Gorgosaurus Albertosaurus Tyrannosaurs from the Late Cretaceous of western Canada Russell, Dale A.  Gorgosaurus  Russell 1970 Gilmore 1946 [208,889,502,529] Reptilia Tyrannosauridae Albertosaurus GBIF Animalia Dinosauria 29 20 Chordata species lancensis comb. nov.    Gilmore(1946) hasdescribed theskull ofa small carnivorous dinosaur from theLance Formation ofeastern Montana. The skull is quite different from that of Tyrannosaurusand Gilmorefounded a new species on it, correctly referringit to    Gorgosaurus(= Albertosaurus).  Although theskull is onlyhalf as long as that ofa fully grown  A. libratus, thesutures between thebones of theskull roof are tightlyinterlocking, and some have been obscured through intergrowth; thesupraoccipital alae of theparietals are welldeveloped, and a clearlyformed tuberosity is present on theventral border of thejugal (  Gilmore1946). The opposite conditions prevail in theskull ofAMNH 5664, a specimen of  A. libratus ofcomparable size. The skull of  A. lancensisis therefore probably froma fully grown individual, and its small size may be characteristic of thespecies.  Albertosaurus lancensisfurther differs from  A. libratusand  A. sarcophagus(AMNH 5222) in that thefrontals meeton themidline throughout their entire length, while in thelatter two species these elements are separatedanteriorly by a small wedge ofbone from the nasals. The frontalsare not sodeeply cleft above theorbits as is thecase in A. libratusand A. sarcophagus.  Gilmore(1946: 6) suggested that theprefrontal may be ratherwell exposed on theskull roof, unlike in themore ancient species of thegenus. Otherwise theskulls of the threeforms are quite similar.