EPS SCI 15 Lecture Notes - Lecture 7: Cambrian Explosion, Polychaete, Cambrian
29 Apr 2018
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Lec 7: Animal Origins
April 24
INTRODUCTION
● trilobite
: an extinct, aquatic animal (521-252 million years ago)
○has 17,000 known species
○serves as an index fossil
- different species are preserved in different rocks at
different periods of time (calibrate the geologic record)
● Darwin says that Silurian trilobites must have descended from one crustacean (that lived
before the Silurian age)
○ if his theory is true → before the lowest Silurian stratum was deposited, long
periods of time had elapsed where many other animals existed
● Since Darwin’s time, geologists & paleontologists have refined the Silurian age → now,
subdivided into multiple periods (Darwin was actually referring to the Cambrian era)
○ however, it is not clear that Darwin’s dilemma has been solved
BIG QUESTION: Did Animal Life Begin with a “Big Bang”?
● Examine the intellectual history behind the Cambrian explosion
● Explore the concept of animal body plans
ABOUT THE CAMBRIAN ERA
● Cambrian
(≈541 - 485 million years ago)
●The Burgess Shale: over 65,000 animal specimens of exceptional preservation (in
lagerstätte), discovered in 1909 by Charles Walcott in the Canadian Rockies
○soft parts can also be seen (ex. eyes, antennae)
■ Canadia
(bristle worm) → can see the bristles (soft, feathery structures)
■ Waptia
(shrimp-like animal) → eyes/antennae preserved
■ Marella
■ Olenoides
● Cambrian Explosion Hypothesis
: the rapid first appearance of most major groups of
animals (rapid diversification of multicellular animal life)
○ There were none of the following in the Cambrian:
■ no mammals
■ no birds
■ no reptiles
■ no fish
■ no insects
■ no snails
■ no starfish
○ phylums: → 2 bodyplans
■ (1) chordates
- have vertebrae
■ (2) arthropods
(ex. scorpions, centipedes, butterflies, crabs)
Document Summary
Trilobite : an extinct, aquatic animal (521-252 million years ago) Serves as an index fossil - different species are preserved in different rocks at different periods of time (calibrate the geologic record) Darwin says that silurian trilobites must have descended from one crustacean (that lived before the silurian age) If his theory is true before the lowest silurian stratum was deposited, long periods of time had elapsed where many other animals existed. Since darwin"s time, geologists & paleontologists have refined the silurian age now, subdivided into multiple periods (darwin was actually referring to the cambrian era) However, it is not clear that darwin"s dilemma has been solved. Examine the intellectual history behind the cambrian explosion. Explore the concept of animal body plans. The burgess shale : over 65,000 animal specimens of exceptional preservation (in lagerst tte), discovered in 1909 by charles walcott in the canadian rockies. Soft parts can also be seen (ex. eyes, antennae)
