The Cambrian Explosion Flashcards
What occurred in the lower part of the Cambrian?
It was a period of time in which there was a very large increase in the number and diversity of metazoan fossils. Almost all of the modern phyla (with shells) appeared within a 15 million year period.
What are two possible explanations for the Cambrian Explosion?
It was either:
1) an explosive evolution of animal life (real evolutionary radiation) or
2) merely the appearance of fossilizable animals (previously “hidden” evolution).
Why is Ichnology important for the Cambrian Explosion?
Paleontologic work largely focuses on body fossils, but Ichnofossils (tracks, trails, burrows, and borings) represent the “other” record. Ichnofossils may provide evidence of soft-bodied organisms that have very low fossilization potential.
What are characteristics of Ediacaran Ichnofaunas?
Low diversity (not many different kinds) with limited behavioural complexity. Dominance of very simple feeding traces and nonspecialized grazing traces associated to microbial mats; evidence is restricted to the upper few millimetres of the sea bottom.
What is the Emerging View of the Ichnologic Record?
1) Initial Phase (in which a dramatic diversification of body plans took place - deep-marine relict Ediacaran ecosystem)
2) Advance Phase (in which further divergence took place and an incipient modern benthic ecology was established)
Where was Laurentia located in the Late Cambrian?
Along the equator.
What animals first appeared in the Cambrian Explosion?
Large animals with skeletons (Trilobites, arthropods with calcified segmented skeletons).
What is characteristic of the early Cambrian fauna?
The first appearance of organisms with shells. The first to appear are small (few mm) sized plates, spines, and cap shaped fossils known as small shelly fossils. They are most commonly found in the earliest part of the Cambrian from around the world. They are the first type of armour that organisms had; many were parts of a more complex armour system. Most had disappeared by the end of the lower Cambrian.
What are Archaeocyathids?
(Lower-Middle Cambrian) A predominantly Early Cambrian phylum with no living representatives. It was the only phylum believe to have gone extinct - they fenerally have skeletons that formed a porous calcareous cup or cone that resembles later Paleozoic corals. They were the reef builders of the Early-Middle Cambrian.
What is the make-up of Archaeocyathids?
The cone-shaped skeletons are commonly constructed of two perforate walls separated by radially arranged vertical blades called septa. They have a grade of organization similar to sponges. They are very useful in biostratigraphy of the Early Cambrian.
What is the Burgess Shale?
Mid-Cambrian rocks from the Rocky Mountains of BC. Discovered by Charles Walcott in 1909, it contains one of the richest faunas of the Cambrian soft body fossils in the world. The remains of soft parts gives us an important window into the early history of metazoans. The Burgess Shale is not the only window, the Chengjiang fossils of the early Cambrian age in China is just as important.
Why do soft-bodied organisms preserved in the Burgess Shale?
The fossils are preserved as thin carbon and aluminum layers in shales, deposited at the base of a Cambrian Cliff (known as the Cathedral Escarpment). This allowed rapid burial and prevent decay.
What are the Fossils of the Burgess Shale?
Most of the fauna lacked a hard shell. This greatly changes the abundances of the taxa compared to the typical Cambrian sites - and similar patterns are seen in Chengjiang.
What is the importance of the Burgess Shale?
One of the important features of the Burgess Shale is it provides us a chance to study a variety of organisms we never would have known about. Some teach us about the evolution of groups, some introduce groups we didn’t even know existed.
What type of organisms were found in the Burgess Shale?
Arthropods (worms), Onychophorans, Chordates (tiny jawless fish), and other “weird stuff”
