For years, scientists have wondered why only males of the rarely seen family of beaked whales have “tusks,” since they are squid-eaters and in many of the species, these elaborately modified teeth seem to actually interfere with feeding.

A newly published study help explain the evolutionary origin of these distinctive “tusks” in beaked whales, a rather mysterious family of whales that live in the deep oceans. Although the tusks are known to be used in competition between males, another purpose seems to be to attract female beaked whales – and to avoid mistakes in choosing a mate.

The study, by researchers in Oregon, New Zealand and Australia, is being published this month in the journal Systematic Biology. It describes one of the first examples of “sexual selection” implicated in the radiation of a group of mammals outside ungulates (deer, elk and antelope).

“Beaked whales are among the least known, least understood and, frankly, most bizarre whales in the ocean,” said Scott Baker, associate director of the Marine Mammal Institute at Oregon State University and a co-author of the article. “Because they live in the deep, they are rarely seen alive and many are described only from specimens found stranded dead on the beach. They are the only cetacean species with tusks and scientists have long wondered why, since their diet primarily is squid and the females are essentially toothless.

“It turns out that tusks are largely an ornamental trait that became a driver in species separation,” Baker added. “The tusks help females identify males within their species, which could otherwise be difficult as these species are quite similar to each other in shape and coloration.”

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