The discovery by two U.S. paleontologists of an extinct, but surprisingly close cousin of the narwhal and beluga whales that inhabit Canada's icy waters has shed fresh light on the relatively recent evolution of the species' ancestors in warmer, more southerly climes.

The previously unknown animal identified by the American researchers, named Bohaskaia monodontoides, is based on a single, three-million-year-old skull fossil unearthed at a Virginia gravel pit in 1969.

Only recently studied using modern scientific techniques, the specimen was found to have come from an extinct whale with strong similarities to both the narwhal, distinguished by its unicorn-like tusk, and the white-skinned beluga — signature residents of Canada's Arctic and subarctic marine environments.

"Fossils referred to as belugas have been known from fragmentary bits, but skulls are so revealing because they contain so many informative features," Nicholas Pyenson, a paleobiologist with the Washington, D.C.-based Smithsonian Institution, said in a summary of the study. "We realized this skull was not something assignable to a beluga, and when we sat down, comparing the fossil side by side with the actual skulls of belugas and narwhals, we found it was a very different animal."

Pyenson and his research partner in the study, Smithsonian post-doctoral fellow Jorge Velez-Juarbe, published their findings on the new whale species in the latest issue of the Journal of Vertebrate Paleontology.

They note in the published article that one other extinct, beluga-related toothed whale, Denebola branchycephala, was previously identified from a fossil discovered in the Baja California peninsula of northwest Mexico.

The southerly origins of the two ancestral whale fossils have led Pyenson and Velez-Juarbe to conclude that the original family of small, toothed whales that gave rise to today's narwhals and belugas inhabited more temperate waters before adapting to the ice-choked habitats they live in today.

"The fact is that living belugas and narwhals are found only in the Arctic and subarctic, yet the early fossil record of the monodontids extends well into temperate and tropical regions," Pyenson said in the research overview. "For evidence of how and when the Arctic adaptations of belugas and narwhals arose, we will have to look more recently in time."

Velez-Juarbe said in the statement that the northward evolution of the two modern whale species, which are considered threatened in some of their Canadian habitats today, may have resulted from changes that happened to the marine food chain before "competition or dietary preferences drove monodontids further north."

Belugas and narwhals, which typically weigh between 1,200 and 1,500 kilograms, form a distinct branch of the Delphinoidea "superfamily" of related whales that includes dozens of porpoise and dolphin species, among them the killer whale.

rboswell@postmedia.com