Study Finds No Non-Avian Dinosaur Under 400 Grams for 180 Million Years
Updated
Updated · Earth.com · Aug 11
Study Finds No Non-Avian Dinosaur Under 400 Grams for 180 Million Years
3 articles · Updated · Earth.com · Aug 11
Summary
A review of 515 non-avian dinosaur species found the lightest known adult weighed about 400 grams, with no rabbit-smaller dinosaur appearing anywhere in 180 million years of fossils.
Using 24 versions of a body-size model that fits 4,062 mammals, 9,385 birds and 260 turtles, researchers still predicted dinosaurs should have clustered near 3 kilograms, with some under 300 grams.
Two fossil sites with unusually good preservation of small animals—the Jehol Group in China and Mongolia's Djadokhta Formation—contain tiny mammals, lizards and birds but no dinosaur below about 0.76 kilograms.
The authors argue physiology alone cannot explain the gap and instead propose small, high-metabolism mammals occupied the food niche that tiny dinosaurs would have needed, while juvenile larger dinosaurs also competed there.
Birds broke that pattern after flight evolved: today's most common bird size is about 33 grams, and flightless birds on mammal-poor islands also shrink far below continental limits.