Paleontology, Macroevolution & Extinction

Frage	Antworten
Missing Fossils	Many spp. are still unrepresented due to not being found yet, not being fossilised = lost forever. Or because they were rare when living & so are even rarer when dead.
Extinction & Fossils	Fossils do tell us that extinction was common & many mass extinctions events have occurred throughout history. E.g. asteroid @ end of Cretaceous period which affected most plant & animal groups.
Living Fossils	Can be regarded as intermediates between modern spp. & fossils. E.g. horse-shoe crab is morpho v. similar to 200 years ago. But despite a static body form, it undergoes precise selection each generation. E.g. Tulip tree - has genes which are no longer used but haven't yet been purified from the population.
Homology	Characters shared by 2 spp. that are the same because they've inherited it from the same common ancestor & have both evolved a trait from it. Must be careful that these traits aren't CONVERGENCE. Accurate homology is required in order the infer correct evolutionary patterns. Also not ANALOGOUS characters which are similar in function but have evolved separately. E.g. Bird wing & bat wing
Caveat with Cambrian	Fossils tell us little about how things were formed -> there are no intermediates. The Cambrian explosion produced lots of FULLY FORMED spp. What happened before?
Missing Intermediates - S. J. Gould	Gould said that the possible explanation for sudden appearance of fully formed spp. is that there was rapid diversification at this point in time. He called it PUNCTUATED EQUILIBRIA and suggests that speciation is faster sometimes than & other times.
Missing Intermediates - Other Explanations	Incomplete fossil record - we just haven't found them all yet. Ecological vacuum - there was just an exponential rate of increase in the no. of spp.
Macro vs. Microevolution	Macro = large evolutionary changes often inferred from the fossil record. E.g. new body plans. Micro = smaller scale changes. E.g. gene freq. alterations
Fossil Record & Macroevolution	Fossils can show the stages of macroevolution. Newest fossils resemble modern spp. closely. Certain characteristics appear in a number of stages throughout the fossil record - can use it to build a picture on evolution. But not always easy to see in which order things evolved.
Paleontology	Scientific study of prehistoric life of stuff
Macroevolution	Evolution above the spp. level. Thought of evolution on a ''grand scale' over long periods of time. The stability of lineages, how long until extinction, how they change etc. Lineages can persist - they don't always go extinct. Or they can diversify/radiate.
Extinction	Defined as the termination of an evolutionary lineage. But is usually associated with species loss. NB. In phylo trees, 'deep' divergences can indicate missing taxa which have not been discovered, not sampled, or may be extinct
Fossils	Any trace of past life (RIDLEY, 1993). Can be structures i.e. bones/teeth/shells. Trace fossils = footprints/casts/bite marks. Chemical fossils = any chemical trace of previous life.
How are fossils formed?	1. Burial in sediment. And then by a) compression before the org. decomposes to leave a shape of the org. b) mineralisation which dissolved minerals precipitate into cells and preserve the internal structures. c) cast formation which is infiltration of the decayed org. which hardens to form rock. d) mold formation where the org. decays and the space remains unfilled. e) unaltered remains (Iceman, amber)
Dating fossils	By looking @ isotopes and how much they've decayed - you know the radioactive decay time & can work out how much time has passed by the leftovers of the nucleus. Gets less accurate with time.
Incomplete fossil record	Fossils are ONLY formed in SEDIMENTARY rock, but is dated from igneous rock. It is rare so many spp. are unrepresented. This is due to not all orgs. being sediment-dwelling, some are too rare, some are unsuitable for fossilisation.
Cambrian Period	565-525 myrs bp. It has a huge no. of different fossils - Cambrian Explosion. It is the 1st time we see life-forms with segmented body plans, shells, exoskeletons & notochords. 1st indication of behaviour - Trilobites walking on surface instead of burrowing = behavioural change.
Plants vs. Animals	Some evidence suggests that animals beat plants out of the primordial seas. There was a 'well trodden' path which has marks of 'wind-blows' sand, so must be on land. Dates indicate 530 mya. Earlier than predicted plants...
Fossils in Use for Behaviour	Fossils of indicating where muscles were can be used to indicate a behaviour. E.g. pleiosaur fossil found was used to create a robot (Madeleine) which demonstrated how the muscles were used during swimming. Showed they probably used all 4 flippers & had good acceleration. Zoooom.
Micro CT	Totally non invasive method of looking @ internal structures in great detail - no specimen damage. E.g. can scan through a piece of amber to show the arachnid inside has a mite on its body. 2nd scan can then look at the body plan of the mite to show its anatomy. GREAT DETAIL & NON INVASIVE. Coooool. E.g Micro CT used to look @ balance organs (inner ear) or Pterosaur fossils & assess brain process/behaviour associated with flying - WILMER ET AL, 2003

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Paleontology, Macroevolution & Extinction

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