Animal origins Flashcards
What was the cause of Darwin’s dilemma?
First fossiliferous rocks contain several main divisions of animals, there are no rich deposits before this.
When was the Cambrian and what defines the start?
541-485mya. Start defined by the start of trace fossils.
What species suddenly become abundant and diversion the Cambrian?
Trilobites
What are BIFs a chemical biomarker for?
Photosynthesis in the pre-Phanerozoic
What biological evidence is there for pre-phanerozoic photosynthesis?
Fossilised stromatolite (cyanobacteria) from the Archaean
What fossil evidence is there for complex life before the Cambrian?
Ediacaran fronds
What are the three types of Ediacaran fossils?
Rangeomorphs, radial, bilateral
What type of morphology and growth do rangeomorphs have?
Frond morphology and fractal growth
What were rangeomorphs previously interpreted as and why?
Cnidarians because of their similarity to sea pens
What distinguishes rangeomorphs from animals?
Fractal growth is not seen in animals
What is Haootia evidence for?
Earliest evidence of animal muscle tissue
What are Haootia usually interpreted as and why?
Cnidarians because of their similarity in morphology to stalked jellyfish
Describe radialomorphs
Can have multiple planes of symmetry and are likely to be holdfasts of rangeomorphs
What type of symmetry to ‘bilateral’ Ediacaran biota have?
Glide symmetry
What do the ‘bilateral’ biota not have?
Mouth, legs, gut
How can ‘bilateral’ biota be interpreted as molluscs?
Soft shell, radula, and mantle
Give two examples of ‘bilateral’ Ediacaran biota
Dickinsonia and Kimberella
What evidence is there to support Dickinsonia being an animal?
Composed of animal-like molecules (gas chromatography shows animal-like cholesterols)
What does Kimberella provide evidence for?
Motility (trace fossils)
Describe the mode of life of most Ediacaran biota
Epibenthic and sessile with high SA:V
Describe the substrate of the Ediacaran ecosystem
Massive microbial mat
What is the difference between the Ediacaran and Cambrian ecosystems?
Ediacaran ecosystem was flat and simple, Cambrian ecosystem was 3D (e.g. burrowing by priapulids) and complex
