Tyrannosaurus rex Osborn 1905
Creators: name: Dalman, Sebastian G.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Dinosauria
Tyrannosauridae
Tyrannosaurus
Tyrannosaurus rex

description: FAMILY Tyrannosauridae Osborn, 1906   GENUS Tyrannosaurus Osborn, 1905    Tyrannosaurus rex Osborn, 1905   
Material. YPM VP 057488(A) and YPM VP 057488B, two isolated digital pedal phalanges II-2 and III-2 of the left foot.  
Horizon and locality. Upper Cretaceous Lance Formation, Buck Creek, 37 km north of Lusk, Wyoming, USA.  
Description. In this description the two isolated digital pedal phalanges are referred to as II-2 YPM VP 057488(A) and III-2 YPM VP 057488(B).  
Pedal phalanx II-2 YPM VP 057488(A) (Figure 5 A–F) is missing a small portion of the distal articular region.The entire length of the phalanx is 16.5 cm. The specimen YPM VP 057488(A) compares well with pedal phalanx II-2 of other examples of Tyrannosaurus rex (e.g., FMNH PR 2081; Figure 6 A–C). In all other tyrannosaurids, including T. rex, the pes phalanx II-2 is constricted at the middle and has expanded proximal and distal articular regions (Brochu 2003), which is the same in YPM VP 057488(A).The long axis of phalanx II-2 YPM VP 057488(A) is not parallel to the sagittal plane and slopes medially (Brochu 2003; Carrano 2007). The dorsal surface of the phalanx is narrower than the ventral surface, which is a common characteristic of tyrannosaurid theropods, including T. rex (Brochu 2003).   
The proximal articular region of phalanx II-2 YPM VP 057488(A) is concave and oval as in other tyrannosaurids from the coeval Hell Creek, Willow Creek and Scollard formations of the northwestern United States and southwestern Canada. As in other tyrannosaurids, phalanx II-2 YPM VP 057488(A) has ventral rugosities that are adjacent to the proximal articular surface (Brochu 2003). These rugosities are well developed within the ventral surface and ventrolateral grooves (Brochu 2003).  
YPM VP 057488(A) preserves the lateral and medial distal condyles, which contain deep ligament pits. In large tyrannosaurids like Tyrannosaurus rex the distal condyles of the proximal pedal phalanges are cleft and asymmetrical (Carr and Williamson 2000; Brochu 2003). This characteristic morphology is also evident in YPM VP 057488(A).   
Pedal phalanx III-2 YPM VP 057488(B) (Figure 7 A–F) is missing a portion of the dorsoanterior surface. The entire length of the phalanx is 12. 5 cm. YPM VP 057488(A) compares well with pedal phalanx III-2 of other examples of Tyrannosaurus rex (e.g., FMNH PR 2081; Figure 8 A–C). The phalanx is shorter distally and constricted at the middle, with expanded proximal and distal articular regions (Brochu 2003). The proximal articular region for the articulation with the corresponding pedal phalanx is concave and oval. The ventrolateral surface of the proximal articular region is rugose as in other tyrannosaurids. These rugosities are large and situated within the ventral and ventrolateral grooves of the phalanx (Brochu 2003). In dorsal view the lateral and medial condyles of the phalanx have linear margins, which are symmetrical. The ligament pits are circular, deep and are visible in dorsal view. The distal articular region of the phalanx is trapezoidal, as in other tyrannosaurids including T. rex.
description: Published as part of Dalman, Sebastian G., 2013, New Examples of Tyrannosaurus rex from the Lance Formation of Wyoming, United States, pp. 241-254 in Bulletin of the Peabody Museum of Natural History 54 on page 246, DOI: 10.3374/014.054.0202, http://zenodo.org/record/3897695