Recent research led by the University of Bristol has uncovered that mammals were transitioning to a ground-based lifestyle millions of years before the asteroid impact that wiped out the dinosaurs. Published in Palaeontology, this study offers fresh insights into mammalian evolution, providing evidence that the ecological shifts in the late Cretaceous period were crucial to the development of terrestrial mammals.
Mammals evolved for land life before the asteroid impact, evidence shows
The research provides evidence that most mammals had already started to evolve to live on land much earlier than the devastating asteroid impact that transformed the planet. This was a turning point in mammalian evolution, as most species, which were adapted to arboreal (tree-dwelling) life, began to adapt to terrestrial environments. The investigators, headed by Professor Christine Janis, used fossil bones of marsupials and placental mammals excavated in Western North America, the only place with a good representation of fossil remains of this era. The bones were mostly from the tips of the limbs, where most important clues of locomotory habits would be seen.
Study shows how limb bones reflect mammal adaptation to terrestrial life
In this groundbreaking study, the team focused on the analysis of limb bone ends, which are vital indicators of how mammals moved. These bones have distinct features that reflect locomotion patterns and offer insight into how these mammals adapted their movement to different environments. By contrasting these ancient fossils with the structures of modern mammal limbs, the scientists were able to understand how the animals’ physical features were changing to move toward a more terrestrial way of life. In contrast to previous research, which primarily relied on complete skeletons, this study led the charge in utilizing small bone components to monitor wider community-level evolutionary change.
In contrast to other methods, which tend to be based on the full skeletons of ancient mammals, this study made use of small bone pieces in order to find out how a whole community of mammals evolved. Through analyzing the minute fossils, scientists could monitor evolutionary change throughout various species and the entire mammalian community. This new technique enabled the researchers to acquire more detailed information regarding how the environmental changes during the period influenced the evolution of mammals.
Study reveals how plant evolution shaped mammals’ shift to ground living
Professor Janis described the vegetational changes during the late Cretaceous as having an important role to play in the evolution of mammals. As the world witnessed the emergence of flowering plants (angiosperms), new and varied habitats appeared on the ground. This transformation of the plant life probably had some effect on the mammals, forcing many of them towards terrestrial habitats as they became accustomed to the new environments. The mammalian transition to ground existence was a reaction to the changing environments, and in due time, this enabled mammals to endure and survive following the asteroid impact.
The research particularly dealt with the bone articular fragments of therian mammals, such as marsupials and placentals. The fossils were examined for hints of their locomotion mode, presenting evidence of the increased frequency of terrestrial movement in some species of mammals. Yet, the research did not involve other groups of mammals, such as multituberculates, whose bones differed structurally and did not reveal the same kind of information on locomotion habits.
Role of plant evolution in shaping mammal adaptations
In this paper, Professor Janis highlighted the fact that ecological factors, in this case the vegetation changes, were more critical to the history of Cretaceous mammals than the impact of dinosaurs. While angiosperms started to predominate and produce new environments and food supplies on the ground, mammals adapted to new ways of living as they found new niches on the ground. This vegetation shift provided room for mammals to change to new methods of living, such as locomotion that became more ground-dependent.
This research is an important milestone in the research on prehistoric mammals because it is studying the locomotion of these ancient animals in a novel manner. Focusing on small bone elements rather than on complete skeletons, this research has broadened the knowledge on mammalian evolution and early mammals’ responses to varying environments. The results are new evidence of behavioral and ecological changes taking place in mammals millions of years prior to the asteroid impact.
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