image: New view of early bird diversification, showing the emergence of pygostyle and U-shaped furcula in the Late Jurassic and the occurrence of crown-group birds (Aves) in the Cretaceous.
Credit: ©Science China Press
The timing of the early diversification of modern birds remains one of the most contested questions in evolutionary biology. One hypothesis proposes a Cretaceous divergence of early bird orders during the age of dinosaurs. A competing hypothesis envisages a main thrust of diversification following the Cretaceous–Paleogene (K/Pg) mass extinction event.
A new review summarizes recent advances in both molecular and fossil-based research on the evolutionary timeline of modern birds. It highlights findings from large-scale phylogenomic studies employing molecular clock models, along with key discoveries of Mesozoic bird fossils. It also examines the main sources of discrepancy among divergence time estimates, such as fossil calibration strategies and model assumptions.
According to the review, an intriguing consensus has gradually crystallized with the publication of recent paleontological and genomic insights: many major lineages of extant birds likely originated during the Late Cretaceous, well before the K/Pg boundary. This early diversification appears to have coincided with a broader ecological transformation known as the Cretaceous Angiosperm Terrestrial Revolution—a period marked by the rapid spread of flowering plants and simultaneous radiations of pollinating insects, mammals, ray-finned fishes, and other groups. The evolutionary emergence of modern birds is interpreted as a key part of this dynamic phase of terrestrial ecosystem restructuring.
These findings shed new light on the deep-time origins of modern birds and underscore their emergence as part of one of the most profound episodes of biotic change in Earth history.
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See the article:
New Fossils Imply a Deeper Origin of Modern Birds in the Mesozoic
https://doi.org/10.1093/nsr/nwaf238
Journal
National Science Review