The biggest animal that has ever existed on Earth is alive today, and swimming around in the oceans. But most land mammals, impressive though an elephant may be, look like a tiny elephant shrew in comparison to the mighty Brachiosaurus.
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The bad news is, we are probably not going to see land mammals the size of Brachiosaurus. After the demise of the dinosaurs, mammals did begin to grow larger all over the world, filling a niche left by the big scaly monsters.
“During the Mesozoic, mammals were small,” University of Georgia Odum School of Ecology professor John Gittleman said in a statement, after conducting research into animal sizes around the world. “Once dinosaurs went extinct, mammals evolved to be much larger as they diversified to fill ecological niches that became available.”
“Having so many different lineages independently evolve to such similar maximum sizes suggests that there were similar ecological roles to be filled by giant mammals across the globe,” Gittleman added. “The consistency of the pattern strongly implies that biota in all regions were responding to the same ecological constraints.”
Among the largest filling the dinosaurs’ massive shoes was Paraceratherium, an ancient ancestor to the rhinoceros, weighing 15-20 tonnes and measuring 5 meters (16 feet) to its shoulders. Impressive though this is, dwarfing today’s land mammals, it’s not up there with the biggest of dinosaurs.
Unfortunately, even if the conditions were right for such a mammal to grow to this size, we are likely limited by our biology.
“Mammals are what are called endotherms,” biologist Felisa Smith explained to EarthSky. “They regulate their own body temperature. A mammal of a given size uses ten times more energy than does a reptile or a dinosaur of the same size.”
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“In other words, mammals can’t evolve bodies as large as the largest dinosaurs because they need to use so much of their physical energy – provided by the food they eat – towards keeping their bodies warm. For example, we humans need to maintain a temperature of 98.6 degrees Fahrenheit, or 37 degrees Celsius, in order to stay alive. But dinosaurs, like today’s reptiles, did not regulate their body temperature, and the extra energy allowed them to grow larger.”
So, to answer the title’s question, no. But keep your eyes on lizards.
An earlier version of this article was first published in April 2023.
Source Link: Why Don't Modern Land Mammals Ever Evolve To Be As Huge As Dinosaurs?
