Dryptosaurus

Dryptosaurus (pron.:"DRIP-toe-SORE-us") is a genus of primitive tyrannosauroid that lived approximately 67 million years ago during the latter part of the Cretaceous period in what is now Eastern North America. Dryptosaurus was a large, bipedal, ground-dwelling carnivore, that could grow up to 7.5 m (24.6 ft) long. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R. Knight made it one of the more widely known dinosaurs of its time, in spite of its poor fossil record. First described by E.D. Cope in 1866 and later renamed by Othniel C. Marsh in 1877, Dryptosaurus is among the first theropod dinosaurs known to science.

Etymology
The genus name Dryptosaurus, means "tearing lizard", and is derived from the Greek words "drypto" (δρύπτω), meaning "to tear" and "sauros" (σαυρος) meaning "lizard".[1] The specific name aquilunguis, is derived from the Latin for "having claws like an eagle's", a reference to the claws on its three-fingered hand. E.D. Cope (1866) published a paper on the specimen within a week of its discovery, and christened it Laelaps aquilunguis at a meeting of the Academy of Natural Sciences in Philadelphia.[2] "Laelaps", which is derived from the Greek for “hurricane” or “storm wind”, was also the name of a dog in Greek mythology that never failed to catch what it was hunting.[3] Laelaps gained popularity as both a poetic and evocative name and became one of the first dinosaurs described from North America, following Hadrosaurus, Aublysodon and Trachodon. Subsequently, it was discovered that the name Laelaps had already been given to a genus of mite, and Cope's lifelong rival O.C. Marsh changed the name in 1877 to Dryptosaurus. The type species is Dryptosaurus aquilunguis.

Description
Dryptosaurus is estimated to have been 7.5 metres (25 ft) long and to have weighed 1.5 metric tons (1.7 short tons), although this is based on partial remains of one individual.[4] Like its relative Eotyrannus, Dryptosaurus seems to have had relatively long arms compared to, for example, Tyrannosaurus. Its hands, which are also relatively large were believed to have had three fingers. Brusatte et al. (2011), however, observed an overall similarity in the shape of the available phalanges of Dryptosaurus with those of derived tyrannosaurids and noted that Dryptosaurus may have had only two functional digits.[2] Each of its fingers were tipped by a talonlike 8 inch claw.[5] Its forelimb morphology suggests that forelimb reduction in tyrannosauroids may not have proceeded in a uniform fashion.[2] Dryptosaurus may have used both its arms and its jaws and as weapons when hunting, capturing and processing prey.

The type specimen is fragmentary skeleton belonging to a single adult individual. ANSP 9995 consists of a fragmentary right maxilla, a fragmentary right dentary, a fragmentary right surangular, lateral teeth, 11 middle-distal caudal vertebrae, both the left and right humeri, three manual phalanges from the left hand (I-1, II-2, and an ungual), the shafts of the left and right pubis bones, a fragmentary right ischium, the left femur, the left tibia, the left fibula, the left astragalus, and a midshaft fragment of metatarsal III. The ontological maturity of the holotype individual is supported by the fact that the neurocentral sutures are closed in all of its caudal vertebrae.[2] AMNH FARB 2438 consists of left metatarsal IV, which likely from the same individual as the holotype.[6]

The fragmentary right maxilla preserves the three alveoli in full and the fourth only partially. The authors were able to ascertain that Dryptosaurus had ziphodont dentition. The shape of the alveolus situated on the anterior portion of the fragment suggests that it housed a tooth that was smaller and more circular than the others; an incisiform tooth which is common in tyrannosauroids. The disarticulated teeth recovered are transversely narrow, serrated (17-18 denticles/cm) and recurved. The femur is only 3% longer than the tibia. The longest manual ungual phalanx recovered measured 176 mm (6.9 in) in length. The morphology of the proximal portion of metatarsal IV suggests that Dryptosaurus possessed an arctometatarsalian pes, an advanced feature shared by derived tyrannosauroids such as Albertosaurus and Tyrannosaurus, in which the third metatarsal is “pinched” between the second and fourth metatarsals.