New species of prehistoric toothless dolphins discovered

Scientists have discovered a new species of a toothless dwarf dolphin in the US that lived about 28-30 million years ago.
The species named Inermorostrum xenops lived during the same period as Coronodon havensteini, a species of ancient whale announced recently, researchers said.
The skull of Inermorostrum was discovered by a diver in the Wando River in Charleston and presents the first clear evidence of suction feeding in echolocating sea mammals.
Researchers estimate that the dolphin grew to be only four feet long, smaller than its closest relatives, and significantly smaller than today's bottlenose dolphins, which measure seven to twelve feet in length.

The dwarf dolphin had a short snout and entirely lacked teeth, said Robert W Boessenecker, geology professor at College of Charleston in the US.
The genus name, Inermorostrum xenops, means "defenseless snout", referring to its toothless condition. The team believes that the suction-feeding dolphin fed primarily on fish, squid, and other soft-bodied invertebrates from the seafloor, similar to the feeding behavior of a walrus.

Furthermore, a series of deep channels and holes for arteries on the snout indicate the presence of extensive soft tissues, likely enlarged lips, and also perhaps even whiskers, researchers said.
"We studied the evolution of snout length in cetaceans, and found that during the Oligocene (25-35 million years ago) and early Miocene epochs (20-25 million years ago), the echolocating whales rapidly evolved extremely short snouts and extremely long snouts, representing an adaptive radiation in feeding behavior and specializations," Boessenecker said.

"We also found that short snouts and long snouts have both evolved numerous times on different parts of the evolutionary tree - and that modern dolphins like the bottlenose dolphin, which have a snout twice as long as it is wide, represent the optimum length as it permits both fish catching and suction feeding," he added.
The discovery is an important step in understanding why the South Carolina Coast provides unique insights into cetacean evolution, researchers siad.
"Coronodon, a filter feeder whale, and Inermorostrum, a suction feeding dolphin, may well have fed on the same prey," said, Jonathan Geisler, an associate professor at New York Institute Of Technology in the US.

The study was published in the journal Proceedings of the Royal Society B.