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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 mass extinctions appear gradual in the fossil record, as the last appearances of different species are smeared backward in time.
1982年，菲利普·W·西格诺（Philip W. Signor）和杰尔·H·利普斯（Jere H. Lipps）提出了西格诺-利普斯效应，该效应解决了解读化石记录的一个根本挑战：其固有的不完整性。任何单个生物体变成化石的概率都极低，而古生物学家发现该化石的概率则更低。因此，一个分类单元的已知化石分布范围（从首次出现到最后一次出现）几乎总是短于其真实的时间分布范围。在分析灭绝事件时，这种效应尤为显著。对于在灾难性事件中同时灭绝的一组物种，它们最后已知的化石不会在同一岩层中被发现。相反，由于随机采样（石化和发现），它们最后一次出现的地点会分散在导致灭绝事件发生的岩层中。
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.
西格诺-利普斯效应
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