Dolphins are known for their intelligence and expert ability in catching fishy meals, but one ancient dolphin shunned the pescetarian lifestyle and instead decided to chow down on squid – and lost its teeth in the process.
The bizarre toothless cetacean has been described from two skulls unearthed in what is now South Carolina, and represents an early offshoot of the group of marine mammals that tend to be known rather ironically as toothed whales. Along with losing its gnashers to tackle soft-bodied cephalopods, the weird dolphin also shrunk in size until it was about half as long as a common bottlenosed dolphin.
Dating to around 30 million years old, the dwarf cetacean is thought to have evolved not long after toothed whales – which include all modern dolphins, as well as orca, beaked whales, and sperm whales – first split from the other major group of cetaceans, the baleen whales. However, the newly named Inermorostrum xenops clearly took a rather different evolutionary path than the others.
The work, published in the Proceedings of the Royal Society B, describes its conspicuous lack of teeth and blunt, shortened snout. “This last feature is perhaps the most critical,” explains lead author Robert Boessenecker in a statement. “Short snouts typically occur in [toothed whales] that are adept at suction feeding – the smaller the oral opening, the greater the suction.”
The addition of deep artery channels running through the snout of the skull also hints at this suction-feeding lifestyle. This increased blood flow may have supplied their large muscular lips with oxygen, allowing them to increase the suction they could generate and to slurp in small fish, squid, and other soft-bodied marine critters.
The shape of the skull, which is all that has so far been found of the creature, also indicates that the dolphin’s head would have pointed downwards somewhat. This, coupled with the fact that it still had echolocation, suggests the cetacean would have swam along the bottom of shallow seas, grubbing around in the mud in order to find food, not unlike a walrus does today. To this end, the researchers also suggest it may too have had short bristly whiskers protruding from its snout.
In life, it would probably have reached just 1 meter (3 feet) in length, something more comparable to the highly endangered vaquita, rather than the more prolific bottlenosed dolphin, and would have looked nothing like any cetaceans that currently swim the oceans today.
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