18 Million Year Old Sperm Whale With 'Needle-Shaped' Snout

The skull of Rhaphicetus (dorsal view and lateral view). (Photo: RBINS)
21/09/2020
18 Million Year Old Sperm Whale With 'Needle-Shaped' Snout
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Reinout Verbeke

Paleontologists have excavated and described one of the oldest fossil sperm whales. The new species from Peru is approximately 18 million years old. Rhaphicetus valenciae was about 5 metres long and had an extremely long snout and slender, pointed teeth. It probably hunted small, fast-swimming prey in shallow waters. Today's sperm whales have a broad snout and 'suction feed' on squid at great depths.

In recent years an international team of palaeontologists has been making important discoveries in the Pisco Basin in southern Peru, a desert where erosion continuously exposes whale fossils. They give us more insight into the evolution of baleen and toothed whales, as well as their common ancestors over the past 45 million years.

Now the researchers have described one of the oldest sperm whales ever, based on a newly excavated skeleton including the partial skull, ear bones, mandibles, teeth, vertebrae, sternum and ribs. This excellently preserved skeleton makes Rhaphicetus valenciae, as this new species was named, one of the best-known extinct sperm whales to date.

Rhaphicetus lived in the Pacific Ocean near present-day Peru between 18 and 19 million years ago. This very early sperm whale may give us a good picture of what the common ancestor of all sperm whales looked like. And that image is quite different from that of today’s sperm whale species: the sperm whale, the dwarf sperm whale and the pygmy sperm whale.

Long Snout With Narrow Teeth

Rhaphicetus valenciae was between 4.7 and 5.7 metres long, three times smaller than the modern sperm whale. “What immediately struck us was the extremely long and narrow snout”, says palaeontologist Olivier Lambert of the Royal Belgian Institute of Natural Sciences (RBINS). Sperm whales today have a broad snout, holding an organ of their forehead containing a waxy liquid. The genus name of this new fossil species therefore became Rhaphicetus, from the Greek for needle (rhaphis) and the Latin for whale (cetus). ‘The whale with the needle-shaped snout'.

This toothed whale had slender, pointed teeth in both upper and lower jaws (in today's sperm whale species the upper teeth have disappeared). The tip of the snout lacks teeth. “We suspect that this allowed the animal to contact, and possibly stun relatively small and fast-swimming prey items. It then grasped them with their numerous small teeth, and gradually transported them to the back of the mouth before swallowing them roughly intact”, describes Lambert.

Different Diet

This feeding strategy differs from later (also extinct) sperm whales such as Livyatan melvillei, a super predator discovered in younger layers of the same Peruvian desert, which hunted large prey (such as whales) with its enormous mouth and teeth. And the feeding strategy of the early sperm whale  Raphicetus also differed from that of the three living sperm whale species: they 'suction feed’ squid at great depths. Rhaphicetus was not a specialized suction feeder and it probably hunted in shallower waters, close to the seafloor.

“This find gives us more insight into the evolutionary beginnings of this fascinating family”. The study was published in the Journal of Systematic Palaeontology.

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