Table 1.
Reference and taxonomic assignment of AMNH 5450, the holotype of Ornatotholus browni with accompanying diagnostic characters and additional comments from this study.
Figure 1.
UCMZ(VP) 2008.001, a flat-headed juvenile Stegoceras validum.
A, dorsal, B,ventral; C, posterior; and D, lateral views. Abbreviations: cf, cerebellar fossa; f, frontal; ln, lateral nodes; o, orbit; p, parietal; pn, posterior nodes; po, postorbital; sq, squamosal; ss, sutural surface for; stf, supratemporal fenestra.
Figure 2.
UALVP 49531, a flat-headed juvenile Stegoceras validum.
A, dorsal; B,ventral; posterior, and lateral views. Abbreviations as in Figure 1.
Figure 3.
Illustration of the 18 linear measurements taken between 26 homologous landmarks.
Abbreviations: aso, anterior supraorbital; f, frontal; fnb, frontonasal boss; n, nasal; p, parietal; prf, prefrontal; po, postorbital; pso, posterior supraorbital; sq, squamosal; ss, sutural surface for; stf, supratemporal fenestrae.
Figure 4.
Growth series of Stegoceras validum in dorsal (top) and lateral (bottom) views.
This series depicts the transition from a flat-headed to domed frontoparietal morphology that occurred through ontogeny in this taxon. A, UCMZ(VP) 2008.001 B, AMNH 5450 (holotype of Ornatotholus browni); C, CMN 138; D, CMN 515 (lectotype of Stegoceras validum); E, UALVP 2; F, ROM 53555. Portions of ROM 53555 are reconstructed including the nasals (cropped) and the lateral margins. Reconstructed portions are visible as dark grey areas in the CT images (Fig. 9).
Figure 5.
Bivariate logarithmic plots with RMA regression lines for selected variables.
A, heights of frontoparietal vs width across frontoparietal suture. Blue, height of nasal; red, height of frontoparietal at the contact of the anterior and posterior supraorbitals; green, thickness of frontoparietal. B, widths of frontoparietal vs width across frontoparietal suture. Blue, width of frontonasal boss; red, width across the supraorbital lobes; green, width across the frontoparietal at the contact of the posterior supraorbital and postorbital sutures. C, lengths of frontoparietal vs width across frontoparietal suture. Blue, length of frontal; red, length of parietal; green, length of frontoparietal. D, lengths of frontoparietal vs length of parietal. Blue, length of anterior supraorbital suture; red, length of posterior supraorbital suture; green, length of postorbital suture; orange, length of frontal. Measurements are log (mm).
Figure 6.
Bivariate logarithmic plots with RMA regression lines for frontoparietal thickness vs. width.
Red, only specimens more domed (thicker) than TMP 84.5.1; blue, includes the three partially domed frontals; and grey, with all specimens included. Measurements are log (mm).
Table 2.
Allometric regression of Stegoceras validum frontoparietal heights against frontoparietal width.
Table 3.
Allometric regression of Stegoceras validum frontoparietal heights against frontoparietal length.
Table 4.
Allometric regression of Stegoceras validum frontoparietal heights against parietal length.
Table 5.
Allometric regression of Stegoceras validum frontoparietal heights against frontal length.
Table 6.
Allometric regression of Stegoceras validum frontoparietal widths against frontoparietal width.
Table 7.
Allometric regression of Stegoceras validum frontoparietal widths against frontoparietal length.
Table 8.
Allometric regression of Stegoceras validum frontoparietal widths against parietal length.
Table 9.
Allometric regression of Stegoceras validum frontoparietal lengths against frontoparietal width.
Table 10.
Allometric regression of Stegoceras validum frontoparietal lengths against frontoparietal length.
Table 11.
Allometric regression of Stegoceras validum frontoparietal lengths against parietal length.
Table 12.
Allometric regression of Stegoceras validum frontoparietal heights against frontoparietal width excluding all specimens less domed (thick) than TMP 84.5.1.
Table 13.
Allometric regression of Stegoceras validum frontoparietal heights against frontoparietal length excluding all specimens less domed (thick) than TMP 84.5.1.
Table 14.
Allometric regression of Stegoceras validum frontoparietal heights against parietal length excluding all specimens less domed (thick) than TMP 84.5.1.
Table 15.
Allometric regression of Stegoceras validum frontoparietal heights against frontal length excluding all specimens less domed (thick) than TMP 84.5.1.
Table 16.
Allometric regression of Stegoceras validum frontoparietal heights against frontoparietal width excluding all specimens less domed (thick) than TMP 84.5.1, except for three partially domed frontals (TMP 78.19.04, 86.71.2, and 2002.12.57).
Table 17.
Allometric regression of Stegoceras validum frontoparietal heights against frontal length excluding all specimens less domed (thick) than TMP 84.5.1, except for three partially domed frontals (TMP 78.19.04, 86.71.2, and 2002.12.57).
Figure 7.
High-resolution CT images of AMNH 5450.
A, dorsal view (left) and frontal section (right); B, lateral view (left) and sagittal section (right); C, anterior view (left) and transverse section through the frontal (right). The histological zones of Goodwin and Horner [37] are denoted. The arrow identifies an artifact likely produced by mineralized collagen fibres present across and along the interfrontal suture. Abbreviations: f, frontal; f-f, inter-frontal suture; f-p, frontoparietal suture; p, parietal; po, postorbital; pso, posterior supraorbital; sq, squamosal; Z-1 to Z-3, histological Zones I to III.
Figure 8.
High-resolution CT images of TMP 84.5.1.
A, dorsal view (left) and frontal section (right); B, lateral view (left), median sagittal section (middle), and lateral sagittal section (right); C, anterior view (left), anterior transverse section through the frontal (middle), and posterior transverse section through the parietal (right). The histological zones of Goodwin and Horner [37] are denoted. The arrow identifies an artifact likely produced by mineralized collagen fibres present across and along the interfrontal and frontoparietal sutures. Abbreviations: f, frontal; f-f, inter-frontal suture; f-p, frontoparietal suture; p, parietal; po, postorbital; pso, posterior supraorbital; sq, squamosal; Z-1 to Z-3, histological Zones I to III.
Figure 9.
High-resolution CT images of ROM 53555.
A, frontal section; B, median sagittal section; C, transverse section through the posterior portion of the frontal. The histological zones of Goodwin and Horner [37] are denoted. The arrow identifies an artifact likely produced by mineralized collagen fibres. Plaster reconstructions are visible as dark grey areas. Abbreviations: f, frontal; f-f, inter-frontal suture; f-p, frontoparietal suture; p, parietal; Z-1 to Z-3, histological Zones I to III.
Figure 10.
Outline of methodology for calculation of relative void-space.
AMNH 5450 (left), TMP 84.5.1 (middle), and ROM 53555 (right). A transverse section was taken from a HRCT scan of the frontal at the contact of the posterior supraorbital and postorbital sutures. Scans were thresholded using the Huang method [54], [55]. Void-space was calculated in a region of interest (red square).
Figure 11.
Bivariate logarithmic plots with RMA regression lines for frontoparietal thickness vs width (A) and frontoparietal thickness vs frontal length (B) and the CT scans for AMNH 5450, TMP 84.5.1, and ROM 5355 and their relative void-spaces (a proxy for vascularity).
Note the substantial decrease of vascularity with increased dome development (thickness) and size (frontoparietal width, A; frontal length, B). Measurements are log (mm).
Table 18.
Ontogenetic changes in the cranial morphology of Stegoceras validum.