(CNN)Dolphins may seem cute and friendly, but the largest member of the dolphin family is actually none other than the ultimate hunter of the sea — the killer whale, also known as an orca.
An extinct giant dolphin behaved like a killer whale, study finds
Now researchers have confirmed that an ancient dolphin that lived during the Oligocene Epoch — 33.9 million to 23 million years ago — was the first cetacean (a type of mammal) using echolocation to navigate underwater and fill the role of apex predator, much like the current-day killer whale.
Echolocation allows dolphins to "see" through sound underwater. They do so by emitting calls to locate distant objects in the water, then interpret the echoes of sound waves that bounce off of those objects.
The skeleton helps to fill the gaps in the evolutionary narrative of these marine mammals who returned to the sea.
Cetaceans are an order of mammal including dolphins, whales and porpoises. Odontocetes, or toothed whales, are an order of cetaceans that includes dolphins, porpoises and all other whales that have teeth, such as sperm whales.
The specimen, named Ankylorhiza tiedemani, was discovered partly in rock formations in South Carolina, said the study published Thursday in the journal Current Biology.
Its 15-foot-long body size, a shorter and stronger snout, tooth wear and vertebral formation indicated that Ankylorhiza was the first Odontocete predator that could eat both small- and large-bodied prey and swim faster than other whales. This indicates for the first time that it was one of the few extinct cetaceans to fulfill an ecological position similar to that of killer whales.
"We see that same pattern in the fossil record of terrestrial carnivores," said Anthony Friscia, an adjunct associate professor of integrative biology and psychology at the University of California, Los Angeles, who wasn't part of the study.
"For instance, you see a 'cat-like' predator arise many different times before you get the modern radiation of cats. This kind of repeated evolution of similar ecologies is the basis of so many studies of how evolution works in the long term."
The rarity of Oligocene Epoch whale skeletons has hindered research efforts to understand the evolution of modern whales' locomotion that is powered by their flukes (tails) but controlled by their forelimbs, the study said.
"We have been waiting for such fossils for decades," said Olivier Lambert, director of operations of Earth and History of Life and Evolution of the Paleobiosphere at the Royal Belgian Institute of Natural Sciences. Lambert wasn't involved in the research.
The skeleton suggested that the features involving their flippers and locomotion might have evolved more recently than 35 million years ago, which was the previous assumption, said study coauthor Robert Boessenecker, a research associate and adjunct instructor in the department of biology and environmental geosciences at the College of Charleston in South Carolina.
"If you're a mammal or reptile invading the water, there's only a certain number of things you can do in order to evolve efficient swimming. And those same features have convergently evolved again and again in different groups," Boessenecker explained. "In this case, they even continued evolving into parallel lineages with common ancestry."
In the 1880s, the partial snout of the dolphin — a toothed whale in the group Odonoceti — was recovered during dredging of the Wando River in South Carolina.
The first skeleton of the dolphin was discovered in the 1970s by then and late Charleston Museum Bunting Natural History curator Albert Sanders. Another nearly complete skeleton, described in the current study, was unearthed during the 1990s, when paleontologist Mark Havenstein found it during construction of a housing subdivision in South Carolina.