Dinosaurs seemed to have generally been so much larger than animals today. Huge dragonflies that dwarf their modern counterparts, turtles 10ft long. What is the mechanism that allowed them to be so large, or conversely makes modern ones smaller? Is it about Oxygen levels, or efficiency, or something else?
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Well here’s the thing, although many people believe mammals have been around for 65 million years, they in fact have been on earth for at least 170 million years, possibly as long as 225 million years.
For most of this time mammals were very small, while dinosaurs evolved to fill virtually every terrestrial niche available, and other reptiles took over the seas and skies.
Yes some dinosaurs got very big, but most species did not grow to the proportions of Tyrannosaurus Rex, Triceratops or Brachiosaurus. Most species that we are aware of were well below the 5000 lbs mark. Even Allosaurus, the “Lion of the Jurassic”, a 30 ft long predator was a 3000 lbs animal.
But there is one niche that Dinosaurs were never able to claim, and that is of the very small. Think mouse or shrew size. During their 170 million year reign, dinosaurs were never able to crack that ecological niche, and that’s because the mammals dominated it and kept them out. Dinosaurs kept mammals from getting big, mammals kept dinosaurs from shrinking. Which I for one is a pretty rad fact.
Another reason animals today tend to not be as large is well, Us. Almost all Mega fauna on this planet is now gone, and the timing of these extinction evens correlates strongly with the arrival of Homo Sapiens entering the local eco system. Look at the mega fauna of Australia, where man did not arrive until relatively recently. Usually bigger animals are the first to die off and go extinct when the environment changes to drastically to quickly, and well humans are arguably the greatest shake up artists the world has ever seen.
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