Dinosaurs became giants — so why did they never become tiny?

Recent research addresses the evolutionary mystery of why dinosaurs, which dominated terrestrial ecosystems at gargantuan sizes, failed to evolve into truly tiny animals. While physiology has historically been cited as a limiting factor, this study suggests that ecological competition played a pivotal role. The researchers propose an inter-class competition dynamic where dinosaurs effectively restricted the ecological expansion of mammals during their reign. Conversely, small mammals likely occupied the specialized niches that would have been required for the evolution of mouse-sized dinosaurs. This reciprocal ecological suppression prevented small-bodied dinosaurs from diversifying into miniature forms, effectively creating a size floor for the clade that remained unchallenged until the end of the Cretaceous period.