The Narluga: New Insights from Old Bones
The Narluga: New Insights from Old Bones

The Narluga: New Insights from Old Bones

DNA analysis of a bizarre, 30-year-old whale skull serves as a reminder of the secrets that museum specimens keep about the natural world.

Oct 1, 2019
Ashley Yeager

ABOVE: © MARKUS BÜHLER 2019

Every time Eline Lorenzen pushes open the basement door of the Natural History Museum of Denmark at the University of Copenhagen, a pungent scent of dust, whale blubber, and chemicals pummels her nose, the biologist tells The Scientist. Hundreds of skeletons and skulls are scattered about the room, but there’s one in particular that Lorenzen has been fixated on since she became the curator of the mammal collection at the museum in 2015. At first glance, the 30-year-old skull has features similar to the face and jaw bones of toothed whales such as narwhals and belugas. It has a row of chompers on the top and bottom jaws, just like a beluga’s. But, bizarrely, all of the teeth jut forward from the jaws, and the bottom row of teeth are twisted, spiraling leftward—just as a narwhal’s tusk does.

One of Lorenzen’s colleagues, narwhal researcher Mads Peter Heide-Jørgensen of the Greenland Institute of Natural Resources, discovered the skull on a hunter’s roof in the early 1990s and suggested it represented a hybrid of a narwhal and a beluga. Back then, researchers didn’t have the tools to test DNA from the skull to determine if that was true. By the time Lorenzen came across the skull, however, scientists had developed techniques to extract and analyze nucleic acids from animals that lived up to several thousand years ago. Extracting genetic material from the teeth and comparing it to DNA from the teeth of narwhal and beluga skulls in the Natural History Museum of Denmark collection confirmed Heide-Jørgensen’s hypothesis: the whale was indeed a hybrid, the son of a narwhal mom and a beluga dad.

“The fact [that they] even managed to find the skull is incredibly surprising in itself,” says Travis Park, a postdoc who studies whales at the Natural History Museum in London and was not involved in the new work. “Personally, I like the fact that the skull is almost exactly what you’d imagine you’d get if you mixed a beluga and a narwhal together. Genetics usually doesn’t work out so cleanly so it’s nice to have an example of this phenomenon that is so clearly illustrated.”

The skull offers the first hard evidence that narwhal-beluga hybrids, or narlugas, can occur, though anecdotal evidence suggests there may be others. The hunter who shot the whale noted that he had seen it with two similar-looking companions, and natives of western Greenland have a common name for a narwhal-beluga hybrid, itorsaq. The new discovery underscores the importance of museum collections, Lorenzen says. Museums often house what she calls “gems”—“specimens that lead to major insights into our natural world and the natural history of the world.” Natalie Cooper, a researcher focusing on vertebrate ecology and evolution at the Natural History Museum in London, agrees. “Museum collections in general are a treasure trove of information for all kinds of research,” she writes in an email to The Scientist.

A skull found in the Natural History Museum of Denmark (center) looks like a cross between the skull of a beluga whale (left) and that of a narwhal (right).
Mikkel Høegh Post

Such gems often go unnoticed, however, as collections at natural history museums are largely untapped, says Ross MacPhee, curator of the mammal collection at the American Museum of Natural History in New York City. The newly analyzed narluga skull is a perfect example, he adds: it sat in the collection for a long time before Lorenzen came along and decided to study it in depth. Although museum specimens present certain challenges for biological analyses—their storage and transport might make them prone to contamination, for example, while treatment with chemicals and changing temperature and humidity conditions could damage genetic material—techniques for extracting information from such samples are improving, MacPhee says.

He and his colleagues have been working to collect ancient collagen and other proteins from samples kept in museums all over the world. In June, the team analyzed collagen while a collaborating group analyzed ancient DNA in the bones of living and extinct sloth species kept in museums in the US, the UK, France, and Argentina. The molecular data completely overturned long-held assumptions based on anatomical analyses about the evolutionary relationships among these animals. Extant three-toed sloths, for instance, appear so anatomically different from other species that researchers had put them on a completely separate evolutionary branch. But both the mitochondrial and protein evidence revealed that three-toed sloths are in fact part of the Megatherioidea superfamily, a group that includes the extinct, elephant-size ground sloth genus Megatherium. Based on the new relationships among the sloths, the researchers concluded that the assumption that extant, tree-inhabiting sloths evolved from a ground-dwelling ancestor was also wrong. Rather, the ancestral sloth might have lived both in the trees and on the ground.

One particularly promising avenue for unlocking museum specimens’ secrets is extracting proteins from teeth, MacPhee says. It’s long been known that certain proteins involved in producing enamel in the teeth get sealed into pockets in the enamel that protect them against degradation like they’re in a “locked vault,” he says. Sequencing one of the proteins, amelogenin, can even provide information about the sex of a specimen, giving scientists with access to multiple individuals’ samples the ability to study population dynamics and sex ratios.

Lorenzen and her colleagues did not analyze the proteins stored in the narluga’s teeth, but they did run the teeth through isotopic analyses and compared the results to data from narwhals and belugas to see if they could figure out what the hybrid whale ate. The results weren’t at all what the team expected, says study coauthor Mikkel Skovrind, who started the project as a graduate student and is now a postdoc in Lorenzen’s lab. Since the whale’s mom was a narwhal, the team thought maybe the narluga would learn to feed from her, eating like a narwhal. These whales create a vacuum of sorts to suck in their food and often eat alone. Belugas, on the other hand, hunt together, corralling schools of fish to chow down on or snagging octopuses, crabs, and snails. According to the analysis, however, the narluga didn’t eat like either parent—it was a bottom feeder. “[It’s an] even more unique individual than previously thought,” Skovrind says.

The findings are a reminder of what’s to learn from studying dusty old bones. “Who knows what else is in these collections?” Lorenzen says. “We just need to ask the right questions.” 

Ashley Yeager is an associate editor at The Scientist. Email her at ayeager@the-scientist.com.