Homologous and Analogous Structures
The toothcomb, a special morphological arrangement of teeth in the anterior lower jaw, is best known in extant strepsirrhine primates, which include lemurs and lorisoid primates (collectively known as lemuriforms). This homologous structure is a diagnostic character that helps define this clade (related group) of primates. An analogous trait is found in the bald uakari (Cacajao calvus), a type of New World monkey.
Toothcombs can also be found in colugos and treeshrews, both close relatives of primates; however, the structures are different and these are considered to examples of convergent evolution. Likewise, small- or medium-sized African antelopes, such as the impala (Aepyceros melampus), have a similar structure sometimes referred to as the "lateral dental grooming apparatus". Living and extinct hyraxes (hyracoids) also exhibit a toothcomb, although the number of tines in the comb vary throughout the fossil record.
Dating to the Eocene epoch over 50 mya, Chriacus and Thryptacodon—two types of arctocyonids (primitive placental mammals)—also possessed an independently evolved toothcomb.
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