Ancient Fossil Reanalysis Reveals Miocene Sperm Whale Was Likely a Fierce Predator.

A recent paleontological study has reexamined a long-overlooked fossil of an extinct sperm whale from Patagonia, revealing that the species may have led a predatory lifestyle quite distinct from its modern relatives. Published in Papers in Palaeontology, the study revisits the only known specimen of Idiorophus patagonicus, shedding light on early sperm whale evolution and behavior.

The fossil, originally described in 1893 by Richard Lydekker and named Physodon patagonicus, underwent several reclassifications after its initial discovery. Due to previous usage of the name Physodon for other marine fossils, Belgian paleontologist Abel proposed the name Scaldicetus in 1905. This name, however, became a catch-all for various hard-to-classify species. In 1925, Kellogg formally assigned the specimen to the genus Idiorophus, giving it the name it holds today.

Unearthed from the Early Miocene Gaiman Formation near Cerro Castillo, Argentina—estimated to be around 20 million years old—the exact site of discovery remains uncertain. Despite the limited fossil record, the recent analysis has provided new anatomical and taxonomic insights.

Researchers determined that the I. patagonicus fossil belonged to a subadult individual measuring approximately 5 to 6 meters in length. Phylogenetic analysis suggests that it was not closely related to other known sperm whale species in the region and may represent one of the earliest members—or even the ancestor—of the Physeteridae family.

The whale's rostrum, or snout, played a central role in the revised understanding of its behavior. According to lead researcher Dr. Florencia Paolucci, the structural features indicate a more aggressive feeding style than seen in modern sperm whales. "Unlike today's sperm whales that use suction to feed on cephalopods or small fish, Idiorophus likely hunted larger fish and possibly seabirds," she explained.

However, some mysteries remain. The absence of the basicranium—the part of the skull that houses the sinus system—prevents scientists from drawing conclusions about the whale's diving capabilities. "Unfortunately, the traits related to diving are mostly found in soft tissues, which don't fossilize, or in parts of the skull that weren’t preserved in this specimen," said Dr. Paolucci.

Dating of the surrounding sediments places the fossil in the Early Miocene, roughly 20–19 million years ago. Yet, with only a single specimen available, it's unclear how long the species persisted or why it eventually disappeared. Dr. Paolucci noted that ongoing research into other fossil sperm whales from different regions and time periods may eventually fill in these gaps.

Further exploration, however, faces major hurdles. “The only known specimen remains our sole source of information,” Dr. Paolucci said. “Unfortunately, recent severe cuts to science and technology funding under President Javier Milei's administration in Argentina have made future fieldwork increasingly difficult.”

While this rediscovery brings a new chapter to light in the story of sperm whale evolution, it also underscores the challenges of scientific progress in the face of limited resources.

Source:https://phys.org/news/2025-05-ancient-patagonian-fossil-sperm-whale.html

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