TYRANNOSAURIDAE Osborn 1906

Carpenter, K., 1992, Tyrannosaurids (Dinosauria) of Asia and North America, Aspects of Nonmarine Cretaceous Geology, Beijing: China Ocean Press, pp. 250-268 : 253

Family TYRANNOSAURIDAE Osborn 1906

Diagnosis: (General) Head large relative to body size; neck, trunk and forelimbs are short. (Cranial) Nasals very rugose,often fused along the midline,and constricted between the lacrymals; frontals excluded from the orbits by the lacrymals; jugal pierced by large foramen; premaxillary teeth D-shaped in cross-section, with carinae along the posteromedial and posterolateral margins; vomer with diamond-shaped process between the maxillae; ectopterygoid with large ventral opening; surangular foramen large. (Postcranial) Cervical centra slightly opisthocoelous, anteroposteriorly compressed,and broad;scapula long and slender;humerus with weakly- to moderately-well developed deltopectoral crest;manus reduced to two functional digits (II and III),with digit IV reduced to a splint;pubis with well developed anterior foot;distal end of the ischium not expanded; ascending ramus of astragulus broad and tall.

Discussion: Among the various specimens which have at one time or the other been referred to the tyrannosaurids, there are several that form a natural, cohesive group. These define the family Tyrannosauridae to the exclusion of all others (a detailed examination of all taxa which have been referred to the Tyrannosauridae is in preparation). The result is that the family is now known only from the Campanian and Maastrichtian of Asia and North America.

The family Tyrannosauridae is considerably more derived from any other theropod. This is especially evident in the reduction of many bones: the cervicals are anteroposteriorly compressed dies, the scapula is a slender bone, the forelimbs reduced in size relative to body size,and the manus has only two functional digits. Other bones, however,are more developed,e.g.,the much larger size of the skull relative to the body, and the anterior foot of the publis is very well-developed compared to Allosaurus . The presence of a jugal fenestra and the large size of the surangular fenestra are also derived conditions over that seen in the Allosauridae and Megalosauridae .

The Abelisauridae is convergent with the Tyrannosauridae in several features, including the relative large size of the skull to body size and reduced forelimbs ( Bonaparte, 1985). However, the elongated quadrate, peculiar peg-like descending process of the squamosal, and enormous antorbital and lateral temporal fenestra are derived conditions for the Abelisauridae .