Ornithordira: the ornithischian dinosaurs Flashcards
Do the ornithischians have any living descendents?
No.
List 3 synapomorphies of the ornithischians.
- Pubis points down and backwards, creating more space for the gut
- Have a predentary bone
- Vertebrae have ossified tendons and ligaments
Why did ornithischians need more gut space?
They were herbivores and needed to eat large volumes of nutrient-poor plant matter.
What is the predentary bone?
An extra single bone at the tip of the snout.
In ornithischians, the vertebrae have ossified tendons and ligaments. This strengthens the spine. What analogous structure did the saurischians have instead?
Hyposphene-hypantrum vertebrae.
Give the 3 main groups or ornithischian.
- Thyreophora
- Ornithopoda
- Marginocephalia
What were the thyreophora?
Largely quadrapedal armoured dinosaurs.
Stegosaurs were thyreophorans:
a) What time period were they from?
b) What was their distribution like?
c) How many species were there?
a) Late Jurassic
b) Global
c) 12-15, not a diverse group
Stegosaurs were thyreophorans. Their fore and hind limbs were the same length. True or false?
False: their hind limbs were longer.
Stegosaurs were thyreophorans. What were the 4 large spikes at the end of the tail used for?
Defence, as a weapon.
Stegosaurs were thyreophorans. They had large, diamond-shaped plates in 2 rows along their spine:
a) What tells us these were NOT used for armour?
b) What might they have been used for?
a) Too weak, they were not joined to the spine.
b) Thermoregulation or mate display. The plates are covered in tiny grooves where blood vessels would have been, thus may have been for heat loss or colour change.
Ancylosaurs were thyreophorans. Explain how they overtook the stegosaurs.
The stegosaurs died out at the Jurassic-Cretaceous boundary, at which point the ancylosaurs radiated to fill the vacant niches in opportunistic replacement.
Describe an ancylosaur.
Heavily built, covered in fused bony scutes with lateral spikes. Had a thick bony skull, armoured neck ring and a bony tail club.
Define the ornithopoda.
Large, bipedal dinosaurs.
Camptosaurus was an ornithopod from the late Jurassic. How did it evade predators?
Shows no defence mechanisms so is likely to have moved in herds. Was lightly built for fast-running, only 3-4m in length.
Ouranosaurus was an ornithopod from the middle Cretaceous of North Africa. This environment was incredibly hot:
a) Why was it so hot
b) How was ouranosaurus adapted?
a) Elevated CO2 levels
b) Ouranosaurus had a large dorsal sail supported by elongated neural spines. This would have increased the body SA by metres squared for thermoregulation.
What were the hadrosaurs?
The duck-billed dinosaurs, the largest ornithopods.
List 3 features of the hadrosaurs.
- Keratinous beaks with teeth further back in the mouth
- High-browsers
- Fast runners
Were the hadrosaurs quadra or bipedal?
Largely quadrapedal, although few were bipedal.
What was characteristic about the skull of iguanodon, a close relative of the hadrosaurs?
It was pleurokinetic: a hinge on the maxilla meant it could swing outwards in a grinding motion.
What were ornithopod teeth like?
Most ornithopods had a single tooth row, except the hadrosaurs.
What was characteristic about the teeth of hadrosaurs?
Had tooth batteries, meaning there was ~2000 teeth in the entire jaw. This was for grinding food.
What was unique about the way ornithopods processed their food?
It was very slow due to lengthy processing. This was because they chewed their food and stored it in cheek pouches.
What evidence is there for ornithipods having cheeks?
- Tooth rows are pushed inwards in relation to the sides of the face, i.e. they are inset to the cheek bones
- Grooves in the skull indicate a neural/blood supply
