Welcome to another episode of “Evolution Events”! We are excited to talk about evolution in Order Cetacea; specifically toothed whales vs. baleen whales!
First, we will reiterate what it means to be a toothed whale or a baleen whale. “Toothed whales” do not always refer to animals commonly called whales; scientifically speaking, toothed whales also include porpoise and dolphins. To further clarify, we urge you to view our article “What’s in a Name? Whales, Dolphins, Porpoises in Order Cetacea”.
Toothed whales are different from baleen whales in a few ways. Toothed whales have, obviously….teeth! Baleen whales have baleen, a keratin-composed “hair-like” structure on their top jaw that acts as a sieve when feeding. Toothed whales can utilise echolocation; producing sound through the top of their head (melon) and capturing sound using the lower jaw (mandible). Though baleen whales can vocalise, they cannot use this natural sonar. They typically have broad lower jaws.
So when and why did this evolutionary change occur to produce baleen and baleen whales? I word it this way because teeth existed well before baleen.
The common ancestor for Cetacea’s two modern groups, toothed whales (Odontocetes) and baleen whales (Mysticetes), was believed to exist around 35-34 million years ago. Astonishingly, this was only 10 million years after the first ancient whales began entering their new aquatic habitats. The closest living relatives to today’s cetaceans are hippos and pigs; this doesn’t mean that today’s whales descended from these animals. Rather, it tells us that they shared a more recent common ancestor than whales do with other animals living today.
But back to teeth and baleen; why did baleen whales evolve?
Some scientists believe that ancestors of modern baleen whales might have once had both teeth and baleen structures, until the teeth were eventually lost with use of intense filter-feeding. However, it was believed that some adaptations of teeth could assist with this method to an extent, similar to how a crab-eater seal feeds. Further evidence to this relationship is found during the embryonic stage of baleen whales, when tooth buds appear briefly. Changes on the planet during the Oligocene (such as summer nutrient availability) pushed the growth, in number of species and actual sizes, of baleen whales.
Though, also within the fossil record, scientists have also found that some ancient whales apparently needed neither structure (teeth or baleen) to feed and even some whales belonging to the toothed group lost their teeth for a method called “suction-feeding”. Therefore, it is clear that whale evolution was a diverse and ever-changing process that we are still discovering.
The common ancestors for both baleen whale and toothed whale groups (meaning two different animals leading to these respective modern groups) both existed between 25-23 million years ago.
Today there exist many more toothed whale species than baleen whale species due to the versatility of teeth. Baleen is efficient and effective, however teeth provide a wider scope of prey types to hunt and consume.
Scientists are learning more about whale evolution all the time, so this information can change very rapidly as new evidence is presented. How exciting it is that we are still learning so many details about whales today, evolution and otherwise!
Take a look at the photos above and you can see a toothed whale, the orca, next to a baleen whale, the humpback whale.
Written By: Alexa D.
Marine Naturalist with Five Star Whale Watching