Figure 1.
Artistic rendering of Pachyrhinosaurus perotorum engaged in head-butting/pushing behavior.
In the first description of Pachryhinosaurus by Sternberg [1], he speculated that the enlarged nasal boss in the taxon might have been used in head battering or pushing behavior, an idea emphasized by this image of two Pachyrhinosaurus perotorum sparring with their craniofacial bosses, while a third looks on. Artwork by K. Carr.
Figure 2.
Map showing approximate location of the Kikak-Tegoseak Quarry, North Slope, Alaska, U.S.A.
Kikak-Tegoseak Quarry indicated by red star.
Figure 3.
Photographs and interpretive line drawings of DMNH 21460, Pachyrhinosaurus perotorum incomplete nasal.
A. Nasal in left lateral view. B. Line drawing of nasal in left lateral view. C. Nasal in right lateral view. D. Line drawing of nasal in right lateral view. E. Nasal in dorsal view. F. Line drawing of nasal in dorsal view. G. Nasal in anterior view. H. Line drawing of nasal in anterior view. I. Hypothetical ‘subadult’ Pachyrhinosaurus perotorum skull outline with DMNH 21460 superimposed to show approximate location of specimen in the skull. Abbreviations: bs, basal sulcus; fr, frontal contact; ms, median sulcus; nh, nasal horn/incipient nasal boss; prf, prefrontal contact; ri, ridge laterally bounding rugose area; rug, rugose patch on dorsal surface of nasal; sb, smooth bone. Gray fill indicates broken bone surfaces or cracks. Scale bars equal 5 cm.
Figure 4.
Comparison of new, immature specimen and ‘adult’ skull of Pachyrhinosaurus perotorum.
A. DMNH 21460, Pachyrhinosaurus perotorum incomplete nasal superimposed on line drawing of hypothetical immature individual skull. B, DMNH 22558, Pachyrhinosaurus perotorum incomplete skull of mature individual. Both images in left lateral view and to scale. Scale bar equals 50 cm.
Table 1.
Ontogenetic stages of nasal boss development in Pachyrhinosaurus (Stage 1 youngest), based upon descriptions and inferences of Currie et al. [4].
Table 2.
New hypothesis of ontogenetic stages for the nasal boss of Pachyrhinosaurus based on new information (marked by asterisks) derived from DMNH 21460, an incomplete nasal from an immature Pachyrhinosaurus perotorum individual from Alaska.
Figure 5.
Osteological correlates for a thick cornified pad in Synceros caffer and Pachyrhinosaurus perotorum.
A. DMNH 2013, Synceros caffer skull in left lateral oblique and dorsolateral view, showing exposed left frontal boss and proximal base of osseous horn core. B. Same specimen in closer, dorsal view centered on rugose frontal boss area. C. Close up of area inside rectangle in B. D. DMNH 21460, Pachyrhinosaurus perotorum, close-up of posterior end of nasal in left lateral and slightly dorsal view. E. Close up of area inside rectangle in D. Ellipses in C and E surround clusters of similar densely spaced, small foramina. Abbreviations: bs, basal sulcus; fb, frontal boss; ri, ridge separating rugose area from smooth bone; rug, rugose patch on dorsal surface of nasal; sb, smooth bone surface. Scale bar in A through C shows divisions in cm. Scale bar in D equals 5 cm. Scale bar in E equals 1 cm.
Figure 6.
Pachyrhinosaurus perotorum skulls and integument reconstruction through ontogeny.
Hypothesis of craniofacial changes in osteology and integument through some of the ontogenetic stages of Pachyrhinosaurus perotorum listed in Table 2. Stage 2 skull based on juvenile P. lakustai of Currie et al. [4]. Stage 4 skull based on DMNH 21460. Stage 6 skull based on DMNH 22558 [5]. Right-side ‘life’ reconstructions based on hypotheses of Pachyrhinosaurus integument structures of Hieronymus et al. [10], and new data from DMNH 21460. Light tan indicates ‘normal’ skin, while dark brown indicates cornified scales, horns, sheaths, or other cornified tissue. Scale bar equals 50 cm.