The Chicxulub impactor wiped out the dinosaurs (except birds). A lot of other species died that day, too.
But, astonishingly enough, some animal species survived, including some reptiles (such as turtles and crocodiles), mammals, and avian dinosaurs, AKA birds. Current estimates are 75-90% of all animal species were killed on this really, really bad day for our planet.
A lot of plants died out, but some survived. Many species non-flowering plants were wiped out, and many flowering plants were killed off. Post-impact ecosystems were dominated by angiosperms.
(We have little information about the microme. Presumably, many species of microbes went extinct at that time, but these lines probably recovered quickly.)
(Ditto for insects.)
This fall researchers at Bath and UNAM report a statistical study of fossil plants from the Cretaceous forward [2]. The basic idea is a Bayesian estimate probably extinction rates for high level lineages, based on the genomes of existing plants.
The fossil record is sparse and geographically biased, and it is especially difficult to classify plant species based on fossil remains. (Classifying plants by appearance without genetic information is always problematic.) There are hundreds of thousands of plant species today, and the phylogenic tree is complex. In sort, estimating the evolutionary history of plants back into the Cretaceous is difficult.
The study considered two (of many) genetic families, and tested Bayesian models for extinction rates. These datasets are built from analysis of existing plant genomes, from which family trees are inferred [1].
The basic finding—at least for these two groups—shows no evidence of mass extinction at the K-Pg boundary.
The fossil record shows extinction of non-flowering plants after the impact. It also shows short term, local die outs of flowering plants (angiosperms). The new findings suggest that many species of angiosperms went extinct at that time, but families survived and thrived.
“The angiosperm fossil record reveals a high rate of species turnover (which entails elevated species-level extinctions) across the K-Pg, but without loss of Cretaceous higher-taxon diversity”
([2], p. 3)
The researchers hypothesize that angiosperms diversified in the Cretaceous, spreading widely and in many environments. The Chicxulub impact surely wiped out many plants over wide areas. But there were so many species of plants that families survived and radiated after the event, rapidly spreading everywhere.
The researchers point out that the definition of the concept of “mass extinction” is ambiguous and can depend on how they are measured. Generally, mass extinctions are recognized by high loss of species diversity, which happens when entire taxonomic groups disappear. But their study shows that “high extinction rates at the species level can be disassociated from the loss of entire taxonomic groups.” ([2], p.4) I.e., there can be massive losses of species, but the family can persist.
Is this a mass extinction, or not? Or something in between?
In any case, assessing a mass extinction needs multiple lines of evidence to get a more complete picture.
“One of the main problems when assessing mass extinction episodes is the definition of what these events entail, and how we measure them. Generally, mass extinctions are characterized and measured by high loss of species diversity that often follow the disappearance of entire taxonomic groups from the palaeontological record. As evidenced by angioperms, high extinction rates at the species level can be disassociated from the loss of entire taxonomic groups. The fossil record indicates that the K-Pg led to mass extinction at the species level, but with no taxonomic selectivity leading to the disappearance of major angiosperm lineages.”
([2], p.4])
- Jack Tamisiea, Wiping Out the Dinosaurs Let Countless Flowers Bloom, in New York Times. 2023: New York. https://www.nytimes.com/2023/09/12/science/flowers-dinosaurs-extinction.html
- Jamie B. Thompson and Santiago Ramírez-Barahona, No phylogenetic evidence for angiosperm mass extinction at the Cretaceous–Palaeogene (K-Pg) boundary. Biology Letters, 19 (9) September 2023. https://doi.org/10.1098/rsbl.2023.0314
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