TOP: This 39-cm-long blue whale (Balaenoptera musculus) fetus was culled from its mother in 1936 at Port Hobron whaling station on what is now Kodiak Island, Alaska. The alcohol-preserved specimen is part of a collection of fetal whales acquired during the commercial whaling era and archived by the Smithsonian’s National Museum of Natural History.
BOTTOM: A 65-cm-long fin whale (Balaenoptera physalus) fetus was collected from an 18.3-m-long mother killed by Norwegian whalers in the Southern Ocean near Australia and brought to the Smithsonian by the US Coast Guard in 1939. This CT scan of the skull reveals developing ear bones (yellow) that house a funnel made of fat, thought to be used for sound reception in baleen whales such as this one. (The baleen has not yet developed in this specimen.) Using the museum’s collection, the marine mammal curator, Nicholas Pyenson, along with postdoc Maya Yamato, charted the acoustic funnel’s development in toothed and baleen whale fetuses.MAYA YAMATOFor more than a year, Smithsonian Institute postdoc Maya Yamato spent her days driving whale fetuses between a storage facility outside of Washington, D.C., and the National Museum of Natural History, where she delicately transferred the irreplaceable specimens—some small enough to fit in her hand, others as long as she was tall—into a CT scanner. “The specimens have been cared for by the Smithsonian’s staff for decades, but it only takes a second to mess them up,” says Yamato in an email.
One by one, Yamato and paleobiologist Nicholas Pyenson, curator of fossil marine mammals at the museum, scanned 56 skeletal or ethanol-preserved whale fetuses at various stages of development to understand how underwater mammals—in particular, filter-feeding baleen whales, or mysticetes—developed their specialized systems of hearing.
“We know they sing,” says Pyenson. “But we really don’t know the anatomical basis by which they hear.” He says that although researchers have characterized the hearing adaptations acquired as whales’ tetrapod ancestors made their transition from land to sea, little is known about the natural history and fetal development of modern marine mammals, and much of what is known comes from stranded animals. “Whales are big, and they don’t exactly lend themselves abundantly to these kinds of investigations. So this ...
