What characters do the ornithiscians have in common?
- predentary bone
- toothless and rough tip of snout
- narrow bone that crosses the outside of the eye socket (palpebral)
- jaw joint set below upper tooth row
- cheek teeth with low, subtriangular crowns
- at least 5 sacral vertebrae
- ossified tendons above the sacral region
- backward pointing pubis
- internal room for digestion
What kind of food did the ornithiscians eat? How can we know this?
Large amounts of tough plant matter
Fossils with flared ribs reveal they would have had lots of room for internal digestion which may have been accommodated for by the backward pointing pubis,
a predentary bone for ripping plant matter,
the toothless rough tip of the snout,
a jaw joint that is positioned below the tooth row for chewing,
and triangular-shaped cheek teeth with low crowns.
Were primitive ornithiscians bipedal or quadrupedal?
Primitive ornithiscians were bipedal.
The genosauria had well developed, muscular
cheeks.
The genosauria were subdivided into groups based on efficiency of chewing, what were the groups?
Thyreophora
Cerapoda: marginocephelia and ornithopods
Define thyreophorans
Genasaurs with dermal armour-boney plates embedded in the skin-along the back surface of the body.
Define ornithiscia
Genosaurs with a pronounced diasterma.
The cerapoda is split into two groups:
marinocephalia
ornithopoda
Define marginocephalians
A group united by having a shelf of bone extending over the back of the skull.
Define ornithopoda
Iguanadon, “duckbilled dinosaurs”, and other excellent chewers.
As we make our way up the cladogram of ornithiscians we get better
chewers.
Why doesn’t a beak fossilize well?
The beak would be made of keratin, the same stuff that makes up hair or finger nails, keratin does not fossilize well.
Why is the term “duckbilled dinosaur” misleading?
The hadrosaur’s beak is actually massively downturned and unlike a duck’s. It would have been used for gripping, ripping, and breaking vegetation rather than anything duck like.
What character do thyreophorans have in common?
They are shield bearers. They have spikey bones in common.
Thyreophornas began as small and ____ but quickly evolved into larger, ____ dinosaurs.
Thyreophorans began as small and bipedal but quickly evolved into larger, quadrupedal dinosaurs.
Osteoderms
Armour is not attached to the skeleton, instead, it is embedded into the skin.
How were the thyreophora as chewers?
Okay
- jaw joint positioned a little below tooth row
- teeth slightly inset
- cropped and stripped foliage with rhamphotheca (beak)
- spaced out and pointy teeth
- no large coronoid process
The thyreophora separate into two clades…
the stegosauria (not armoured all over body) and the ankylosauria (full back is entirely covered, like a turtle)
Stegosaurs fossil location
- few fossils
- global distribution
- limited fossils means limited knowledge
- none in Alberta (none for you gretchen wieners), because our rocks are cretaceous and the stegosaurs were alive around the Jurassic to early cretaceous periods.
How do we know stegosaurs were slow walkers?
Despite being quadrupedal, they had long hind limbs and short forelimbs.
Why do most stegosaurs have at least one row of osteoderms on each side of their back? And how can we know?
Osteoderms were likely for defence, we know this from finding broken and healed spikes, which heal in a deformed way.
Stegosaurs have plates that are thin and visually impactful only from the side, what might they have been for?
Plates were different shapes and sizes, if they were for defence they should have been all the same size and shape. They could have been for
- identifying different species
- identifying different sexes
- thermoregulation: plates have vessels, the arrangement would help dissipate heat (this was proved wrong in 2005)
Where/when did we find Ankylosauria?
Canada, China, and Mongolia
Early Jurassic-late cretaceous
The Ankylosaurs were mid-sized and encased in
armour.
