Cenozoic Era
Age of Mammals
- Groups of giant mammals went extinct, allowing smaller species of mammals (dogs, horses, primates, elephants) to thrive in the absence of their primary predators
- Without dinosaurs, plant life thrived
Levels of biodiversity
- Genetic diversity - total number of genetic characteristics in the genetic make-up of a species
- Species diversity - how many species are in an ecological community
- Ecological diversity - variation of ecosystems found in a region
Allopatric speciation
- Parent population becomes separated due to physical barriers, preventing the flow of genes between the two populations
- Populations experience different selection pressures that favour different genotypes
- Over time this results in different genetic makeups that cause members of each species to be unable to interbreed fertile offspring
micro-evolution
changes within a population over a short period of time
e.g. peppered moth
macro-evolution
the accumulation of micro-evolution over a long period results in the formation of new species
speciation
the formation of new species due to a combination of micro-/macro-evolution and change in environment
Case study of macro-evolution: fossil record of horses
Sudden large changes in cheek teeth span between horses of the different geological eras is unsupported by evidence of transitional fossils → punctuated equilibrium
- Early Eocene: small, dog-sized mammals with 4-toed hoofs. Cheek teeth span was around 4.5cm
- Early Oligocene: fossils show cheek teeth span suddenly increased to 7.2cm. No evidence show transition between Eocene and Oligocene teeth spans
- Early Miocene: multiple cheek teeth spans occurring simultaneously shows radiation. This was because horses moved out into the plains and colonised different niches. Cheek teeth span jumped again from ~8cm-10 to 14cm between early and late Miocene
- Pliocene: more radiation can be seen from fossil record. One genus had cheek teeth span of 21.5cm, while another contemporaneous one had only 11cm.
Increases in cheek teeth span over 60 million years indicate a change in diet to become primarily herbivorous grazers
Horse evolved from a dog-sized mammal with four-toed feet to the much larger modern horse with a single hoof.
Case study of common ancestor - Platypus
- Retains primitive traits- reptilian genes for egg-laying and venom
- Species on South America died out
- Southern variety (Tasmania) is larger than Northern (Australian)
- More specialised to aquatic lifestyle -smells underwater, detects electrical impulses of other creatures in the water, stable body temperature (radio telemetry)
Radio telemetry (platypus)
Little body temperature variation.
From radio transmitters detecting body temperature e.g. freezing winter in Thredbo River.
Radio tracking (platypus)
Uses radio transmitters to detect nocturnal activites.
Max 2.2 kilometres from the burrow, and the distance varied greatly within the study, as little as 0.4 kilometres.
Molecular biology techniques (platypus)
DNA microsatellite sequences (genetic fingerprinting)-
the spur on male platypus’ increases in size during mating season is to compete for partners or territory.
Genetic makeup of platypus to determine gender. 52 chromosomes, with 4Y + 4X or 8X
Divergent evolution
When colonising species adapt to their new environment, resulting in differences between populations, and eventually evolution.
Often through isolation, no longer intermingles
Example of divergent evolution
- Darwin’s finches
- amphibian to mammal evolution due to death of the dinosaurs
Convergent evolution
When completely different species live in a similar environment have the same selective pressures applied to them. The unrelated organisms develop similar characteristics in response to experiencing similar selection pressures.
Evolutionary model: Gradualism
Tiny variation in an organism that happens over a long time to make a better fit for its environment. This variation allows them to survive and thrive resulting in a slow and consistent process of change in the whole population
Evolutionary model: Punctuated equilibrium
A species reacts to rapid change in the environment and dramatically adapts, then followed by a long period of no change (equilibrium) until the next environmental event.
e.g. fossil record of horses. In each era, there is a change of their cheek teeth size, indicating a change of diet that resulted in this change.
Example of convergent evolution
dolphins and sharks: fins, streamlined body shape and flippers
water rat and platypus:
