Dryptosaurus (Dryptosaurus): a genus of primitive tyrannosauroids

Dryptosaurus is a genus of primitive tyrannosauroids that lived in the eastern part of modern North America. Dryptosaurus aquilunguis is the only species of Dryptosaurus. It was a large predatory dinosaur up to 7 meters long, moving on the ground on two legs.

Dryptosaurus, first described in 1866 by American paleontologist Edward Cope but renamed in 1877 by another paleontologist, Othniel Marsh, was one of the first theropods known to science.

The generic name “Dryptosaurus” (Dryptosaurus) means “tearing lizard”. The specific name “aquilunguis” means “having claws (on the forelimbs) like an eagle”. In 1866, within 1 week of the discovery of E.D. Cope published a description of the dinosaur specimen he had discovered and at a meeting at the Academy of Natural Sciences in Philadelphia called it “Laelaps aquilunguis”.

The generic name “Laelaps” in Greek meant “hurricane or storm wind”, besides, that’s what (Lelaps) was the name of a magical dog in Greek mythology, from which prey never escaped during hunting. Following hadrosaurus, aublysodon, and trachodon, Laelaps became one of the first North American dinosaurs to be described. However, later it turned out that this name had already been assigned to one genus of ticks, so in 1977 G.H. Marsh renamed the lizard Dryptosaurus aquilunguis.

Driptosaurus is estimated to have been 7.5 meters long and 1.5 tons in weight, although this assumption is based on only partial remains of a single specimen. Like its relative Eothyran, it appears to have had three-toed and relatively longer forelimbs than, for example, Tyrannosaurus Rex.

At the end of each finger was a claw of about 20 cm long. The morphology of the front extremities of the driptosaurus suggests that their dimensions could decrease in the process of evolution to varying degrees in different tyrannosaurides. So, it is possible that this dinosaur used to capture and cut production during hunting not only the jaw, but also the front limbs.

The typical copy of the driftosaur is skeleton fragments belonging to only one adult individual. Holesry of the species Dryptosaurus aquilunguis under the Anti 9995 number includes fragments of the right parts of the maxillary, mandibular and inflammatory bones, side teeth, 11 mediumonhand tail vertebrae, left and right humerus, 3 phalanx of the left hand (first phalanx of the first finger, second and kugte phalang second finger), the bodies of the left and right pubic bones, fragments of the right sciatic bone, the left femur, the left tibia, the left fibula, the left thawed bone and fragment of the middle part of the third of the third metatarsal bone. The ontogenetic maturity of the holotype specimen is supported by the fact that the sutures between the bodies of all caudal vertebrae are closed. Specimen number AMNH FARB 2438 consists of the fourth metatarsal of the left foot, which appears to be from the same holotype specimen.

A fragment of the right part of the maxillary bone contains 3 fully preserved and one partially preserved dental sockets. Based on this fact, some scientists have suggested that Dryptosaurus had zyphodont (flattened laterally and with serrated cutting edges) teeth.

The shape of the tooth socket, located in the anterior part of the bone fragment, suggests that the tooth that was in it was smaller and more rounded in cross section compared to other teeth and had a common incisor shape for tyrannosauroids. The teeth detected separately are flattened in the transverse direction, have sawtust edges (17-18 teeth per 1 cm) and bent back. The femur is only 3% longer than the tibia.

The length of the longest ungual phalanx found is 176 mm. The morphology of the proximal fourth metatarsal suggests that the proximal third metatarsal of Dryptosaurus was sandwiched between the second and fourth metatarsals, a common evolutionary feature of its descendant tyrannosauroids such as Albertosaurus and Tyrannosaurus.

Before the discovery of Dryptosaurus in 1866, New World theropods were known only from individual teeth, which were discovered in 1856 in Montana by Joseph Leidy. The discovery of Dryptosaurus allowed North American paleontologists to see an articulated, albeit incomplete, theropod skeleton. Unfortunately, in the 19th century, this genus of dinosaurs turned out to be a taxon, belonging to which they began to attribute scattered fragments of a wide variety of theropods from all over North America, as a result of which many of their individuals were erroneously attributed to it.

