Week 13 Flashcards
The cerapoda are genosaurs that include
marginocephalians and ornithopoda
What are the two main groups of marginocephalians and what character distinguishes them from each other?
Pachycephalosauria and ceratopsia
They are distinguished by the shape of their heads.
Pachycephalosauria
Dome headed marginocephalians, thick headed lizards, bipedal.
Where did we find the pachycephalosauria? How?
The pachycephalosauria were found in both Asia and North America. We think this was because there was a land bridge between Russia and North America (Beringia) during this time.
Pachycephalosaurs brains
Not as large as the skull would lead us to believe, tiny brain is mostly dedicated to smelling, we know this because it had enlarged olfactory lobes.
Brain was tilted down toward back of skull.
The bones on the back of the pachycephalosaur’s skull are tilted down, in fact the bigger the dome…
the more bones toward the back face downward.
Evidence FOR pachycephalosaurs using their thick skulls for head butting
- skull acts like a big helmet
- the bigger the dome the more rotation, the more bones toward the back face downward, this prevents skull dislocation
- strong neck muscles
- further down the spine the vertebrae are uniquely linked in such a way that prevents lateral rotation
- injuries are concentrated at the apex of the dome, this is unique to head-to-head combat
Evidence AGAINST pachycephalosaurs using their thick skulls for head butting
Stygimoloch: the North American pachycephalosaur
Its skull cap contained a network of canals for blood vessels, if the stygimoloch is a distinct species then this suggests the dome was for aesthetic and not head-butting.
It could be that stygimoloch is a juvenile pachycephalosaur which means head-butting is an adult behaviour.
Pachycephalosaurs display features
- dome
- canine like teeth (looking vicious)
- knobby/spiney osteoderms on the sount/side of the face and marginocephalian shelf
Why kind of pachycephalosaur fossils were discovered in Asia?
Complete skulls and articulated skeletons, suggesting no transport, which means they must have lived in a sahara type desert while seasonal streams were running
What kind of pachycephalosaur fossils were discovered in North America?
Water worn skull caps that had undergone a lot of transport, suggesting they were living in mountains.
What characters do all ceratopsians possess?
- a rostral bone (unique bone at tip of snout)
- narrow skulls with hooked beak
- jugal horns (a skull that flares in the cheek region)
- frill (a boney shelf that extends off the back of the head)
- thick hooves on all toes
Not all ceratopsians had ___ and not all of them were ____.
Not all ceratopsians had horns and not all of them were quadrupedal.
We only found ceratopsian fossils in the
Northern hemisphere
Primitive forms of ceratopsia
- small
- bipedal
- without horns
- migrate to North America from Asia, diversify, and we see huge quadrupedal beasts!
Ceratopsia Horns
- made of keratin, so the fossils we find of it are just the core, which means the horns would have been large during life
- unlike antlers, horns are not shed
- most ceratopsia had facial horns, but primitive forms lack this feature
2 main groups of the ceratopsidae and what distinguishes these two groups from each other?
centrosaurines and chasmosaurines
Centrosaurines have short frills, short horns over the orbitals, and typically more ornamented frills. Chasmosaurines have long frills and long horns over the orbitals, and elongated snouts.
What might ceratopsidae frills be used for?
- defence
- display
- ritualized combat
- defence of territories
- maturity
- species identification
Centrosaurs and triceratops frills as defence
Centrosaurs have fewer injuries to the skull so may have focused on flank attacks. They may have locked horns in combat.
Triceratops tend to have more injuries around the face, suggesting more face-to-face combat.
