Dinosaurs

Question 1

What are the key features of the Archosaurs?

Answer 1

• 2 fenestra (skull openings)
• Teeth in sockets (not fused to jaw)
• Reduction of 5th toe
• Secondary palate
• Calcaneal tuber (attachment of lower leg flexor muscles)

Question 2

What are the 2 major clades within the Archosaurs?

Answer 2

Pseudosuchian and Ornithodian

Question 3

Describe the Pseudosuchaurs

Answer 3

e.g Crocodylomorphs
Highly diverse during mid-late Triassic
Limbs more erect than primitive reptiles
Semi erect posture

Question 4

Describe the Ornithodirs

Answer 4

e.g Pterosaurs, Dinosaurs
- Simple hinge-joint ankle
- Very long hindlimbs
- Longer S-shaped neck

Question 5

Name some defining features of a dinosaur

Answer 5

-Semi-erect to erect posture:
- Pubis bone orientated downwards and backwards
- Hip is essential to understanding phylogeny of group
- Open acetabulum (hip socket)
- S-shaped neck
- Reduced 4th and 5th digit on hand
- Reduced to 3 main toes (foot)
- Sacrum - fused vertebrae

Question 6

What orders make up the Dinosauria?

Answer 6

Ornithischians and Saurischians (made up of Sauropodomorphs and Theropods)

Question 7

Describe how phylogeny of the Saurichians and Ornithiscians has change.

Answer 7

• Originally thought that Saurichians were ‘lizard hipped’ while Ornithiscians were ‘bird hipped’
• But, in 2017 a new hypothesis was proposed:

Question 8

What has changed about our understanding of Dinosaur egg laying?

Answer 8

• Until 2020 we believed all dinos were laying eggs with hard (calcium carbonate) shells
• There was covergent evolution of a soft (calcareous) eggs
• Suggesting that the ancestral state was a soft shell

Question 9

Briefly describe the timeline of dinosaur diversity

Answer 9

Most dino diversity is concentrated in the Jurassic and Cretaceous

Question 10

What factors drove the decline of the Dinosaurs, prior to their extinction (by asteriod)

Answer 10

• Global cooling climate
• Density of herbivorous