There were small dinosaurs. Microraptor is a good example. It was about the size of a crow, weighed roughly 1 to 3 pounds, and was only about 2½ feet long. They don’t get much smaller than that. There were no frog-sized dinosaurs. No dino hamsters. Scientists have wondered why for years, and might have finally come up with an answer. Or rather, they might have found someone to blame: mammals.
A new study published in Evolution used mathematical models to figure out why dinosaurs were generally so big and were rarely small enough that you would seriously consider turning them into a pet no matter how much they wanted to eat you. The model suggests that basic physiology and energy requirements alone can’t explain why non-bird dinosaurs never evolved into teeny tiny pocket-sized little guys.
With those ruled out, ecology became the next best possible solution. Specifically, competition with mammals.
Early mammals that shared the planet with dinosaurs were usually pretty small, and usually only ate small stuff like insects and seeds. Their size offered them the benefit of reproducing more quickly and needing to eat last two stay alive. Researchers suspect that mammals may have so thoroughly fulfilled the role of the Earth’s resident small creatures during dinosaur times that there was just no room for small dinosaurs to thrive.
Mammals Were Better at Being Small Than Dinosaurs
It was probably for the best, since evidence suggests that dinosaurs were just better at being big and mammals were better at being small. It was a balance that was working out just fine until that asteroid slammed into the Earth, reducing food supplies. Suddenly, the gigantic dinosaurs that needed to eat a lot to stay alive weren’t spoiled by the Earth’s abundance of big fleshy creatures to snack on. All the smaller mammals that just ate bugs and seeds eventually realized that they didn’t need to limit themselves anymore. They had unlimited access to all the giant-animal food, eventually evolving into giant herbivores and sleek, deadly apex predators.
None of this is to say that there were absolutely no tiny dinosaurs ever. It’s just that the fossil record hasn’t turned up any, and researchers say that that’s likely to stay that way. Fossil beds don’t just preserve big T. rex bones, but also tiny bones from mammals, lizards, and amphibians.
If there were some dino hamsters scurrying around hundreds of millions of years ago, we probably would’ve found at least some evidence of them by now. That’s disappointing. It would be really cool to find a tiny, pocket-sized dinosaur. But now we know why they (probably) never came to be, and we know who to blame. And since we’re mammals, it’s technically us.
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