Janjucetus hunderi

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Janjucetus hunderi


© @ Brian Choo

Temporal range: Late Oligocene (Chattian: ~25Ma)

Scientific classification:

Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Suborder: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Boreoeutheria
Superorder: Laurasiatheria
Clade: Ungulata
Clade: Paraxonia
(unranked): Cetartiodactyla
Suborder: Mysticeti
Family: †Mammalodontidae
Genus: †Janjucetus
Species: †J. hunderi

Janjucetus hunderi is a species of mammalodontid mysticete that lived in Australia during the Late Oligocene. Like its fellow mammalodontid Mammalodon itself, it was a toothed baleen whale and was likewise rather small for a mysticete (~3.5 meters long). However, unlike Mammalodon, it wasn't a suction feeder. Instead it was a macrophagous predator as indicated by certain features it possessed. Janjucetus had well-developed, recurved, and incrassate teeth that were deeply rooted. The incisors and canines also had "mesial and distal carinae and sharp longitudinal ridges on their labial and lingual surfaces" and the premaxillary incisors were oriented in a robust rosette. The premolars and molars were also sharp (they also sheared) and there was a lot of room for temporalis muscles. The skull was quite triangular in shape from dorsal view with a short rostrum that wasn't dorsoventrally flattened. Incidentally, some of these features imply Janjucetus was a predator that relied on delivering powerful bites to kill prey. The skull also shows that Janjucetus was likely incapable of echolocation, but in exchange, its relatively large orbits suggest it relied on well-developed eyesight to locate prey. Janjucetus aids in demonstrating the notion that mysticetes had initially experimented with different niches before they generally became baleen-possessing filter feeders.[1]

References:

[1] "A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales" (Fitzgerald, 2006).

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Ancient whales did not filter feed with their teeth
David P. Hocking, Felix G. Marx, Erich M. G. Fitzgerald, Alistair R. Evans

The origin of baleen whales (Mysticeti), the largest animals on Earth, is closely tied to their signature filter-feeding strategy. Unlike their modern relatives, archaic whales possessed a well-developed, heterodont adult dentition. How these teeth were used, and what role their function and subsequent loss played in the emergence of filter feeding, is an enduring mystery. In particular, it has been suggested that elaborate tooth crowns may have enabled stem mysticetes to filter with their postcanine teeth in a manner analogous to living crabeater and leopard seals, thereby facilitating the transition to baleen-assisted filtering. Here we show that the teeth of archaic mysticetes are as sharp as those of terrestrial carnivorans, raptorial pinnipeds and archaeocetes, and thus were capable of capturing and processing prey. By contrast, the postcanine teeth of leopard and crabeater seals are markedly blunter, and clearly unsuited to raptorial feeding. Our results suggest that mysticetes never passed through a tooth-based filtration phase, and that the use of teeth and baleen in early whales was not functionally connected. Continued selection for tooth sharpness in archaic mysticetes is best explained by a feeding strategy that included both biting and suction, similar to that of most living pinnipeds and, probably, early toothed whales (Odontoceti).

rsbl.royalsocietypublishing.org/content/13/8/20170348