Recent research conducted by the University of Bristol hypothesizes that mammals started to adapt to a more ground-oriented lifestyle several million years before the 66 million-year-old Chixculub asteroid impact that led to the extinction of dinosaurs.
The study says that evidence for the potential development of terrestrial habits before the mass extinction is available.
The researchers studied fossilized limb bone fragments from placental and marsupial mammals found in western North America. This area is one of the very few locations that is known to have terrestrial fossil records from this period and scientists were able to find anatomical elements that suggest these mammals were adapting to living on land.
“It was already known that plant life changed toward the end of the Cretaceous, with flowering plants, known as angiosperms, creating more diverse habitats on the ground. We also knew that tree dwelling mammals struggled after the asteroid impact. What had not been documented, was whether mammals were becoming more terrestrial, in line with the habitat changes,” said lead author Christine Janis from the University of Bristol’s School of Earth Sciences.
Fossil clues reveal evolutionary trends
The scientists studied the extremities of limb bones, which contain traces of movement patterns that can be quantitatively analyzed against present-day mammals.
Unlike most scholars who relied on completely intact skeletons to deduce the movement patterns of ancient mammals, this study is one of the first to rely on minute fragmentary bones in tracking alterations within a community of mammals over a stretch of time.
The researchers collected statistical information from museum databases from New York, Colorado, and Calgary for the purposes of analyzing tiny fossilized bones and shifting locomotor behavior through time.
Professor Janis said, “The vegetational habitat was more important for the course of Cretaceous mammalian evolution than any influence from dinosaurs.”
The researchers focused on bone articular fragments from therian mammals, a group that includes modern marsupials and placentals. However, they did not analyze more primitive mammals, such as multituberculates, due to differences in their skeletal structure.
A new perspective on mammalian evolution
The findings offer new insights into how prehistoric mammals adapted to changing environments well before the asteroid impact reshaped life on Earth. While this study marks the conclusion of the project, it opens new avenues for understanding how early mammals evolved in response to habitat transformations millions of years ago.
“We’ve known for a long time that mammalian long bone articular surfaces can carry good information about their mode of locomotion, but I think this is the first study to use such small bone elements to study change within a community, rather than just individual species,” Janis concluded.
The study has been published in Paleontology.
