Featured Image Credit: Wikipedia
By: Jessica Kittel
No one would ever suspect that this rather ferocious-looking sea creature with razor sharp teeth is the great-great-great-great-great (plus a few more greats) grandpa of the very creatures that embody the phrase “gentle giants,” i.e. baleen whales. Baleen whales, also known as mysticete whales, are known for, well, their baleen (shockingly). They are filter feeders, meaning they use strips of baleen, made of keratin and attached to their jaws, to strain out a lot of very small sea creatures from seawater.
It is due to this rather remarkable and effective trait that this group of whales has risen to rank among some of the largest animals on the planet and includes the largest animal to ever inhabit the earth, the blue whale. So how does one go from razor sharp teeth to baleen-wielding gentle giants? Very gradually it would appear, according to new research.
Once upon a time, in a mystical land known as Australia, a 1990s amateur fossil hunter discovered a very well preserved skull and partial skeleton of what would come to be known as Janjucetus hunderi, later revealed as one of the earliest baleen whales to be discovered to date. Janjucetus lived approximately 25 million years ago and is thought to have been about the size of a dolphin.
This skull was left mostly unexplored until halfway through the first decade of the 2000s when Erich Fitzgerald, who was working on his graduate thesis at the time, re-discovered it in a private collection and decided to take another look.
The skull was clearly a cetacean of some kind but at first glance, it looks more likely to be related to a fish-hunting dolphin (a member of the odontocetes, the other branch of cetacean besides mysticete) than a krill-sieving humpback.
This is not the first baleen whale ancestor to be discovered with teeth, however, all of the others are thought to have used their teeth for a primitive form of filter feeding. Some of them may have even had both teeth and baleen.
Since Fitzgerald began investigating Janjucetus many traits belonging to this early mysticete have been analyzed resulting in some very interesting pieces of information. It had very large eye sockets (suggesting it relied heavily on vision for hunting) and very sharp teeth indicative of a creature that hunted and killed decent sized prey rather than a creature that takes large gulps of water and strains out all the tiny animals. However, like its filter feeding decedents, Janjucetus had a very wide upper jaw, suggesting that this particular trait may have been the initial step towards modern whales’ large mouths and subsequent filter feeding.
Unlike today’s mysticete whales, Janjucetus did not have the flexible lower jaw that allows modern day baleen whales to take large gulps of water. Instead, this widening of the upper jaw was likely initially meant to aid in the efficiency of suction feeding. The Jajucentus is believed to have pulled in water to suck prey into its mouth. The wider upper jaw would have increased the volume of the mouth and therefore the efficiency of suction feeding.
Over time, the evolution of baleen and of a flexible jaw, in coalition with the already widened upper jaw, would have allowed whales to efficiently capture food by filter feeding.
This new research contributed to our understanding of baleen whales by helping us create a more accurate timeline about the order at which known traits of baleen whales evolved and by reaffirming that baleen whales evolved baleen long after splitting off from other whales.