who are thyreophoras?
another main group of genasauria(cheek lizards) from the ornithischians
what are thyreophora?
shield bearer or armour dinosaurs. diagnostic characters are:
1. parallel rows of bones that are embedded in the skin(osteoderms) running down the necks, backs and tails
is there any other disnasour with armour?
Dermal armour is also inferred in another dinosaur lineage, in sauropods which might have been for calcium storage, sexual selection or protection in the teenage age
some other have bony structures along their spine, a flap of skin may have joined the spines into a sail like structure
Thyreophora basal and shared primitive characters?
1-presence of osteoderms that run down the necks, backs and tails
2- sturdier build, quadropedal
what are osteoderms?
parallel rows of bones that are embedded in the skin
characters of primitive scutellosaurus?
small, bipedal, gracile(lightly build) rows of osteoderms
characters of primitive scelidosaurus?
quickly evolved into large quadrupedal dinosaurs
Thyreophora diet characteristics?
-cropping and stripping using their rhamphotheca(beak)
-like all genasaurs, had inset tooth row but with low surface for grinding and chewing, coronoid process, which means chewing likely existed but is was inefficient
-heads were low to the ground, restricted to low level plants
what are the two big clades of thyreophora?
1- Stegosauria
2- Ankylosauria
what do we know about stegosauria?
- few fossils found with global distribution
-medium sized dinosaurs
-osteaoderms developed into plates and spines in two rows along the back
-long hind limbs, short forelimbs for each hind stride there was 6 forelimb stride since is was shorter and slower
-walked very slowly, they couldn’t lift their forelimbs up since thither weight was distributed towards the head
-very very small brain with an enlarged olfactory lobe for smelling
-very rare specimens
-few juveniles have been found but no nests, eggshells or hatchling material == no idea about their family structure
-mass accumulation of their remains suggest at least these animals were social, herding animals
-they have at least one row of osteoderms in each side of their back, the end of the tail is equipped with pointed, splayed spikes
how was the sexual dimorphism in fossil records?
sexual dimorphism may exist in stegosaurus, two extinct sizes and shapes of plats, equal number of both sizes, no intermediate forms, all adults from a single bonebed
but they are all hypothesis and not facts
what was going on inside the setegosurias plates and spines?
maybe thermoregulation, exterior surfaces have many grooves and interior may have a network of channels, some thinks it was for heat dissipation and others thinks if was just for supplying nutrients to the keratinized sheath that would have covered the plates in life
were the spines and plates present for both stegosaurias?
based on the limited fossil evidences, juveniles didn’t have plates and spikes
what are some contradictions about stegosaurias?
they are chewers but with weird teeth that is not good
small brain, slow moving thermoregulations
sexual display seems prominent but little evidence for living in groups, then why dimorphism?
we gotta find more fossils to answer these questions
Ankylosauria
fused lizard, parallel rows of osteoderms
encased in an armour, forms a continuous shield around neck, throat, back and tail and sometimes head, cheeks and eyelids
-large gut (barrel shape)
-longer hindlimb than forelimbs
-global fossil distribution except Africa
what are two groups of Ankylosauria?
1- Ankylosauridae: shorter, broader head/beak, large, triangular plates, well armoured but fewer tall spikes along body, tail with massive bony club, sometimes with paired tail spikes or knobs
small brains, good at smelling , incredibly slow moving
extensive armours which allowed them be slow
tail club sometimes with spikes(tail first defense)
2- Nodosauridae: longer, narrow snouts/beaks, well muscled shoulders, tall spikes at the shoulder, no tail club
string front end with tall spines (head first defense)
the difference of beak size in ankylosauridae and nodosauridae?
Nodosaurids had narrow beaks which suggests selective feeding(plucking fruits and foliage)
Ankylosauids had broad beak, suggest that they were less selective
what is their tail structure?
paired masses of bones, densest around the exterior
base of tail was flexible, but rear was stiffened with interlocking vertebrae and ossified tendons, served as muscle attachment sites for a powerful swing
