reading: chapter 5 lecture 22. evolution of multicellularity, colonization of land

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reading: Chapter 5





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.





Vendian Fauna



Cyclomedusa - most common and widespread Vendian fossil - few mm to m in diameter- bottom-dwelling, like a sea anemone



Charnia- one of the largest Vendian fossils- up to a m in length- disk shaped holdfast attaching to the bottom- similar to “sea pens”



Cnidariastinging cells

sea anemones, jellies, sea pensradial symmetry

simple body cavity

Vendian Fauna, cont.



Eoporpita- thick tentacles surrounding central body- 6 cm across- cnidarian? (jellyfish)



Nemiana- simplest of all Vendian fossils- sac-like body- never found alone, always in colonies- alga or sea anemone?




Pteridinium- not known what it once was- usually found squished flat- bottom-dweller



Arkarua- small disk-like fossil- echinoderm?



Echinodermssea urchins, sea stars

exoskeleton with plates




Dickinsonia- annelid worm or a cnidarian?



Spriggina- soft-bodied, only found in the Precambrian- 3 cm long- annelid worm or arthropod



Arthropod-segmented body

appendages on segmentsmolting exoskeleton



Annelid wormearthworms, leachescomplex body cavity




Tribrachidium- bizarre, disk-shaped fossil- three-part symmetry- may be cnidarian or echinoderm



Kimberella- tough shell that stuck up out of the

sediment covering the organism- box jellyfish or mollusc?



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!









Spongesessile, tube shaped

filter feedersno true tissues

Terminal Proterozoic

Small shelly fossilsunknown what they were





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.



Anomalocarislarge >60 cmarthropod-like predator

Burgess Shale, cont.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Marrellasmall arthropod similar to a trilobiteone of the most common fossils




are needed to see this picture.Trilobitesseveral speciessome soft appendages preserved





Burgess Shale, cont.



Vauxiasponge with branches

Tuzoiabivalve crustacean similar to brine shrimp



Wiwaxianot sure what it is



Burgess Shale, cont.QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

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



liverworts

hornwortsmosses

vascular plants

Land Plants Are Related to Green Plants







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



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



reading: Chapter 5

Lecture 23. Mass Extinctions, K-T boundary, Buckyballs.

reading: chapter 5 lecture 22. evolution of multicellularity, colonization of land

Documents

largest vendian fossils

vendian fossils sac

vendian organisms

widespread vendian fossil

abundant fossils

vendian faunacyclomedusa

vendian period

softtissue fossils