Prehistoric Whale Reveals Extreme Skull Asymmetry 

Sperm whales and pygmy sperm whales are known among mammals for their unusually shaped heads. Unlike most vertebrates, which are bilaterally symmetrical, toothed whales have asymmetrical skulls that accommodate highly specialized organs used for echolocation and sound production.

An international research team has now described a previously unknown extinct species of pygmy sperm whale, Scaphokogia huachafo, in which this asymmetry reached unprecedented levels. The fossil skull, dating from between 6.3 and 5.6 million years ago in the Late Miocene, belonged to an animal around 2.7 meters long and shows the most extreme facial asymmetry known in any cetacean – and possibly in any mammal.

“Cranial asymmetry in toothed whales is directly linked to the development of fatty structures in the forehead that are involved in sound production. But in Scaphokogia huachafo, this asymmetry went far beyond the area around the blowhole. Both bony nostrils are shifted entirely to the left side of the skull, while the facial bones differ dramatically in size and position. The skull looks completely crooked,” explains Aldo Benites-Palomino, lead author of the study. Benites-Palomino studied the fossil as part of his doctoral research at the University of Zurich’s Department of Paleontology. He is now an assistant professor at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU).

The scientific name of the new species, Scaphokogia huachafo, reflects both its unusual appearance and a distinctly Peruvian expression. The species name huachafo is a term in Peruvian Spanish used to describe something extravagant, bizarre, tacky or over-the-top. “In Peru, huachafo is an everyday word for anything that is flashy, over-the-top, bizarre, extravagant or difficult to categorize aesthetically,” says Benites-Palomino. “When we looked at the proportions of this whale – with its face strongly shifted to the left and its oversized, downward-curving snout – it broke every rule of symmetry and elegance seen in living cetaceans. Its anatomy is so extravagant and odd that huachafo seemed the perfect name for it.”

The skull of Scaphokogia huachafo was found in the mid-1990s in the Pisco Formation of southern Peru, whose desert outcrops are internationally known for their exceptionally well-preserved marine fossils. Benites-Palomino first came across the fossil in 2015 while working on his Bachelor’s thesis at the Museo de Historia Natural in Lima. “The initial suspicion with skulls this distorted is always taphonomy – that the specimen may have been flattened or twisted by sediment pressure over millions of years,” says Benites-Palomino. “But the sutures are fully closed, and there are no fractures, pathologies or deformations elsewhere on the skull. This was genuine biology, not a result of poor preservation.”

Unlike living sperm whales, which hunt squid in deep ocean waters, the anatomy of Scaphokogia huachafo points to a specialized bottom-feeding lifestyle in shallow coastal environments. Its snout formed a thick, tubular structure reinforced by dense bone and ossified cartilage that acted as natural ballast, shifting the animal’s center of gravity forward and downward. The snout was also angled downward by 31 degrees relative to the rest of the skull. Reconstructions of the neck joint – where the skull connects to the atlas vertebra – show that Scaphokogia could bend its head downward by as much as 55 degrees.

“The entire cranio-cervical complex is modified to point the snout directly toward the bottom,” explains Gabriel Aguirre-Fernández, co-author of the study and doctoral advisor at the University of Zurich. “The combination of dense bone, the downward-curving snout and the flexible neck articulation allowed the animal to move directly above the seabed and feed close to the sediment.” Because Scaphokogia lacked the facial whiskers or visual specializations found in other bottom-feeding marine mammals, the researchers suspect that it used its asymmetrical biosonar system to scan soft coastal sediments for prey. This specialized seafloor-feeding niche disappeared as oceanic conditions changed at the end of the Miocene, giving way to the marine mammal ecosystems seen today.

Literature
Aldo Benites-Palomino et al. Extreme Cranial Asymmetry in Extinct Benthic Feeding Sperm Whales. Communications Biology. 9. November 2026. DOI: DOI: 10.1038/s42003-026-11074-2