New research suggests that physiology alone can’t explain this missing miniature end of the dinosaur spectrum—and that early mammals may have been partly responsible.
In a study published in the journal Evolution, researchers from the American Museum of Natural History and Princeton University used mathematical models to examine how body size evolved among vertebrates. Their results show that energy use and physiology can account for the range of sizes seen in mammals, birds, and turtles. Those same factors, however, cannot explain why even the smallest dinosaurs other than birds remained relatively large.
The researchers instead suggest that ecology may have imposed a lower size limit on dinosaurs. In particular, competition with early small mammals could have prevented dinosaurs from moving into the mouse-sized and sparrow-sized niches that are filled by many vertebrates today.
"Everyone loves a giant dinosaur," said study co-author Roger Benson, the Macaulay Curator of Dinosaur Paleobiology at the Museum. "But we decided to look at the other end of the scale. The absence of tiny dinosaurs may be just as interesting as the existence of giant ones. We already knew that dinosaurs prevented mammals from evolving to large sizes before the end-Cretaceous mass extinction. Here we suggest that mammals in turn prevented dinosaurs from evolving to small sizes."
https://www.sciencedaily.com/releases/2026/08/260807035137.htmOpen linkView original on slrpnk.net
4 replies
It just has to keep saying "non-bird dinosaurs". Is it not clear that birds were the tiny dinosaurs they think are missing?
Birds evolve pretty late in terms of the dinosaur evolutionary story, so you can think of the question as “why are there no little dinos prior to the evolution of birds” if it helps. The researchers hypothesize that this is because there was too much competition with mammals in the small range, but when birds came along they were able to evolve smaller because flying gave them a special tool to allow them to access resources mammals couldn’t.
Does this mean pterosaurs are not dinosaurs or birds then? Same for crocs.
Indeed, their lineages break off before “dinosaurs” in the way we currently classify things. Marine reptiles split off beforehand too so most of the ancient ocean behemoths aren’t technically dinosaurs.