What does an ancestor of today's baleen whales look like, some 24-27 million years ago? Probably something a bit like this:
Erich Fitzgerald, in 2006, with the type specimen of Janjucetus. Credit: Museum Victoria
In 2006, my colleague Erich Fitzgerald dropped a bombshell on the rest of paleocetology. In a sole-authored paper published in Proceedings of the Royal Society B (written while he was a graduate student at Monash University), he described an entirely new kind of early baleen whale from the Oligocene of Australia: Janjucetus hunderi, with anatomical features nearly unlike any putative early baleen whale reported at the time. (Larry Barnes, now emeritus curator of vertebrate paleontology at the Natural History Museum of Los Angeles, remarked to me at the time, with wild eyes, "That things looks like a horse!"). In fact, without close inspection of its ear bones and skull, you wouldn't be wrong for thinking it was an odontocete. Or a plesiosaur. Based on Erich's analysis, Janjucetus actually fit in very close to the base of the mysticete family tree, leading to some startling ideas about how many hallmark baleen whale traits evolved in the first place.
A 2011 reconstruction of Janjucetus by Carl Buell.
Anything from the Oligocene is interesting for fossil marine mammalogists because we have so little fossiliferous marine rock outcrops, globally, from this period of time, which covers episodic sea-level lows following the onset of Southern Hemisphere glaciation. The fact that Janjucetus came from the Oligocene of Australia was even more enigmatic (though, not without precedent). Curious readers can read more about in Carl Zimmer's excellent piece.
Today Erich reports on more information about Janjucetus in today's Biology Letters. Based on an incomplete lower jaw representing additional material of this early whale, Erich describes how Janjucetus possessed lower jaws that were fused at the tip (near the mandibular symphysis), unlike every single previously described baleen whale (fossil or modern), but very much like the condition we see in the ancestors of today's whales (the so-called "archaeocetes"). The implication of this find is that the earliest baleen whales were feeding using a mode unlike their descendents, who have much more mobile jaws. Carl Zimmer provides another great take; see also these news reports (ScienceNOW/AAAS and BBC news), which include comments from lab members and associates.
