2. The First Animals

Question 1

How do we know what species aren’t animals? 3

Answer 1

1. It is hard to tell what aren’t classed as animals as the indicators are based on absence rather than presence
2. Bacteria, protists, fungi, plants aren’t animals
3. Animals are also called metazoa

Question 2

What were Darwin’s concerns over his theory of natural selection? 3

Answer 2

1. He was worried about the lack of fossils that depict simple life
2. He found that animals tended to suddenly appear in the fossil record
3. His theory involved gradual change, and this lack of evidence made him doubt himself

Question 3

What is the geological timescale? 5

Answer 3

1. Measured in eons
2. Hadean : 4000-4600m years ago
3. Archean: 2500-4000m years ago
4. Proterozoic: 540-2500m year ago
5. Phanerozoic: 0-540m year ago (paleozoic, mesozoic, cenozoic)

Question 4

How did life develop through time? 4

Answer 4

1. Prokaryotes emerged in late Hadean
2. The hadean and archean eons were made up of mostly protozoic and archean life
3. In the protozoic, snowball earth happens and eukaryotes and multicellular life appear, along with the animals
4. land plants, mammals, dinos and hominids appear in phanerozoic

Question 5

What is neontology? 4

Answer 5

1. paleantology but more recent things studied
2. DNA suggests we don;t see everything in the fossil record so we use a genetic molecular clock
3. Unicellular chanoflagellates are the closest living relative to animals, but there is a large difference in DNA sequence
4. The two groups diverged in cryogenian/adiacaran

Question 6

What are the limitations of paleantology? 3

Answer 6

1. The earliest animals didn’t biomineralise as they were soft bodied
2. This includes common ancestors of lots of animals
3. rocks that are very rare are old as they get metamorphosed as earth changes and so destroyed

Question 7

Describe the archaen period. 3

Answer 7

1. Banded iron formation in rocks tells us there was low oxygen because the iron is not oxidised
2. High levels of co2 and methane
3. biomolecules produced only in photosynthesis called 2 alpha methylopanes have been found in these rocks

Question 8

Describe archean life. 5

Answer 8

1. Fossil stromatolites are layered structures thought to be photosynthesising cyanobacteria
2. There is a mineralized layer left behind
3. oxygen is released into the environment
4. oxygen released was quickly consumed by iron and removed from system
5. mostly bacteria living at this time

Question 9

What was snowball earth? 7

Answer 9

1. 2400m year ago
2. great oxidation event
3. collapse of greenhouse effect (methane and co2) leading to glaciation and positive feedback
4. Light is reflected off ice so temperature drops until most of surface covered in ice
5. terrible for life at the time as oxygen was toxic to many
6. volcanoes released co2 recreating the greenhouse effect, which may have caused release of more oxygen into environment
7. This was not the only mass glaciation

Question 10

Describe the proterozoic. 3

Answer 10

1. Birth of eukaryotes caused by multiple endosymbioses to create mitochondria and choloplasts
2. Multicellularity also arose more than once in plants, animals and algae
3. This included the origins of metazoa

Question 11

What happened at Charnwood forest? 3

Answer 11

1. In Leicestershire, a schoolboy found a Charnia masori fossil and showed his teacher
2. It turned out to be older than we ever thought it could be due to good bedding plains at the forest
3. It was 560m year old

Question 12

What were the 3 main types of ediacaran biota? 3

Answer 12

1. Branched and look like leaves
2. Radial type
3. Possibly some bilaterally symmetrical ones

Question 13

Describe branching ediacaran biota. 4

Answer 13

1. Called vendobionta
2. Have fronds that have been compared to sea pens - an extant coral, as they have similar structure but growth is different
3. Vendobionta have glide symmetry and fractal growth - growth on growth
4. They have alternate arrangement of tubules/fronds around centre

Question 14

Describe radial ediacaran biota. 3

Answer 14

1. Were interpreted as jellyfish, but probably incorrect
2. more likely to be holdfasts or microbial growths
3. triradial, tetraradial, pentaradial and octoradial discs are more difficult to interpret.

