cambrian explosion - university of...

Paleobiology!March 14, 2016

Cambrian Explosion

Epicontinental Oceans

Epicontinental Oceans

Epicontinental Oceans

Review: long-term trends

n  Carbonate to Siliciclastic!

n  Paleocontinent migration!n  Northward migration!n  Fission and Fusion!

n  Increasing bed thickness!

n  Aragonitic vs. Calcitic Seas/Ice House vs. Greenhouse!

n  Emergence of Pelagic Calcifying Organisms!n  Planktonic Foraminifera!n  Pterapods!n  Coccoliths!

n  Paleozoic vs. Modern faunas!

Review: long-term trends

Ediacaran biota

n  Phylogenetic relationships of these organisms is unclear.!

n  The ecological behavior of these organisms is unclear.!

Ediacaran biota

Fronds

n  Classified by their similarity to the genus Rangea!

n  Sessile – Recumbent or Stalked!

n  Marine!

n  No known mouth or gut - fed by osmosis, or filter feeding, or photosynthesis…!

Rangeomorphs

Discoids n  Multiple types!

n  Multiple concentric rings!n  Radial!n  Spiralled!n  Others!

n  Either a jellyfish, a fungus, or neither of those things…!

n  Some may just be holdfasts of rangeomoprhs!

Are these just shapes?

Are these just shapes?

Cambrian explosion

Cambrian explosion Artiopoda

Medusae

Xiphosura

Kutorginata

Conodonta

Trilobita

percentage of total generic diveristy

0.0 0.1 0.2 0.3 0.4 0.5

Cambrian explosion

n  A type of Arthropod!

n  Considered close relatives to modern day horse-shore crabs!

n  Mobile benthic organisms!

n  Varied trophic behaviors!

Cambrian explosion

Cambrian explosion

Cambrian explosion

Cambrian explosion

Why did it happen

n  A change to the abiotic environment!

n  A change to the genetic capacity of the taxa involved!

n  A change to the ecology of organisms!

n  “Part of the difficulty in developing an explanation for the Cambrian “explosion” also stems from the fact that it is an un unfolding in history; each successive step not only flows from the conditions established in the previous steps, but also is shaped by interactions at the current stage of unfolding.”!

Why did it happen

n  A change to the abiotic environment!

n  A change to the genetic capacity of the taxa involved!

n  A change to the ecology of organisms!

n  “Part of the difficulty in developing an explanation for the Cambrian “explosion” also stems from the fact that it is an un unfolding in history; each successive step not only flows from the conditions established in the previous steps, but also is shaped by interactions at the current stage of unfolding.”!

Environmental changes

n  Oxygen Levels!

n  Snowball Earths!

n  Large negative carbon isotopic anomaly!

n  True polar wander!

Developmental changes

Ecological changes

n  Predator/Prey and the Evolutionary Arms race!

n  The emergence of new guilds and life habits!

All of the above

One last possibility

n  Where did all of the water come from?!

n  Habitable area does not seem to be as strong of a constraint on biodiveristy as historically thought.!

n  Increased nutrient flux is more closely associated with increases in biomass than biodiversity.!

n  How does this relate to disparity vs. diversity?!