Some scientists now accept that there may have been another species of Dryptosaurus, Dryptosaurus macropus, known from a hind limb fragment found in the Upper Cretaceous Navesink Formation, New Jersey. Joseph Leidy originally classified this species as a coelosaurus (Coelosaurus).

Cope later recognized it as a separate species and gave it the name Laelaps macropus, since this specimen differed from the other, now known as Dryptosaurus, by longer fingers of the hind limbs. Subsequently, most scientists decided that the bones probably belonged to the colosaurus, but in 2004, paleontologist Thomas R. Holtz classified this dinosaur specimen as an indeterminate tyrannosauroid species, which may be related to the genus Dryptosaurus.

Since its discovery, Dryptosaurus has been placed in a variety of theropod families. So, Cope (in 1866.), Leidy (in 1868.) and Richard Lydekker (in 1888.) noted clear features of its similarity with the genus Megalosaurus, which at that time was known from the remains found in the south-east of England. Based on this line of reasoning, Cope classified this dinosaur as a megalosaurus.

However, Marsh studied the remains and later classified them as an independent monotypic family of dryptosaurids (Dryptosauridae). Fossil material attributed to Dryptosaurus was re-examined by Ken Carpenter in 1997 due to the fact that since the discovery of E. Copa, many different theropods have been discovered.

Carpenter realized that, given some of the unusual features of this reptile, it could not be placed in the framework of any of the existing families, and, like Marsh, confidently ranked it among the dryptosaurids. Such a phylogenetic classification was also supported by the work of Syokon Russell (1970).) and Ralph Molnar (1990.).

According to other phylogenetic studies that were carried out in the 90s of the 20th century, it is assumed that Dryptosaurus was a member of the Coelosaurus genus, although it seems impossible to accurately determine its place within this genus.

In 1946 Charles Wu. Gilmour was the first paleontologist to notice that certain anatomical features made it possible to link Dryptosaurus with its Upper Cretaceous contemporaries, Albertosaurus and Tyrannosaurus Rex. This observation also found support in the studies of Roland Byrd and Jack Horner (1979).), but was not widely accepted until a new discovery in 2005.

Dryptosaurus remained the only large carnivorous dinosaur known from eastern North America until the discovery in 2005 of the parent tyrannosauroid genus, Appalachiosaurus. The latter, which is known from more complete remains, is similar to Dryptosaurus both in body size and morphologically. This discovery clearly showed that Dryptosaurus was a primitive tyrannosauroid.

A detailed phylogenetic analysis conducted in 2011 by a team of scientists led by Steve Bruceatt confirmed the relationship of this dinosaur to tyrannosauroids and allowed it to be identified as an “intermediate” genus of tyrannosauroids, more advanced than basal taxa such as Guanlong and Dilong ( Dilong), but at the same time more primitive compared to representatives of more advanced tyrannosaurids.

The type specimen of Dryptosaurus (the holotype of Dryptosaurus aquilunguis ANSP 9995) was found in the New Egypt formation at the West Jersey Marl Company quarry in New Jersey. Driptosaurus fossils were found by quarry workers in marl and sandstone deposits formed during the Maastrichtian stage of the Cretaceous about 67 million years ago.

The researchers suggest that the New Egypt Formation is an offshore formation and believe that it is the deeper water equivalent of the Tinton formation and the Red Bank formation. It is located above the Navesink Formation, from which Dryptosaurus bone material may have been recovered.

What did the dryptosaurs eat, it is difficult to determine. It is known that hadrosaurids lived simultaneously with them and on the same territory (on the island-continent of Appalachia), which could make up a significant part of their diet. In addition, nodosaurs also lived here, although it seems unlikely that Dryptosaurus preyed on these armored herbivorous dinosaurs.

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