fossils

The tiny toothy ancestor of today’s modern giant whales

3986b46bb4f35aa1ff4d42167a12e0fc

Vasika
Udurawane

Writer
A tiny new species of whale is filling the gaps of the family tree, providing clues to how baleen evolved and how they became the giants they are today.

It's well known that modern baleen whales are the heaviest animals of all time, with the blue whale outclassing the largest dinosaurs in terms of weight though maybe not in terms of length. While they have a well-known reputation for gentility, all of them are carnivorous. They feed by gulping down huge masses of small animals, filtering out the water via their baleen plates. Even within this group there are different feeding styles.


The streamlined rorqual whales are active feeders, and sometimes pursue large schools of fish. Right whales are far more passive, feeding by merely sifting out small planktonic animals from the water while swimming along the surface. They do not use power, speed and lunge feeding to capture their prey.


Baleen whales may be huge now but they started out tiny. They were hardly bigger than small dolphins and porpoises at one time. These were the so-called "archaeomysticetes". This is a rather loose grouping of animals that emerged somewhere during the Priabonian Stage of the Late Eocene, roughly 38 to 33 million years ago. They evolved from the earlier archaeocetes. The later archaeocete whales, members of the Basilosauridae, were the first to truly exploit the oceans. Some of them retained the peg-like teeth in their toothed descendents.


Others however took a different route. The aetiocetids are a transitional stage between the hypercarnivorous archaeocetes and the passive predators that modern baleen whales are. Recently an aetiocetid Fucaia buelli, the very smallest of all baleen whales has been discovered, in rocks dating back to the Oligocene. This puts it at around 33 to 30 million years ago, making it one of the most ancient baleen whales ever. The animal's remains consist of teeth, which are important given that most of the very oldest baleen whales had them. The aetiocetids certainly did, even though Aetiocetus itself, their most derived member probably had both.


Other early baleen whales are the mammalodonts. There are just two members in the entire family, both from Australia. They are the 3.5-meter Mammalodon and Janjucetus. Both are miniscule compared to today's leviathans, but the newfound whale is much smaller and more unique than either. At 2 meters long, Fucaia buelli is the smallest baleen whale in history. It also did not feed like any other with teeth. It was not just grabbing and ripping apart animals with its teeth like the bigger Janjucetus but instead used it lips and gums to suck in small prey items like a beaked whale  today. But it is not just these that practice suction feeding.


Muscles at the back of Fucaia's mouth and throat helped to suck in its prey and its massive gums helped to expel excess water from its mouth. Oddly enough, the expulsion of water in this manner is also a trait of modern baleen whales. Over time these animals lost their teeth altogether, switching them out for long comblike baleen plates. The mammalodont Mammalodon itself might have been a suction feeder, but one that fed on the seabed. The tiny Fucaia gets its name from the Strait of Juan de Fuca and the species name buelli comes from Carl Buell, an accomplished paleoartist who specializes in restoring extinct mammals.

Image Credit: Jaime Bran

3986b46bb4f35aa1ff4d42167a12e0fc

Vasika
Udurawane

Writer


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