A newly-discovered fossil is helping close a significant gap in the evolutionary history of the baleen whales by revealing how the ancestors of modern-day filter feeders with the humpback and blue whale began to diverge from toothed creatures like the sperm whale.
According to Nature and Science News, the approximately 36-million-year-old fossil skeleton is the oldest known specimen of the mysticete group, predating what had been the oldest remains of a fossilized whale predecessor by at least 2 million years and shedding new light on the transition that caused some species of whales to have their sharp teeth replaced by fibrous plates.
“This is the fossil that we’ve been waiting for,” explained Nicholas Pyenson, a paleobiologist at the Smithsonian National Museum of Natural History in Washington DC who was not among the authors credited on a new Current Biology paper detailing the research, during an interview with Nature. It can answer many of the questions scientists have regarding the origins of living whales and the appearance of the first known ancestors of modern baleen whales, he added.
The original whales were predators with extremely sharp teeth, closer in nature to modern orcas than humpbacks or blue whales, said Science News. At some point, however, mysticetes evolved and replaced those teeth with baleen, using those fibrous plates to filter fragments of food out of seawater. The newfound specimen marks the beginning of that transition, the authors noted.
Scientists still uncertain why filter-feeding eventually won out
Identified as Mystacodon selenensis, the fossil whale is described as a small to medium-sized creature that had teeth, but in other ways resembled modern humpbacks and blue whales, they explained – hence its name, which Science News said translates to “toothed mysticete.”
The remains were discovered in the deserts of Peru by a team led by Royal Belgian Institute of Natural Sciences paleontologist Olivier Lambert. It was approximately four meters long, or about as big as a modern-day pilot whale, and like primitive whales, still had a protruding hip bone indicating that it still had hind legs left over from when its ancestors were terrestrial quadrupeds.
However, the creature also had a flat snout similar to those of modern-day baleen whales, and while ancient whales had elbow-like joints in its front flippers, M. selenensis does not – nor do modern-day baleen whales, according to the authors of the new Current Biology paper.
Lambert’s team believes that M. selenensis might have used vacuum-like suction to gather prey from the ocean floor, according to Nature. While the earliest whales used a variety of feeding mechanisms, the researchers believe that this could have been one step towards the development of filter-feeding techniques used by modern-day baleen whales, which had taken hold by around 23 million years ago for reasons not fully understood by the scientific community.
“I don’t think suction feeding alone is the primary step,” Lambert told Science News. Rather, he believes that the answer lies in yet-to-be-discovered ancient whale remains likely residing in the same area where M. selenensis was found – the Pisco Basin on the southern coast of Peru. As he explained, “There is huge potential for the area where we excavated.”
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