Lecture 15 Flashcards
Many different kinds of –
appear suddenly at or near the Precambrian-Cambrian boundary
mineral skeletons
Animals with newly evolved mineral
skeletons include – brachiopods and
molluscs, arthropods, and echinoderms
archaeocyaths and
spicular sponges,
– attributable to animals also
appear abruptly.
Trace fossils
In fact, the GSSP for the Precambrian-Cambrian boundary lies at the
lowest occurrence of–
Treptichnus pedum
One hypothesis: There was an – of animals following their origin in late
Precambrian (Ediacaran) time
explosive radiation
One hypothesis: There was an explosive appearance of
– because animals – which had existed for a long time – became large,
muscular, and/or mineralized
fossils
The NULL hypothesis or – Also known as the
“Sigmoid Fraud”. Put Cloud, Gould, and Sepkoski
What you see is what
you get”
INTRINSIC hypotheses such as “–” Glaessner, “genome
restructuring” Valentine and Erwin, or “microRNA regulation” (Peterson
bioenergetic
improvement
EXTRINSIC hypotheses such as oxygen increase
(Nursall, 1959), the – (Towe,
1970), or the breakup of a supercontinent
(Valentine and Moores,
invention of collagen
“The famous Cambrian explosion is nothing more than the log phase of this continuous process, while the post-
Cambrian leveling represents the initial
filling of ecological roles in the world’s
oceans (terrestrial life evolved later).”
Stephen Jay Gould,
sigmoid fraud
Ordovician, some 50 million years later (GOBE
The Cambrian Explosion is really about the
production of –.
MORPHOLOGICAL DISPARITY
differences among organisms
The challenge is to find a cause for the Cambrian
Explosion that accounts for the sudden increase in
disparity. In animals, this means the origins of –
phyla.
T/F: extraordinary disparity among distantly related deuterostomes
true
diversity crosses – to become disparity
functional threshold
