3 Cambrian to Cretaceous Flashcards
Marine Radiation of Fishes - Paleozoic
Cambrian saw the origin of Chordates
450-420MYA - jawed fish radiation ‘Gnathostomata’
Fish are split into 2 main groups - chrondricthyes = cartilaginous fish / osteichthyes = bony fish (sub groups - actinopterygii = lobe finned fish / sarcopterygii = lung fish)
Enabling feature for jawed fish radiation - genome duplication
Early chordates had 2 genome duplication events
4 Hox gene clusters
Enables morphological complexities (jaws, limbs) —> Devonian
Jawless fish to jawed fish timeline
100 MYA of stasis as ‘jawless fish’
Genome duplication enables complexity
Radiation of jawed fish and later tetrapods
The Greening of the Land - Paleozoic
Land plant life cycle evolved from algal plants
In algae most of their life is spent in the diploid cell
Large change is the diploid phase
Bryophytes - the early land plants (liverworts and mosses)
Long haploid phase, short diploid
No vascular tissue
Don’t requre soil
Evidence by fossilised sporangia
Mosses also evolves stomata (gas and water regulation)
Land plants accompanies by terrestrial fungi
Evolution of desiccation-resistant fungal hypha from aquatic form
Hypothesised fungi enabled plant life on land through symbiosis
Fungal plant interactions essential for many bryophytes
Plant death —> organic bearing terrestrial soil
Creates soil = breakdown of plant matter (fungal, microbial action) / soil enables the growth of larger plants
Bryophytes don’t need soil but do create soil
Paleo soil in the Devonian
Vascular Plants (Devonian)
Phloem / xylem transport system
Bifurcating (branching) growth / increased size through lignification
Leaves and fronds —> above ground photosynthetic surfaces / evolved on multiple occasions
Vascular plants result in richer soil - PO4 / NO3 are fuel for plant growth (but may have poisoned oceans via eutrophication)
Devonian Mass Extinction
75% in 3 million years (many taxa disappear)
Land plant evolution accompanies by terrestrial arthropods
First insects - flightless / derived from Crustacea (in silurian)
Devonian - winged formed (+ millipedes / aranaea spiders)
The Carboniferous - Paleozoic (age of coal)
Carboniferous rocks —> appearance of organic rich deposits
Coal beds have abundant plant and other fossils - large woody plants appear, alongside large ferns / derived from lowland marsh and wetland
Paleozoic - Why did the increased deposition of organic carbon occur
Tall woody plants had become dominant —> wood Is rigid and plants can grow tall due to lignin = complex carbohydrate, decomposes much more slowly which results in more organic carbon buried and coal strata
Palaeozoic - Impacts of high oxygen levels
Biological consequences —> insect giganticism (aerobic respiration is more efficient —> more growth)
O2 limits body size where diffusion supports gas exchange —> O2 content of water increases with latitude and decreases in saltwater —> larger fish found in cooler oceans
Fire - 10-20% of coal beds are charcoal based (common) wildfires
Paleozoic- Carboniferous also saw radiation of tetrapods
Warm, wet climate, green terrestrial biome enables movement out of water
Amphibian lifestyle - still linked to laying eggs in water
Closest ancestors - lobe finned fish
Giganticism also seen in amphibian - dominated predators of the Carboniferous
The Permian
Rise of reptiles and the Permian mass extinction
End of the Carboniferous / eaely Permian saw a period of drying —> one large land pass (Pangea)
This drying makes a poor environemnt for amphibians —> selection for water retention
Adaptations of reptiles for life away from water (4)
- Amniotic egg
- Keratinous scales
- Alteration in excretion
- Internal fertilisation
Adaptations of reptiles for life away from water - amniotic egg
zygote in fluid filled cavity / chorion and shell - able to gas exchange but retains water
Adaptations of reptiles for life away from water - keratinous scales
water impermeable skin
Adaptations of reptiles for life away from water - alteration in excretion
uric acid / utilise arid landscape areas
Adaptations of reptiles for life away from water - internal fertilisation
Reproduction on land necessitates transition to internal fertilisation
Permian also saw the rise of metamorphosing insects
- Hemimetabolous development
- Holometabolous development
The Permian mass extinction
End of the Permian saw largest mass extinction event in fossil record ‘The Great dying’
Causes of the Permian Mass Extinction
- Occurred at the same time as very high volcanic activity in Siberia
- Massive SO2, CO2 release
- Ocean acidification
- Reduced primary productivity
- Death of consumers
Does mass extinction hit evenly
No - in general large things die out more than small things and non-motile things die out more than motile things
The Mesozoic
Age of dinosaurs origins of birds, mammals (and flowers)
252-66 MYA
Why cant DNA be used to reconstruct biology of dinosaurs
The DNA is decomposed
Scientists study the new remains to determin relationshios to other known species and genera
Comparisons are made between these and living animals —> reconstruct skeleton and lifestyle
Aspects such as size, movement, weight and shape can also be determined
Can also look at trackways of footprints and use principles of anatomy and biomechanics -> movement and running speed
Thermal biology
SA/V ratio - retained heat - can’t tell behaviour (eg. Basking or metabolism) - try to use species today to infer what their behaviour was likely to be
Current idea is that dinosaurs were both endothermic and edothermic
What does brain size indicate
Indicates cognitive complexity - birds and mammals have complex cognitive capacity
Origin of mammals
220 MYA
Derived from synapsids (non-dinosaur reptiles, no living examples) / mammals remained a minor taxa during the age of the dinosaurs
Origin of birds
160 MYA
Evolved from theropod dinosaurs during the Jurassic (165-150MYA)
Classic small, lightweight, feathered and winged body plan —> evolved over tens of millions of years of evolution rather than one burst of innovation
Many non-avian dinosaurs had feathers
Origin of Angiosperm (flowering plants)
130 MYA
First fossils 130MYA —> fast growing compared to gymnosperms (conifers)
Initially wind pollinated / insect pollination (110 MYA)
Origin of Plant and insect diversification
Massive plant diversification 100-70MYA —> resulted in 250k species today
Loss of gymnosperms in the tropics
Diversification in beetles
Plants and their herbivores escape and radiate process
Plant group —> novel defences —> escaped herbivores colonise new niches —> radiates —> herbivore that establishes onto that group (creates large number of new niches that then radiate again and REPEAT)
