An ancient beaked whale that was fossilized along with its last meal reveals how the ancestor of today’s deep foragers hunted in shallow waters. The work, published in Proceedings of the Royal Society B this week, is the first direct evidence of a predator-prey relationship between a beaked whale and near-surface fish.
These days, the tusk-bearing beaked whales with dolphin-like snouts are notoriously difficult to study because they forage in deep water habitats far from shore. Just a year ago, two Cuvier’s beaked whales smashed mammalian records for both dive depth and duration. One dove 2,992 meters (more than 1.8 miles) below the surface, and another stayed under for two hours, 17 minutes, 30 seconds. But things weren’t always this way.
Olivier Lambert from the Royal Belgian Institute of Natural Sciences examined what appeared to be the nine-million-year old stomach contents of a toothed whale unearthed last year from Late Miocene sediments in the Pisco Basin of Peru, exposed at Cerro Colorado. The whale fossils – which include the skull, lower jaw, vertebrae, ribs, and ulna – belonged to an extinct, echolocating beaked whale ancestor called Messapicetus gregarius. It was likely an adult male between 4.1 and 4.5 meters long with a body weight of 1,842 kilograms (4061 pounds).
In addition to fossilized fish remains near the whale’s chest region, there were also multiple fish around its head (pictured below). These are the most likely places for prey that’s been recently swallowed, or possibly regurgitated. The team counted 40 to 60 individual fish, which had an average body length of 38.8 centimeters (15 inches) and weight of 410 grams (14.5 ounces). Together, they weighed up to 24.6 kilograms (54 pounds) – not inconsistent with stomach content analyses of similar sized modern whales.
Based on the position of the fish along the head and chest region and the lack of digestion marks on their remains, the researchers think this assemblage resulted from the whale’s death – possibly via toxic algae poisoning – less than a few hours after capturing prey from a single school.
The fish were closely related to today’s Pacific sardines, Sardinops sagax, which feed on surface-dwelling, planktonic crustaceans. That means this archaic beaked whale hunted in the upper part of the water column, likely along the coast, and that the highly specialized deep divers showed up much later. In fact, Lambert explains, the extinction of these near-surface forms may have coincided with the diversification of true dolphins, which dominate shallow coastal waters today.
Fossil remains of the extinct beaked whale Messapicetus gregarius and associated fish Sardinops sp. cf. S. sagax found in Cerro Colorado. O. Lambert et al., Proc. R. Soc. B 2015