1. How many of today\'s continents were included in the Paleozoic continent call

Question

1. How many of today's continents were included in the Paleozoic continent called Gondwana/Gondwanaland? How many Paleozoic continents are in Asia?

2. What animal groups are in Sepkoski's "Cambrian fauna"?

3. What is a Lagerstatte deposit and why are these important?

4. How does the assemblage of organisms reconstructed from the Burgess Shale fossils compare to what we would usually see in the fossil record based only on easily fossilized "hard parts"?

5. How old is the first known fish and where was it found?

Explanation / Answer

Ans: 1) Several cratons underwent accretionary stages to form the Gondwana or Gondwanaland supercontinent about 550 million years ago. This supercontinent included most of the landmasses which make up today's continents of Antarctica, South America, Africa, Madagascar, India, Arabia, Australia-New Guinea and New Zealand.

Six major Paleozoic continents are recognized after Rodinia breakup (which lasted from 825 Ma to 550 Ma): Gondwana, Laurentia, Baltica, Siberia, Kazakhstania, and China. Of these, today's Asia includes:

Ans: 2.) Jack Sepkoski introduced three major evolutionary faunas in 1981, starting from the Cambrian to the present day. The Cambrian Fauna was the first and oldest. It described as a "Trilobite-rich assemblage", encompasses the bulk of the fossils which first appeared in the Cambrian explosion, and largely became extinct in the Ordovician-Silurian extinction event. This fauna comprises trilobites, small shelly fossils (grouped by Sepkoski into "Polychaeta", but including cribricyathids, coleolids, and volborthellids), Monoplacophora, inarticulate brachiopods and hyoliths. ( Sepkoski, J. J.; 1981)

Ans:3.) The extraordinary fossil deposits, where organisms are so well preserved that even their soft parts remain as carbon films, are referred to as Lagerstätten, a German word meaning "deposit places". These are geological fossil deposits that are rich with varied, well-preserved fossils, representing a wide variety of life from a particular era. They indicate a rapid burial scenario, usually in an anaerobic environment with minimal bacteria, thus delaying decomposition. Conservation Lagerstätten are crucial in providing answers to important moments in the history and evolution of life. For example, the Burgess Shale of British Columbia is associated with the Cambrian explosion, and the Solnhofen limestone with the earliest known bird, Archaeopteryx.

Ans: 4.) As far as fossil remains go, almost always, only scraps of bone or shell or a few carbonized leaves are all that remain of past organisms. Too often the soft parts decompose, and even the hard parts degrade. The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years (Middle Cambrian) old, it is one of the earliest fossil beds containing soft-part imprints. The biota of the Burgess Shale appears to be typical of Middle Cambrian deposits. Although the hard-part bearing organisms make up as little as 14% of the community, these same organisms are found in similar proportions in other Cambrian localities. This means that there is no reason to assume that the organisms without hard parts are exceptional in any way; indeed, many appear in other lagerstätten of different age and locations.

Ans: 5.) The oldest known fish is the 518 million-year-old fish Metaspriggina walcotti, which was about 6cm long, bore a pair of large protruding eyes and small paired nasal capsules. It breathed through seven pairs of external gills. It had a stout rod supporting its spine (notochord) enabling strong W-shaped muscle bands to develop along its entire body. Metaspriggina was first discovered and named in 1993 as it was thought then to be related to Spriggina from the Ediacaran fauna of Australia, dated at 560 million years old. The fossils came from the famous Burgess Shale sites in British Columbia, Canada,

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