New Zealand’s 25 million year old “Dawn Whales”

Robert
Katz

Guest Writer

Twenty-five million year old rocks in New Zealand have yielded two species of archaic baleen whale. These whales, both members of the genus Tohoraata, retained teeth at the tips of their jaws in addition to baleen.

The evolution of whales is one of the most intriguing stories in natural history. Shortly after the extinction of the non-avian dinosaurs, mammals diversified to fill the niches that were left by their reptilian predecessors. Some of those mammals took advantage of the abundant resources found in the shallow water. Over time, evolved such a dependency on their new habitat that they would lose their limbs. These were the first whales, which appeared a mere 10-15 million years after the K/Pg extinction – an incredibly short amount of time for such drastic changes in morphology and physiology.

The most specialized whales are undoubtedly the baleen whales. These marine mammals are characterized by a highly specialized tissue growing from their palates. They lost their teeth in favor of keratinous gum tissue which has evolved into massive walls of bristly, thin plates called baleen, or whalebone. These huge rows of baleen act as sieves, straining out tiny prey such as krill and baitfish from the water. This feeding strategy, engulfing whole shoals protein in one mouthful, has led to the massive size of these whales – the blue whale, a filter-feeder, is not only the largest whale and the largest mammal, but the largest animal to ever live.

Paleontologists from New Zealand have recently identified a pair of ancestral baleen whales, and have shown that this remarkable adaptation evolved not very long after true whales themselves evolved. They belong to the new genus Tohoraata, represented by two species: T. raekohao and T. waitakiensis. These whales, members of the extinct family Eomysticetidae (the “dawn mysticetes”, Mysticeti being the modern order of baleen whales), lived in the shallow, warm waters of Zealandia 27-25 million years ago, during the Oligocene.

This period immediately follows the Eocene, when whales first evolved, so the adaptation for filter feeding seems to have evolved quickly for a major adaptation. Tohoraata was a small, slender whale, similar in length to the modern minke, but much more serpentine. Its lighter build, along with its slender jaws which were anchored with strong muscles, may suggest that it was a much more active predator than larger baleen whales, which rely on their huge size to capture as much prey as possible. Its smaller braincase and relatively primitive hearing capabilities, similar to even earlier whales rather than more derived ones, suggest that its senses were not as highly-developed as those of more modern whales. This, however, is to be expected – modern whales are extremely derived animals, fine-tuned for a wholly marine lifestyle.

Tohoraata raekohao was collected from the Kokoamu Greensand near Duntroon, NZ, a site that preserves a diversity of early Cenozoic marine life. In addition to the two species of Tohoraata, two other Oligocene whales are known from the formation, as well as a handful of early penguin fossils. The abundance of marine invertebrate fossils here also indicate a rich marine ecosystem. While T. raekohao was collected recently, T. waitakiensis, a slightly older species, was identified from fossils collected in the 1940s and ’50s. These fossils were labeled as another Oligocene baleen whale, Mauicetus.

Due to the fragmentary nature of T. waitakiensis, it is likely that its fossils were lumped with Mauicetus for convenience’s sake at the time – however, upon closer inspection and comparison to the newfound T. raekohao, it is clear that these two are not only closely-related, but belong in a different family altogether from Mauicetus itself.

The discovery of Tohoraata raekohao and reanalysis of T. waitakiensis shows that early baleen whales gradually moved from hunting to suspension feeding. Surely new discoveries will allow us to expand our understanding of these incredible animals.

Reference

Robert W. Boessenecker, R. Ewan Fordyce. A new Eomysticetid (Mammalia: Cetacea) from the Late Oligocene of New Zealand and a re-evaluation of ‘Mauicetus’waitakiensis. Papers in Palaeontology, 2014; DOI: 10.1002/spp2.1005

Image Credit: Robert Boessenecker

Robert
Katz

Guest Writer

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New Zealand’s 25 million year old “Dawn Whales”

Robert Katz

Guest Writer

Robert Katz

Guest Writer

Robert
Katz

Robert
Katz