Crocodile Lineage

Question 1

What type of skull does archosaurs have?

Answer 1

diapsid skulls

Question 2

What are some examples of soft tissues and archosaur antorbital fenestras?

Answer 2

• extant crocodiles - antorbital fenestra closed
• paranasal air sacs
• pterygoideus muscle - jaw movements

Question 3

Describe thecodont teeth

Answer 3

• held in sockets by periodontal ligaments
• replacement tooth underneath
• crocodilians, extinct archosaurs, mammals

Question 4

Describe the fourth trochanter

Answer 4

• process on femur - attachment for caudofemoralis (CFL)
• thigh retracting tail muscle
• most powerful alligator muscle

Question 5

Describe crurotarsal ankles

Answer 5

• astragalus - sutured to tibia
• calcaneum - functionally part of foot
• ankle joint - peg on astragalus - socket on calcaneum

Question 6

What are the types of crocodylomorphs?

Answer 6

• protosuchians - terrestial, <1m, upright limbs
• goniopholipids - semi-aquatic, 2-4m, brackish/fresh-water
• thalattosuchians - marine, up to 7m, some with flipper-like limbs and tails, salt gland

Question 7

What are the 2 gates in living crocodiles?

Answer 7

• erect posture - relictual ancestral pattern
• sprawling posture - derived with 2 degrees aquatic habits

Question 8

Describe crocodilian pelvis and femur

Answer 8

• slightly angles and round head of femur - flexible articulation with pelvis
• femur angle below horizontal: 20 degrees sprawl, 55 erect

Question 9

Describe crocodilian pelvic aspiration

Answer 9

• inspiration: unique diaphragmatic muscle pulls liver, ischiopubic muscle pulls mobule pubis
• expiration: rectus abdominis muscle returns pubis

Question 10

Describe crocodilian gastralia

Answer 10

• dermal bones in ventral abdomen
• attached to rectus abdominus and other muscles
• stiffen and unify abdominal wall
• found in many dinosaurs but not birds

Question 11

Describe the dermal skeleton

Answer 11

• forms in superficial tissues without preformed cartilage
• early vertebrate skeletons - link to Ordovician jawless fish with bony plates
• 3 types: cranium (top), gastralia (middle), osteoderms (bottom)

Question 12

Describe crocodilian scales

Answer 12

• keratinized scutes cover skin
• dorsal scutes reinforced with bony plates - osteodoerms often with keel

Question 13

Describe osteoderm structure

Answer 13

• inner porous core and outer dense cortex
• connective fibres at junctions
• vascularized - heat exchange

Question 14

Describe the most armoured crocodile-lineage archosaurs

Answer 14

• aetosaurs - late triassic, terrestrial
• covered by osteoderms - common fossils

Question 15

Describe chromatophores

Answer 15

• epidermal melanocytes - stripes, patches, sports in dorsal scales
• dermal melanophores - dark/gray background
• dermal xantophores - brown, yellow-orange

Question 16

What are the integumentary sensory organs?

Answer 16

• minute skin elevations on jaws
• body of crocodiles not alligators
• arrays of tactile receptors on epidermis and dermis of integumentary sense organs
• detect movements of water and prey in jaws