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Edited by Scott Lidgard, Field Museum of Natural History, Chicago, IL, and accepted by Editorial Board Member David Jablonski February 28, 2021 (received for review September 27, 2020)
Significance
“Dead clade walking” refers to fossil groups that suffer major drops in their biodiversity at a mass extinction but do not completely disappear from the fossil record. Why these groups were able to survive but not rediversify remains a relative mystery. Controls on the timing of their eventual extinction are additionally unclear. By gauging the frequency and cause of dead clades walking, we may be able to better understand how mass extinction events have shaped the evolution of animal lineages over Earth history.
Abstract
D. Jablonski [Proc. Natl. Acad. Sci. U.S.A. 99, 8139–8144 (2002)] coined the term “dead clades walking” (DCWs) to describe marine fossil orders that experience significant drops in genus richness during mass extinction events and never rediversify to previous levels. This phenomenon is generally interpreted as further evidence that the macroevolutionary consequences of mass extinctions can continue well past the formal boundary. It is unclear, however, exactly how long DCWs are expected to persist after extinction events and to what degree they impact broader trends in Phanerozoic biodiversity. Here we analyze the fossil occurrences of 134 skeletonized marine invertebrate orders in the Paleobiology Database (paleobiodb.org) using a Bayesian method to identify significant change points in genus richness. Our analysis identifies 70 orders that experience major diversity losses without recovery. Most of these taxa, however, do not fit the popular conception of DCWs as clades that narrowly survive a mass extinction event and linger for only a few stages before succumbing to extinction. The median postdrop duration of these DCW orders is long (>30 Myr), suggesting that previous studies may have underestimated the long-term taxonomic impact of mass extinction events. More importantly, many drops in diversity without recovery are not associated with mass extinction events and occur during background extinction stages. The prevalence of DCW orders throughout both mass and background extinction intervals and across phyla (>50% of all marine invertebrate orders) suggests that the DCW pattern is a major component of macroevolutionary turnover.
Footnotes
- ↵1To whom correspondence may be addressed. Email: bdavisbarnes{at}psu.edu.
Author contributions: B.D.B. and A.Z. designed research; B.D.B. performed research; B.D.B., J.A.S., and A.Z. analyzed data; and B.D.B., J.A.S., and A.Z. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission. S.L. is a guest editor invited by the Editorial Board.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2019208118/-/DCSupplemental.
Data Availability
All study data are included in the article and SI Appendix.
Published under the PNAS license.
References
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Dead clades walking are a pervasive macroevolutionary pattern
Article Classifications
- Biological Sciences
- Evolution
- Physical Sciences
- Earth, Atmospheric, and Planetary Sciences
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