Contrary to previous beliefs that the evolution of flowering plant species that occurred about 100 million years ago was beneficial for mammals, researchers found that this boom in flowering plants actually led to a decline in early mammal varieties.
The great angiosperm radiation of the mid-Cretaceous was a time when a variety of flowering plant species evolved. Previously, researchers believed that this boom in flowering species was extremely beneficial for mammals that existed during the time. However, in a new study, researchers from Indiana University Bloomington found new evidence that portrays this evolution in a different light.
Researchers of the study found that during this period, the variety of mammals declined drastically. This conclusion was made after David Grossnickle and P. David Polly studied fossil discoveries in the past 30 years to better understand mammalian evolution. This study is the first to track morphological, taxonomic and dietary changes of mammals during the mid-Cretaceous.
"At the middle of the Cretaceous, a time when the early angiosperms are radiating, we find a surprising decrease in the diversity of mammals," Grossnickle said. "It's not until the end of the Cretaceous, close to the time of the extinction of the dinosaurs, that we actually see a rebound in mammalian diversity and the first appearance of purely herbivorous mammals."
Previous studies have suggested that this spread of angiosperms increased the number of pollinating insects. This meant more plants, which in turn meant more food for mammals. This led researchers to conclude that this evolution would lead to more mammal species. While they were right about the increase in number of mammal species, the variety of these species declined during this period and most of the mammals that evolved were small, insect-eating creatures.
"From the fossil record, the time of the angiosperm radiation doesn't look like a very good time for mammals," Grossnickle said. "There's not as much variation as there was before and after that time, and there's not as much as you would expect at a time when angiosperms were radiating."
Researchers also found that the early therians did well in the mid-Cretaceous. Therians gave rise to most modern mammals, including humans.
"Without the ecological changes brought about by the Cretaceous radiation of flowering plants," Grossnickle said, "the world would be a very different place and may not have triggered crucial adaptations of our clever primate ancestors."
