Dinosaur size limits research

Researchers from the American Museum of Natural History and Princeton University have reinforced their earlier findings with a new paper in *Evolution*. Using the same mathematical model of vertebrate body‑size evolution, the authors show that energetics and physiology explain size ranges in mammals, birds and turtles, but not the persistent absence of truly tiny non‑avian dinosaurs. The smallest known non‑bird dinosaurs – *Microraptor* (≈430 g), *Fruitadens* (≈730 g) and *Anchiornis* (≈530 g) – remain orders of magnitude larger than the tiniest modern birds, mammals and lizards. Co‑lead researcher Stephanie Lechki notes that small animals require fewer resources and mature faster, while co‑author Roger Benson argues that early shrew‑sized mammals already occupied the smallest‑body niches, preventing dinosaurs from evolving mouse‑ or sparrow‑sized forms. The study continues to reproduce size ranges for mammals, birds and turtles, yet fails to match the size distribution of dinosaurs, snakes, lizards and crocodilians, supporting the hypothesis that competition with small mammals constrained dinosaur miniaturisation.