Geopedia by Marcia Bjornerud

Author:Marcia Bjornerud
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2021-11-02T00:00:00+00:00

Lazarus Taxa

Zombie fossils

Charles Darwin dedicated an entire chapter in On the Origin of Species to the “Imperfection of the geologic record.” His intent was to preempt arguments from skeptics that the fossil record lacked transitional fossils and thus did not support his theory of evolution by natural selection. More than 150 years later, most of these so-called missing links have been found, and geologists have discovered that the rock record is far less “imperfect” or incomplete than Darwin had suggested. Still, there remain some puzzling silences, including those of the “Lazarus taxa”—species or higher-level groups that disappear from the fossil record only to reappear, seeming to rise from the dead, millions or tens of millions of years later.

In some cases, the failure of certain lineages to show up for roll call in the fossil record can be chalked up simply to the low odds of preservation; fossilization is, after all, the exception rather than the rule, especially for soft-bodied organisms with no mineralized shells or skeletons. But when organisms that are normally well represented in the fossil record go missing for long periods of time, their absence may signal something important.

The most dramatic examples of Lazarus taxa are “reef gaps” that follow many of the great mass-extinction events in geologic history: the apparent disappearance of once-abundant reef-building organisms (not only corals but also other calcifying organisms) for millions of years after these episodes of ecosystem collapse. Of these, the longest is the reef gap in the aftermath of the worst mass extinction of them all: the end-Permian event, a near-death experience for the biosphere. Unlike the more famous end-Cretaceous dinosaur extinction, for which a rogue meteorite can be blamed, the end-Permian cataclysm had an internal source within the earth system. A “perfect storm” of environmental factors—rapid warming, ozone destruction, ocean anoxia, and acidification—seems to have conspired together to devastate both marine and land-based food chains.

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