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Dryptosaurus
Temporal range: Upper Cretaceous
Laelops-Charles Knight-1896.jpg
A painting of Dryptosaurus
by Charles R. Knight
Scientific classification
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Dryptosauridae

Marsh, 1890
Genus:
Dryptosaurus

Dryptosaurus ("tearing lizard") was a theropod dinosaur of the Tyrannosauroidea type. It was found in Upper Cretaceous strata of Eastern North America. It was formerly known as Laelaps.

It was given its name because it had 8-inch (21-cm) long finger claws. Fossils have been found in New Jersey. It is known only from a partial skeleton.

Description

Dryptosaurus SIZE
Estimated size, compared to human

Dryptosaurus is estimated to have been 7.5 metres (24.6 ft) long and to have weighed 1.5 metric tons (1.7 short tons), 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 a talonlike 8 inch claw. 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 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. AMNH FARB 2438 consists of left metatarsal IV, which are likely from the same individual as the holotype.

Dryptosaurus by Durbed
Restoration

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 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.

A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group. 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.

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