New Zealand paleontologists said on Friday that they had identified previously unknown ancient whale species that could help to explain the evolution of the creatures.
University of Otago researchers said they had described two further genera and three species of fossil baleen whales found in the South Island.
They had named these newly described filter-feeding baleen whale species Waharoa ruwhenua, Tokarahia kauaeroa and re- identified Tokarahia lophocephalus, a poorly known species discovered in the 1950s.
All were eomysticetids, a whale family occupying an important position in the evolutionary tree of cetaceans, and Tokarahia appeared to be a transitional fossil between primitive toothed baleen whales and modern baleen whales.
The filter-feeding whales lived around 25 million to 30 million years ago when the continent of Zealandia was just low islands surrounded by shallow seas.
"The skulls of these three specimens were spectacularly preserved, revealing that eomysticetids had unusually long and delicate surfboard-like snouts, with blowholes placed far forward on the skull, and enormous attachment areas for jaw muscles," Dr. Robert Boessenecker said in a statement.
The delicate nature of the jaws and skulls indicated they were likely not "lunge feeders" like humpback whales, but were adapted for skim feeding.
"They would have been a sort of slow-cruising vacuum cleaner for krill," he said.
The adult size of the whales was estimated to be between five and six meters long.
The discovery helped to fill in an important gap in the history of the evolution of primitive toothed whales into baleen whales.
Tokarahia kauaeroa had skeletal features falling between those of primitive "archaeocete" whales and modern baleen whales.
"They fill in major gaps of knowledge, anatomy, growth, paleoecology, in whale evolution between 'toothy' archaeocete ancestors and toothless modern species," he said.
Prof. Ewan Fordyce said these "dawn" baleen whales probably ranged south into the richly productive waters of the Southern Ocean, newly developed after the last remnants of the Gondwana continents broke apart.
"These early baleen whales are children of climate change since their history is linked closely to an Antarctic cooling pulse that led to the development of modern ocean circulation," he said in the statement.