Researchers reanalyzing 15-million-year-old fossils unearthed in California over a century ago have described a new sperm whale genus: Albicetus, after the toothy white leviathan of Herman Melville’s Moby Dick. The findings are published in PLOS ONE this week.
These days, there are only three species of sperm whales, and they’re found throughout the world’s oceans. The largest of them, Physeter macrocephalus, is a deep diver that can grow 18 meters (59 feet) long. The other two, Kogia breviceps and Kogia sima, are much smaller at 2.7 meters (9 feet) and 3.5 meters (11 feet) in length, respectively. Sperm whales in the fossil record, however, were a diverse array of different forms.
Described in 1925, Ontocetus oxymycterus is a large but incomplete fossil sperm whale specimen unearthed in the middle Miocene Monterey Formation along sea cliffs near the original Santa Barbara Lighthouse in Santa Barbara County, California. The incomplete skeleton – which consisted of the rostrum (or snout), both mandibles (lower jaws), and several isolated but associated teeth fragments – were first spotted as early as 1879, and then moved to the National Museum of Natural History in 1924. The whale was placed in the genus Ontocetus based on similarities with another sperm whale called Ontocetus emmonsi.
But! Ontocetus emmonsi was first reported based on a single tooth from the 19th Century, and researchers have since discovered that the fossil is actually the tusk of an extinct walrus – not a cetacean tooth. That makes Ontocetus a genus in the walrus family, Odobenidae.
After re-examining the Ontocetus oxymycterus fossils, Smithsonian Institution’s Alexandra Boersma and Nicholas Pyenson assigned this species to the new genus Albicetus, creating the new combination of Albicetus oxymycterus. The new genus combines the Latin words "albus" for white and "cetus" for whale. It pays tribute to Moby Dick, a whale of "unwonted magnitude" with a "remarkable hue" and a "deformed lower jaw." These traits, according to the authors, are coincidentally similar to the Albicetus specimen: a white fossil sperm whale whose jaws have been displaced due to burial and fossilization processes. The species name, which combines the Greek words "oxy" for sharp and "mycter" for nose, remains the same.
Additionally, the team created 3D models of the heavy Albicetus specimen (to better view it from all angles), and they also estimated its total length. "Albicetus has really huge upper and lower teeth," Boersma tells IFLScience. "The teeth are on the same scale as those of the modern sperm whale, but considering Albicetus was around 6 meters [20 feet] long, the teeth are almost comically large."
Modern sperm whales only have teeth in their lower jaw, and they don't seem to use them when feeding. "It was these really large teeth that led us to think that this fossil sperm whale was likely feeding on very different prey from its modern relative, whose diet consists primarily of squid," she adds. The middle Miocene – when Albicetus was swimming around the Pacific Ocean – was a period of peak marine mammal richness and diversity. Albicetus likely preyed on smaller whales and seals, which is rarely seen in the oceans these days and limited only to some orca populations.
When the team conducted phylogenetic analyses with other fossil and living members of the sperm whale superfamily, Physeteroidea, they found that Albicetus is a stem physeteroid – suggesting that large body size and robust teeth evolved multiple times in distantly related sperm whale lineages.
A pod of Albicetus traveling together through the Miocene Pacific Ocean, surfacing occasionally to breathe. A. Boersma/Smithsonian
