Albertosaurus lancensis (Gilmore), Russell, 1970

Russell, Dale A., 1970, Tyrannosaurs from the Late Cretaceous of western Canada, Ottawa: National Museum of Natural Sciences, Publications in Palaeontology, No. 1 : 20

Albertosaurus lancensis (Gilmore)

Gilmore (1946) has described the skull of a small carnivorous dinosaur from the Lance Formation of eastern Montana. The skull is quite different from that of Tyrannosaurus and Gilmore founded a new species on it, correctly referring it to

Gorgosaurus (= Albertosaurus ).

Although the skull is only half as long as that of a fully grown A. libratus , the sutures between the bones of the skull roof are tightly interlocking, and some have been obscured through intergrowth; the supraoccipital alae of the parietals are well developed, and a clearly formed tuberosity is present on the ventral border of the jugal ( Gilmore 1946). The opposite conditions prevail in the skull of AMNH 5664, a specimen of A. libratus of comparable size. The skull of A. lancensis is therefore probably from a fully grown individual, and its small size may be characteristic of the species.

Albertosaurus lancensis further differs from A. libratus and A. sarcophagus (AMNH 5222) in that the frontals meet on the midline throughout their entire length, while in the latter two species these elements are separated anteriorly by a small wedge of bone from the nasals. The frontals are not so deeply cleft above the orbits as is the case in A. libratus and A. sarcophagus . Gilmore (1946: 6) suggested that the prefrontal may be rather well exposed on the skull roof, unlike in the more ancient species of the genus. Otherwise the skulls of the three forms are quite similar.