LISTEN, I’M NOT going to sit here and tell you that baleen whales are big. You know that. In fact, I bet you know that at 300,000 pounds, the blue whale is the heaviest creature to ever exist. But I bet you don’t know why such filter-feeding whales are so big—because not even scientists know that.
Today, though, one group of researchers offers a fascinating theory in Proceedings of the Royal Society B: Fusing the fossil record and phylogenetic work (that is, determining the relatedness of species to one another), they found that baleen whales probably got colossal just 3 million years ago—a sliver of time in the grand evolutionary scheme of things—and climate change probably triggered the transformation. That, of course, carries troubling implications for how the giants might fare as Earth’s oceans warm and acidify.
Baleen whales—which gulp massive amounts of water and filter out tiny critters like krill—have been around for about 30 million years. But for the vast majority of that time, they were modestly proportioned, topping out at 30 feet or so, or about one-third the length of the modern blue whale. Now, being small offered some perks. For one, it’s easier to open your maw when it’s smaller.