Invertebrate Palaeobiology Flashcards
Define Fossil
Any vestige of past life. A trace fossil is evidence of the behaviour, like burrowing. A chemical fossil is a relic of biogenic compounds, like blood in a mosquito.
What are the three periods of fossilisation?
Taphonomy - process of fossilisation
Biostratinomy - processes occurring between death and burial
Diagenesis - processes occurring between burial and discovery
What factors affect what parts of fossil are found?
Decay - muscles decay first, bone last.
Destruction - disarticulation can disconnect bones, erosion and corrosion can break down fossils
Deformation - by weight of sediment
How can a fossil be preserved?
The fossil can be made out of the original material or be replaced in permineralisation. This is often pyrite, phosphate or silica.
Moulds or casts can be made with sediment covering or infilling
How can soft parts be preserved?
Decay must be slowed by conditions like low T or acidity, or fossilisation must happen quickly, like in early mineralisation
What is a molecular clock?
Works out how similar DNA of molecules are, hence modelling the evolutionary rates of different species and phyla.
Words to describe a fossil’s habitat?
Marine, freshwater or terrestrial
Benthic - seafloor
Infaunal - in the substrate
Epifaunal - on the substrate
Pelagic - in the water column
Words to describe an organism’s movement?
Vagrant - actively moving
Sessile - don’t actively move, like corals
Nektonic - actively swimming in the pelagic zone
Planktonic - drift with pelagic currents
Words to describe a fossil’s diet?
Photoautotrophs - energy from the sun and carbon from CO2
Chemoheterotrophs - energy and carbon from organic compounds.
Grazers - plant eaters
Suspension feeders
Deposit feeders
Predators
How can sponges, cnidaria and Bilateria be differentiated?
Sponges have one germ layer and no organs
Cnidaria have two germ layers and single mouth/anus
Bilateria have three germ layers and seperate mouth/anus
What are protostomes and deuterostomes?
Two types of Bilateria:
Protostomes developed mouths before anuses and vice versa for deuterostomes.
Protostomes comprise arthropods, molluscs, brachiopods and bryozoans
Deuterostomes comprise echinoderms, chordates and hemichordates.
3 types of coral?
Tabulate - only colonial with no septa and small polyps
Rugose - large polyps, hollow calyx in the centre
Scleractinian - only current form, no epitheca.
What makes a good zone fossil?
Rapid evolution
Wide distribution
Independent of sedimentary setting
High preservation
What is GEODISPERSAL and VICARIANCE
Geodispersal can also be used, and this is when barriers like large oceans are removed, allowing animals to travel through continents. Vicariance is the opposite, when physical barriers result in closely related species.
Define EVOLUTION
the observation that lineages of organisms change through time, for example the changes in ammonoid sutures.
Define SUPERFECUNDITY
Individuals produce more offspring than can survive
How does speciation occur and what are the two types?
By reproductive isolation, when they can no longer interbreed. This can occur either by allopatric speciation (geographically become isolated) or sympatric speciation (simply from variation in the same population).
Define ALLOMETRY and HETEROCHRONY
Allometry - the change in shape during growth, like from baby to adult.
Heterochrony - stopping the development during growth at different times to have different benefits.
What is the Sepkoski Curve?
A plot of diversity through time showing trends in macroevolution (large scale evolution)
There are three main fauna; Cambrian, Palaeozoic and modern.
What is the Cambrian explosion?
Emergencce of major phyla and predator-prey dynamics. Also the start of bioturbations.
What is the Mesozoic Marine Revolution?
Loss of epifaunal suspension feeders. Increase in burrow depth. Shell morphology changes, and crinoids move deeper.
Primarily due to predators becoming prolific and achieving durophagy (eat hard prey). Their size and metabolic rate increased so they needed more food. This is facilitated by changes in primary producers, with larger plankton.
Shells became thicker with evidence of boring.
Why is extinction hard to quantify?
It is often estimated from the last appearance of species, which can be affected by the available rock record or fossil process. This is the Signor-Lipps Effect.
Species are often arbitrarily assigned too.
What is the End Permian Mass Extinction
Up to 90% of marine species extinct.
The Siberian Traps Eruption produced 10^6 km3 of rock, and released toxic gases like CO2 and SO2. This caused acidification of the oceans and warming (~15K). As a result many CaCO3 organisms went extinct. High metabolic organisms also disappeared as there was less oxygen, especially in the poles.
Disaster taxons like bivalves and lystrosaurus were able to dominate.
What is the Cretaceous-Palaeogene Mass Extinction
Up to 75% of species go extinct including dinosaurs and ammonites.
Caused by Chicxulub impact, in turn causing the Deccan traps eruption, large scale earthquakes, acid rain and ejecta.
The meteorite theory was formed when increased iridium levels were found in limestone.
What are Stromatolites?
Biogenic sediment formations. They form as sediment covers bacteria, which then burrow thorough as they need light, over and over.
What are the possible causes of the Cambrian Explosion?
- environmental changes with oxygen increase allowing photosynthesis and hence plants provide more energy
- predator prey dynamics and competition emerging, inducing evolution to survive with more complex ecosystems
- some significant evolutionary development, perhaps vision, deep roots
Two good zone fossils?
Graptolites - Palaeozoic
From Ordovician to Silurian, number of stripes reduced, and orientation changes from pendant (theca point down) to scandent (theca point up)
Ammonites - Mesozoic
From Cambrian to Cretaceous, suture changes to more complex.
Examples of Ecology from fossils?
Eurypterids - comparison to other known animals suggests chasing predatory lifestyle. High eye parameter shows it lives in darkness, but angle between lenses show they see little detail - probably an ambush predator.
Ammonoids - changing sutures show increasing risk of predators. Comparison to nautilus shows pelagic lifestyle. Supported by chambers with siphuncles. Nautilus teeth are sharper with ammonites doing sieve feeding. Centre of buoyancy far from centre of mass so stable
