Figure 1.
Selected pathological pachycephalosaurid specimens.
(A) TMP 72.27.01, Gravitholus albertus in dorsal view of erosive lesions; (B) TMP 1992.2.3, Stegoceras validum in dorsal view with arrows denoting dorsal lesions; (C) TMP 2011.012.0009, Stegoceras validum in dorsal view with arrow denoting dorsal lesion; (D) TMP 1997.99.2, an unidentified pachycephalosaurid in dorsal view with arrows denoting lesions; (E) AMNH 0044, Sphaerotholus buchholtzae, in dorsal view with arrows denoting dorsal lesions; (F) BMRP 2001.4.1, Pachycephalosaurus wyomingensis in dorsal view with arrows denoting large depression features and high magnification of deep erosive lesions (G, H). Rostral portion of the frontal denoting “r”.
Table 1.
Analyzed pachycephalosaur genera and frequency of pathologic frontoparietals.
Figure 2.
Schematic diagram illustrating the morphometric landmark-defined regions of lesion distribution in dorsal (A), ventral (B), and left lateral (C) views.
Abbreviations: f, frontal; p, parietal; fp, frontoparietal suture; pso, posterior supraorbital; po, postorbital; ecf Modified from Schott et al., 2011 with permission.
Table 2.
Hypothesized mechanisms of dome modification, and predictions made for each hypothesis.
Figure 3.
Computed tomography images from TMP 79.14.853, Hansseusia sternbergi.
Scale bar equals 5 cm. Sagittal section (A, B) of frontoparietal with arrow annotating low-density region immediately ventral to dorsal lesion (C); Coronal section (D, E) of frontoparietal dome illustrating low-density region immediately ventral to dorsal lesion (F).
Figure 4.
Frequency of pathologic frontoparietal domes of the total sample size (n = 109).
Figure 5.
Distribution of total observed lesions on pachycephalosaurid cranial model (UALVP 2, Stegoceras validum).
Skull in dorsal (A), left lateral (B), rostral (C), and caudal views (D).
Figure 6.
Distribution of lesions among frontal, sutural, and parietal regions in high- and low-domed specimens.
Table 3.
Pathologic frontoparietal dome specimens and distribution of lesions.
Figure 7.
Distribution and frequency of injuries on the postcranial skeleton of extant bovids; Capra, Ovis, and Bison.
Figure 8.
Frontal lesions identified on skulls of Ovis.
Ovis canadensis (A) illustrating smaller lesions clustering around main depression (B), and Ovis dalli (C) illustrating irregular lesion floors (D). Scale bars for A and C equal 5 cm. Scale bars for B and D equal 10 mm.
Figure 9.
Reconstruction of Pachycephalosaurus wyomingensis with cranial lesion.
Figure 10.
Apex of frontoparietal dome of UA2 (Stegoceras validum) (A), and cranial orientation during combat (B); Apex of frontoparietal dome of ZPAL MgD-I/104 (Prenocephale prenes) (C), and cranial orientation during combat (D).
Figure 11.
Hypothetical head-to-head interactions among pachycephalosaurids.
(A) Bison-like head-shoving in large, broad-domed specimens such as Pachycephalosaurus wyomingensis; (B) Ovis-like clashing in Prenocephale prenes; (C) Capra-style broadside butting in high-domed and large-horned specimens such as subadult Pachycephalosaurus (“Stygimoloch” and “Dracorex”).
Figure 12.
Hypothetical head-to-body interactions among pachycephalosaurids.
Giraffa-style necking and parietal clashing in high-domed and large-horned specimens such as subadult Pachycephalosaurus (“Stygimoloch” and “Dracorex”).