week 4 - evolution Flashcards
fossil basics
- Trace fossils (ichnology)
o Footprints
Imprints not necessarly accurate but do give us a lot of information about the species
o Coprolites, tracks, trails, nests - Perimineralisation and petrification
o Chemical process
o Minerals replaced - Moulds and casts
taphonomy
The what and how of fossilisation
- Why are some bones more common than others?
o Very common to find teeth (because survives more often)
o Heavy bones more likely to be fossilised
- Why are fossils not found everywhere
o Where matters (understanding habitat) eg rainforest too acidic for fossils
Geological time, stratigraphy and dating
Stratigraphy: how the layers in the earth are put together
Don’t need to remember all the eras but should be familiar with the eras
Cenozonic era
Not as simple as the deeper you go the older it is
* Shit happens (caves
* Dating is really complicated
* So there is lots of agreements with dating
how do you determine a species
Splitters
- Different species unless there is a convincing reason to untie them
o Variation = new species
Lumpers
- Same species unless there is a convincing reason to divide them
o Intra-species varitation normal
i.e. age; sex; disease; genetic variation
A lot of disagreement about this
Element of ego
* E.g. named a new species
interbreeding
- Different, related species can interbreed
- Often infertile
o But not always; can take 2Ma of separation for infertile hybrids - Hybrid zones: 10% of primate species engage in cross-species hybridization
- Hybrids can result in new species
We (homo sapiens) are proof of this
fossil remains are limited
- Complete skeletons are incredibly rare
- Usually find a mix of fragment bones and teeth
- Often impossible to link cranial and post cranial remains
o And they don’t always link
what defines the genus homo?
Original definintion of homo genus compared to previous genus:
- Small, ‘modern’ teeth
- Bipedal
- Tool use
- Brain size
what defines the genus homo?
small teeth
Comparatively our teeth are smaller
BUT
There in an older species (Australopithecus sediba (MH2)) in another genus with teeth smaller than some of the early human species
So not a clear dividing line
what defines the genus homo?
bipedal
- Upright posture/bipedality goes back to at least 7Mya with Sahelanthropus tchadensis
Far more likely our ancestors were upright - Like uranagtang
Goes back at least 7 million years
This upright body posture far predates our genus
what defines the genus homo?
tool use
- First homo species ~2.6 Mya
- ~3.3 Mya ‘Lomekwian’
o West Turkana, Kenya
o Kenyanpithecus platyops - ~3.4 Mya cut marks on bones
o Dikika, Ethiopia
o Australopithecus afarensis
Plently of other species can use tools - Stone tool far predate our homo genus
what defines the genus homo?
brain size
- Homo habilis 500cm3 low end
- Paranthropus robostus 550cm3
For a long time was considered an absolute cut off - This is not the case
- There is a trend towards bigger brain sizes
- No clear line to draw
Is our definition of Homo wrong and why all these problem with the Homo genus?
The year fossils were found is important
* Knowledge avaiable
Homo habilis
* Small brain
But had all the other aspects
Does this make them human
- There was an obsession of humans being more advanced (tool use) so wanted it part of our group
- So need all the evidence
Ancestry and interbreeding
- A lot of interbreeding
- We know this exists
Who evolved from who?
- Things get really messy
- Impossible to know
Unless in a modern situation can use genetics (this can still give different answers)
All of these species were alive at the same time
genetics and interbreeding
- H. sapiens show evidence of interbreeding with
o Denisovans
o H. neanderthalnsis
Shows how there was a constant flow of humans
o Unknows archaic European populations (Eurasians)
o Unknown archaic African population - H. neanderthalenisis and Denisovans interbred.
o Female remain from around 90 kya fund to have a a neanderthal m other and Denisovan father
Can see this with fossils
90,000 years ago
Very rare to catch
