Eukaryotes and Cambrian explosion W5L1 Flashcards
Eukaryotes origin
endosymbiotic origin
evident in genetics of different cell parts
Eukaryotes sexual reproduction
greater genetic variability > evolution
greater diversity and disparity •
Eukaryotes size
larger size thank bacteria cells
resources
metabolism
this can easiyl place fossil cells bcs little chance that internal structures will prevail so other diagnostic features
Endosymbiotic events
ndosymbiotic events (bacterial cell eats other cell) → organelles in cells various engulfing events → eventually genetically coded → complex cells with remnants of engulfed prey inside them
bacterial cells reproduce
bacterial cells (prokaryotes) reproduce asexually (cloning/ splitting)
eukaryotes reproduce
eukaryotes can also produce asexually (single cell algae) but also add sexual reproduction
recombining genetic material
mixing DNA “speeding up evolution”
Snowball earth
single cells can live under ice but most organisms struggle
little pulse of banded iron formations, relatede to end of one snowball earth
Precambrian provides
the Precambrian geological record provides context for the timing, environmental conditions
and types of early life
• the record reveals a very long period (~3.5 b.y.) characterised by small, microbial organisms,
prior to the rapid emergence of large metazoans
• nevertheless, this interval saw the emergence of life, anoxygenic phyotosynthesis, then oxygenic
photosynthesis, oxygenation of the planetary surface, aerobic respiration and eukaryotic cells
Ediacaran Fauna
Ediacaran fossils 540-580 Ma
• large, relatively complex and diverse structures (radial, bilateral)
• unmineralized, i.e., soft bodied
• appeared after the final snowball episode (Gaskiers)
diverse group of animals
Ediacaran animals as precursors for “ real animal” still big gap betwee new ones
Animals definition
Animals are multicellular eukaryotic organisms that usually consume organic material, breathe oxygen, are able to move, can reproduce sexually
Animal body definition
everal distinct body plans defined by number of enveloping walls of tissue and presence or absence of coelom (body cavity)
parazoan
groups of cells in 2 layers not differentiated into tissue types
Diploblastic
2 layers separated by the acellular, gelatinous mesogloea
Triploblastic
3 layers of tissues from the outside in: the ectoderm, mesoderm and endoderm. Also bilateral symmetry
Animal cells
Animals are unique in having the ball of cells of the early embryo develop into a hollow ball or blastula
Around 12 major animal groups or phyla, 35 in total
EEdiacaran fossils
Ediacarans preserved as moulds/casts/impression
often in sands, shallow-water environments
no mineralised skeletons
some multicellular fossils
Ediacaran fossils perserved
no predation or scavenging pervasive microbial mats low oxygen? different ocean chemistry pyrite ‘crusts’ silica cementation? usually get eaten scavenged immediately, will be deconstructed (bacteria etc) so kinda strange that the fossils are still present must have been unusual environment
Ediacaran animals meaning
why did they go extinct?
are they the precurosur, well gap in evolutional
are the Ediacaran fossils remains of animals?
what happened to the Ediacarans?
extinction?, gave rise to other animals?
when did true animals appear?
How reliable ediacaran fossil record?
embryo fossil evidence
molecular clock evidence
stromatolite decline
trace fossils
• is the Cambrian explosion ‘real’
why the acceleration of animal evolution?
environmental trigger?
genetic trigger?
• why rapid ‘disparity’ followed by 530 my of stablility?
problems
correlation and dating of unfossiliferous rocks
preservation: old rocks, soft-bodied and or small animals?
Molecular clock evidence
biomarker to date where fossils were found
but markers often dont match - they more suggest that fossil record didnt cpature it as “explosion”
given the discrepancies there is still a period where a lot happened
why cambrian expolsion
Oxygen when did the rise occur? threshold respiration ozone • predation - ‘arms race’ evolution of eumetazoans move into planktonic niche food that allows to move out into new habitats eyes for the first time first time using sight senses, for hunting • climate - oceans post-Snowball Earth genetic ‘leap’ trigger genes, e.g., Hox genes, allow spinal shape neural tissue
Tommotian
Lower cambrain, small shelly fauna
sponges and mullosc
Burgess SHale
really changed how Cambrian was percieved, unique window cambrain life submarine landside deposit • high diversity (120 spp.) • ~98% soft bodied more mature ecosystem Simple ecosystem 40% trilobites, 25% worms Preservation as carbon films soft bodied animals
Anthropod as
rthropod as first Apex predator maybe
“normal” animals many many arthropods
primitive arthropods such as Opabinia
fossil record of precambrian tells us
evolution of eumetazoan grade and predation ecological strategy led to
acceleration of evolution
• last common ancestor of eumetazoans was a sponge
• trigger may have been lack of food following a snowball glaciation forcing a
switch in trophic strategy
• move into the pelagic realm may have driven second Ordovician radiation
• rapidity of disparity due to expansion of regulatory genes acting on
relatively conservative animal genome
