Marginocephalia
- includes the Ceratopsians and the Pachycephalosaurs
Evolutionary novelties:
- frill on the back of the skull
- all plant eating ornithischians
- primarily Late Cretaceous
Ceratopsia
- made up of 2 groups:
- Psittacosauridae
- Neoceratopsia
-Evolutionary novelties
- rostral bone in skull
- skull with narrow beak and flaring jugals (cheeks)
- deep jugal with distinct ridge
- a frill
- a highly vaulted palate in front of mouth
Psittacosauridae
- Psittacosaurus, the "parrot dinosaur"
- earliest ceratopsian (lower Cretaceous)
- did not exceed 2 m. in length
- rudimentary frill
- short snout, high position of nostrils
- tall rostrum resembles a parrot's beak
- reduction of function toes of hand to 3
- skeletal structure similar to early ornithischians:
a) hind limbs longer than fore-limbs
b) fore-foot on 3 functional toes, hind foot on 4 function toes
c) short neck and moderately long tail
e) ossified tendons in dorsal and sacral regions of some specimens
- teeth well worn (plant eater)
- gastroliths found with some skeletons
- teeth had broad, flat wear surfaces with self-sharpening edges
- teeth inset from sides of skull = ?"cheek pouches"?
Neoceratopsia
- among most diverse Late Cretaceous dinosaurs
- 2 families:
a) Protoceratopsids
b) Ceratopsids
- these groups are differentiated from Psittacosaurids by:
1) extremely large heads
2) broad, prominent frill
3) pointed and sharply keeled rostrum
4) limb structures = obligate quadruped
Protoceratopsidae
- small ( 1 to 2.5 m )
- all Late Cretaceous but represent an evolutionary intermediary between Psittacosaurus and ceratopsids
- Protoceratops:
- larger skull and frill than Psittacosaurus
but frill rather short with no horns and small nostrils
- fore- and hind limbs nearly equal in length
- more massive limbs with broader feet
Ceratopsidae
- only Late Cretaceous of North America
- large ( 4 to 8 m )
- habitual quadrupeds
- Evolutionary novelties:
a) very large skulls ( 1 to 2.4 m long )
b) large nostrils
c) prominent frills
d) variety of horns
- 2 types of ceratopsids:
1) pachyrhinosaurines ( more primitive group)
- relatively short and high face
- short frill
- horns near nostrils ( nasal horns ) are much larger than paired horns behind eyes
( postorbital horns )
2) ceratopsines
- long, narrow face
- long frills
- postorbital horns larger than postnasal
Triceratops
- typical ceratopsine
- long, low snout
- large post-orbital horns
- short frill which lacked fenestrae
- edge of frill lined with small conical horns called epoccipitals
- teeth form complete dental battery
- large jaw moving muscles attached to frill
- bone of horn and over frill bore numerous grooves and channels for bloodvessels
- fore-limbs and hindlimbs almost equal in length
- ossified tendons only in hip region
- pelvis fused to backbone along 10 sacral vertebrae
Pachycephalosauria
- dome-headed dinosaurs ( greatly thickened bone on skull roof )
- bipedal ornithischians
- 2 families (all Cretaceous):
a) Homalocephalidae
b) Pachycephalosauridae
Homalocephalidae
- more primitive family of the two
- flat, table-like skull roof of even thickness from side to side and pitted dorsally
- skulls have open supratemporal fenestrae
- short, canine-like teeth in both upper and lower jaws
- remaining teeth sharp with serrated edges for cutting vegetation.
NOTE: \cf12post-cranial skeletons unknown!
Pachycephalosauridae
- advanced pachycephalosaurs
- prominent dome-like thickening of skull roof produced by fusing and thickening frontal and parietal bones
- no supratemporal openings
- smooth dome
- no complete skeleton is known
- possibly similar to ornithopods
- Evolutionary novelties:
- long, low illium bone of pelvis
- 6 to 8 sacral vertebrae
- joint surfaces between vertebrae ridged
( "locked" together to stabilize back )
- head set at angle to vertebral column so that in normal posture head hung down with nosed pointed to ground and "dome" pointed forward
HEAD BUTTING - features designed to resist impacts:
1) greatly thickened dome of skull (protected brain )
2) shortened base of skull
3) inclination of skull relative to vertebral column
4) widely expanded back of skull
5) strengthening of vertebral column
6) reinforced upper lip of hip socket