Figure 12. Pedal phalanges of Talos sampsoni (UMNH VP 19479). Digit one of right pes in lateral (A) and medial (B) views; digit two of left pes in medial (C), lateral (D), and extensor (E) views; digit three of left pes in medial (F), lateral (G), and extensor (H) views; digit four of left pes in medial (I), lateral (J), and extensor (K) views. Abbreviations: er, extensor ridge; dl, dorsal ‘‘lip’’; ird, dorsal intercondylar ridge; irv, ventral intercondylar ridge; p, pathology; pp, proximal pit; PI-1, first phalanx of digit 1; PI-2, second phalanx of digit 1; PII-1, first phalanx of digit 2; PII-2, second phalanx of digit 2; PII-3, third phalanx of digit 2; PIII-1, first phalanx of digit 3; PIII-2, second phalanx of digit 3; PIII-3, third phalanx of digit 3; PIII-4, fourth phalanx of digit 3; PIV-1, first phalanx of digit 4; PIV-2, second phalanx of digit 4; PIV-3, third phalanx of digit 4; PIV-4, fourth phalanx of digit 4; PIV- 5, fifth phalanx of digit 4. Scale bar equals 5 mm. doi:10.1371/journal.pone.0024487.g012 New Troodontid Theropod from North America condyle exhibits a similar, yet less angular, outline. The lateral collateral ligament pit on this phalanx is asymmetrically enlarged, with the ventral and proximal margins of the pit extended in their respective directions (Figure 13A). Notably, phalanx II-1 of Talos exhibits extreme pathological modification and several aspects of its morphology cannot be considered representative for the species. A surface lesion, demarcated by a narrow raised edge of cortical bone, is visible just proximal to the lateral collateral ligament pit (Figure 13A). MicroCT analysis of phalanx II-1 reveals an extensive accumu- lation of cortical bone consistent with post-traumatic or post- infection exostosis (Figures 13B–C and 13G). The internal bony organization of II-1 has also been modified in accordance with these external alterations. Reorganization is particularly pro- nounced in the distal half of the element in specific association with the subcortical condylar areas (see additional discussion of osteopathology below). Thus, the unusually straight shaft and highly asymmetrical distal condyles are clearly attributable to secondary osteogenesis. Phalanx II-2 is generally similar to other deinonychosaurians. It is compact, and in contrast to phalanx II-1, the proximal articular facet exhibits a pronounced median ridge and markedly well- developed heel (Figure 12C–E). The medial distal condyle shares the asymmetrical outline of phalanx II-1 to a minor degree (the lateral condyle is incomplete along the dorsal margin). In contrast to the situation in phalanx II-1, there are no external signs of osteopathology on II-2. Moreover, a micro-CT based comparison of the left and right II-2 reveals near identical internal organization. Phalanx II-3 has asymmetrical grooves, a hint of a caudodorsally projecting lip (as evidenced by a slight depression between the main body of the ungual and the dorsal aspect of the proximal articular facet when viewed laterally), and a moderately developed flexor tubercle (Figure 12C–D). Phalanges of the third pedal digit of Talos exhibit proximoven- tral heels, weak (III-3) to absent (III-1, III-2) intercondylar ridges, and generally lack extensor pits (Figure 12F–H) (an extensor pit is slightly expressed on PIII-1). Lateral collateral ligament pits are subcircular and deep, whereas medial pits are shallower and proximodistally elongate (Figure 12F–G). The medial distal condyle of phalanx III-3 is slightly asymmetrical in circumference, mirroring the condition of II-I and II-2. The distal condyles are also asymmetric in overall size, the lateral being more robustly developed. This asymmetry is consistent with the modified weight- bearing role of this digit and is not attributable to pathology. All phalanges of the fourth pedal digit lack extensor pits and possess shallower lateral collateral pits (Figure 12I–K). The proximal three phalanges have well-developed heels, the medial aspect of which is more robust. Phalanx IV-1 exhibits a concave proximal facet (taller than wide), with a medially inclined dorsal aspect. The medial distal condyle of phalanx IV-4 is more robust than the lateral. The proximal articular surfaces of phalanges IV-3 and IV-4 are subtriangular and relatively symmetrical. Two pronounced pits incise the ventrolateral and ventromedial aspects of phalanx IV-1 close to the proximal articular facet and dorsal to the planar heels. Only a ventrolateral pit is present on phalanx IV-2 and both pits are absent on IV-3 and IV-4. A similar trait is seen on the phalanges of the third digit, which also exhibit well-developed heels; however this feature is expressed as a slight depression on these phalanges in contrast to a distinct pit. These depression are distinct on both sides of phalanx III-1, the lateral aspect of III-2, and both lateral and medial aspects of III-3. Histological description. Proximal femur. The femoral sample (Figure S1) consists of only a small portion of the overall PLoS ONE | www.plosone.org 12 September 2011 | Volume 6 | Issue 9 | e24487