Mammalodontidae

Mammalodontidae Temporal range: Late Oligocene
Skull of Janjucetus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Infraorder:	Cetacea
Parvorder:	Mysticeti
Family:	†Mammalodontidae Mitchell, 1989
Genera
Janjucetus Mammalodon
Synonyms
Janjucetidae Fitzgerald, 2006

Mammalodontidae is a

There are currently two genera in this family: Janjucetus and Mammalodon. After a new cladistic analysis by Fitzgerald (2010), Janjucetus was transferred into Mammalodontidae, thereby making Janjucetidae a junior synonym of Mammalodontidae.^[1]

Analysing the jaw morphology of the toothed mysticetes, Fitzgerald 2012 found eight mandibular characters unique to the members of Mammalodontidae:^[3]

• the mandibular symphysis is short, has a rugose joint surface, but lacks a symphyseal groove. In archaeocetes the symphysis is long. In modern mysticetes, in contrast, the symphysis is very small, its joint surfaces are smooth, and there is a groove on the interior side of the mandible that accommodates the symphyseal ligament which enables them to open their mouth wide.
• the external foramina on the mandible are relatively large (smaller or absent in later mysticetes)
• the postcanines sit in a longitudinal groove flanked by a lateral edge (the "alveolar margin")
• the alveolar (upper) margin forms an angle with the ventral (lower) margin (like in archaeocetes)
• the ventral margin is straight in the posterior half of the mandible
• teeth have longitudinal ridges
• posterior postcanines have two roots joined below the crown base
• postcanines are densely packed without long
  diastemata

From these mandibular features, Fitzgerald 2006 concluded that in mysticetes enlarge oral cavities adapted for

, like for example, kinetic jaw joints.

References

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