22 Archaic dolphin connects oceans of Zealandia to endangered river resident

Cetacea, Waipatiidae: Waipatia maerewhenua

The seas around Zealandia were rich with a diversity of whale and dolphin species during the Oligocene. The beds of these ancient seas were later uplifted and now form the iconic limestone landscape of North Otago and South Canterbury. In the early 1990s Ewan Fordyce developed a field program supported by the National Geographic Society which sought to learn more about the diversity of life in these ancient seas from the fossils in these Oligocene rocks. By 1994 the bones from a fossil dolphin named Waipatia maerewhenua had been described, revealing an incredible connection between the fossils of North Otago and a species living today in the Ganges River, India.

Skull of Waipatia maerewhenua (specimen OU 22095). Image credit: RE Fordyce.

The location of the Waipatia maerewhenua fossil was first revealed when an earbone and some teeth were found in an outcrop of limestone. Ewan Fordyce, Andrew Grebneff and Bob Connell spent two days excavating the fossil to reveal a skull lying upside down, with the upper jaws crossed over the skull. Many loose teeth were found along with more ear bones and a few fragments of bones from the skeleton behind the head. In the laboratory, it took Andrew Grebneff several months to excavate all the bones from the rock.

Did you know there is a 3D printable model of this fossil for you to view online and download? Follow this link to learn more: 3D model—Archaic dolphin connects oceans of Zealandia to endangered river resident.

Waipatia maerewhenua has a well-preserved skull that is about 600 mm long. The skull has a long and broad-based snout, small triangular teeth, and a face that is a slightly different shape on the left side compared to the right. The eyes sit on the side of the skull. The blowhole sits above the eyes and in life would have been surrounded by muscles that helped to produce high-frequency echolocation sounds. Each lower jaw has a region of thin bone by the hinge with the upper skull. In life, this thin pan bone was probably filled with fatty tissue which helped transmit sound from the side of the head towards the ear region.

Waipatia answered some important questions in dolphin evolution. For more than a century, small dolphin teeth had been known from Oligocene rocks around the world. Waipatia revealed the sort of skull to which such small teeth belong. Importantly though, Waipatia also revealed the existence of a previously unknown taxonomic family within the toothed-whales. The closest living relatives of Waipatia appears to be the endangered Ganges River dolphin Platanista gangetica.

The unique specimen of Waipatia maerewhenua is on loan to Tūhura Otago Museum in Ōtepoti Dunedin and may be seen in the Southern Land, Southern People gallery. A cast and interpretive graphics are displayed at the Vanished World Centre, Duntroon, North Otago.

—Written by Daniel B Thomas