Two questions and perspectives that can take:

• What does the fossil record tell us about plate tectonics?
• How might have plate tectonics affected the evoluton of life?
• The first question was more important during early arguments on continental drift and the second has become more important as plate tectonics accepted.

Biogeography a critical discipline here. Two important concepts within:

• Speciation of peripheral communities that get isolated.
• Niches - think of job availability, what are the opportunities for making a living.

Hallam's faunal assemblage behavior in plate tectonics context:

• Convergence: increase in faunal assemblage similarity with time.
• Divergence: decrease in faunal assemblage similarity with time.
  • Good example in looking at shallow water marine invertebrates across the North Atlantic (see handout).
• Complementarity: convergence of marine at time of divergence of terrestrial or vice versa (one organisms barrier is anothers pathway).
• Disjunct Endism: fossil species limited to distinct environments of limited distribution, that are found on now widely separated continents. What would be a good index organism for disjunct endism?

Dispersal mechanisms:

• Darwin, Charles: considered dispersal mechanisms at length because he had to explain how South American critters got to the Galapagos to then evolve. Chapter 11 of On the Origin of Speices, was on Geographical Distribtion, and still makes good reading today. Darwin did an experiment where he took 87 kinds of seeds immersed in seawater, 64 germinated after immersion of 28 days, and a few survived after immersion of 137 days. "In the course of two months, I picked up in my garden 12 kinds of seeds out of the excrement of small birds ... and some of them, which I tried, germinated."
• George Gaylord Simpson
  • Corridors: free migration in both direction (e.g. Panamanian isthmus).
  • Filter bridges: a corridor with some feature that filters (e.g. mountains).
  • Sweepstakes routes: life on floating logs. Galapagos
• Ice bridges at time of polar ice caps.

Barriers to migration:

• physical vs. climate.
• Physical: mountains, land for marine, sea for terrestrial.
• For shallow shelf organisms the sea is critical.
• Role of sea level changes in producing barriers and pathways:
  • example of ammonite diversity as function of shallow seas (see handout).
  • examples of changes in circulation and pathways (see handout).

More diversity in warmer climates than colder.

Earthworms: if look at geographic distribution of 7 genera in the family Megascolecina see that they are not restricted to continents, but occur on several (Du Toit, 1937). Most striking is the genera Chilota that is found in both South Africa and the south tip of South America. Dichogaster also is found in S. America, Africa, and Australia. In a Gondwanaland reconstruction they seem to make better sense. However, this would suggest that earthworms are a much more stable form evolutionarily if this pattern was inherited from over 100 million years ago. I don't know for sure, but I don't think there is an extensive earthworm fossil record. Dispersal mechanisms may exist.

A variety of ant eaters:

• South America, Ant Bear (Edentata).
• North Africa and Asia, Pangolin (Philodata).
• Southern half of Africa, Aardvark (Tubulidentata).
• Australia, Spiny Anteater (Monotremata).
• 4 orders have filled the same niche, and have long snouts and tongues. Convergent (homoplesy) evolution in divergent faunas.

Wallace's line:

• Wallace: codiscoverer of natural selection mechanism for evolution with Darwin, spent many years in the Malay archipelago (wrote a very interesting account of it), was very much a biogeographer.
• sharp faunal gap between the islands of Bali and Lombok. On one side are SE Asian fauna, on the other Australasia. Line between the two became known as Wallace's line.
• developed a set of biogeographic principles (some of which listed below, taken from Brown & Lomoline, 1998):
  • distance does not alone determine biogeographic affinitiy.
  • climate is important.
  • the fossil record provides insight into past migrations.
  • living biota are very much influenced by recent geologic and climatic events (thinking of Ice Age).
  • speciation occurs through geographic isolation.
  • the distribution of organisms not adapted for long-distance dispersal gives evidence to past connections (another type of index fossil).
  • extinctions are caused by development of connections.

De Geer Route of mammal dispersal (based on McKenna, 1975).

