Latania loddigesii palm fruits and leaves in Xishuangbanna Tropical Botanical Garden, China
Picture: Renske Onstein/iDiv
A prediction of the Theory of Evolution is that a major change in a species' environment will result in evolutionary adaptation to that change. One such major change in the environment of plants was the sudden extinction of the large herbivorous dinosaurs, followed by a period of some 25 million years until the large herbivorous mammals had evolved. According to the TOE, then, we would expect to see these changes recorded in the genetic and fossil record of plants.
This is exactly what a research team led by the German Centre for Integrative Biodiversity Research (iDiv) and Leipzig University found when they examined the genetic and fossil records of palm trees, which they chose as a model system for the study. They were also able to show that the changes following the extinction of large, non-flying dinosaurs were so profound that they were only partially reversed by the evolution of large mammals such as elephants.
From the iDiv press release:
With the extinction of large, non-flying dinosaurs 66 million years ago, large herbivores were missing on Earth for the subsequent 25 million years. Since plants and herbivorous animals influence each other, the question arises whether, and how this very long absence and the later return of the so-called "megaherbivores" affected the evolution of the plant world.The technical details of the study are outlined in the abstract to the team's paper, published recently in the Royal Society's journal, Proceeding of the Royal Society B:
To answer this question, a research team led by iDiv and Leipzig University analysed fossil and living palms today. Genetic analyses enabled the researchers to trace the evolutionary developments of plants during and after the absence of megaherbivores. Thus, they first confirmed the common scientific assumption that many palm species at the time of the dinosaurs bore large fruits and were covered with spines and thorns on their trunks and leaves.We were thus able to refute the previous scientific assumption that the presence of large palm fruits depended exclusively on megaherbivores. We therefore assume that the lack of influence of large herbivores led to denser vegetations in which plants with larger seeds and fruits had an evolutionary advantage.
Defence traits without predators apparently no longer offered evolutionary advantages, however, they returned in most palm species when new megaherbivores evolved, in contrast to the changes in fruits, which persisted.
Dr Renske Onstein, first author
Evolution and Adaptation
German Centre for Integrative Biodiversity Research (iDiv)
Halle–Jena–Leipzig, Leipzig, Germany
However, the research team found that the "evolutionary speed" with which new palm species with small fruits arose during the megaherbivore gap decreased, whereas the evolutionary speed of those with large fruits remained almost constant. The size of the fruits themselves, however, also increased. So, there were palms with large fruits even after the extinction of the dinosaurs. Apparently, much smaller animals could also eat large fruits and spread the seeds with their excretions.
[…]
However, the defence traits of the plants; spines and thorns on leaves and stems, showed a different picture: the number of palm species with defence traits decreased during the megaherbivore gap.
With their work, the researchers shed new light on evolution and adaptation during one of the most enigmatic and unique periods in the history of plant evolution, during and after megaherbivore extinctions. Understanding how megaherbivore extinctions affected plant evolution in the past can also help predict future ecological developments. For example, the authors have noted the loss of traits during the megaherbivore gap. This loss can affect important ecosystem functions and processes, such as seed dispersal or herbivory. The ongoing extinction of large animals due to human hunting and climate change may thus also affect trait variation in plant communities and ecosystems today and in the foreseeable future.
Copyright: © 2022 The authors. Published by the Royal SocietyOpen access
AbstractAgain, we see a prediction of the TOE confirmed by observation and analysis, and again we see how the TOE is the foundation of modern biology and the only theory capable of making these predictions and explaining the observable facts. We also see the stupidity of any designer who would design large herbivores to eat plant seeds, then protects the seeds against being eaten by the large herbivores it designed to eat them. Then, apparently, had to redo those protective designs when it designed a new lot of large herbivores to eat the seeds, having exterminated the first lot 25 million years earlier.
The Cretaceous–Palaeogene (K-Pg) extinction of the non-avian dinosaurs (66 Ma) led to a 25 million year gap of megaherbivores (>1000 kg) before the evolution of megaherbivorous mammals in the Late Eocene (40 Ma). The botanical consequences of this ‘Palaeocene megaherbivore gap’ (PMHG) remain poorly explored. We hypothesize that the absence of megaherbivores should result in changes in the diversification and trait evolution of associated plant lineages. We used phylogenetic time- and trait-dependent diversification models with palms (Arecaceae) and show that the PMHG was characterized by speciation slowdowns, decreased evolution of armature and increased evolution of megafaunal (≥4 cm) fruits. This suggests that the absence of browsing by megaherbivores during the PMHG may have led to a loss of defence traits, but the absence of megaherbivorous seed dispersers did not lead to a loss of megafaunal fruits. Instead, increases in PMHG fruit sizes may be explained by simultaneously rising temperatures, rainforest expansion, and the subsequent radiation of seed-dispersing birds and mammals. We show that the profound impact of the PMHG on plant diversification can be detected even with the overwriting of adaptations by the subsequent Late Eocene opening up of megaherbivore-associated ecological opportunities. Our study provides a quantitative, comparative framework to assess diversification and adaptation during one of the most enigmatic periods in angiosperm history.
Onstein, Renske E.; Kissling, W. Daniel; Linder, H. Peter (2022)
The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms
Proceedings of the Royal Society B: Biological Sciences, 289(1972); DOI: 10.1098/rspb.2021.2633
Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
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