Week 4: Locomotion & Ecology + Palaeobiodiversity

From lecture notes

What kind of animals are hard to observe?

• nocturnal

• deep sea

• fossorial (underground)

• extinct

What does posture + gait indicate?

• How an animal moves

• needs fossil in articulation (in tact) to make inferences

Three kinds of posture

1. Sprawling → position of bones e.g femur horizontal

2. Semi-erect

3. Erect → expensive energetically → position of bones almost vertical

What does upright posture enable?

• a switch from lateral undulation of the spinal column to dorsoventral undulation→ flexibility → synapsids did this

• Ribcage no longer restricted by locomotion from lateral undulation

• Lumbar region modified: ribs are shortened to accommodate the new style of locomotion→ synapsids evolved fewer ribs

• running more efficient

Alligator posture + gait

• sprawling

• holding limb bones - humerus and femur horizontally

• low position on ground- but can hold themselves up

• sprawling - less pressure on rib cage

• slower than similarly sized mammal

Extinct crocodile

• more upright

• faster runners

What information can we use other than fossil skeletons?

• Trace fossils, tracks, claw marks, tail traces

• Footprints→ walking speed, running speed, indication of size of animal→ problem: rarely know track makers

• Track ways→ definitely represent where the animal stood→ skeletons can be moved/ washed away etc.

Frog anatomy/ adaptations

• outside of amniote radiation

• otic notches

• elongated limbs

• sacrum = vertebrae within pelvis - where the tail would be

• frogs have urostyle→ modified pelvic and tail region - shock absorption adaptation from jumping

• prominent feet- launching off of them

• light skeleton - easier to jump far

• Huge orbits→ allows for large muscle structures → pumping up and down - breathing

Kangaroo anatomy/ adaptations

• tail→ stability and balance

• modified pelvic region → elongated pelvis

• lower leg bones elongated

• similar adaptations convergent to frogs- not homologous

What kind of environments do limbless animals live in?

• Trees (arboreal) / on the ground e.g snakes

• Fossorial

Adaptations of Amphisbaenian to their environment

dome-like skulls for burrowing

What are amphisbaenians?

• lizards

• limbless burrowing squamates

What is a caecilian?

limbless amphibian

Adaptation of moles to their fossorial mode of life

• skull not ideal for burrowing

• huge hands/ arms are

• mole hands have something that superficially resembles a 6th digit

• grew from sesamoid bone in mole’s wrist → increases surface area of mole’s hand so it can dig through the soil more effectively

Examples of arboreal animals

• birds

• snakes

• squirrels

• sloths

• monkeys

Adaptations of birds for arboreal life

• 3 toes forward, hallux (first toe) points backwards

• Owls→ additional toe points backwards - extra support- fall asleep in trees standing up

Adaptations of mammals for arboreal life

• limb elongation e.g sloths

• squirrel→ bracing structure in limbs

How does the blue whale swim?

• pectoral fins

• streamlined body

• pelvic bones remain

• dorsal fin/ tail → cartilage not bone

• moving tail up and down

• change direction using flippers

• dorsal fins for stability

How do fish swim?

• move side to side

• lateral movement of body + caudal fin

How do penguins swim?

• use arms + legs

• streamlined

Examples of secondarily marine reptiles

• plesiosaurs, icthyosaurs, mosasaurs, crocodyliform

• ^ all mesozoic diapsids

How do ichthyosaurs swim?

• paddle like structure of the fin

• pectoral fin heavy

How do plesiosaurs swim?

• fins

How did mosasaurs swim?

• moved more like a snake

Where did sauropod dinosaurs live?

• Initially thought to be whale reptile

• thought that they couldn’t carry their weight on land

• but mainly terrestrial

• prominent columnar limbs held their weight

• hollow vertebrae → air sacs→lightens load

Where did Spinosaurus live?

• Giant theropod dinosaur

• Cretaceous Egypt

• initially thought to be entirely on land

• marine → remains of fish in stomach

• new information about limb proportions → primarily lived in water

• dense bones→ indicative as spending time in water

Methods for correcting biases in the fossil record

1. Subsampling methods

2. Simulations

3. Modelling approaches

4. Phylogenetic diversity methods

The Basics of Subsampling

• enables us to compare the number of species in samples of different sizes

• Standardise (randomly sample) to the smallest sample size, repeating to get an average result.

• Means a loss of some data

• Doesn’t address all issues.

Is Sepkoski’s curve wrong?

• Yes according to subsampling methods

• no major increase in diversity towards present day

Simulations

• Can develop approaches that provide a ‘null’ hypothesis to test the fossil record against

• Can use data from the modern, entirely simulated data, or a combination

• Possible to carry out on desktop equipment (more intense hardware needed for some simulations).

Modelling

• Allows us to use the known fossil record alongside relevant covariates to understand drivers and controls on diversity/preservation through time

• Variety of approaches; simple linear models to machine learning algorithms

• Can be used alongside outputs from other models (e.g. palaeoclimate models)

Example of modelling

Ecological Niche Modelling (ENM)

How does ENM work?

1. On a map plot out geographic distribution of where the species lives

2. Combine with variables e.g nitrate conc. sea surface temp etc.

3. use information to build niche model showing inferred habitat suitability

4. can change the variables that are put in