Janjucetus

The holotype of Janjucetus was found in Australia in the late 1990s by a teenaged surfer named Staumn Hunder, near the Victorian township of Jan Juc, in marine sediment that was deposited 26.05–24.2 million years ago (mya) in the Late Oligocene. In June 2019, a partial cetacean skull was recovered from the lowest beds of the Jan Juc Marl by Ross Dullard, who prepared the specimen and subsequently donated it to Museums Victoria in August of that same year. Catalogued as NMV P256471, this would become the type specimen of the new species Janjucetus dullardi. The elements of the skull were found in close association, including bones of the ear, jaws, and teeth. The species was named in honour of Ross Dullard. ==Description==

Janjucetus is estimated to have been about in length, about the size of the modern bottlenose dolphin (Tursiops spp.) and much smaller than any living baleen whale. The snout was broad and triangular, and was not flattened or elongated like those of modern baleen whales. The upper jaw (maxilla) made up around 79% of the snout. The two halves of the lower jaw were fused (mandibular symphysis), as opposed to the flexible mandibular symphysis of modern baleen whales which allows them to significantly increase the size of their mouth. Compared to archaeocetes, primitive whales, the snout is wider, which may have been a precursor to the large mouths of modern baleen whales. Like other baleen whales, Janjucetus did not possess the ability to echolocate; however, it may have had a large line of fat along its lower jaw, similar to modern toothed whales (Odontoceti), which would mean it could detect ultrasonic signals. It had unusually large eyes for baleen whales compared to its body size, which were positioned high up on the skull; likewise, it probably relied on good eyesight instead of echolocation to navigate. Janjucetus did not have baleen, and instead had large teeth. The incisors and canines formed a row of conical stabbing teeth, while the premolars and molars were shaped like serrated blades. The teeth were deeply rooted, and the cheek teeth had two roots, perhaps adaptations for handling large prey. The teeth decreased in size towards the back of the mouth. It had sizable temporalis muscles, indicated by their location on the top of the head, meaning it had a strong bite. It had four or six incisor teeth, two canine teeth, eight premolars, and four or six molars in the upper jaw. The teeth had heavily ridged enamel, and upper teeth were more widely spaced apart than the lower teeth. ==Classification==

Janjucetus is considered to be a baleen whale (Mysticeti), despite not having baleen, due to key synapomorphies of the skull anatomy, for example in the way the nasal bones meet the bones of the braincase. Janjucetus is one of two genera, along with the extinct Mammalodon which is also from south-eastern Australia, in the family Mammalodontidae. Janjucetus was initially assigned to its own monotypic family, Janjucetidae, but a subsequent cladistic analysis by Fitzgerald in 2010 reassigned it to the Mammalodontidae, making Janjucetidae a junior synonym. Janjucetus is one of the six toothed baleen whales of the Oligocene, the other being M. colliveri, M. hakataramea, Chonecetus, Aetiocetus and Llanocetus. A phylogenetic tree showing the position of Janjucetus within Cetacea is reproduced below. ==Palaeobiology==

(Canis lupus dingo), the crabeater seal (Lobodon carcinophaga) and Janjucetus using three-dimensional surface models Unlike other baleen whales, Janjucetus did not use baleen to filter feed, and instead used teeth to catch large prey such as fish and sharks. Its skull morphology seems to be convergent with the modern-day leopard seal (Hydrurga leptonyx), and so it may have used a similar grip-and-tear feeding method. ==Palaeoecology==

Jan Juc Beach, where Janjucetus was discovered, also has yielded some fragmentary vertebrate species, such as sharks, rays and teleost fish. A couple of unidentified bird fossils have been found. Other than Mammalodon, the other cetacean remains found there were those of Prosqualodon and Waipatia. ==See also==