Week 3: How to Grow a Planet- Origin of Animals

Answer 1

photosynthesing microorganisms
mostly prokaryotes, some eukaryotes
mostly single cells some multicellular

Question 2

How and when did life make the transition from small, simple life to large complex life?

Question 3

What are the 3 domains?

Answer 3

Bacteria=unicellular prokaryotes with fatty ester lipids
Archaea=unicellular prokaryotes with isoprene ether lipids
Eukaryotes=have a cell nucleus and membrane bound organelles, can be multicellular

Question 4

What are the 6 kingdoms of life?

Answer 4

Plantae
Fungi
Animalia
Protista
Bacteria
Archaea

Question 5

What are the main differences between Plantae, Fungi and Animalia?

Answer 5

Plantae= Multicellular autotrophs with chloroplasts and cellulose cell walls
Fungi= Multicellular and unicellular heterotrophs with chitin cell walls
Animalia=Multicellular heterotrophs without a cell wall (Motility: they move, at least in part of the life cycle) Most are bilaterians: left side, right side & a head with mouth and through gut

Question 6

Key moments in geological time scale of Earth?

Answer 6

1.4550Ma= formation of Earth
2.4527Ma= Formation of Moon
3. 4000Ma= End of the Late Heavy Bombardment of Life
4. 3200Ma= Earliest start of photosynthesis
5. 2300Ma= Atmosphere becomes oxygen rich, first Snowball Earth
6. 750-635Ma= The Snowball Earths
7. 530Ma= Cambrian explosion
8. 380Ma= first vertebrate land animals
9. 230-66Ma= non-avian dinosaurs
10. 2Ma= first hominins

Question 7

Order of organisms groups formation in geological time scale?

Answer 7

1. Prokaryotes
2. Eukaryotes
3. Multicellular life
4. Animals
5. Land plants
6. Mammals
7. Hominins

Question 8

What are the 4 Eons?

Answer 8

Hadean 4600-4000
Archean 4000-2500
Proterozoic 2500-540
Phanerozoic 540-today

Question 9

What were Proterozoic oxygen levels like?

Answer 9

Photosynthesis lead to accumulation of atmospheric O2 at Great Oxygenation Event

Modern levels not reached until near end of Proterozoic
Evidence= banded iron formations

Question 10

What were the Proterozoic glaciations? Name? When?

Answer 10

Gaskier’s glaciation
580 million years ago, (about 9 my before the appearance of large Ediacaran fossils)

Widespread glaciation deposits toward end of Proterozoic

Question 11

When did large fossils turn up in geological record?

Answer 11

Ediacaran

Large organisms first appear in the Ediacaran fossil biota
After a long period of relative stasis, large fossils turn up in the Ediacaran deposits in Newfoundland, Australia, Russia, and UK

Question 12

What are fronds?

Answer 12

Ediacaran fossils
-Variety of different morphologies with branching structures
-Some lay flat on sea floor surface, some attach via a holdfast
-Similar fundamental morphologies, but different sizes and shapes
-They undergo the same patterns of fractal growth

Question 13

What are Rangeomorphs?

Answer 13

Clade of the frond taxa
Rangeomorphs are weird fractally growing fronds and are hard to characterise

-The frond taxa are fundamentally similar in their morphology and fractal growth, just differ slightly in their proportions and patterns
-They can’t be plants because the environment is too deep: no light= no photosynthesis
-unlikely to be proper animals given anatomy and asexual reproduction
-unique and weird

Question 14

What are bilaterians?

Answer 14

Ediacaran fossils
-these taxa have different sizes and shapes but fundamental similarities in their constructions: a ‘head’, and a left side and a right side
-the symmetry is not classically bilaterian, it is ‘glide’ symmetry.
Examples: Dickinsonia and Kimberella

Question 15

What is the evidence for possible Ediacaran animals?

Answer 15

Some Ediacaran organisms appear to be candidates for the first animals given their anatomy, composition, and behaviour:

-Dickinsonia leaves traces of ‘footprints’ indicating it was digesting the underlying microbial mat
(This is consistent with osmotrophy, as is their high surface area)

-Dickinsonia has also been demonstrated to be composed of animal like molecules
(Gas chromatography of organic remnants shows evidence of animal-like cholesteroids and not typically algae lipid biomarkers)

-Kimberella leaves mollusc style feeding grazing traces (suggests kimberella was an animal?)

-Some Ediacaran taxa show evidence of muscle fibres, therefore movement

-Traces of tiny burrows at the very end of the Ediacaran, possible movement

Question 16

What are the possible Ediacaran Triggers? Why did large fossils appear in the fossil record during this time after long period of stasis?

Answer 16

1. Deglaciation:
   -Gaskier’s Glaciation was about 9 my before the appearance of large Ediacaran fossils
   -However there had been many previous glaciations :‘snowball earth’ so doubts
2. Oxygen:
   -increasing atmospheric oxygen may have facilitated evolution of larger body sizes in the Ediacaran.
   -increased tectonic activity could have led to more oxygen
   -All Ediacaran organisms appear to have very high-surface area to volume ratios, important for gaseous exchange
3. Carbon Excursion:
   -massive Shuram Carbon Isotope Excursion occurs in the Ediacaran

Question 17

What is the classification of animals as bilaterians?

Answer 17

-they have a left/right sides
-head and tail
-top and bottom
-gut from mouth to anus
-many phyla of bilateria

Question 18

What is a phylum?

Answer 18

A phylum is a unique body plan
There are around 30 modern animal phyla
Most are bilaterians