ALBERTOSAURUS ARCTUNGUIS Parks, 1928a
TYPE— ROM 807
best specimens—type, TMP 81.10.1 ?
time—latest Campanian to early Maastrichtian of the late Late Cretaceous
horizon and distribution—Horseshoe Canyon Formation of Alberta
| Type | TMP 81.10.1 | |
|---|---|---|
| SKULL LENGTH— | 970 mm | |
| TOTAL LENGTH— | ~8.6 m | ~8.0 |
| FEMUR LENGTH— | 1020 mm | 950 |
| HIP HEIGHT— | 2.7 m | 2.5 |
| TONNAGE— | 2.5 | 2.0 |
To be frank, I am not sure what to do with this species and the below A. sarcophagus, which are both from the Horseshoe Canyon Formation. This is because both species’ old type remains leave a lot to be desired, and new specimens do not have enough comparable parts. This species’ type, for example, is missing its head. There do appear to be two big, common tyrannosaurs in the Horseshoe Canyon. One is a robust species that may be A. sarcophagus, the other is gracile. The type of A. arctunguis is lightly built and long legged, and the same is true of the very nice new skull and partial skeleton, TMP 81.10.1 (both are missing their tails). So these may be the same gracile species. I have taken a bit of a risk and combined the two individuals to come up with a skeletal drawing that it is hoped represents A. arctunguis. If so then A. arctunguis had smaller arms and finger claws, and longer legs, than A. libratus . Also, the orbit is nearly cut in half by a postorbital bar like that of Tyrannosaurus . These characters imply that A. arctunguis was a direct descendant of A. libratus, and the direct ancestor of later A. megagracilis .