Flowering plants are much more ancient than indicated by their fossil record, according to a study lead by the University of Fribourg.
Flowering plants emerge spectacularly in the fossil record in the middle of the Cretaceous, the last era of the age of dinosaurs, and rapidly dominate the diversity of plants on land. However, genomic data suggest a much earlier origin, as early as the Jurassic or even the Triassic, the dawn of the age of dinosaurs around one hundred million years earlier. No fossils of flowering plants are known from the Jurassic, not even fossil pollens. This shocking discrepancy has been an enduring mystery for scientists.
Maths to the rescue
Now a team of researchers from Switzerland, Sweden, the UK and China has analysed the fossil record of flowering plants with a large data set and new mathematical tools. They showed that the fossil record is actually compatible with the very early date of apparition suggested by genetic data. Flowering plants might have remained relatively rare and discrete for very long periods until their explosive success in the Cretaceous. According to that study, fossils of flowering plants from the Jurassic exist, they are just extremely rare and remain to be found.
«A diverse group of flowering plants had been living for a very long time in the shadows of ferns and gymnosperms, which were dominating ancient ecosystems.» says Daniele Silvestro, from the University of Fribourg, lead author of the paper. «Not unlike the mammals, who spent a long time laying low in the age of dinosaurs before becoming a dominant component of modern faunas.»
Flowering plants are by far the most abundant and diverse group of plants in modern ecosystems, far outnumbering ferns and gymnosperms, and include almost all crops sustaining human life and livelihood. The fossil record shows this pattern of dominance and diversity emerging rather suddenly, 80-100 million years ago. This sudden emergence famously puzzled Charles Darwin, who called it an «abominable mystery». The mystery is compounded by recent DNA technologies: dating methods based on phylogenetic analyses of modern plants and their genomes point to a much older time of origin for flowering plants, in apparent contradiction with paleontological data.
Reconciling paleontological and molecular evidence
The new study published in the scientific journal Nature Ecology & Evolution, may have solved this puzzle. The team of scientists show that flowering plants indeed originated in the Jurassic or earlier – much before the oldest undisputed fossil evidence. They suggest that the lack of older fossil results from the rarity and low probability of fossilization of early flowering plants.
«A literal reading of the fossil record cannot be used to estimate realistically the time of origin of the group» explains Christine Bacon, from the University of Gothenburg in Sweden, co-author of the paper. «Instead, we developed new mathematical models and use computer simulations to solve the problem». The new study is based exclusively on fossils and does not include genomic data. It shows that the earlier age found in genomic data is also in fact supported by the paleontological data as well.
The research conclusions are based on a large database of more than 15’000 fossils compiled at the Xinhuangbanna Tropical Garden in China compiled, from many groups of plants, including the families of palms, orchids, sunflowers and peas.
Original publication: «Fossil data support a pre-Cretaceous origin of flowering plants», Daniele Silvestro, Christine D. Bacon, Wenna Ding, Qiuyue Zhang, Philip C. J. Donoghue, Alexandre Antonelli, Yaowu Xing, 2021, Nature Ecology & Evolution