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The Signor–Lipps effect is a paleontological principle stating that, because the fossil record is incomplete, the last known fossil of a species will almost certainly predate the actual extinction of that species. This artifact can make abrupt extinções em massa appear gradual in the fossil record, as the last appearances of different species are smeared backward in time.
Proposed by Philip W. Signor and Jere H. Lipps in 1982, the Signor–Lipps effect addresses a fundamental challenge in interpreting the fossil record: its inherent incompleteness. The chance of any individual organism being fossilized is extremely low, and the chance of paleontologists finding that fossil is even lower. Consequently, the known fossil range of a taxon (its first to last appearance) is almost always shorter than its true temporal range. The effect is particularly significant when analyzing extinction events. For a group of species that went extinct simultaneously in a catastrophic event, their last known fossils will not be found in the same rock layer. Instead, due to random sampling (fossilization and discovery), their last appearances will be scattered through the rock layers leading up to the event.
This creates an illusion of a gradual decline in biodiversity, even if the extinction was geologically instantaneous. For example, before the Alvarez hypothesis gained wide acceptance, many scientists argued that the fossil record showed dinosaurs dwindling in diversity for millions of years before the K-Pg boundary, suggesting a gradual cause. The Signor–Lipps effect provides a powerful counter-argument: this apparent decline could simply be an artifact of an incomplete fossil record approaching a sudden termination point. To counteract this effect, paleontologists now use statistical confidence intervals to estimate the true extinction horizon and prioritize searching for fossils in the layers immediately preceding a suspected mass extinction boundary, a practice known as “ground-truthing” the last appearance data.
O Efeito Signor-Lipps
(Caso a data seja desconhecida ou irrelevante, por exemplo, "mecânica dos fluidos", é fornecida uma estimativa aproximada de seu surgimento notável)
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