Ornithordira: the ornithischian dinosaurs

Question 1

Do the ornithischians have any living descendents?

Answer 1

No.

Question 2

List 3 synapomorphies of the ornithischians.

Answer 2

1. Pubis points down and backwards, creating more space for the gut
2. Have a predentary bone
3. Vertebrae have ossified tendons and ligaments

Question 3

Why did ornithischians need more gut space?

Answer 3

They were herbivores and needed to eat large volumes of nutrient-poor plant matter.

Question 4

What is the predentary bone?

Answer 4

An extra single bone at the tip of the snout.

Question 5

In ornithischians, the vertebrae have ossified tendons and ligaments. This strengthens the spine. What analogous structure did the saurischians have instead?

Answer 5

Hyposphene-hypantrum vertebrae.

Question 6

Give the 3 main groups or ornithischian.

Answer 6

1. Thyreophora
2. Ornithopoda
3. Marginocephalia

Question 7

What were the thyreophora?

Answer 7

Largely quadrapedal armoured dinosaurs.

Question 8

Stegosaurs were thyreophorans:

a) What time period were they from?
b) What was their distribution like?
c) How many species were there?

Answer 8

a) Late Jurassic
b) Global
c) 12-15, not a diverse group

Question 9

Stegosaurs were thyreophorans. Their fore and hind limbs were the same length. True or false?

Answer 9

False: their hind limbs were longer.

Question 10

Stegosaurs were thyreophorans. What were the 4 large spikes at the end of the tail used for?

Answer 10

Defence, as a weapon.

Question 11

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?

Answer 11

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.

Question 12

Ancylosaurs were thyreophorans. Explain how they overtook the stegosaurs.

Answer 12

The stegosaurs died out at the Jurassic-Cretaceous boundary, at which point the ancylosaurs radiated to fill the vacant niches in opportunistic replacement.

Question 13

Describe an ancylosaur.

Answer 13

Heavily built, covered in fused bony scutes with lateral spikes. Had a thick bony skull, armoured neck ring and a bony tail club.

Question 14

Define the ornithopoda.

Answer 14

Large, bipedal dinosaurs.

Question 15

Camptosaurus was an ornithopod from the late Jurassic. How did it evade predators?

Answer 15

Shows no defence mechanisms so is likely to have moved in herds. Was lightly built for fast-running, only 3-4m in length.

Question 16

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?

Answer 16

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.

Question 17

What were the hadrosaurs?

Answer 17

The duck-billed dinosaurs, the largest ornithopods.

Question 18

List 3 features of the hadrosaurs.

Answer 18

1. Keratinous beaks with teeth further back in the mouth
2. High-browsers
3. Fast runners

Question 19

Were the hadrosaurs quadra or bipedal?

Answer 19

Largely quadrapedal, although few were bipedal.

Question 20

What was characteristic about the skull of iguanodon, a close relative of the hadrosaurs?

Answer 20

It was pleurokinetic: a hinge on the maxilla meant it could swing outwards in a grinding motion.

Question 21

What were ornithopod teeth like?

Answer 21

Most ornithopods had a single tooth row, except the hadrosaurs.

Question 22

What was characteristic about the teeth of hadrosaurs?

Answer 22

Had tooth batteries, meaning there was ~2000 teeth in the entire jaw. This was for grinding food.

Question 23

What was unique about the way ornithopods processed their food?

Answer 23

It was very slow due to lengthy processing. This was because they chewed their food and stored it in cheek pouches.

Question 24

What evidence is there for ornithipods having cheeks?

Answer 24

1. Tooth rows are pushed inwards in relation to the sides of the face, i.e. they are inset to the cheek bones
2. Grooves in the skull indicate a neural/blood supply

Question 25

Did all dinosaurs have cheeks?

Answer 25

No, only the ornithopods.

Question 26

Most species of ornithopod have crests. Give 3 functions of a crest.

Answer 26

1. Species recognition
2. Vocalisation
3. Air conditioning

Question 27

Having crests was important for ornithopod lifestyle. Why?

Answer 27

They were herd animals.

Question 28

Explain how a crest functioned as an air conditioner.

Answer 28

The nasal passages run through the crests, meaning air can be warmed/moistened before in enters the lungs. This warmth/moisture can be reclaimed as the air is exhaled. This prevents dehydration.

Question 29

Ornithopods displayed no parental care. True or false?

Answer 29

False: due to their herd lifestyles it appeared they had fewer offspring that stayed with the parents.

Question 30

Define the marginocephalia.

Answer 30

The thick-headed, horned dinosaurs.

Question 31

Give 2 major groups of marginocephalian.

Answer 31

1. Pakicephalosaurs

2. Ceratopsians

Question 32

What was unique about the skull of a pakicephalosaur?

Answer 32

They had a bony dome on the skull that was up to 9 inches thick.

Question 33

It was previously thought that the bony dome of a pakicephalosaur was used for headbutting in mate competition. Why is there dispute over this?

Answer 33

1. The females also had them

2. They do not have reinforced necks

Question 34

Define the ceratopsians.

Answer 34

The ‘horn-faced’ dinosaurs. Also had keratinous beaks and bony frills.

Question 35

Describe the appearance of a) protoceratops, b) triceratops and c) styracosaurus.

Answer 35

a) No horns, only a beak and bony frill
b) A beak, bony frill and 3 horns: 2 brow and 1 nasal horn
c) Frill is made of multiple spikes instead of a bony plate. Had 2 large openings covered by skin.

Question 36

Fossils of protoceratops are found commonly in Mongolia along the silk road trail. In ancient times they were thought to be what?

Answer 36

Monsters, which lead to the myth of the Griffin.

Question 37

What is the purpose of the ceratopsian frill? Give 2 explanations.

Answer 37

1. Thermoregulation: it increased SA by ~4m.

2. Defence: protects the back of the neck.