Â鶹ÒùÔº

Ancient Patagonian fossil sperm whale may have been active predator, reanalysis indicates

A recent study, in Papers in Palaeontology, discusses the reanalysis of the only known Idiorophus patagonicus specimen.

After a nearly 130-year scientific slumber, the study, titled "Awakening Patagonia's sleeping sperm whale: A new description of the Early Miocene Idiorophus patagonicus (Odontoceti, Â鶹ÒùÔºeteroidea)," provides new insights into early sperm whale evolution, body size, and feeding behavior.

The fossils were first described by Richard Lydekker in 1893 and given the scientific name Â鶹ÒùÔºodon patagonicus. However, as the name Â鶹ÒùÔºodon had already been used for both isolated teeth found in the Miocene layers in Lecce, Italy, and was an earlier name given to sharks, a new name was suggested in 1905 by Abel. He suggested the taxon ought to be called Scaldicetus, which became a wastebasket taxon for any species that did not fit neatly into any other taxonomic group.

Eventually, I. patagonicus was given the name Idiorophus by Kellogg in 1925.

The fossil specimen was recovered somewhere in the Early Miocene Gaiman Formation (20 million years old), at Cerro Castillo, in front of Trelew, Argentina, although the exact location is unknown.

Of the many sperm whales (Â鶹ÒùÔºeteridae) that existed during the Miocene, today only three species remain: Â鶹ÒùÔºeter macrocephalus (Giant Sperm whale), Kogia sima (Dwarf sperm whale), and Kogia breviceps (Pygmy sperm whale).

The I. patagonicus specimen underwent a thorough anatomic and taxonomic revision, revealing several new insights.

The I. patagonicus specimen was a subadult, measuring between 5 and 6 meters in length. Based on its phylogenetic analysis, it was not closely related to any other Â鶹ÒùÔºeteridae species in the region. Additionally, it may have been one of the earliest species of physeterids or possibly even the ancestor of all physeterids.

Its rostrum (snout) provided some of the most intriguing insights pertaining to its feeding habits, according to Dr. Florencia Paolucci, "The ecomorphological features of Idiorophus point to a lifestyle quite different from that of modern sperm whales. It was likely an active predator of large fish and possibly some seabirds, while extant sperm whales feed mostly on cephalopods or small fish through suction feeding.

"Unfortunately, most of the traits related to diving behavior in living cetaceans are found in soft tissues, which don't preserve in fossils. In some cases, parts of the basicranium, especially the bones that house the sinus system, can give clues about diving abilities—but in this case, the basicranium of Idiorophus wasn't preserved."

Despite the insights gained from this study, there are still many unanswered questions about I. patagonicus. When asked about the timespan this species existed, Dr. Paolucci acknowledges the limitations of their research: "Unfortunately, I don't have clear answers yet, and it's hard to draw conclusions based on a single specimen. We know the age of the fossil based on the surrounding sediments, which indicate an Early Miocene age (around 20–19 million years ago).

"Since the studied specimen is the only one known for Idiorophus, we can't determine whether the species lasted for a longer time span—we just know it was present in the Early Miocene.

"As for its extinction, we've recently been working on sperm whales from a more global perspective, looking at specimens from other regions and different time periods (e.g., Late Miocene). So, there's still a lot of work to be done on this topic.

"For now, any hypothesis is on the table—from global climate changes that may have altered ocean dynamics and prey availability, to potential competition with other marine mammals (e.g., dolphins). Hopefully, future analyses will allow us to test these ideas properly."

However, recent science and technology funding cuts have made future fieldwork difficult, explains Dr. Paolucci, "The type specimen is the only one known for this species so far. I really hope to find more during future fieldwork. But with the severe cuts to science and technology currently happening in Argentina under President Javier Milei's government, that possibility is becoming increasingly distant."