The fossil record of the group is very sparse before the end of the Late Cretaceous, but among those forms are some with well-developed domes on their skulls (Fig. 6a, b) and others (Fig. 6c) with a flat skull (recent research shows that we need to be careful that the fossils all represent adults, as domed pachycephalosaur skulls were flat when they were young).
Macrotarsomys petteri has a large and robust skull with well-developed zygomatic arches (cheekbones).
The rostrum (front part of the skull) is well-developed and contains a pronounced nasal swelling, which is less pronounced than in Paratriaenops; the depression behind the swelling is relatively shallow.
The skull lacked the well-developed crests and massive brow ridges found in modern apes.
Individual philosophies can be simple, developing, or well-developed.
Nasal openings on top of the skull indicate a large, well-developed snout.
The frontal bones (part of the skull roof) bear a well-developed sagittal crest (a crest that provides support for muscles of the head).
Although it is one of the earliest known members of this group, its thickened skull dome is surprisingly well-developed for its geological age," study researcher David Evans, the curator of vertebrate paleontology at the Royal Ontario Museum, said in a statement.
"These frogs have well-developed delivery mechanisms, utilizing bony spines on the skull that pierce the skin in areas with concentrations of skin glands," the study says.
Moreover, with a total of 15 well developed horns or horn-like structures (1 nasal horncore, 2 postorbital horncores, 2 epijugals, and 10 well-developed epi-ossifications), Kosmoceratops possesses the most ornate skull of any known dinosaur.
