Over the last thirty years, a number of important baleen whale fossils have been reported from Oligocene marine rocks in the Pacific Northwest, Japan, and South Carolina which have bridged the anatomical gap between basilosaurid archaeocetes and Miocene “cetotheres”. These included toothed baleen whales such as the aetiocetids (Aetiocetus, Chonecetus, Morawanacetus), mammalodontids (Janjucetus, and Mammalodon – described in the 30’s but more recently identified as a mysticete), and the earliest toothed mysticete Llanocetus. However, there still appeared to be a large anatomical gap between these toothed mysticetes and the baleen-bearing “cetotheres” of the Miocene – which, for all intents and purposes, look like modern baleen whales.
Skulls of the toothed mysticete Aetiocetus weltoni (Late Oligocene, Washington, USA) and a typical Miocene "cetothere", Isanacetus laticephalus (Early Miocene, Japan).
In 2002, Al Sanders and Larry Barnes described a new genus and species of toothless mysticete from the late Oligocene of South Carolina. Eomysticetus whitmorei (named after the late paleocetologist Frank Whitmore) has a nearly 2 meter skull, with an elongate, narrow palate, and a blowhole placed very far forward on the snout. Furthermore, the braincase of Eomysticetus is very narrow, with enormous muscle attachment areas for the temporal musculature – the jaw closing muscles. Ten years later, a new genus and species of eomysticetid was reported from similarly aged rocks in Japan by Okazaki (2012), who named Yamatocetus canaliculatus. Although the earbones of Yamatocetus are not very well prepared – unlike the well preserved earbones of Eomysticetus – the skull is otherwise virtually complete, unlike the rather fragmentary skull of Eomysticetus.
The type skull of Eomysticetus whitmorei (Late Oligocene, South Carolina, USA) on the left, and the type of Yamatocetus canaliculatus (Late Oligocene, Japan) on the right, with interpretive anatomical illustrations.
Starting in the 1980’s my Ph.D. adviser Ewan Fordyce
collected numerous strange, long snouted baleen whales that belonged to a
then-unknown family – later appearing to belong to the Eomysticetidae. These
fossils helped identify some problematic species of baleen whales described by
Brian J. Marples in 1956. Marples described three new species of Mauicetus
– Mauicetus lophocephalus (represented by a partial skull, mandible,
tympanic bullae, and postcrania), Mauicetus waitakiensis (very partial
skull, tympanic bullae, and some cervical vertebrae), and the underwhelming Mauicetus
brevicollis (vertebrae, scapula). The type species – Mauicetus parki,
described by professor Benham in 1939 – is now known to represent a latest
Oligocene/earliest Miocene “cetothere” like baleen whale. Mauicetus
lophocephalus and Mauicetus waitakiensis, on the other hand, are a
bit more archaic and resemble Eomysticetus and some of the material
collected more recently from New Zealand. This indicates that these two species of Marples are in need of new genus names
Illustrations and a photograph of the holotype specimen of "Mauicetus" lophocephalus, from Marples (1956). A speculative line drawing is at left, and stipple drawings of the left tympanic bulla are in the middle; the skull, photographed at right, has been missing since the mid 1970's or longer.
The purpose of my Ph.D. thesis is to describe this rather impressive collection of eomysticetids from New Zealand, conduct a cladistic analysis to place them within a phylogenetic analysis, determine their feeding ecology based on the functional anatomy of the feeding apparatus, in addition to some details of their taphonomy. I’ll be presenting some preliminary results of this research later this fall and winter at the annual meetings of the Society of Vertebrate Paleontology in Los Angeles and the Society for Marine Mammalogy here in Dunedin.
Benham, W.B. 1937. On Lophocephalus, a new genus of zeuglodont Cetacea. Transactions and Proceedings of the Royal Society of New Zealand 67:1-7
Marples, B.J. 1956. Cetotheres (Cetacea) from the Oligocene of New Zealand. Proceedings of the Zoological Society of London 126:565-580.
Okazaki, Y. 2012. A new mysticete from the upper Oligocene Ashiya Group, Kyushu, Japan and its significance to mysticete evolution. Bulletin of the Kitakyushu Museum of Natural History and Human History Series A (Natural History) 10:129-152.
Sanders, A.E. and Barnes, L.G. 2002. Paleontology of the Late Oligocene Ashley and Chandler Bridge Formations of South Carolina, 3: Eomysticetidae, a new family of primitive mysticetes (Mammalia: Cetacea). Smithsonian Contributions to Paleobiology 93:313-356.