Biodiversity

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Biodiversity
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How has the diversity of multicellular life
changed over time?

• Multicellular life started from only one kind and
  is now many kinds, so, duh. Yes, the number of
  different kinds of organism must have increased
  over time.
• BUT has it been a steady increase? Is diversity
  still increasing now? Or has the earth reached
  some kind of limit on the number of kinds of
  creatures that can exist?

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Look at the numbers

• How many species are there now?
• About 1.8 million species of plants and animals
  described
• Is that all there is? How could you know how
  many more there might be?
• Estimates range from 5 million to 20 million
• How many fossil species are there?
• About 300,000 have been named
• Hard to figure out from this how many species
  have lived

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Why is it hard to figure out past diversity?

• Level of tabulation
• Species problem are we accurately recognizing
  species? Some groups probably overestimated,
  others underestimated.
• Orders and above are pretty far from natural
  groups and are contentious
• Family level is reasonable compromise close to
  natural classification but easier to recognize
  than species

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Why is it hard to figure out past diversity?

• Missing groups unfossilizable taxa
• Perhaps at some times there were many soft-bodied
  organisms contributing to diversity
• The insect problem unfossilizable but most of
  the described species

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Remember this?
Two thirds of all described multicellular life
are insects
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Why is it hard to figure out past diversity?

• Discovered fossil problem sampling depends on
• Exposure of rocks of that age
• Volume of rocks of that age
• Silurian-Devonian transgression means theres a
  lot of fossils of that age, Carboniferous
  regression means theres few of that age
• Interest of paleontologists different ages have
  attracted different amounts of attention from
  paleontologists
• Ease of access, economics, coolness factor

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Why is it hard to figure out past diversity?

• Pull of the Recent tops of fossil ranges are
  usually underestimates EXCEPT for extant species.
• So living families count more (e.g. are
  represented in more time periods) than extinct
  ones.

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So what can we do with the data we have?

• Look at family or genus level data for
  skeletonized marine invertebrates
• Eliminates the problem of identifying species
• Helps standardize identification (researchers may
  be splitters or lumpers when it comes to species,
  but families are universally recognized)
• Eliminates the problem of selective preservation
  were only comparing critters with hard parts
  across time
• Eliminate the insect bulge

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We can recognize three great faunas in the
history of life Cambrian Paleozoic Modern
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The three faunas

• Cambrian Trilobites, lingulate brachiopods,
  archeocyathids, primitive echinoderms
• Paleozoic rhynchonelliform brachiopods, stony
  bryozoans, stromotoporoids, cephalopods,
  crinoids, blastoids, graptolites
• Modern bivalves, gastropods, echinoids,
  crustaceans, vertebrates

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The three faunas ecologically

• Cambrian benthic organisms living only a few cm
  above below sea floor
• Paleozoic sessile (attached) benthic organisms,
  some rising above sea floor up to a meter or so,
  slightly deeper burrows
• Modern more mobile benthic fauna, deeper
  burrowers, swimmers, abundant planktonics

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Notice that the faunas exist outside of the time
period they are named for, but are most important
during the time period of their name.