filter feeding. However, its teeth may have interlocked, much like those of the modern-day filter-feeding crabeater seal (Lobodon carcinophaga), which would have allowed some filter-feeding behaviour. Its hunting behaviour was probably similar to the modern-day leopard seal (Hydrurga leptonyx), probably eating large fish. Like baleen whales, Janjucetus could not echolocate; however, it did have unusually large eyes, and so probably had an acute sense of vision. The only specimen was found on the Jan Juc beach, where the remains of the extinct whales Mammalodon, Prosqualodon and Waipatia
have also been discovered.
Discovery and naming
Restoration of Janjucetus
The only known
Late Oligocene. The name Janjucetus hunderi honours both the township and the discoverer. Hunder is said to have seen the brown fossils on a boulder while he surfed. Soon after discovering the site, Hunder and his father removed the boulder and transported it to Monash University for further research. The well-preserved fossil remains, specimen NMV P216929, include a nearly complete skull, mandibles, vertebrae, ribs, scapulae and a radius, and are held in the Museums Victoria Palaeontology Collection in Melbourne. It was formally described by Erich Fitzgerald in 2006, and it represents the most complete Paleogenecetacean fossil from Australia.[1][2]
Description
Restoration of Janjucetus
Janjucetus is estimated to have been about 3.5 m (11 ft) in length, about the size of the modern
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.[1][3][4]
Janjucetus did not have
evolutionary dead-end given the later proliferation of baleen-bearing baleen whales.[5]
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.[6]
Palaeoecology
Comparison of teeth of the dingo (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.[2] 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.[1][7]
However, it is possible that the front teeth interlocked, and the cheek teeth sheared against each other when the mouth was closed, which perhaps allowed the whale to filter feed similar to the modern day crabeater seal (Lobodon carcinophaga). This may have been a precursor to the evolution of baleen and associated feeding habits. The head of Janjucetus is similar to the wide and blunt heads of modern-day, suction-feeding toothed whales, indicating it could suction feed.[1][7]
Palaeobiology
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.[1]
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