In the aftermath of such events, environmental conditions are severely disrupted: the oceans become less oxygenated, water becomes poisonous, there is increased competition, collapse of food chains, etc. Until now, it has generally been accepted that certain marine organisms, such as gastropods or bivalves, were affected by a drastic reduction in size in response to major disruptions of this nature, both during and after the event. It took several million years for such organisms to return to sizes comparable to those that existed prior to the crisis. This is what scientists call the "Lilliput effect," in reference to the travels of Gulliver (3) who was shipwrecked on the island of the same name, inhabited by very small Lilliputians.
An international team of French, German, American and Swiss paleontologists has recently discovered large gastropod fossils dating from only 1 million years after the P-T mass extinction. The researchers have spent several years studying the re-conquest phase that followed the P-T crisis. By focusing their efforts on fossil-bearing outcrops in Utah dating from the Early Triassic, which have not yet been studied in detail, they have uncovered some outstanding specimens of gastropods, up to 7 cm, which can be termed as "giants" in comparison to those generally found, normally no bigger than 1 cm.
Complementary studies of these new gastropod fauna also indicate that they are not any smaller than older or present-day fauna. This discovery therefore refutes the existence of a Lilliput effect on gastropods during the major part of the Early Triassic or, at the very least, suggests that its importance has been overestimated. Quite surprisingly, the presence of these large gastropods also coincides with an explosive re-conquest of the ocean by organisms such as ammonites (4, 5). Taken together, these events therefore suggest that restructuring of marine ecosystems was already well underway only one million years after the P-T crisis, a very short time after a mass extinction of such magnitude.
The researchers plan to continue to study the fossils discovered in this locality in Utah while searching for other species and groups, such as bivalves, to confirm this new data. However, these findings already suggest that paleontologists are going to have to re-think the immediate and long term impact of mass extinctions on species.
Notes:
(1) The gastropods concerned by this study are mollusks that lived on the sea bed and are related, for example, to present-day land snails.
(2) The Permian-Triassic mass extinction, named after the two geological periods that encompass it, namely the Permian (299 -- 252.6 Ma) and the Triassic (252.6 -- 201.6 Ma), is the greatest mass extinction ever documented. It marks the end of the Primary (or Paleozoic) era and the beginning of the Secondary (or Mesozoic) era.
(3) Gulliver's Travels, written by Jonathan Swift in the 18th century.
(4) Ammonoids, related to present-day nautilus, cuttlefish and squid, are free-swimming cephalopod mollusks with external shells. They disappeared from the world's oceans at the same time as the dinosaurs, 65 million years ago, after having been a major part of the marine fauna for nearly 400 million years.
(5) See also Brayard et al. 2009. Science 235: 1118-1121.
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Adapted from materials provided by CNRS.
Journal Reference:
1. Brayard A., Nützel A., Stephen D.A., Bylund K.G., Jenks J. and Bucher H. Gastropod evidence against the Early Triassic Lilliput effect. Geology, 2010; 38 (2): 147 DOI: 10.1130/G30553.1
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CNRS (2010, February 11). Mass extinctions: 'Giant' fossils are revolutionizing current thinking. ScienceDaily. Retrieved February 16, 2010, from
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