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Animal Diversity > 2. The First Animals > Flashcards

2. The First Animals Flashcards

1
Q

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

A
  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
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2
Q

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

A
  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
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3
Q

What is the geological timescale? 5

A
  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)
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4
Q

How did life develop through time? 4

A
  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
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5
Q

What is neontology? 4

A
  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
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6
Q

What are the limitations of paleantology? 3

A
  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
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7
Q

Describe the archaen period. 3

A
  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
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8
Q

Describe archean life. 5

A
  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
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9
Q

What was snowball earth? 7

A
  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
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10
Q

Describe the proterozoic. 3

A
  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
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11
Q

What happened at Charnwood forest? 3

A
  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
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12
Q

What were the 3 main types of ediacaran biota? 3

A
  1. Branched and look like leaves
  2. Radial type
  3. Possibly some bilaterally symmetrical ones
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13
Q

Describe branching ediacaran biota. 4

A
  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
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14
Q

Describe radial ediacaran biota. 3

A
  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.
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15
Q

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

A
  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
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16
Q

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

A
  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?
17
Q

How were ediacaran fossils preserved? 3

A
  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
18
Q

Describe dickinsonia trace fossils. 2

A
  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

19
Q

Describe kimberella trace fossils. 3

A
  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
20
Q

Describe the theory behind the rock band trace fossils. 3

A
  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
21
Q

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

A
  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
22
Q

How did ediacaran animals reproduce? 3

A
  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
23
Q

Describe ediacaran ecology. 3

A
  1. Fossils preserved in flat planes - this historic sea bed
  2. mostly epibenthic (flat) or semi-endobenthic (half buried)
  3. Almost all were sessile
24
Q

Describe the ediacaran diet. 3

A
  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
25
Q

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

A
  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
26
Q

Define bioturbation. 1

A
  1. Change in soil caused by animals/plants
27
Q

What are namacalathus and cloudina? 6

A
  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
28
Q

Descrbe ediacaran cell clusters. 4

A
  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
29
Q

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

A
  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.
30
Q

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

A
  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
31
Q

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

A
  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
32
Q

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

A
  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
33
Q

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

A
  1. Low taxonomic diversity but high morphological diversity
  2. Difficult to determine phylogenetic relationships
  3. Unique body plans not repeated since
34
Q

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

A
  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
35
Q

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

A
  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
36
Q

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

A
  1. We don’t know if gradual or sudden

2. We cannot test causes without better documentation

Animal Diversity (13 decks)

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