66 million years ago, the impact of an asteroid on our planet wiped out non-avian dinosaurs and three-quarters of life on Earth. And, according to a new study, the only mammals that survived were the early ancestors of primates and marsupials, which at the time lived in trees.
One of the consequences of the impact was global deforestation due to numerous forest fires but, according to the authors, these species were versatile enough to adapt to the loss of trees and thus survive the extinction event, known as the Cretaceous-Paleogene boundary (K-Pg).
The first mammals appeared approximately 300 million years ago and would have begun to diversify along with the expansion of flowering plants about 20 million years before the K-Pg event. At the time of the asteroid impact, many of these animals died. ” At the same time, the mammals that survived diversified into all the new ecological niches that opened up when dinosaurs and other species went extinct, ” explains Jonathan Hughes of Cornell University.
In the study, the researchers used published phylogenies – tree-like branching diagrams showing the evolutionary relationship between groups of organisms – for mammals. They then classified each living mammal in those phylogenies into three categories: arboreal, semi-arboreal, and non-arboreal, based on their preferred habitats. They also designed computer models that reconstructed the evolutionary history of mammals.
This is how mammals changed over time
Mammalian fossils around the K-Pg are scarce and offer little data on an animal’s habitat preference. The researchers compared known information from living mammals with available fossils to help provide additional context for their results.
Overall, the models showed that the surviving species were predominantly non-arboreal through the K-Pg event, with two possible exceptions: the ancestors of primates and marsupials. The ancestors of primates and their closest relatives were found to be arboreal just before the K-Pg event in all models. Marsupial ancestors were found to be arboreal in half of the model reconstructions.
“We could see that before the K-Pg event, around that time period, there was a large increase in transitions from arboreal and semi-arboreal to non-arboreal, so it seems that many species were already leaving the heights “, concludes the investigator.
Referencia: Hughes et al. 2021. Ecological selectivity and the evolution of mammalian substrate preference across the K–Pg boundary. Ecology and Evolution. https://doi.org/10.1002/ece3.8114