• Many are familiar with the Bering strait Asian-American link. However, a Paleogene seaway linking the Arctic Ocean and Tethys (with W margin along the Urals) should have isolated Europe from east Asia (see hand out figure 1). This is known as the Turgai straits marine barrier. Biota then suggest a Europe American link across the north part of the Atlantic.
• One possible link was Iceland - Faero hot spot, but that is too young.
• There is evidence that a Euramerican biota link was severed about 49 Ma.
• A better possibility is across the continental transform area between Greenland and Svalbard on the Barents Shelf.
• Is there a polar position filter? Early Tertiary flora and fauna of Svalbard suggest a cool-temperature climate with abundant conifers, with an absence of palms.
• Present understanding would suggest the link should have been finally severed about 37 Ma, when transtension happened in this area. One can suspect that the Tertiary fold-thrust belt on Svalbard was at least a partial physiographic barrier before that.

Gondwana associated examples:

• Mesosaurus: occurs near the Carboniferous-permian boundary, this was a 2 foot long aquatic reptile that is found in fresh and brackish water deposits. Fossils are found both in Brazil and South Africa.
• Glossopteris flora: Glossopteris itself was a seed fern. Seeds of the flora are millimeters in diameter (not going to be windborn).
• Lystrosaurus: a fat, short, squat, mammal-like, herbiverous reptile (definitely not traveling large distances easily) found in Africa, southeast Asia and Antarctica, and from the lower Triassic.
• 
• Source of image - USGS publication - Dynamic Earth.

Panamanian isthmus related examples:

• Classic example is North and South America (see Hallam's figures in handouts). 29 families of mammals in the S, different from 27 in the N. After bridge 22 in common. Bridge developed 2.5 million years ago. Note time scale here. In longer time frame would appear almost instantaneous.
• Debate as to how much is tectonics vs. change in sea level.
• Divergence seen in marine assemblage on either side of Panamanian isthmus (Jones and Hasson, 1985). It would be interesting to see if have divergence or similarity of deeper water species. This would help sort out the tectonics vs. sea level debate.
• An example of complimentarity.

Two faunal provinces of Cambrian trilobites on either side of the Caledonides, but by Silurian they converge ­ Caledonide ocean narrow enough. Trilobites informative in general - see Whittington and Hughes (1973) handouts.

Ural moutains in Russia:

• should provide clear test case.
• Devonian Heterostraci (jawless freshwater fish), distinctly different on Asian and European sides.
• Start of Mesozoic amphibians and reptiles across Urals the same.

A paper waiting to be done - what is the role of suspect and exotic terrance tectonics in biogeographic behavior.

Role of mantle convection and hotspots:

• could argue that this may be as crucial as plate motions.
• major punctuations in history of life:
  • Cambrian faunal explosion.
  • Permian-Triassic extinction boundary - same time as Siberian LIP.
  • Cretaceous - time of accelerated sea floor spreading, LIP production and much else.
  • Cretaceous-Tertiary extinction boundary.

   

• Brown, J. H., Lomolino, M. V., 1998, Biogeography, Sinauer Associates, Sunderland, Massachusetts, 693 p.
• Du Toit, A. L., 1937, Our Wandering Continents, Oliver & Boyd Ltd., Edinburgh,
• Hallam, A., 1972, Continental Drift and the Fossil Record: in Wilson, J. T., 1976, Continents Adrift and Continents Aground; Scientific American, W. H. Freeman & Company, San Francisco, 186-195.
• Hughes, N. F. (ed.), 1972, Organisms and continents through time: a symposium. Spec. Pap. Palaeont., London, 12, 334 p.
• McKenna, M. C., 1973, Sweepstakes, filters, corridors, Noah's Arks, and beached Viking funeral ships in paleogeography. in Tarling and Runconr, Implications of Continental Drift to the Earth Sciences, v. 1, 295-308. New York , Academic Press.
• McKenna, M. C., 1975, Fossil Mammals and Early Eocene North Atlantic Land Continuity; Annals of the Missouri Botanical Garden, v. 62, p. 335-353.
• Stanley, S. M., 1986, Earth and Life Through Time; Freeman, N. Y. 690 p.
• Stehli, F. G. & Webb, S. D., 1985, The Great American Interchange, Plenum Press, New York, 532 p.
• Valentine, J. W. & Moores, E., Plate Tectonics and the History of Life in the Oceans. in Wilson, J. T., 1976, Continents Adrift and Continents Aground; Scientific American, W. H. Freeman & Company, San Francisco, p. 196-206.