Fossils Flashcards
Give the rough dates of;
-Origin of prokaryotic life
-Formation of the Earth
-Big bang
Origin of prokaryotic life (3.5 billion)
Formation of the Earth (4.57 billion)
Big bang (13.7 billion)
What are fossils?
*Transformed body parts-shells, bones, teeth
*Activity (‘trace fossils’) -burrows, footprints
*Preserved remains (‘sub fossils’)- shells, remains in amber
*Organic chemicals any body part
How are fossils formed?
(By a series unlikely of events) what are they ?
- Body survives long enough after death to undergo fossilisation this could be difficult as;
-Soft parts are destroyed quickly
-Eaten, degraded by microbes
-Few fossils of soft bodied organisms e.g. worms and plants
-Even hard parts are likely to be destroyed e.g Crushed by rocks, wave action, scavengers - Remains must become buried in sediment at the bottom of a water column.
-Fossils are only found in sedimentary rocks (e.g limestone and sand stone) - The chance of fossilisation depends on proximity to sediment. Chance for fossilisation gets higher in water organisms closer or in the sediment
- Permineralization
Sediment covered by more layers
Compacts into rock – may deform or destroy the fossil
Hard minerals leach out of rocks and impregnate the remains
Original compounds replaced and leach out - Exposure – The final ‘unlikely event’ ‘Fossil’ means ‘something dug up’
Tectonic processes can move the fossil around and re-expose it in a terrestrial area which makes it easier to be lost for ever
Fossils are rare in comparison to the number of organisms that have existed in the 3.5 billion year history of life.
What does the quality of the fossil depend on?
State of body at the start of the process and geological factors – pressure, minerals present
What are alternative routes to fossilisation of buried remains
external or internal mould or marks
How do we date fossils?
*Radio-carbon dating
5730 years after death ½ the C14 → N14
Can work out date of death by examining the ratio
Only for fossils up to 40,000 years old
only if sediments has some sort of organic compound
(absolute dating)
Volcanic ash
Many sediments contain volcanic ash (‘tephra’)
Potassium and Argon
Decay more slowly than C14 – fossils older than
100,000 years
Paleomagnetic dating (older fossils)
Currents in Earth’s core change direction of magnetic field ‘Normal’ / ’Reversed’
Determines alignment of magnetic particles when rocks form
Age rocks by comparing the polarity of sediments to cores of rock from sea bed
(relative dating)
What is relative dating?
Compare fossils to fossils of known age from other strata that look similar
Why are fossils important?
e.g Fossil butterflies, 65 Myr BP nb
Molecular evidence reveals increasing amounts of information about evolution
Shows how closely extant species are related and how quickly they may have diverged – e.g. ‘molecular clocks’
Only fossils tell us what extinct species were like and how they lived.
‘Functional morphology’ ADAPTATIONS
Describe the fossil record
What is fossil study called?
when did serious analysis of fossils begin?
Study of fossils is called ‘Paleontology’
Fossils provide a record of the history of life
Deeper ‘strata’ (layers) equate to greater age of the rocks and any fossils they contain.
Serious analysis began in the 1960
Evermore detailed analysis; 2020, 11k species at 0.1my resolution (Fan et al. 2020)
When was the first human around?
When did mammals diversify?
First humans 195-160000 yr bp
Mammals diversify – 65 Myr bp
How is the geological time scale divided ?
‘Eras’, ‘Periods’ and ‘Epochs’
Based on rock strata and refined with new dating techniques
Each stretch of time has a characteristic fossil fauna
Boundaries reflect sudden changes in fauna
When was the extinction of most dinosaurs
Cretaceous, 65 – 144 Myr BP
Sinosauropteryx
How do we know perhaps some dinosaurs had feathers?
Melanosomes – contain the pigment in hair and feathers
What are extant saurischian dinosaurs
lizard-hipped dinosaurs
birds evolved from lizard hipped dinosaurs not bird-hipped dinosaurs
Jurassic, 144 – 206 Myr BP
‘Quarry dinosaurs’
Very large herbivores
4 species
Up to 26m
Est. weight 50 – 113 tonnes
Triassic, 206 – 251 Myr BP
Before dinosaurs evolved
Ichthyosaur (‘fish-lizard’)
Evolved from terrestrial reptiles that returned to the sea
Predated earliest dinosaurs by 20 Myr
Extinct in the cretaceous, just before the last dinosaurs
Cetaceans were not the first group to return to the sea!
Permian 251-290 Myr BP
Terrestrial tetrapods, arthropods plants and fungi
such as;
Fusulinids – protists with a hard shell
Ammonites – molluscs with a hard shell
also dimitrodon a syapsid which was a mammal-like reptile
mammal like in the sense it had a mammal shaped skull and they perhaps could have some sort of regulation of its body temperature.
Carboniferous 290-354 Myr BP
Coal deposits due to appearance of bark bearing trees
No lignin digesting bacteria
Atmospheric oxygen 80% higher than today
Allowed Gigantism to evolve on land and in the sea
-Giants insects Dragonflies, cockroaches and grasshoppers
e.g. Meganeura spp.
Devonian 354 - 417 Myr BP
Lungfish
Tetrapod colonisation of land
First fossil insects
First angiosperms
Rhynie Chert - Plants
It showed fungi associating with roots
Fungal fillaments (‘hyphae’) growing in the plant tissue
Rhynie Chert - Animals
Trigonotarbid – an arachnid (but not a spider)
Oldest known terrestrial arthropods
Describe gigantism in Devonian sea scorpions and some reasons
Jaekelopterus rhenaniae
Early Devonian
Largest arthropod discovered so far
Chelicera 46 cm long
Different reasons for gigantism – high resources, competition or courtship
Silurian 417 - 443 Myr BP
Some type of moss
Ordovician 443-490 Myr BP
Nautiloids
Shell producing cephalopods
Straight or curled shells
Divided into chambers
Extant species
Cambrian ‘explosion’ 490-543 Myr BP
Trilobites
Heavily armoured marine arthropods
Earliest example of an animal using weapons
Rapid evolution
15000+ species recognised
9 Orders
Most animal classes first appear in the Cambrian e.g;
The Burgess shale (Opabinia) (Wiwaxia corrugata)
The ‘ abnormal shrimp’ (Anomalocaris)
Hallucigenia (Large scales)
Summary: What does the fossil record show?
Evidence for evolution
Lineages appear, change and disappear
Evolution not directed towards a ‘goal’
Sudden changes rather than smooth transitions
Does this matter for Neo-Darwinian model of evolution?
