PACHYCEPHALOSAURUS

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'''Pachycephalosaurus''' ('thick headed lizard', from Greek '''pachy-/παχυ-''' meaning 'thick', '''cephale/κεφαλη''' meaning 'head' and 'saurus/σαυρος' meaning 'lizard') was a dinosaur of the family ''Pachycephalosauridae'', from the Late Cretaceous Period of what is now North America. Remains have been excavated in Montana, South Dakota, and Wyoming (hence the species name). It was an omnivorous creature, which is only known from a single skull and a few extremely thick skull roofs.

Contents

Anatomy

Classification

Lifestyle

Diet

References

External links

Anatomy

''Pachycephalosaurus'' was probably bipedal and was the largest of the bone-headed dinosaurs. It is famous for having a large, bony dome atop its skull, up to 25cm (10 inches) thick, which safely cushioned its brain. The dome's rear aspect was edged with bony knobs and short bony spikes were projected upwards from the snout. These features suggest that, despite their bipedal stance, they were more likely to have been relatives of the ceratopsians, rather than ornithopods.
Using data from other Pachycephalosauridae, it has been estimated that ''Pachycephalosaurus'' was approximately the length of a large car, maybe around 4.6m long (15 feet) and had a fairly short, thick neck, short fore limbs, a bulky body, long hind legs and a heavy tail, which was likely to have been held rigid by ossified tendons. Large eye-sockets that faced forward suggest that the animal had good vision and was capable of binocular vision.

Classification

''Pachycephalosaurus'' gives its name to the Pachycephalosauria, a large clade of herbivorous dinosaurs which lived during the Late Cretaceous Period in North America and Asia. It is the most famous member of the group (though not the one which is best-preserved). The clade also includes ''Stegoceras'', ''Homalocephale'', and ''Prenocephale''. Within the tribe Pachycephalosaurini, ''Pachycephalosaurus'' is most closely related to ''Tylosteus'', ''Dracorex'', and ''Stygimoloch''.

Lifestyle

Scientists once suspected that ''Pachycephalosaurus'' and its relatives were the bipedal equivalents of bighorn sheep or musk oxen; that male individuals would ram each other headlong. It was also believed that they would make their head, neck, and body horizontally straight, in order to transmit stress during ramming. However, it is now believed that the pachycephalosaurs would not have used their domes in this way.
Foremost, the skull roof could not have adequately sustained impact associated with such ramming. Also, there is no evidence of scars or other damage on fossilized ''Pachycephalosaurus'' skulls.^[1] Furthermore, the cervical and anterior dorsal vertebrae show that the neck was carried in an "S"- or "U"-shaped curve, rather than a straight orientation. Lastly, the rounded shape of the skull would lessen the contacted surface area during head-butting, resulting in glancing blows.
It is more probable that the ''Pachycephalosaurus'' (and others) engaged in flank-butting, which entails individuals standing roughly parallel, rather than facing each other directly. They would then orient their head downwards and to the side, striking the rival pachycephalosaur on their flank. This theory is supported by the relatively broad width of most pachycephalosaurs, a trait that would have protected vital organs from harm.

Diet

Scientists do not yet know what these dinosaurs ate. Having very small, ridged teeth they could not have chewed tough, fibrous plants as effectively as other dinosaurs of the same period. It is assumed that pachycephalosaurs lived on a mixed diet of leaves, seeds, fruit and insects. The sharp, serrated teeth would have been very effective for shredding plants.

References

1. Goodwin, Mark and Horner, John. 2004. Cranial histology of pacycephalosaurs (Ornithischia: Marginocephalia) reveals transitory structures inconsistent with head-butting behavior. Paleobiology 30(2):253-267.

External links

★ Dinodictionary