Cantius is a genus of adapiform primates from the early Eocene of North America and Europe. It is extremely well represented in the fossil record in North America and has been hypothesized to be the direct ancestor of Notharctus in North America. The evolution of Cantius is characterized by a significant increase in body mass that nearly tripled in size. The earliest species were considered small-sized and weighed in around , while the later occurring species were considered medium-sized and likely weighed in around . Though significantly smaller, the fossil remains discovered of the various species of Cantius have striking similarities to that of Notharctus and Smilodectes. It is likely Cantius relied on arboreal quadrupedal locomotion, primarily running and leaping. This locomotor pattern comparable to that of extant lemurs, which has fostered the hypothesis that Cantius and other strepsirrhine adapiforms may have a close phylogenetic affinity to living lemurs. Description The upper and lower dental formula of Cantius consisted of two incisors, one canine, four premolars, and three molars. In the lower molars, it is common to see a trigonid consisting of three cusps as well as a broad-basined talonid. The upper molars are interesting for North American species of Cantius, as earlier species had simple tritubercular teeth while the later species develop a pseudohypocone from the postprotocingulum (also known as the nannopithex fold). Given its unfused mandibular symphysis and molar cusp morphology, it has been inferred that Cantius was likely a frugivore that consumed fruit (as opposed to a folivorous diet of leaves and other plant material). Cantius also exhibits canine dimorphism, with males possessing relatively larger canine teeth than females. Thus Catnius can be considered a sexually dimorphic species. Specifically, C. torresi lower canines clearly demonstrate sexual dimorphism in having a male/female [canine] length ratio that falls within the range of an expected dimorphic primate. The postcranial skeletal anatomy of Cantius suggests it was arboreal quadruped capable of running and leaping. This locomotor behavior of Cantius has been interpreted from its relatively long ischium and much more distal inferior tibial tuberosity. These features indicate that Cantius was capable of powerful extension of the thigh and flexion at the knee. These actions were crucial for the locomotor and postural behavior of Cantius. The orbits of Cantius have fueled a long-standing debate regarding the activity pattern of the extinct adapiform. After examination of orbital shape and depth, researchers interpreted Cantius