Overview
- Researchers used mathematical energy‑use and life‑history models and found those models reproduce size patterns for mammals, birds, and turtles but cannot explain why non‑avian dinosaurs stayed relatively large.
- The smallest known non‑avian dinosaurs weigh about 450 grams, far heavier than the tiniest modern birds and mammals, a gap the models could not bridge even when testing many physiological scenarios.
- The team examined fossil sites that preserve small vertebrates and concluded that poor preservation alone is unlikely to explain the absence of mouse‑ or sparrow‑sized non‑avian dinosaur fossils.
- Authors propose ecological factors, especially competition from early small mammals, as the most plausible reason small terrestrial dinosaurs did not evolve, framing this as a testable hypothesis rather than a settled fact.
- The paper highlights powered flight as the key ecological escape hatch that let early birds enter new habitats and evolve much smaller body sizes, and it calls for more fossil and ecological work to test the idea and identify the exact mechanisms.