Homalocephale: a genus of ornithischian dinosaurs

Homalocephalus (lat.: Homalocephale) is a genus of flat-headed ornithischian dinosaurs from the infraorder Pachycephalosaurs (Pachycephalosauria). The skeleton of a homolocephalus is considered one of the most fully preserved among all the fossilized remains of representatives of this infraorder found.

History of discovery and naming

The first dinosaur fossils were found on the territory of the Mongolian aimag Umnegovi (mong.: Өmnogov aimag) and first described in 1974. The later fossils were found in the Tibet Autonomous Region of China.

The Latin generic name Homalocephale comes from the Greek words ωμαλος (homalos; “flat”) and κεφαλή (kephalē; “head”) and means “flat-headed”.

The typical and only known type of gomalocephal is Homalocephale Calathocercos. The fossils found belong to the upper period (late campan tier or early Maastricht). Their age is about 69-76 million years.

Anatomical features and type of power

Gomalocephalus reached a length of about 3 meters and thus belonged to the number of mediumsized Pachycephalosaurs. Like all representatives of the infrast detachment, this dinosaur was distinguished by a noticeably thickened arch of the skull, consisting of the frontal and parietal bones. In flatheaded pachycephalosaurs, the arch of the skull was not convex and at the same time had noticeable cranial seams and welldeveloped upper windows in the temporal regions of the skull. The purpose of the arch of the skull of this form is the subject of scientific discussion.

There were small bone growths on the back and side parts of the skull. The preserved teeth of the upper jaw of the dinosaur found were small with triangular tops. It is assumed that, like all pachycephalosaurs, Homalocephalus consumed mainly plant foods, which may have been supplemented by insects.

Unlike most other representatives of this infraorder, this dinosaur, in addition to the skull, also has a well-preserved torso skeleton. The torso of the homolocephalus was relatively squat, its dorsal vertebrae were strengthened by mutually penetrating ligaments, and long sacral ribs departed from the sacral vertebrae fused with the sacral bone.

The anterior tail vertebrae of the dinosaur also had ribs, while the posterior ones were reinforced with chevrons (v-shaped processes on the underside) and ossified tendons.

The pelvis of Homalocephalus was very wide. Long lower limbs allow us to conclude that the dinosaur could move relatively quickly.


Within the infraorder Pachycephalosaurs, Homalocephalus has traditionally been assigned to the Homalocephalid family (lat.: Homalocephalidae, uniting the oldest flatheaded pachycephalosaurs and named after him in honor of him. This family was opposed to the Pachycephalosauris family (lat.: Pachycephalosauridae), to which more highly developed vitriological pacycephalosaurs were attributed.

Currently, the family of homalocephalids is considered parafilet, that is, it is not considered as a natural related group, since pichycephalosaurus developed from it. So, according to the results of the planned analysis conducted by a group of Polish researchers, led by Teresa Maryanskaya (Polish.: Teresa Maryańska), Homalocephalus was classified as a relatively ancient representative of the infrareant Pachycephalosaurus.

However, the opening of a flatheaded, but at the same time highly developed Pachycephalosaur Darrex (lat.: Dracorex) shared a recognized internal systematics. The American paleontologist Robert Sullivan.: Robert Sullivan) and does suggest that evolution could have taken place in the opposite direction (from dome-headed to flat-headed dinosaurs), that is, a flat skull could be a derived feature.

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