as nocturnal, as its orbital dimensions fall well-above the distribution of extant nocturnal primates. Taxonomy There are currently 11 recognized species of Cantius: C. abditus, C. angulatus, C. eppsi, C. frugivorous, C. mckennai, C. nunienus, C. ralstoni, C. savagei, C. simonsi, C. torresi, C. trigonodus. The earliest of these species (for North American Cantius) is believed to be C. torresi, which has laso been reconstructed as the smallest species within the genus (with C. eppsi being closest in size). Thus, considering the gradual pattern of body size increase documented in the Cantius lineage, C. torresi is likely to be considerably older than the later species, if not the oldest species. Along with the size comparison, C. torresi remains were identified within the Big Red Sequence within the Bighorn Basin PETM chart, thus restricting it to a geologic age older than later Cantius species. Morphological change and key taxa The established age and antiquity of the Cantius lineage reveals an interesting and well-resolved timeline of adaptation and evolutionary change within Notharctidae. Noteworthy and well-studied species of Cantius include C. torresi and C. abditus. C. torresi, the oldest confirmed species of Cantius, exhibits sexual dimorphism in the canines body size. Thus, it can be inferred that Cantius (and its descendants) were polygynous. After a nearly complete C. abditus skull was discovered in the Early Eocene Willwood Formation of the Bighorn Basin, where many fossils of several species of Cantius have been found, the geologic age of the fossil was ascertained and a comparative study was conducted. The study revealed that C. abditus was roughly 2 million years younger than the older species of Cantius to which it was compared. Moreover, the reconstructed body mass of C. abditus was estimated to be ~3000 grams, which is larger than earlier Cantius species, and thus conforming to the well-documented pattern of gradual body size increase within the lineage. Through comparison of C. abditus, various other species of Cantius, Notharctus, and Smilodectes, researchers were able to identify near identical features in the auditory regions of these species, as well as that of extant lemurs. References Prehistoric strepsirrhines Eocene primates Prehistoric primate genera Fossil taxa described in 1962 Extinct mammals of Europe