Week 6: Carnivorous Crocodiles and Herbivorous Dinosaurs

Nile crocodile feeding

• opportunistic

• fish, snails, birds, humans

• powerful bites

How many extant crocodile species are there?

26

Crocodile attack styles

• ambush predators

• lurk in water

• mimic logs

• too near to the edge- lunge forward

Gavial feeding strategy

• elongated snouts

• specialist fish eaters

• long snout helps them grab fish

Examples of extinct crocodiles

• Dyrosaurid

• Goniopholis

• Sarcosuchus→ late Cretaceous, N. Africa

convergent evolution of long snouts for fishy diet

Other ways for crocodiles to feed e.g Notosuchian

• herbivorous crocodiles → short snouted form

• Terrestrial predator dinosaurs → converged on theropod-like skull

Why do crocodiles need robust, akinetic skulls?

• cannibalism

• fights over territory

• less aggression in long, elongated snouted crocodiles

• powerful, strong jaw in saltwater crocodile

Palate evolution

• blue area= bone

• thin orange line = flesh area

• bones in red→ secondary palate = extra portion of bone spanning distance of upper teeth row

• expands and moves backwards

• internal nostril pushed towards back of the skull

• greatly strengthens snout against tortial forces

• can sit with water in mouth but can still breathe

Ornithischians jaw

• all Ornithischians are herbivores

• have an extra bone called the predentary bone in the lower jaw

Examples of armoured dinosaurs

• Stegosaurus

• Euoplocephalus (genus of ankylosaur)

Pachycephalosaurs adapatations

• thick- headed animals

• several inches of solid bone

• weapon → predation/ male-male combat

Ceratopsians

Examples: Protoceratops, Triceratops

• bone thrill at back of head

• beak like structure

• herds/ large social groups

• horns + bony thrills as display structures

• evidence of injury consistent with horns of same species

• Vertical slicing/shearing bite in ceratopsians→ microwear on teeth shows evidence of slicing action

Pleurokinesis

• complex multiple jointing thought to occur in ornithopods, such as hadrosaurs

• hinge in skull in maxilla (large bone that houses most of the teeth)→ maxilla moves outwards as lower jaw moves upwards

Sauropods Adaptations/ Features

• all members= herbivorous

• stout body, 4 column like legs, long neck, small head, long tail

• members of Diplodocus group evolved shorter necks secondarily → to do with level at which they are browsing

• variety of head shapes in sauropods

• all heads relatively small compared to neck length + bodies

  small brains

• some species have a club e.g Shunosaurus

• very little oral processing of food→ teeth pointing out

• sever vegetation from plant then swallow- no a lot of chewing happening

  ^ no evidence for fleshy cheeks

• food processed deeper down in digestive system

Why did Sauropods get so big (bulk processing of plants/ evolutionary feedback loop)?

Example: Argentinosaurus → 35m in length, 70 metric tons

• small heads, long necks, herbivory, lack of oral processing

• able to tap into high browsing vegetation

• ability to process large quantities of plant material → can extract energy from not very nutritious plant

• while you are chewing food, you’re not taking your next bite

• living off of food it ate 3-4 days previously- can wait longer for food unlike small animals

• need a big body to have a big neck

• long neck - biomechanically can’t have a large neck - too much muscular energy required to lift head

• long neck prevents large head

• small head → no oral processing- can’t have lots of teeth

Why did sauropods get so big (air sacs systems and pneumatisation)?

• neck bones are honeycombs of air spaces and thin sheets of bones

• air sac system enables light skeletons for their strength - replace bone with air in places where bone is not needed

• neck bones can be ~80% air

• as sauropods get bigger- issue with over heating

• modelling suggests problems with excess heat → dump excess heat into air sac system and exhale it

• increased relative SA for their size→ long neck → additional surface for heat loss