What are coral tropical coral reefs of today built by?
- Today they are build by scleractinian (stony or hard) corals along the framework building.
- They create shelters where numerous other species survive
- Fossil records have shown how much these have changed throughout time
What are the 6 major successions of reef building organisms?
1- Cambrian: Archaeocyathid and algae
2- Silurian- Devonian: Stromatooraids; tabulate and rugose corals
3- Carboniforous- Permian: calcic sponges and algae
4- Triassic: Scleractinian corals and calcic sponges
5- Cretaceaus: Rudist clams and scleratinian corlas
6- Scleratinian corals
- After each mass extinction of the entire reef, there was a long period before another creature could fill the environmental void.
- Species are different in each reef stage
- We see contingency and the ecological roles of species replaced by newcomers
What is the mesozoic era also known as?
The mesozoic era is sometimes called ‘The age of the reptiles’. It spans the Triassic and Cretaceous, punctuated by the P-T and K-T extinctions. This was a time of great tectonic, climatic and evolutionary change.
Outline the Triassic Period.
- (251 mya) Early dinosaurs; first mammals; diversification of marine invertebrate; mass extinction at end of period (-65% of species disappear)
- Pangea
- Dominated by mammal-like reptiles at the start
- Dry conditions suitable for Conifers, ginkgo, cycads and ferns.
Outline the Jurassic Period.
- ## (200 mya) Diverse dinosaurs present; radiation of ray finned fishes; first fossils of flowering plants.
Outline the Cretaceous Period
- (145 mya) Dinosaurs continue to diversify; mass extinction at the end of the period (-75% of species)
When is the moment of extinction defined?
The moment of extinction is generally considered to be the death of the last individual of that species. (Although the capacity to breed and recover may have been lost before this point) - this is known as functional extinction.
Understanding of pseudo extinction
- Did the dinosaurs become birds?
- Do horses descend from Hyracotherium?
- This is generally easier to prove for larger clades and groups, difficult for genes.
Observed changed in populations can be due to extinction; mass extinction; or direct competitive replacement. Describe these.
- Gradually extinction- One species reduces in diversity and gradually become extinct therefore leaving their niche available. Another species diversifies more in order to fill this niche.
- Mass extinction- many factors can cause mass extinction and as before another species will fill the available niche.
- Competitive replacement- The extinction of one species is due to direct competition and diversification of another species. One species will reduce in diversity while the other increases.
What defines mass extinction?
“Any substantial increase in the amount of extinction (i.e. lineage termination) suffered by more than one geographically widespread taxon during a relatively short interval of geologic time, resulting in at least temporary decline in standing diversity” (Jablouse)
What effect can a high ecosystem ‘connectedness’ have?
Mass extinction tends to be more prevalent towards the end of an era when ecosystem connectedness is very high.
Outline the three extinction drivers.
Terrestrial
- Plate tectonics and sea level changes; volcanic
- Climate change; clathrate guns
Extra Terrestrial
- Bolide/ Superbolid impacts
- Transit through the Galaxy arms
- Supernovae and Gamma barots
Biological
- Atmospheric poisoning (cyanobacteria 2.4 Gya)
- Competitive failure (Darwin’s theory)
- Intolerance to extreme biotic change
To produce a mass extinction, multiple causes are required (Press/pulse model)
Describe the events of the P-T extinction “The Great Dying”
- 2/3 loss of diversity in Brachipod filter feeders.
- Bivalves replaced them
- An increase in marine predation caused a dramatic restructuring called the Mesozoic Marine Revolution
- Mammal- like Therapsid reptiles were being killed off on land. Paving way for archosaurs/reptiles.
(There were two periods of extreme volcanism covering over 2 million square kilometers with lava, the output appears to be proclastic and basaltic, probably containing large quantities of CO2)
Outline the Triassic Period.
- (251 mya) Early dinosaurs; first mammals; diversification of marine invertebrate; mass extinction at end of period (-65% of species disappear)
- Pangea
- Dominated by mammal-like reptiles at the start
- Dry conditions suitable for Conifers, ginkgo, cycads and ferns.
- Dinosaurs/mammals appear at the end of the Triassic
- Oxygen levels drop during this period to 15%
Outline the Jurassic Period.
- (200 mya) Diverse dinosaurs present; radiation of ray finned fishes; first fossils of flowering plants.
- Breakup of Pangea (probably no polar ice)
- Similar flora composition with new insects
- Dinosaurs become dominant large invertebrates.
- Small carnivorous dinosaurs become large carnivores (Allosaurus)
- High browsing (prosauropods/sauropods) and low browsing herbivores (stegosaurs)
- CO2 levels exceptionally high
- Oxygen levels drop again to 11%
Outline the Cretaceous Period
- (145 mya) Dinosaurs continue to diversify; mass extinction at the end of the period (-75% of species)
- Pangea completes it’s breakup
- First appearance of angiosperms near equator, quickly spreads.
- Butterflies, ants, grasshoppers and wasps
- Placental, marsupial and monotreme mammals appear (mouse to dog size)
