AGE:
Late Cretaceous (Late Campanian-Early Maastrichtian), Nemegt Formation, 70 million years ago

SIZE:
Both about 2-3 metres in length

MEANING OF NAMES
:Prenocephale - 'Sloping head
'Homalocephale - 'Even head'

PRONUNCIATION:
Pre-know-CEPH-ah-lee,Home-al-oh -CEPH-a h -lee

CLASSIFICATION:
PACHYCEPHALOSAURIA:

Pachycephalosauridae and Homocephalidae Prenocephale prenes and Homalocephale calathocercos are both pachycephalosaurids, literally 'thickheads'. The top of their skulls were 8 to 10 centimetres thick, solid bone apparently protecting a walnut-sized brain. This thickening of the skull has been interpreted as allowing these animals to act like the living mountain sheep in which the males compete for females by holding head-butting contests.

In addition to the domed heads other indications that these dinosaurs head butted can be seen in the stiff spinal column, thus giving it strength for the forces applied when contact occurred, and the angle of articulation of the skull and the neck vertebrae-which puts the head in just the right position to make butting safe and not a back-breaking exercise.

These dinosaurs have very small teeth with serrated crowns, ideal for shredding plant material.

Pachycephalosaurids may have had a lifestyle very like that of modern sheep and goats and even may have moved about in small herds.