Introduction:
A comprehensive analysis of the fossil record has uncovered that placental mammals, the group that includes humans, dogs, and bats, originated during the Cretaceous period and co-existed with dinosaurs for a brief period before the catastrophic event that led to the mass extinction of non-avian dinosaurs. The debate over the timing of placental mammal evolution has been ongoing, with fossils found only in rocks younger than 66 million years old, suggesting they evolved after the extinction event. However, molecular data has hinted at an older origin for placental mammals.
Study Findings:
In a recent publication in the journal Current Biology, a team of palaeobiologists from the University of Bristol and the University of Fribourg conducted a statistical analysis of the fossil record to shed light on the origin of placental mammals. The researchers collected extensive fossil data from various placental mammal groups, spanning the time leading up to the mass extinction 66 million years ago.
Lead author Emily Carlisle from Bristol's School of Earth Sciences explained that by examining thousands of placental mammal fossils, the team could observe the patterns of origination and extinction among different groups, allowing them to estimate when placental mammals evolved.
Using a statistical model, the researchers estimated the ages of origin and extinction based on the appearance and disappearance of lineages in the fossil record. The analysis revealed that placental mammals, including primates (the group that includes humans), Lagomorpha (rabbits and hares), and Carnivora (dogs and cats), had already evolved just prior to the mass extinction event. This indicates that their ancestors coexisted with dinosaurs for a short period.
Co-author Daniele Silvestro from the University of Fribourg explained that the model used in the study could estimate the origination and extinction ages by analyzing the appearance and disappearance of species within lineages.
Co-author Professor Phil Donoghue from Bristol further emphasized that examining both the origins and extinctions of placental mammals provides a clearer understanding of the impact of major events such as the mass extinction that wiped out the dinosaurs.
Conclusion:
The in-depth analysis of the fossil record conducted by the research team reveals that placental mammals originated before the mass extinction event that eradicated non-avian dinosaurs. While these mammals co-existed with dinosaurs for a brief period, it was after the asteroid impact that modern lineages of placental mammals began to diversify. The loss of competition from dinosaurs may have played a role in the rapid diversification of placental mammals following the mass extinction. This study contributes to our understanding of mammalian evolution and the dynamics of life during the age of dinosaurs.
