The largest living whales – including the gigantic 30-metre blue whale – are fast predatory hunters that support their massive bodies by filtering large volumes of tiny prey from cool near-polar waters. They do this using baleen: plates of a tough substance hanging from their upper jaw.

Evidence of early evolution of baleen whales remains both sparse and controversial, with several ideas competing to explain the origin of baleen-based bulk feeding.

New evidence published today, based on our detailed analysis of a large, 34 million year old Antarctic fossil whale, Llanocetus denticrenatus (“yano-seetus” denticrenatus), shows that this whale was all gums and teeth, but had no baleen.

Our findings suggest that large gums gradually became more complex over time and, ultimately, gave rise to baleen – and that these ancient whales became giants before they evolved their baleen feeding habits.

A snapshot of Llanocetus

The specimen is the second oldest “baleen” whale ever found. It is an ancestor of modern baleen whales, such as humpback and blue whales, except that it had no baleen. Instead, this whale had large gums and teeth, likely used to bite prey some 30 centimetres long.

The size of this whale is surprising, given its place in the evolution of whales. Its skull proportions indicate a body length of 8 metres, about the size of a modern minke whale.

Partially reconstructed cast of the skull of Llanocetus. Andrew Grebneff, who prepared much of the fossil, gives an idea of its size. R Ewan Fordyce, CC BY-SA

The nearly complete skull, minus the tip, is more than 1.6 metres long, and in life was probably more than two metres. Other parts of the skeleton are similarly large and strongly built. There are other unexpected features: Llanocetus has huge openings for jaw muscles, implying a powerful bite, but its teeth are small relative to skull size.

Further, adjacent teeth are separated by wide gaps, and the bony palate has multiple grooves for soft tissues, reminiscent of baleen-related grooves of living species. Yet, we propose that Llanocetus was a predator that bit and sucked its prey, rather than filtering it from the surrounding water like modern baleen whales.