PRELIMINARY REPORT OF A NEW JUVENILE TYRANNOSAURID SKELETON FROM THE HELL CREEK FORMATION OF CARTER COUNTY, MONTANA

During the summer of 2007 the partial skeleton of a mid-sized theropod (femur length 770 mm) was excavated from the Hell Creek Formation (latest Maastrichtian) of western Carter County, Montana. The skeleton is represented by disarticulated postcranial elements including pedal phalanges, a first digit pedal claw, three manus claws, partial fibula and tibia, a complete left femur, four dorsal vertebrae, a partial gastralia basket, thoracic ribs, and a partial right humerus, that were recovered from a sandy clay-pebble conglomerate. Skeletal elements are well preserved and referable to the Tyrannosauridae . Based on their size, and the presence of morphological features suggestive of immaturity, this new specimen may provide important information on the ontogeny of Tyrannosaurids. Of particular interest are three manus claws recovered with the specimen. These consist of two first digit claws and a second digit claw which are remarkable for their large size (180mm). The manus claws are well preserved and display typical Tyrannosaurid morphology including a large proximal condyle and proximally placed flexor tubercle. At present, it is unclear whether the claws belong to the aforementioned juvenile skeleton or if they indicate a second tyrannosaur skeleton is buried at the site.