Orcas: Fossil hints that killing whales is a recent adaptation

A 1.4-million-year-old fossil relative of killer whales had tooth that recommend it ate small fish moderately than giant marine mammals


7 March 2022

Artistic reconstruction of Rododelphis stamatiadisi

Artistic reconstruction of Rododelphis stamatiadisi

Rossella Faleni

A 1.4-million-year-old ancestor of orcas and false killer whales appears to have dined on small fish – which suggests its descendants tailored to hunt bigger prey equivalent to different dolphin and whales comparatively just lately.

“This is an extraordinary fossil that helps qualify the origin of the unique diet of killer whales and false killer whales,” says Giovanni Bianucci on the University of Pisa, Italy. “It’s difficult to give a precise date, but these cetaceans seem to have evolved to eat marine mammals less than a million years ago.”

Orcas (Orcinus orca) – also called killer whales – and false killer whales (Pseudorca crassidens) are the one dwelling species of cetaceans that feed on different marine mammals. When they developed to take action is unclear as a result of cetacean fossils are exceptionally uncommon, says Bianucci.

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So Bianucci was pleasantly shocked to study {that a} personal collector had discovered a skeleton of a Pleistocene-epoch false killer whale on the Greek island of Rhodes, in 2021. The specimen was donated to the Stamatiadis Museum of Mineralogy and Paleontology on the island.

Analyses of the specimen revealed that the fossil was new to science, says Bianucci. His group named it Rododelphis stamatiadisi in honour each of Rhodes and of the collector, Polychronis Stamatiadis.

The scientists famous that the R. stamatiadisi fossil had a physique about 5-metres lengthy, which is analogous to fashionable false killer whale – however it had smaller tooth, says Bianucci. In addition, its tooth lacked the deep grooves seen in killer whale and false killer whale tooth – that are diversifications vital for crunching robust mammal bones.

This means that the species in all probability hunted smaller prey – extra proof for which comes from the fossilised stays of blue whiting fish (Micromesistius poutassou) discovered inside the historic dolphin. M. poutassou – which nonetheless exists in the present day – is a 30-centimetre-long fish. It was clearly the R. stamatiadisi’s final meal, says Bianucci.

Fitting R. stamatiadisi into cetacean family tree, Bianucci and his colleagues decided that the animal shared a typical ancestor with fashionable false killer whales – and that this ancestor descended from the identical line that orcas did.

Significantly, early members of the orca group additionally appear to have hunted small prey moderately than dolphins and whales. The group features a 4-million-year-old species (Orcinus citoniensis) discovered fossilised in Italy within the nineteenth century, which additionally lacked mammal-crunching tooth, says Bianucci.

The findings hints that cetacean-hunting predators developed independently in each killer and false killer whales throughout the second half of the Pleistocene, starting about 1.3 million years in the past, says Bianucci.

The discover is vital, he says, as a result of it would assist overturn a preferred concept that baleen whales, equivalent to blue and humpback whales, grew to become gigantic in dimension with the intention to keep away from assault by killer whales. The baleen whales had been already big by about 3 million years in the past – lengthy earlier than Bianucci believes the orcas and false killer whales started searching them.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2022.02.041

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