forelimbs ending in large claws and lithe hindlimbs. Size estimates place it at in length and in mass. The genus had ziphodont (sharp, blade-like, laterally compressed) dentition, dissimilar to that of larger tyrannosaurs.
Dryptosaurus is a member of Eutyrannosauria, the clade including Tyrannosauridae and tyrannosaurs like Nanotyrannus and Bistahieversor but excluding more basal tyrannosaurs like Dilong. This puts Dryptosaurus in an intermediate position between lithe, early tyrannosaurs and the large tyrannosaurids. However, some studies have also put it in its own family, Dryptosauridae, or in Nanotyrannidae. Dryptosaurus is one of few Cretaceous dinosaurs known from the Eastern United States. During the Late Cretaceous, North America was divided into two continents; Appalachia and Laramidia. The breakup of North America into these continents spurred the evolution of unique characteristics in Appalachian tyrannosaurs not observed in Laramidian tyrannosaurs. Fossils of Dryptosaurus are known from the marine New Egypt Formation where dinosaur bodies floated out to sea and became fossilized. Mosasaurs, fish, sharks, and other marine fauna are represented in this formation.
Discovery and species
Up until 1866, theropods from the United States 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 associated theropod skeleton in sediments coming from the New Egypt Formation in a quarry near Barnsboro, New Jersey. This formation dates to the Maastrichtian stage of the Late Cretaceous period and is part of the Monmouth Group. In August 1866, American 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 were also noted by Cope, however they have since been lost. Several sacral vertebrae Cope assigned to Dryptosaurus are now believed to belong to the protostegid turtle Pneumatoarthrus. An isolated metatarsal IV (AMNH FARB 2438) possibly belonging to ANSP 9995 was found at the same locale, but this has come into question. It was in Cope's possession and purchased by the American Museum of Natural History in 1902, however it was not mentioned by Cope until an 1870 paper. 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. Some of the bones have evidence of molding, which was possibly done by Benjamin Waterhouse Hawkins during his failed project to erect a Paleozoic Museum in Central Park, New York.
On 21 August 1866, Cope presented his description of ANSP 9995 to the American Philosophical Society at what is now the Academy of Natural Sciences, 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. In the 1870s, conflict began between Cope and another American paleontologist, Othniel Charles Marsh, leading to the onset of the Bone Wars. In 1877, Marsh pointed out that Cope's genus name Laelaps was preoccupied by a genus of mite, leading to Marsh to erect the genus name Dryptosaurus. This name derives from the Greek δρύπτω drypto "tear" and σαῦρος sauros "lizard", creating "tearing reptile". Despite this, Cope continued to use the name Laelaps, refusing to use Dryptosaurus. 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 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.
Other species
Dubious species Laelaps trihedrodon was first discovered by Oramel W. Lucas, a schoolteacher from Garden Park, Colorado, who collected an incomplete dentary with teeth from 1877 to 1878 in strata of the Late Jurassic-aged Morrison Formation in Garden Park. Cope described this material as belonging to a new species of Laelaps, Laelaps trihedrodon, "three-hedged tooth", in 1877. Additionally, Cope assigned five teeth, a femur, and some skull fragments to the species, however all of these fossils, including the holotype dentary, but the five teeth have since been lost. The lost fossils were originally part of Cope's personal collection, however when his collection was purchased by the American Museum of Natural History in 1903, none of the fossils but the teeth could be located. Cope, as in many of his descriptions, failed to figure or meticulously describe the L. trihedrodon holotype. In a 1939 catalog, Oskar Kuhn listed the species as Antrodemus (?) trihedrodon, while listing Allosaurus as a synonym of Antrodemus. In 2001, Chure argued that AMNH 5780 probably belongs to Allosaurus. In 1865, Joseph Leidy described two theropod tibia that had been found in the Maastrichtian-aged Navesink Formation of New Jersey as belonging to a new genus and species of dinosaur, Coelosaurus antiquus. Along