Question 15

Describe the examples of possible metazoa from the ediacaran period. 3

Answer 15

1. Quadrilateral symmetry and bundled fibres that could be muscles
2. Ripples are potential muscles, leading to interpretation as an animal
3. Believed to be cniderian, therefore metazoan

Question 16

Describe the creatures from the ediacaran that may have been bilaterians. 5

Answer 16

1. Spriggina, dickinsonia and yorgia could be annelids or arthropods
2. however, they have vendobionta style glide symmetry
3. no mouth, legs or gut
4. kimberella could be cnidarian/ctenophore
5. there has been a recent interpretation of soft shell, radula and mantle - mollusc?

Question 17

How were ediacaran fossils preserved? 3

Answer 17

1. organisms lived on flat, microbial mat, and were buried under sediment and mineralized
2. this is supported by geochemistry
3. there are different morphologies for different stages of decay eg. rough, rotted surfaces

Question 18

Describe dickinsonia trace fossils. 2

Answer 18

1. Circles near it suggest it settled, then moved on

2. May have flopped in manner similar to placozoa, of which there is one existing species

Question 19

Describe kimberella trace fossils. 3

Answer 19

1. Grazing traces on rock - may have moved like limpet
2. Muscles used to move along rock and graze on algae and bacteria
3. suggests mollusc

Question 20

Describe the theory behind the rock band trace fossils. 3

Answer 20

1. Bands where round organism may have moved along
2. team explored deep ocean and found giant bacteria that roll in marine snow and leave traces
3. fossil could be from metazoa or giant bacteria

Question 21

How do ediacaran fossils fit into any kind of phylogeny?5

Answer 21

1. There are numerous interpretations, but vendobionts could be early animals related to rangeomorphs (more primitive than sponges)
2. Dickinsonia likely to be placazoan or between sponge and cnidarian
3. some radial forms (tri, tetra, penta, octa) may relate to early cnidarians or belong to bilaterian stem
4. Some ediacarans could be early bilaterians eg. spriggina
5. Kimberella is the only ediacaran interpretable as a real bilaterian, due to possible shell/muscle skirt

Question 22

How did ediacaran animals reproduce? 3

Answer 22

1. Spatial distribution analysis suggests asexual reproduction
2. ecosystem is structured, with random large organisms surrounded by medium, surrounded by small
3. This suggests complex, multigenerational life cycle of asexual stolon branching and water bourne propagules

Question 23

Describe ediacaran ecology. 3

Answer 23

1. Fossils preserved in flat planes - this historic sea bed
2. mostly epibenthic (flat) or semi-endobenthic (half buried)
3. Almost all were sessile

Question 24

Describe the ediacaran diet. 3

Answer 24

1. Creatures lived on microbial mat surface
2. Little evidence of predation meaning short food chains
3. High surface area to volume ratio suggests osmotrophy

Question 25

What are theoretical ecospaces and how do they relate to the adiacaran period? 3

Answer 25

1. During ediacara, many ecosystems were large and unfilled 2. The ediacaran had a 2D ecosystem 3. After the cambrian substrate reduction, we had bioturbation leading to 3D ecosystem

Question 26

Define bioturbation. 1

Answer 26

1. Change in soil caused by animals/plants

Question 27

What are namacalathus and cloudina? 6

Answer 27

1. strange ediacaran fossils 2. tiny, mineralised reef-builders with a similar skeleton to modern corals laying down 3. found in Namibia, 550m year old 4. Cloudina have a hole that some have interpreted as evidence for predation 5. it was thought this was similar to the radula of a mollusc, which is used to suck out insides, but was actually formed by rock crystals 6. fossils appear to be sessile, epibenthic filter feeding metazoans

