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The Early Paleozoic Fauna: The significance of the Burgess Shale

The Early Paleozoic Fauna: The significance of the Burgess Shale. EPSC233 Earth & Life History (Fall 2002). Recommended reading: STANLEY “Earth System History” Chapter 13, pp. 345-354.

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The Early Paleozoic Fauna: The significance of the Burgess Shale

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  1. The Early Paleozoic Fauna: The significance of the Burgess Shale EPSC233 Earth & Life History (Fall 2002)

  2. Recommended reading: STANLEY “Earth System History” Chapter 13, pp. 345-354. Keywords:phyla (arthropods, brachiopods, echinoderms, mollusks), reef formers (archeocyathids), deposit feeders (trilobites, mollusks), filter feeder (eocrinoids, crinoids, brachiopods, mollusks), predators (cephalopods).

  3. Wednesday October 2nd (next week) • Next Wednesday afternoon, at 1h30, the Sedimentary Geology class will be taking a field trip to see the limestone exposures at the Laval Nature Centre (St Vincent de Paul Quarry). • There will be a few extra seats in the • vans. If you are interested in joining them, contact Mairi Best at mmrbest@eps.mcgill.ca. • - This outing lasts the entire afternoon. If 6 students (or more) wish to go, we will cancel the lecture and I will accompany you.

  4. In Namibia and Siberia, the Precambrian-Cambrian boundary can be dated isotopically. Many other localities lie below or above the boundary or have big gaps in the rock record.

  5. Where igneous rocks are not available, chemo-stratigraphy is being used as a correlation tool. This section is from Death Valley.

  6. Chemostratigraphy Comparing Death Valley (AZ, U.S.) and Mackenzie Mountains (Canada)… Is this a reliable correlation tool? Are there gaps in the section?

  7. Drift of continents during the Cambrian: 600, 540 and 525 million years ago. A “proto-Atlantic” called Iapetus is created along east coast of N. America.

  8. Cambrian trilobites, lacking claws or specialized mouth parts for chewing, were probably not predators… There were larger animals around. Scattered remains of a diverse Cambrian soft-bodied fauna were found first in the Rocky Mountains of B.C., in the Burgess Shale…

  9. Most Cambrian sandstones are poor in fossils. As sea level rose worldwide, continental shelves were flooded. Vast areas on the continental margins became hospitable to shelly marine faunas. Cambrian sandstones grade upward to shallow-water limestones. These limestones rarely contain stromatolites, unlike Precambrian limestones. They contain the remains of a diverse shallow-water community of animals and algae.

  10. View of the Walcott Quarry, in the Burgess Shale. Walcott, from the Smithsonian Institute started quarrying here in 1909. He sent about 65,000 specimens to the Smithsonian. Named UNESCO World Heritage Site in 1981. 505 Ma.

  11. Mud accumulated (and became shale) atthe edge of a CaCO3 platform (algal reef).

  12. Tuzoia Tuzoia-Anomalocaris hybrid Some of the middle Cambrian fossils were so different from anything known today that the first reconstructions mistakenly included parts from different animals... If Tuzoia is a bivalved shrimp: is this its shrimp-like body?

  13. Paleontologists were groping in the dark until complete specimens were found in the Early Cambrian strata from Chengjiang,China. • - soft bodied fauna, like the Burgess Shale • - but 30 million years older • - evidence of predation and burrowing • - most phyla surviving today are represented • but complex fossils of uncertain affinities • are also present

  14. Some re-assembly was required... jaws interpreted as jellyfish claws = Anomalocaris Up to 2 meters long

  15. The Burgess Shale fauna is not unique, other exceptional fossiliferous deposits of Cambrian age have been found (Emu Bay, Australia; Chengjiang, South China, Orsten, Sweden). All confirm: - the predominance and diversity of arthropods - the existence of body plans that seem to have disappeared - some include earliest chordates

  16. The finding of the Chengjiang fauna, 30 million years older (535 Ma), confirm the diversity of the early Cambrian fauna.

  17. Burgess Shale fauna is a diverse assemblage of soft-bodied organisms. Some display body plans that have no counterparts to this day.

  18. Opabinia: five eyes, a clasping limb…

  19. Fossilized Ayshea Hallucigenia Reconstructed as various types of worms, whose descendants now living in moist forests.

  20. Left:Hyolithes… an early mollusk. Became lunch for Ottoia (right), who knew to swallow them head first to avoid choking on them…

  21. This worm-like creature, 4 cm-long, had a notochord (the precursor of the vertebrate backbone).

  22. We can come up with plausible links between these strange animals and “modern” groups but many Cambrian groups left no direct descendants.

  23. The end of the Cambrian was marked by extinctions. The trilobites survived but many families were wiped out. Orders within new phyla became far more widespread. The food web (trophic structure) became more complex. Organisms also continued to make better use of sediments as source of food and shelter.

  24. The Ordovician period saw a new wave of diversification among the survivors from the Cambrian. Elrathia Middle Cambrian western Canada Ceraurus (Neuville, Quebec) Ordovician

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