cambrian explosion Flashcards
bangiomorha pubescens
one of two contenders of first evidence for multicellular life
red alga
fossil found 1.2bya
2 features of evidence:
1.different body parts that do different things (root like strcuture that anchored organism)
2.first known to exhibit sexual reproduction and 2 sexes (sex considered to be prereq for multicellular eukaryote)
Grypania spiralis.
discovered 2.1bya (even older than earliest red alga)
tube shaped fossil thought to be ribbon like alga
too large to be bacterium (10cm long) thought to be alga
the first origin of organelle bearing
why has multicellularity occured?
-surface area to volume problem
-multicellularity allows far more complex organisms as there are specialized cells
-larger life span
3 theories of multicellularity
1.symbiosis
2.cellularization
3.colonial
symbiosis theory (proof and criticism)
different uni-cellular organisms work together and become dependent on eachother. their genomes combine and eventually become multicellular organisms.
proof for this is endosymbiosis (creation of chloroplasts and mitochondria)
criticism: no proof of genomes combining. symbiosis relationships that exist do not combine their dna eg) lichen-seperate dna and seperately reproduce
cellularization theory
cell w multiple nuclei that overtime form cell membranes and become specialized cells
proof: ciliates-cells with multiple nuclei
criticsim:
-complicated process and no actual example of this process
colonial theory
symbiosis of same species and leads to multicellular organism and cells become specialized
proof:Dictyostelium amoeba
criticism:
difficult to differentiate between colonial protists and multicellular organisms
more accepted than others
Dictyostelium amoeba
proof for colonial theory:
a cellular slime mold. groups together in times of food storage. the amoeba become slightly differentiated from eachother
ediacaran fauna
first macroscopic fossils
group of fossil animals and plants that are dominantly soft-bodied and have been found in rocks from the late Precambrian Eon.
thin and flattened,
some leafy, some quilted. no obvoius head, digestive systems, nervous, or circulatory system
What happened to Ediacarans? (extinction)
- preservation bias (couldve been unable to preserve fossils or simply no edicarans there)
2.Predation/ Competition (when cambrian, skeleton organisms rose they could have fed on the soft body ediacarans) - Change in environmental conditions -end of the Precambrian and the start of the Early Cambrian caused many enviornmental changes
evidence of extinction of ediacarans
As animals moved about on the seafloor, dug burrows in sediment, and actively
filtered food from the water, they disrupted the seafloor habitat and competed with Ediacans,
eventually driving them to extinction.
What triggered the Cambrian explosion?
higher oxygen levels. gradually accumulated after the evolution of modern photosynthesis
genetic reasons- few hox genes in first animals; genomes of first animals were easily changed
ecological reasons- predators; shelled animals from the Cambrian are evidence
that a predator drilled through and ate the animal inside, and new niches as animals diversified (filter feeders, burrow feeders etc)
Some biases associated with usage of fossils are
- hard vs soft parts
- abundant vs rare species
- long-lived vs short-lived
species - size of geographical range
benefits of being a larger organism
easily engulf smaller ones
more difficult to be ingested
may escape faster
gain mobility to seek better habitat
what is multicellularity
composed of multiple cells that do not express the same genes (all have the same dna tho), allows for specialization