Question 28

Descrbe ediacaran cell clusters. 4

Answer 28

1. Clusters of microscopic, fossilized cells 2. Found in Chinese Doushantuo (rock) formation, 580m years old 3. Was thought they may be embryos or giant bacteria 4. Evidence suggests algae/protsits as they have nuclei so eukaryote and nature of growth cleavage is consistent with this

Question 29

What caused the ediacaran period to progress in this way? 5

Answer 29

1. Gaskian glaciation (Canada) - end coincides with sudden oxygenation and diversification. 2. Massive oxygenation led to other environmental changes and ways of living developed 3. Gene regulatory networks - genes interact during growth. A change in this can lead to sudden evolutionary explosion, but we can't test this 4. Ecological interations eg. predation may have led to arms race. Can't test but can study ecology and lifestyles 5. Closing fossilization window due to change in conditions. It may be that 'extinct/out-competed' organisms may have survived without fossilisation.

Question 30

On the eve of animal radiation, by S. Xiao and M. Laflamme, 2008, Trends in ecology and evolution. Describe the ediacaran biota. 3

Answer 30

1. vendobionta not closely related to metazoa 2. vendobionta may be an extinct kingdom of its own 3. ecology and evolution research limited by lack of phylogenetic certainty

Question 31

On the eve of animal radiation, by S. Xiao and M. Laflamme, 2008, Trends in ecology and evolution. Describe the ediacaran biota in space and time. 2

Answer 31

1. Most ediacaran species did not survive to or have descendants in the Cambrian 2. lack of ediacaran fossils in Burgess Shale suggests not taphonomic artefact

Question 32

On the eve of animal radiation, by S. Xiao and M. Laflamme, 2008, Trends in ecology and evolution. What are the 3 ediacaran assemblages? 10

Answer 32

1. Avalon assemblage - Newfoundland and England 2. Lived in deep water, ventilated ocean 3. No trace fossils 4. White sea assemblage (russia) 5. Most diversity 6. First stem group bilaterians 7. Shallow water 8. Nama assemblage (Namibia) 9. Shallow, turbulent waters 10. Thought to represent 3 areas of ediacaran evolution

Question 33

On the eve of animal radiation, by S. Xiao and M. Laflamme, 2008, Trends in ecology and evolution. Describe ediacaran body plans. 3

Answer 33

1. Low taxonomic diversity but high morphological diversity 2. Difficult to determine phylogenetic relationships 3. Unique body plans not repeated since

Question 34

On the eve of animal radiation, by S. Xiao and M. Laflamme, 2008, Trends in ecology and evolution. Describe phylogenetic diversity in the ediacaran. 6

Answer 34

1. appear to be some stem group bilaterians but we don't have enough information to classify them 2. may be spread between cnidarians and bilaterians at point of divergence and base of crown group 3. Rangeomorphs probably not bilaterian due to different symmetry patterns 4. Early diploblasts had greater developmental diversity than those extant, yet sea anemones retain complex genomes 5. Some discoidal forms interpreted as marine fungi - evidence lacking 6. Probably have stem groups of those extant so unwise to banish to vendobionts or push into modern metazoa

Question 35

On the eve of animal radiation, by S. Xiao and M. Laflamme, 2008, Trends in ecology and evolution. Describe ediacaran ecological diversity. 7

Answer 35

1. most non-motile probably holdfasts or on sea bed 2. Fewer trace ediacaran than phanerozoic, suggesting motility nnot common 3. may have had chemo/photosynthetic symbionts in syncytial tissue 4. fractal structures may increase surface area for osmotrophy 5. More nutrients near sea bed explains 2D lifestyle 6. taller epibenthos occured later in succession 7. Feeding not active

Question 36

On the eve of animal radiation, by S. Xiao and M. Laflamme, 2008, Trends in ecology and evolution. What was the cause of extinction of ediacaran biota? 2

Answer 36

1. We don't know if gradual or sudden | 2. We cannot test causes without better documentation