Lecture 7 Flashcards
Microbial Cells
- first fossils of these 3.5 billion years ago and origin of earth around 4.6 billion years ago with life arising just around 4.2 billion years
- 2.4 billion years ago, there is an oxygen spike due to cyanobacteria, not permanent and levels fall again with changes the acidity of the ocean
Cambrian
- refers to the flowering of animal evolution
- more unstable–>competition
Trigger for multicellularity
-rise in oxygen levels
Precambrian ecosystems and cellular life
- stable because there’s no predation
- Eubacteria-include cyanobacteria in stromatolites
- later fossil cells-younger than 2byr indicate Eukaryotes
- the third great kingdom: Archaea. Primitive in many ways and specialized to strange environment and some odd metabolism
Snowball Earth
- when earth had very big ice ages and glaciers were almost to the equator
- after this earth starts seeing first, faint trace fossils as well as the first large Ediacara Fauna animals
- you can see these even if you can’t see the animal itself–>something walked/burrowed here
- oxygen level rise to roughly modern levels, and animals appear in the fossil record for the first time
Ediacara Fauna
-found all over surface of Earth
Bacterial mat
- dominae earth from 3.5 bry 550 myr ago
- earth was this way for at least three billion years of its 4.5 byr existence
Cambrian radiation
-started 542 myr ago
End of Precambrian
- precambrian ecosystems stable, slow evolution, saturated
- 2 bya first good signs of eukaryotes
- 635 mya first signs of multicellular animals
- most striking effect on PC ecology is stromatolites. Old stability gone by start of the Cambrian. Increased competition, unsaturated world, dynamic
- due to direct grazing of microbial films by animals
- rise on free oxygen
- change in 12C/13C ratios in buried organic carbon
- heterotrophs were eating photosynthetic carbon and it was buried rapidly in fecal pellets
Ediacara Fauna
- body fossils of elaborate large creatures that potentially are ancestral animals.
- unusual enough to require critical evaluation
Small shelly fossils
-tiny simple tubes at first with later increase in diversity
Order of origin life
- sponges come first, then rest of metazoans
- edicara fauna and trace fossils
- burrows (start of cambrian)
- small shelly fossils
- skeletons
- arthropods
- burgess shale like faunas
Precambrian thing and yellow (seapen)
- analog has been made many times in appearance of body orientation
- can’t tell if Precambrian one has polyps like yellow guy
Spirgiania
-related to living arthropods? can it move? oriented vertically and acts as fan in sediment?
Kimberella
-seemed to have covering on top and fed by crawling on the sea floor
What were edicara animals?
- vendazoans, not animals at all fungal grade
- extinct group of creatures related to animals
- odd cnidarian and ctenophore radiation
- primitive memebers of living phyla and ancestors to living phyla
- new data supports 3 and 4 even with a creature that is likely an ancestral bilaterian (Kimberella)
The metazoan radiation and origins of the phyla
- timing
- problem of interpreting fossils of very long ago animals
- origins of body plans=phyla? old ones still extant?
- phylogenetic relationships to each other and to living animals
- rates and mechanisms
Diploblast
-two body layers: ectoderm and endoderm
Triploblast
- three germ layers: ectoderms, mesoderm, endoderm
- bilateral symmetry
Celomic
- body cavity
- innovation that is a sac that contains all the organs outside the gut
Body plans
-different body plans evolve independently because heart and nerve cord can be on either side
Metazoa
- 35 phyla
- most primitive but no tissues or organs
- advanced animals: eumetazoa-symmetry and tissues two groups Cnideria and Bilateria
Cnideria
- radial symmetry
- tissues
- no organs
- ctenophores of similar grade
Bilateria
- bilateral symmetry
- complex organs
- major actors in Cambrian radiation
Cambrian soft-bodied faunas
- Burgess Shale, Canadian Rockies discovred by Charles Walcott
- Sirius Passet Greenland
- Chenjiang, China
- even with invention of skeletions, most animals in sea are and were soft-bodied
- skeleton only preserve a small part of entire living animal
Advances in metazoan body structure
- bilateral symmetry and polarity
- three germ layers
- complex organs
- coelomic body cavity
- segmentation
- important in making possible the Cambrian Radiation
Segmentation
Not all animals are segmented, but most are
- Matamerism or segmentation
- repeats of segments that resemble one and other as you go down the body axis
- segmentation allows for the building of a body plan in a very economic way
- used in annelidia, arthropoda, and chordata
