This ancient, gummy whale is breaking all the rules.

The weird marine beast, called Llanocetus denticrenatus, lived about 34 million years ago. It was big. It was an early ancestor of modern humpbacks and blue whales. And (this is the maverick, rule-breaking bit for a whale of its type) it had thick gums studded with teeth.

Today, all the biggest whales are filter feeders, while only small whales of the odontocetl group (including belugas, sperm whales, and all dolphins and porpoises) still chew their food.

Modern large whales instead suck huge volumes of water through stringy bristles in their mouth called baleen, separating out tons of tiny organisms, which they digest en masse. This is such an essential feature of the group of massive whales, or Mysticetes, to which L. denticrenatus also belongs, that biologists call whales in this group baleen whales. [Whale Album: Giants of the Deep]

But L. denticrenatus, according to a paper published today (May 10) in the journal Current Biology, didn't have any baleen.

After the flesh of ancient creatures has long rotted away, it can be tricky to determine what these animals looked like when they were alive. But researchers studied a remarkably complete L. denticrenatus skull found in Antarctica and were able to make some judgments about the flesh it likely supported, based on its ridges, grooves, and holes for blood vessels and nerves.

L. denticrenatus, they found, did have large gums, which included some signs of features that may have preceded baleen. But those gums were studded with teeth — the sort of teeth creatures use to take bites out of one another.

That's bizarre, because L. denticrenatus was also huge, growing to be up to 26 feet (8 meters) long, according to researchers. And, as Live Science previously reported, researchers have long believed that only filter-feeding whales could grow larger than about 20 feet (6 m).

"The giants of our modern ocean may be gentle, but their ancestors were anything but," study author Felix Marx, a paleontologist at the Royal Belgian Institute of Natural Sciences, said in a statement. "Llanocetus was both large and a ferocious predator and probably had little in common with how modern whales behave."

This finding also reverses the order researchers had long assumed for whale evolution. L. denticrenatus may have been what researchers call a "suction-assisted raptorial feeder" — a big animal that sucks smaller animals into its mouth before noshing on them — but it didn't do any filter feeding.

"Until recently, it was thought that filter feeding first emerged when whales still had teeth," researcher R. Ewan Fordyce, a paleobiologist at the University of Otago in New Zealand, said in the same statement. "Llanocetus shows that this was not the case."

Originally published on Live Science.