Plagiaulacoid

A plagiaulacoid is a type of blade-like, usually serrated tooth present in various mammal groups, usually a premolar. Among modern species it is present chiefly on diprotodontian marsupials (specifically, Potoroidae, Bettongia and Burramys), which have both the upper and lower first premolars converted into serrated blades. However, various other extinct groups also possessed plagiaulacoids, such as multituberculates, some "Plesiadapiformes" such as Carpolestes and various metatherians such as Epidolops and various early diprotodontians. In many of these only a lower premolar became converted into a blade, while the upper premolars showed less speciation.

The various independent development of these teeth is considered a good example of convergent evolution.

Multituberculates in particular probably own the most specialised of all plagiaulacoids. In early taxa all lower premolars became plagiaulacoids, forming a "saw"-like arrangement. However, in Cimolodonta premolars 1-3 degenerated and became peg-like or disappeared altogether; instead, only the fourth lower premolar remained, which increased in size. While earlier multituberculates displayed a normal tooth replacement for their plagiaulacoids, in cimolodonts this tooth was not replaced, being the last tooth to erupt and remaining through the animal's life.

Most taxa with plagiaulacoids are omnivores with granivore tendencies; as such, it i speculated that plagiaulacoid premolars evolved to help these mammals break or saw through tough seeds and other tough plant matter with precision, as well as to help manipulate food items in the mouth. Modern diprotodontian marsupials often use their plagiaulacoids this way.

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