with the tibiae, Leidy assigned several fossils from the same site, consisting of an incomplete right tibia (AMNH 2550), the proximal (close to body) end of a right metatarsal II or IV (AMNH 2553), the distal (away from body) end of a right metatarsal II (AMNH 2552), and three pedal phalanges (AMNH 2551), as a syntypse of the species. However, in 1868 Cope described this specimen (AMNH 2550-2553) as belonging to its own species of Laelaps (Dryptosaurus) which he named L. macropus. Thomas R. Holtz listed it as an indeterminate tyrannosauroid in his contribution to the second edition of the Dinosauria.Holtz, T.R. (2004). "Tyrannosauroidea." Pp. 111-136 in Weishampel, Dodson and Osmolska (eds). The Dinosauria (second edition). University of California Press, Berkeley. In 2017, Chan-gyu Yun informally gave it the new generic name Teihivenator, stating that it was its own genus of tyrannosauroid.Chan-gyu Yun (2017). "Teihivenator gen. nov., a new generic name for the tyrannosauroid dinosaur "Laelaps" macropus (Cope, 1868; preoccupied by Koch, 1836)". Journal of Zoological And Bioscience Research. 4 (2): 7–13. doi:10.24896/jzbr.2017422. However that same year Chase Brownstein argued that "Teihivenator macropus" is actually a chimera and a nomen dubium. Brownstein stated that only the partial right tibia could definitely be considered tyrannosauroid, whereas the metatarsal fragments came from either a tyrannosauroid or an ornithomimosaur and the pedal phalanges were ornithomimosaurian. This makes the specimen invalid and a chimera.Brownstein, C. D. (2017). Theropod specimens from the Navesink Formation and their implications for the Diversity and Biogeography of Ornithomimosaurs and Tyrannosauroids on Appalachia (No. e3105v1). PeerJ Preprints. In 1876, Cope named Laelaps falculus on the basis of ten isolated teeth that had been found by Jno. C. Issac from the "Fort Union Beds" (now considered the Judith River Formation) of Montana dating to the Campanian stage of the Late Cretaceous period. Oliver Hay reclassified L. falculus as a species of Dryptosaurus in 1902, Henry Osborn considered it a species of Deinodon, a dubious genus of tyrannosaurid, that same year, and George Olshevsky placed it as a species of the dromaeosaurid Dromaeosaurus based on the small, thin nature of the teeth. However, L. falculus is a nomen dubium and likely is based on juvenile tyrannosaur teeth. In 1876, Cope named Laelaps incrassatus on the basis of two isolated maxillary teeth that had been found by Jno. C. Issac from the "Fort Union Beds" (now considered the Judith River Formation) of Montana dating to the Campanian stage of the Late Cretaceous period. In 1892, Cope assigned two incomplete tyrannosaur skulls from rocks of the Horseshoe Canyon Formation in Alberta, Canada to L. incrassatus on the basis of their similar tooth anatomy. In 1903 and 1904, Lawrence Lambe used the valid generic name Dryptosaurus incrassatus for the skulls, however both of these skulls are now assigned to Albertosaurus sarcophagus, while L. incrassatus is considered a nomen dubium. In 1876, Cope named Laelaps explanatus on the basis of several teeth that had been found in rocks of the "Fort Union Beds" (now considered the Judith River Formation) of Montana dating to the Campanian stage of the Late Cretaceous period. It was later classified as a species of Deinodon and Dryptosaurus, however it is now considered a dubious species of tyrannosaurid. Laelaps hazenianus was described by Cope in 1876 on the basis of seven teeth from the Judith River Group of Montana dating to the Late Campanian stage of the Late Cretaceous period. It was later classified as a species of Deinodon and Dryptosaurus, however it is now considered a dubious species of tyrannosaurid.
Reassigned species Megalosaurus (Dryptosaurus) saharicus was an alternative combination for Megalosaurus saharicus proposed by Charles Depéret and Justin Savornin in 1927, however it is now classified in its own genus, Carcharodontosaurus. Erectopus (Dryptosaurus) superbus was an alternative combination for Megalosaurus superbus proposed by Depéret and Savornin in 1927, however it is now classified in its own genus, Erectopus.Allain, R. (2005). The enigmatic theropod dinosaur Erectopus superbus (Sauvage, 1882) from the Lower Albian of Louppy-le-Château (Meuse, France). in Carpenter, K. 2005. The Carnivorous Dinosaurs, Indiana University Press: 72-86.
Indeterminate remains