6/ cambrian explosion of animal life Flashcards
what characteristics do metazoans share
- multicellular body formed from dif kinds of cells
- ability to manufacture collagen
- reproductive cycle with gametes produced by mitosis
- nervous system composed of neurons (except sponges)
what 4 recent advances have been important in addressing origins of metazoans
- new fossil finds
- phylogenetic analysis of anatomical and molecular data - look at phylogeny, work out when animal diversified, not suitable for rly long ago
- molecular clock studies
- molecular genetics of animal development - take out a gene and put it in another animal. see how its passed around
classification of animals - 2 groups
- diploblastic: sponges + archaeocyathlds, jellyfish + corals
- triploblastic: other animals
late precambrian (ediacaran) at 630- 542 Ma
- the edicara biota
- trace fossils of triploblastic organisms
- egg cases containing embryos
- large acritarchs
late precambrian at 580 Ma
- phosphatised embryos
early cambrain (manakayan) at 542-530 Ma
- small shelly fossils
middle cambrian (tommotian and atdabaian)
- cambrian explosion
- fossilized hard parts appear
- soft tissue rare in certain biota preserved
describe ediacaran biota fossils
- unusual symmetry, compartments
- not like life we have now
- 2 types:
- had stem, attached to sea floor and swayed
- lay on floor, shrunk down when covered in sand
what did edicaran organisms not have, how did they feed?
- no mouth, gut or anus
- compartments contained unicellular photosynthetic algae (unlikely - deep) or
- they took substances through the body wall or
- chemosymbiosis - compartments contained sulphide oxidising bacteria
what have ediacara organisms been interpreted as
- simple ancestors of sponges, jellyfish etc
- diploblastic animals showing variation not seen in modern animals - didn’t leave relatives
- entirely separate attempt at multicellular life that failed
- new geochemical evidence suggests they are actually animals
what environments preserve soft tissues well, whats been preserved
- phosphate rich
- small stuff only:
- water bears
- embryos - some large ‘acritarchs’ are in fact cases of animal embryos
early cambrian/ manakayan fossils
- small shelly fossils, adapted against predation
- represent extinct phylum close to mollusca
- or some form of annelid / worm
examples of locations w exceptional preservation
- chenjiang biota, china
- sirius passet biota, greenland
- emu bay biota, Australia
- burgess shale biota, canada
describe fossils that appear during middle cambrian
- archeopods
- preservable hard parts
- include representatives of all modern phyla w hard parts
Cambrian explosion: appearance of fossilizable parts or true evolutionary burst
- long history of precambrian animals - molecular clocks, fossilized embryos. only get fossils once they developed armour.
- diversity exploded rapidly with little subsequent change
how could environment have caused cambrian explosion
- 2 long lived supercontinents that dominated precambrian start to break apart
- snowball glaciation events
- mysterious short low c isotope values in latest precambrian
- atmospheric ox increases at precambrian/cambrian boundary - most important
how could ecology have caused cambrian explosion
- bottleneck - predators forced soft bodies animals to shell up or bury into sand
- 1st predators hunted by hearing, then evolved eyes
evolutionary progression outline: late precambrain, early middle cambrain, late cambrian
- ediacaran animals inhibit sea floor, unprotected but no predators, triploblastic animals present but small
- triploblastic w teeth - predators evolve, most ediacara extinct, evolve armour for ptotection
- predators more efficient (eyes), better armour, burrowing niches
