Using the fossil record to accurately estimate the timing and pace of past mass extinctions is no easy task, and a new study highlights how fossil evidence can produce a misleading picture if not interpreted with care.
Florida Museum of Natural History researchers used a series of 130-foot cores drilled from the Po Plain in northeastern Italy to test a thought experiment: Imagine catastrophe strikes the Adriatic Sea, swiftly wiping out modern marine life. Could this hypothetical mass extinction be reconstructed correctly from mollusks — hard-shelled animals such as oysters and mussels — preserved in these cores?
When they examined the cores, the results were “somewhat unnerving,” said Michal Kowalewski, Thompson Chair of Invertebrate Paleontology and the study’s principal investigator.
Paleontologists use the age of a species’ last-known fossil to estimate the timing of extinction. A sudden extinction in the Adriatic Sea today should leave the youngest remains of many mollusk species in the sediments currently forming on the shore and seabed, the “ground zero” of the hypothetical extinction event. But the team found only six of 119 mollusk species — all of which are still alive in the area — at the top of the cores. Instead, the last fossil examples of many of these species often appeared in clusters dotted throughout the cores, suggesting smaller bursts of extinctions over a longer timeline, not a single massive die-off.
Taken at face value, the cores presented a dramatically distorted record of both the timing and tempo of extinction, potentially calling into question some of the methods paleontologists commonly use to interpret past mass extinctions.
“We’re not saying you cannot study mass extinctions. You can,” Kowalewski said. “What we’re saying is that the nature of the geological record is complicated, so it is not trivial to decipher it correctly.”
Here’s one example of the difficulties:
The problem is a phenomenon known as the Signor-Lipps effect: Because the fossil record is incompletely sampled, the last-known fossil of a given species is almost certainly not the last member of that species, which muddles our ability to date extinctions. Paper. oa12 – Rafał Nawrot, Daniele Scarponi, Michele Azzarone, Troy A. Dexter, Kristopher M. Kusnerik, Jacalyn M. Wittmer, Alessandro Amorosi, Michał Kowalewski. Stratigraphic signatures of mass extinctions: ecological and sedimentary determinants. Proceedings of the Royal Society B: Biological Sciences, 2018; 285 (1886): 20181191 DOI: 10.1098/rspb.2018.1191 More.
Indeed. It’s hard to get a clear picture of evolution without a clear picture of extinction and stasis (nothing happens for tens of millions of years): What worked, what didn’t work, and what didn’t seem to need any changes? It’s great to know someone even care about extinctions.
So many lecterns may have been splintered in vain.
See also: Just in! Evolution favors the survival of the laziest
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