A recent study conducted by the University of Bristol presents evidence that many mammals had already transitioned towards a more ground-based lifestyle prior to the final Cretaceous mass extinction that eradicated the non-avian dinosaurs 66 million years ago.
Dryolestes late Jurassic relatives of Cretaceous treatment mammals. Image credits: James Brown/Pamelagill/University of Bristol.
Present-day mammals thrive in a varied environment mainly dominated by angiosperms (flowering plants).
In contrast to the habitats provided by coniferous vegetation, forests and woodland environments possess intricate lower levels and towering trees, offering rich biodiversity and resources for terrestrial mammals of all sizes.
Yet, the angiosperm-dominated habitat is relatively recent in Earth’s history, primarily characteristic of the Cenozoic era (66 million years ago to the present), with initial developments towards the end of the Cretaceous period.
“Mesozoic mammals were typically small, mostly weighing under 5 kg, with few surpassing 10 kg,” noted Professor Christine Janice from the University of Bristol and a colleague.
“While it holds true that the majority of present-day mammals are small, averaging around 0.5 kg, the Cenozoic era saw the evolution of greater mammal diversity.”
“The small size of Mesozoic mammals has commonly been attributed to dinosaur predation, but recent recognition of the late Cretaceous proliferation of angiosperms and the habitats they offered may be more crucial than dinosaurs in elucidating the patterns of Mesozoic mammal evolution and diversification.”
“Did these mammals prefer trees or terrestrial substrates? And did this preference alter towards the close of the Cretaceous period with the changes in angiosperm habitats?”
In their research, the authors scrutinized tiny bone fragments of ancient mammalian taxa (marsupials and placentals) unearthed in western North America, specifically the extremity bone edges.
They identified indications that these mammals were adapting to a terrestrial lifestyle.
The analysis of extremity bone edges entailed signatures of locomotive patterns that could be statistically compared to modern mammals.
“There was a known shift in plant life towards the Cretaceous boundary, characterized by angiosperms,” stated the researchers.
“It was also acknowledged that arboreal-dwelling mammals faced challenges post-asteroid impact.”
“However, what remained undocumented was whether mammals were inclining towards a more ground-dwelling lifestyle alongside habitat transformations.”
Former studies utilized complete skeletons to study the movement patterns of ancient mammals, but this study was among the first to employ small bone elements to track alterations across the community.
“The plant habitat appears to have played a pivotal role in the trajectory of Cretaceous mammal evolution beyond dinosaur influences,” remarked Professor Janice.
Published in the March/April 2025 issue of the journal Paleontology, the study unveils intriguing insights into ancient mammal adaptations.
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Christine M. Janice et al. 2025. Paleontology 68(2): E70004; doi: 10.1111/pala.70004
Source: www.sci.news
