Palaeo - Functional Morphology

Question 1

What controls morphology?

Answer 1

The morphology of an organism is a product of fitness (its efficacy in converting biotic and abiotic resources into biomass) and evolutionary history (reflected in its genetic constitution).
In some cases (e.g. Tyrannosaurus rex teeth) there is a very clear link between morphological form and fitness.
• Evolutionary pressure
• T-Rex skull bones can withstand great pressure + stress, therefore evolved for biting
In other cases (e.g. the ‘jaws’ of velvet worms / onychophorans) morphology is largely sculpted by evolutionary history and developmental constraints - Modified claws
Developmental constraints:
• Morphological constraints on adaptations
• Velvet worms’ jaws have to fit in logarithmic shape to shed off – therefore constraints potential function

Question 2

Plants and their environment

Answer 2

Plants tend to be very closely tied to their environment – to the extent that some plant systematists feel that morphology is almost useless for systematics.
• Leaves have a pretty limited range of constraints
• They need to maximise surface area (for photosynthesis) and minimise water loss (through stomata) whilst remaining attached to their branch.
• Plants in hot or arid environments (where evaporation is extreme) tend to have fewer stomata.
• Plants in wet environments have drip tips (so leaves don’t fall off, and water/algae doesn’t block photosynthesis).
• Plants in warm environments are more likely to have large, ‘leathery’ leaves with entire (smooth / non-serrated) leaf margins.
Therefore, plant leaf morphology is dictated by environment

Question 3

Morphology in response to energy

Answer 3

Trees offer a familiar example of morphology being controlled by local environmental factors.
• Fluid medium
o In this case air
o Causes tree to streamline in wind direction
Similar effects can be seen in the marine realm:
Porites and Diploria (Scleractinian corals)
• Porites: Grows as more of a solid unit in higher energy environment – more branched in lower energy
• Diploria: More streamlined for higher energy environment
Murex (spikey) vs. Patella (Semi-circular)
More energetically costly but protected
Ribbed shells can provide ‘corrugated cardboard’ style resilience: but in brachiopods a ribbed appearance may arise as a product of commissure shape.
Morphology is of course also linked to behaviour, which may itself be a function of the environment: as in the cases of encrusting or burrowing organisms.
• Presence of encrusters means there is something to encrust
o Also, likely its high energy as the species has anchored itself

Question 4

Predations effect on a community

Answer 4

Predators play a key role in establishing the structure of an ecosystem; they will crop back any particularly dominant K strategists, creating new substrate for r strategists.
At a large scale, this capacity to generating diverse ecosystems has been linked to two major diversifications in Earth history: the Cambrian ‘explosion’ and the Mesozoic Marine Revolution – increased predation

Question 5

Determining the presence of predators

Answer 5

Direct evidence of predators / predation
• Hard body fossils that show consuming behaviour
• Gut evidence
• Teeth plates which show molars for shell crushing predation
Predation damage
• Tubes in Ediacaran – have bore holes – some predation
• Mesozoic – gastropods – countersunk holes – shell drilling frequency increased
o More predation
o Cracks show shell crushing
• Not a perfect proxy as not all predation leaves damage
Morphological defences
• Many soft body organisms in Ediacaran
• More shells and spines in Mesozoic
o Using more energy on defences must be beneficial and therefore necessary
Predatory adaptations
• Claws
• Molars
Local extinctions