Taxonomy & Evolution

“Mythical” Jurassic angiosperms perhaps not so mythical

Modelling that accounts for an incomplete fossil record doesn’t reject a pre-Cretaceous origin.

As I mentioned in my last post when discussing new insights on Darwin’s “abominable mystery”, the angiosperms have stymied botanists for many years with their apparently meteoric rise from nothing to abundance to dominance during the Cretaceous and Cenozoic periods. The precise timing of their origin has been contentious, because while there are no unambiguous angiosperm fossils known from prior to the Cretaceous, inferential methods using molecular clocks place the date much earlier, as far back as the Jurassic or even the Permian. This discrepancy has been referred to as the “Jurassic Gap,” and may be due to either biases in molecular dating methods or the absence of sufficient fossil evidence.

Image: Canva.

In a new article published in Nature Ecology & Evolution, lead author Daniele Silvestro and colleagues attempted to develop a method for dating the origin of the angiosperms which takes into account the gaps in the fossil record, while not relying on molecular clocks. Using a dataset comprising circa 15,000 fossil records in 198 plant families, coupled with the living diversity of those families, the authors established a Bayesian statistical method to estimate family ages.

Analyses showed that if fossil data is interpreted while making allowances for sparse preservation, one can’t reject a pre-Cretaceous origin scenario. “[W]e have shown that literal interpretations of the fossil record can be rejected and that the palaeobotanical quest for the “mythical Jurassic angiosperm” […] is supported by the currently known and accepted fossil record; it is not just a product of molecular phylogenetics,” write the authors.

The 198 families sampled for the analysis had origin times that span both the Triassic and Jurassic, and seem to corroborate recent molecular clock estimates. “The estimated family-level diversification rates through time suggest a pre-Cretaceous phase of slow diversification of flowering plants, which is consistent with the hypotheses that early angiosperms were rare and slowly evolving. This phase was followed by a rapid radiation of lineages between 125 Ma and 72 Ma, as shown by a strong increase in diversification rates, resulting in the increasing levels of taxonomic diversity observed during the Cretaceous,” write the authors, noting that this finding is supportive of Darwin’s postulation of a rapid Cretaceous diversification.

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