Laelaps (dinosaur)

''Dryptosaurus'' ( ) is a genus of tyrannosauroid that lived approximately 67 million years ago (mya) during the latter part of the Cretaceous period, New Jersey. ''Dryptosaurus'' was a large, bipedal, ground-dwelling carnivore, that grow up to long and weigh up to . Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R. Knight made ''Dryptosaurus'' one of the more widely known dinosaurs of its time, in spite of its poor fossil record. First described by Edward Drinker Cope in 1866 and later renamed by Othniel C. Marsh in 1877, ''Dryptosaurus'' is among the first theropod dinosaurs known to science.

Discovery and species

Prior to the discovery of ''Dryptosaurus'' in 1866, New World theropods were known only from some isolated theropod teeth discovered in Montana by Joseph Leidy in 1856. The discovery of this genus gave North American paleontologists the opportunity to observe an articulated, albeit incomplete, theropod skeleton. During the 19th century, this genus unfortunately became a wastebasket taxon for the referral of isolated theropod elements from across North America given that tyrannosauroids were not recognized as a distinct group of large theropods in the late 19th century, and numerous theropod species were assigned to it (often as ''Lælaps'' or ''Laelaps'') only to be later reclassified.

The genus name ''Dryptosaurus'', means "tearing lizard", and is derived from the Greek words "dryptō" (), meaning "I tear" and "sauros" () meaning "lizard". 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 named it ''Laelaps aquilunguis'' at a meeting of the Academy of Natural Sciences in Philadelphia. "''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. ''Laelaps'' gained popularity as both a poetic and evocative name and became one of the first dinosaurs described from North America, following ''Hadrosaurus'' and ''Trachodon''. Later 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''.

Brusatte ''et al.'' (2011) noted that well-preserved, historic casts of most of the type material ANSP 9995/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.

Misassigned species

''Laelaps trihedrodon'' was coined by Cope in 1877 for a partial dentary (now missing) from the Morrison Formation of Colorado. Five damaged partial tooth crowns (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. However some of the ''Allosaurus''-like characters of the teeth are primitive to theropods as a whole and may have been present in other large-bodied Morrison Formation theropod species.

''Laelaps macropus'' was coined by Cope for a partial hind limb 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''.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, 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 Tyrannosauroid and that the distal metatarsal could’ve been from an Ornithomimosaur.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. Brownstein also placed the pedal phalanges in Ornithimimosauria, though didn’t create a lectotype for ''Laelaps macropus.''

Description

''Dryptosaurus'' is estimated to have been long and to have weighed , although this is based on partial remains of one individual. Like its relative ''Eotyrannus'', ''Dryptosaurus'' seems to have had relatively long arms when compared with more derived tyrannosaurs such as ''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. Each of its fingers were tipped by an eight-inch, talon-like claw.Dryptosaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 112-113 Its forelimb morphology suggests that forelimb reduction in tyrannosauroids may not have proceeded in a uniform fashion. ''Dryptosaurus'' may have used both its arms and its jaws and as weapons when hunting, capturing and processing prey.

The type specimen is a 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 pubic 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. AMNH FARB 2438 consists of left metatarsal IV, which are likely from the same individual as the holotype.

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 in length. The morphology of the proximal portion of metatarsal IV suggests that ''Dryptosaurus'' had an arctometatarsalian foot, 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.

According to Brusatte ''et al.'' (2011), ''Dryptosaurus'' can be distinguished based on the following characteristics: the combination of a reduced humerus (humerus: femur ratio = 0.375) and a large hand (phalanx I-1:femur ratio = 0.200), the strong mediolateral expansion of the ischial tubercle, which is approximately 1.7 times as wide as the shaft immediately distally, the presence of an ovoid fossa on the medial surface of the femoral shaft immediately proximal to the medial condyle, which is demarcated anteriorly by the mesiodistal crest and demarcated medially by a novel crest, the presence of a proximomedially trending ridge on the anterior surface of the fibula immediately proximal to the iliofibularis tubercle, the lip on the lateral surface of the lateral condyle of the astragalus is prominent and is overlapping the proximal surface of the calcaneum, metatarsal IV is observed with a flat shaft proximally, resulting in a semiovoid cross section that is much wider mediolaterally than it is long anteroposteriorly.

Classification

Since the time of its discovery, ''Dryptosaurus'' has been classified in a number of theropod families. Cope (1866), Leidy (1868) and Lydekker (1888) noted obvious similarities with the genus ''Megalosaurus'' which was known at the time from remains discovered in southeastern England. Based on this line of reasoning, Cope classified it as a megalosaurid. Marsh, however, examined the remains and later assigned to its own monotypic family, Dryptosauridae. 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 like Marsh, felt that it warranted placement in Dryptosauridae. This phylogenetic assignment was also supported by the work of Russell (1970) and Molnar (1990). Other phylogenetic studies during the 1990s suggested that ''Dryptosaurus'' was a coelurosaur, though its exact placement within that group remained uncertain.

In 1946, Charles W. Gilmore was the first to observe that certain anatomical features may link ''Dryptosaurus'' with coeval