Cambrian explosion Flashcards
What has been found in the Burgess Shale and what is it evidence of?
Metaspriggina is evidence for a Cambrian chordate
Define a crown group
All living members of a clade, its common ancestor, and all descendants
Define a stem group
Extinct organisms outside the crown group, on the lineage to the most recent common ancestor.
What happens in the Cambrian explosion?
Most animal phyla appear for the first time. Many diverse body plans are established in a very short time.
Give two possible biological explanations for the Cambrian explosion
Predator-prey arms race and developmental explosion of novelty (new body plans were easier to develop without constraint or competition)
Describe a possible geological reason for the Cambrian explosion
The breakup of Rodinia resulted in lots of exposed shelf, which is a good habitat. More exposed continental rock leads to more weathering and carbonate input into the sea (increasing alkalinity)
Why is the Burgess Shale so useful?
It shows soft-tissue preservation
How was the Burgess Shale preserved?
A deep sea bed was buried suddenly by an obrution of fine sediment. Bacterial decay was slowed by oxygen absence.
What chemical environment was present at the Burgess Shale?
Low sulphur and high alkalinity.
Name another country that has a Burgess Shale type of preservation
China
What type of organisms are found at the Burgess Shale?
Porifera, ctenophora, cnidarians, annelids, molluscs, priapulids, onychophora, deuterostomes, arthropods
What is Pikaia, found in the Burgess Shale, sometimes interpreted as?
A chordate because it has a notochord and muscle bands (but don’t get it tattooed, might not be a chordate)
What is the most common type of specimen found at the Burgess Shale?
Arthropod
