New Fossil is Missing Link in Sperm Whale Evolution

Since the tale of Moby Dick and Captain Ahab was first written, scientists have been fascinated by the remarkable sperm whale as well as its kin, the smaller pigmy and dwarf whales. However, these deep-diving relatives have remained rather elusive and little is known about their history. Now, a new fossil has been discovered in Panama that is the missing link in sperm whale evolution, helping to shed light on this amazing species.

An international team of scientists found the Panamanian fossil of an extinct pigmy sperm whale, and it's revealing an unexpected level of complexity in the evolution of the spermaceti of these whales. Spermaceti is an organ, located within the head, which plays a key role in the whale's generation of sound and capacity for echolocation. (You can learn more about how whales produce sound here).

While whales, along with dolphins and porpoises, have a long fossil record that dates back to their terrestrial ancestors, the same cannot be said of the smaller relatives of the well-known sperm whale. Most of what experts know of the 8- to 12-foot-long pigmy and dwarf sperm whales comes down to maritime folklore, and as thus has limited our understanding of the evolution of these mysterious animals.

But now, discovered and studied by a team of scientists from the Natural History Museum, Iowa State University, and the Smithsonian Tropical Research Institute, the new Panamanian fossil whale is finally giving us some answers.

"The new discovery gives us a better understanding of the ancient distribution of these poorly known relatives of the sperm whale," Dr. Jorge Velez-Juarbe, who led the research, said in a statement. "Previously we knew of similarly-aged pigmy and dwarf whales from Baja California and Peru, but this new fossil fills in an important geographic gap in the group's ancient distribution." (Scroll to read on...)

The new whale species, named Nanokogia isthmia after the Isthmus of Panama, is known from the well-preserved skulls of two individuals. These remains were unearthed at a sea cliff along the Caribbean coast of Panama and from rock layers dated to about 7 million years ago.

Like with other, more well-studied whales, the new fossil will allow scientists to better understand how changes in climate and continental distribution have influenced this species.

"Our study is part of a larger scientific effort aimed at understanding the changes in the marine habitats that resulted from the complete closure of the Isthmus of Panama," explained Velez-Juarbe.

That is, sometime within the last 10 million years, the eastern Pacific Ocean and the Caribbean Sea separated.

This discovery is not just shedding light on the distribution of pigmy sperm whales, but also on the evolution of characteristics related to sound emission and echolocation, which was more complex than scientists previously thought.

The rare fossils show that at one time, these small sperm whales had a much larger spermaceti organ than they do now. Over the course of their evolutionary history, their spermaceti got downsized at least twice - including during the event that gave rise to the living pigmy and dwarf sperm whales. However, the reason for this downsizing remains unclear. Velez-Juarbe plans to continue searching the prehistoric seas of Central America to find the answer, hoping to find more complete skeletons of Nanokogia and other closely related species.

The findings were published in the journal PLOS ONE.

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