Lecture 7

Question 1

Microbial Cells

Answer 1

• 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

Question 2

Cambrian

Answer 2

• refers to the flowering of animal evolution

- more unstable–>competition

Question 3

Trigger for multicellularity

Answer 3

-rise in oxygen levels

Question 4

Precambrian ecosystems and cellular life

Answer 4

• 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

Question 5

Snowball Earth

Answer 5

• 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

Question 6

Ediacara Fauna

Answer 6

-found all over surface of Earth

Question 7

Bacterial mat

Answer 7

• 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

Question 8

Cambrian radiation

Answer 8

-started 542 myr ago

Question 9

End of Precambrian

Answer 9

• 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

Question 10

Ediacara Fauna

Answer 10

• body fossils of elaborate large creatures that potentially are ancestral animals.
• unusual enough to require critical evaluation

Question 11

Small shelly fossils

Answer 11

-tiny simple tubes at first with later increase in diversity

Question 12

Order of origin life

Answer 12

• 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

Question 13

Precambrian thing and yellow (seapen)

Answer 13

• analog has been made many times in appearance of body orientation
• can’t tell if Precambrian one has polyps like yellow guy

Question 14

Spirgiania

Answer 14

-related to living arthropods? can it move? oriented vertically and acts as fan in sediment?

Question 15

Kimberella

Answer 15

-seemed to have covering on top and fed by crawling on the sea floor

Question 16

What were edicara animals?

Answer 16

• 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)

Question 17

The metazoan radiation and origins of the phyla

Answer 17

• 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

Question 18

Diploblast

Answer 18

-two body layers: ectoderm and endoderm

Question 19

Triploblast

Answer 19

• three germ layers: ectoderms, mesoderm, endoderm

- bilateral symmetry

Question 20

Celomic

Answer 20

• body cavity

- innovation that is a sac that contains all the organs outside the gut

Question 21

Body plans

Answer 21

-different body plans evolve independently because heart and nerve cord can be on either side

Question 22

Metazoa

Answer 22

• 35 phyla
• most primitive but no tissues or organs
• advanced animals: eumetazoa-symmetry and tissues two groups Cnideria and Bilateria

Question 23

Cnideria

Answer 23

• radial symmetry
• tissues
• no organs
• ctenophores of similar grade

Question 24

Bilateria

Answer 24

• bilateral symmetry
• complex organs
• major actors in Cambrian radiation

Question 25

Cambrian soft-bodied faunas

Answer 25

1. Burgess Shale, Canadian Rockies discovred by Charles Walcott
2. Sirius Passet Greenland
3. 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

Question 26

Advances in metazoan body structure

Answer 26

• bilateral symmetry and polarity
• three germ layers
• complex organs
• coelomic body cavity
• segmentation
• important in making possible the Cambrian Radiation

Question 27

Segmentation

Answer 27

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