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reading: Chapter 5
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Lecture 22. Evolution of Multicellularity, Colonization of Land.
Vendian Period 650-543 Ma
before 600 Mafossils are rare, simplemostly trace fossilsworm-like creatures moving across sediment surfacesradially-symmetric impressions of animals
575-544 Mawider diversity of fossilsradially symmetric fossils andbilaterally symmetric fossil (bilaterians)
Biological interpretation controversial.Several distinct body plans, many don’t exist today.Vendian=EdiacaranDiverse algae, simple animals.
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Vendian Fauna
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Cyclomedusa - most common and widespread Vendian fossil - few mm to m in diameter- bottom-dwelling, like a sea anemone
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Charnia- one of the largest Vendian fossils- up to a m in length- disk shaped holdfast attaching to the bottom- similar to “sea pens”
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Cnidariastinging cells
sea anemones, jellies, sea pensradial symmetry
simple body cavity
Vendian Fauna, cont.
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Eoporpita- thick tentacles surrounding central body- 6 cm across- cnidarian? (jellyfish)
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Nemiana- simplest of all Vendian fossils- sac-like body- never found alone, always in colonies- alga or sea anemone?
Vendian Fauna, cont.
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Pteridinium- not known what it once was- usually found squished flat- bottom-dweller
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Arkarua- small disk-like fossil- echinoderm?
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Echinodermssea urchins, sea stars
exoskeleton with plates
Vendian Fauna, cont.
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Dickinsonia- annelid worm or a cnidarian?
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Spriggina- soft-bodied, only found in the Precambrian- 3 cm long- annelid worm or arthropod
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Arthropod-segmented body
appendages on segmentsmolting exoskeleton
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Annelid wormearthworms, leachescomplex body cavity
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Vendian Fauna, cont.
Tribrachidium- bizarre, disk-shaped fossil- three-part symmetry- may be cnidarian or echinoderm
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Kimberella- tough shell that stuck up out of the
sediment covering the organism- box jellyfish or mollusc?
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Mollusc-shells
body cavity, muscular footmantle and gills
Duoshantuo Formation 570 Ma
Exceptionally preserved fossils in phosphate minerals.Preserves soft-tissue fossils, cellular structures.Nuclei and cytoplasmic contents (organelles) preserved!
Well-preserved algae/seaweed.
Sponges most primitive metazoans - multicellular animals with differentiated tissuesfew occurrences in Precambrian
Preserved animal embryos -bilaterian animals, althoughno adults are seen!
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Spongesessile, tube shaped
filter feedersno true tissues
Terminal Proterozoic
Small shelly fossilsunknown what they were
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Cloudina
Microdictryon
Cambrian 543-490 MaFirst 10-12 Ma:- few animal taxa- some Vendian organisms survived- diverse sponges, rare cnidarians- small skeletal fossils- complex tracks, trails, & burrows (more complex behaviors)
After that:- abundant crown group animals- diversification of crown group animals- wide expansion of mineralized skeletons- arthropods the most abundant fossils- > 80 skeletal taxa- some with 3-fold symmetry- mollusc spiral shells, arthropods, bivalve shells of brachiopods
Burgess Shale
Yoho National Park, Canada40 Ma after start of Cambrian.Exceptional preservation of soft-bodied organisms.Wide diversity of fossil invertebrates.
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Anomalocarislarge >60 cmarthropod-like predator
Burgess Shale, cont.
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Marrellasmall arthropod similar to a trilobiteone of the most common fossils
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QuickTime™ and aTIFF (Uncompressed) decompressor
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Burgess Shale, cont.
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Vauxiasponge with branches
Tuzoiabivalve crustacean similar to brine shrimp
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Wiwaxianot sure what it is
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Burgess Shale, cont.QuickTime™ and a
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Ottoiacommon worm
carnivorousburrowed
Hallucigeniaone side has tentacles one has spinestentacles have claws at the end, so they
were probably the “feet”don’t know which end is the head, which the tail
Snowball Earth Episodes
Early evolution of animals coincides with global glaciations.Possibly 3 glaciation events.Duoshantuo animal embryos and sponges at 570 Ma.
What Factors Contributed to the Cambrian Explosion?
1. Increasing oxygen concentrations in the Neoproterozoic- limits size due to energy yields- larger organisms need more oxygen- early animals limited by diffusion- animals need at least 50% PAL O2
2. Decreased temperatures from cold T’s- global glaciations 800-550 Ma- disruption in biosphere - carbon isotopes disrupted
3. Origination of body armor- arms race of predatory relationships
4. Origination of developmental pathways- metazoans have modular body plans
5. Abundant food sources- microbial mats and stromatolites
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liverworts
hornwortsmosses
vascular plants
Land Plants Are Related to Green Plants
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Coleochaetae
Chara
Colonization of Land
Need to obtain traits- to deal with lack of water- to deal with gravity- how to obtain nutrients- new reproductive strategies
Traits Needed For Animals to Colonize Land
First land vertebrates retained a tail fin, suggesting they spent most of their time in water.
First land animals are amphibians.
A strong support system- bones, vertebrae
Locomotion- limbs (adapt fins to legs)
Able to breathe air- get rid of gills, lungs evolved from the swim bladder
Prevent drying out- need tear glands to wet eyes- thick skin, scales, keratin coating to prevent drying out
Mechanism for hearing- fish have hair cells that sense vibration- evolution of the ear (fluid filled channel with hair cells)
Lay eggs on dry land ~310 Ma- amniotic egg
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Traits Needed For Plant to Colonize Land
Waxy cuticles - keeps plant from drying outVascular tissue - transports water to tissuesWoody tissue - supports the structure against gravityStomata - allow for gas exchange, minimizing drying outPollen, seeds, flowers, fruit - new reproductive strategies,
wind pollination (then insect, animal pollination)
Early land plants (liverworts, hornworts, mosses)-water is a critical part of the life cycle-no cuticle, vascular tissue, woody tissue-reproductive cells swim-can’t grow tall, restricted to wet environments
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reading: Chapter 5
Lecture 23. Mass Extinctions, K-T boundary, Buckyballs.