New Troodontid Theropod from North America Figure 13. Micro-CT renderings of the pathological first phalanx of the left second pedal digit (II-1) of Talos sampsoni (UMNH VP 19479). Phalanx II-1 in lateral (A, H), flexor (C–D). extensor (F–G) views. Cross-sectional images of Talos taken through axial (B), transverse (E), and parasagittal (I) planes. Hashed lines in A and F represent the plane of section for images in B (1), E (2), and I (3). Anatomical reference lines show position of axial cross section (B) only. Green arrows in B, E, and I depict the boundary between the original cortical contour (shown in purple on C, G, and H) and the exostotic bone. Abbreviations: bc, bony collar; Ic, lateral condyle; mc, medial condyle; oc, original cortical surface. doi:10.1371/journal.pone.0024487.g013 cross-section. The sample is 2.8 mm wide by 3.7 mm radially. A large portion of the inner cortex (approximately 60% of the entire sample) appears diagenetically altered, obscuring much of the original bone histology. A small area consisting of circumferentially organized lamellar bone with possibly one or two widely spaced lacunae represents the only visible portion of endosteal bone. Small patches of adjacent tissue exhibit a more varied extinction pattern and more numerous and randomly oriented lacunae. Examination of the remainder of the inner cortex under cross-polarized light reveals a faint pattern suggestive of fibro-lamellar bone. The outer 40% of the cortex is better preserved, yet also displays evidence of diagenetic alteration. Mineral precipitants are concentrated at and around the central canal of primary osteons. Nevertheless, this region clearly consists primarily of fibro-lamellar bone with longitudinally arranged osteons. The extinction pattern under cross-polarized light differs from that expected in unaltered bone, and instead large, more irregular patches of extinction suggest crystal growth and replacement. Three circumferential bands of cellular, lamellar bone divide the fibro-lamellar region. The middle and outer bands exhibit parallel extinction patterns consistent with circumferentially arranged crystals and lamellar bone. Greater recrystallization towards the cortex interior likely eliminates or obscures this extinction pattern from being fully expressed by the innermost band. Each of these bands is approximately 60–75 mm and contains three or more closely spaced lines. Two circumferential rows of primary osteons lie inward from the innermost band and six osteonal rows separate this band from the next. Three additional rows occur between this middle band and the outermost one. These separations measure 600 and 220 mm respectively. The periosteal surface has a scalloped outline reflecting the development of a single row of primary osteons exterior to the third lamellar band. These retain large and somewhat oval vessel cross-sections indicating that these osteons were not fully developed at the time of death. Proximal fibula. The histologic sample of the proximal fibula (Figure 14A) represents an incomplete cross section 6.0 mm64.1 mm in size, taken from the cranial aspect of the shaft. The overall geometry of the preserved tissues suggests that in comparison to the femur and fibula midshaft samples, the PLoS ONE | www.plosone.org 13 September 2011 | Volume 6 | Issue 9 | e24487