|P. lakustai (C) Nobu Tamura|
31 August 2016
The key feature of Pachyrhinosaurus is its wonderful nasal boss. That boss gives the dinosaur its name ("Thick-nosed Lizard") and also serves as a major point of contention among paleontologists. Charles M. Sternberg initially described the first remains of Pachyrhinosaurus in 1950 under the specific name P. canadensis and recognized the boss as a distinctly hard patch of bone that appeared to be completely devoid of horn. It was thus inferred, by many and not necessarily Sternberg, that the boss was used for butting heads. Fantastical images, perhaps the result of illustration creation rather than any specific comment from researchers, have depicted the dinosaur with an enormous horn on the boss area. This may have also resulted from misinterpretation of the location of a small supraorbital horn in the midline or confusion with Einiosaurus, a ceratopsian dinosaur with rostrally curved nasal horn of some girth. The frill of Pachyrhinosaurus was elaborate an well decorated around the edges, as far as we can tell, with small osteoderm horns. The boss and the small supraorbital horns, perhaps most apparent in P. lakustai, were not sexually indicative traits, as it appears all adults possessed these two anatomical characteristics.