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Prehistoric Whale Fossil Reveals How Whales Evolved Baleen

A 25-million-year-old fossil has provided Melbourne palaeontologists with evidence of when whales evolved from using teeth to filter-feeding with hair-like baleen.

The fossil skull, nicknamed “Alfred”, is from an extinct group of whales called aetiocetids that, despite having teeth, were an early branch of the baleen whale family tree. Alfred’s teeth show rare evidence of feeding behaviour that suggests an entirely new evolutionary scenario – before losing teeth and evolving baleen, these whales used suction to catch prey.

“Filter-feeding is the key to the baleen whales’ evolutionary success,” explains Dr Erich Fitzgerald of Museums Victoria. “But what has really eluded scientists since Charles Darwin is exactly how whales made the complex evolutionary change from biting prey with teeth to filtering plankton using baleen.”

The discovery of Alfred’s ancient bones on the coast of Washington state, USA, gave clues to this palaeontological puzzle, with tiny horizontal scratches apparent on the inner surface of its teeth. This unusual type of tooth wear is only seen in a few living marine mammals, such as the walrus, that use the back-and-forth movement of their tongue to suck in prey, along with rough material like sand.

“These horizontal scratches on Alfred’s teeth suggest that he would have sucked small prey into his mouth, much like we would suck a milkshake up through a straw,” said Dr David Hocking of Museums Victoria and Monash University.

“Alfred shows how ancient baleen whales made the evolutionary switch from biting prey with teeth to filtering using baleen,” adds Dr Felix Marx of Museums Victoria and Monash University. “They first became suction feeders. Feeding in this way resulted in reduced need for teeth, so over time their teeth were lost before baleen appeared.”

The team is now uncovering the rest of Alfred’s skeleton, as well as other fossils from Australia that provide exciting insights into how baleen whales first evolved. “There are genuine surprises,” Fitzgerald says. “We’ve only just begun to decipher the earliest and strangest pages of the baleen whale story.”

The discovery has been published in the peer-reviewed journal Memoirs of Museums Victoria (http://tinyurl.com/jxvlkcx).