What is a Dinosaur?

Question 1

Describe the dinosaur acetabulum

Answer 1

• perforated
• open hole in pelvis

Question 2

Describe the avian hip joint

Answer 2

• perforated acetabulum in modern birds
• inner acetabular membrane & other soft tissues prevent femur displacement

Question 3

What does the closed acetabulum mean?

Answer 3

• marasuchus cannot be an ancestor of modern birds
• all modern bird ancestors have open/perforated acetabulum

Question 4

Describe the pelvic musculature of Tyrannosaurus Rex

Answer 4

• outermost muscles ‘removed’
• appendicular muscles ‘restored’
• protrusions on pelvis for muscle attachment

Question 5

Describe the caudofemoral muscles of T-Rex

Answer 5

• 4th trochanter on femur - insertion point of large caudofemoral (femur retractor) musculature
• caudofemoral muscle from tail to femur, enables movement of tail

Question 6

Describe the offset femoral head in the dinosaur in comparison to the crocodilian

Answer 6

• dinosaur: subvertical orientation of acetabulum, leads to offset femur, buttress erect
• croc: ventral orientation of acetabulum, straight femur, pillar erect

Question 7

Compare avian and crocodilian femoral heads in relation to posture

Answer 7

• Avian: offset head, bipdedal posture
• Croc: rounded head, no offset, erect or sprawling posture

Question 8

Compare the avian and crocodilian 4th trochanter

Answer 8

• avian: no 4th trochanter, short tail, small caudofemoralis longus (CFL)
• croc: prominent 4th trochanter, long tail, large CFL