adapiform
Adapiformes is a group of early primates. Adapiforms radiated throughout much of the northern continental mass (now Europe, Asia and North America), reaching as far south as northern Africa and tropical Asia. They existed from the Eocene to the ...
primate
Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s from the early
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
of
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
and
Europe
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
. It is extremely well represented in the fossil record in North America and has been hypothesized to be the direct ancestor of ''
Notharctus
''Notharctus'' is a genus of Adapiformes, adapiform primate that lived in North America and Europe during the late to middle Eocene.
The body form of ''Notharctus'' is similar to that of modern rats. Its fingers were elongated for clamping onto ...
'' 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
''Smilodectes'' is a genus of Adapiformes, adapiform primate that lived in North America during the middle Eocene. It possesses a post-orbital bar and grasping thumbs and toes. ''Smilodectes'' has a small cranium size and the foramen magnum was l ...
''. 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 ''Cantius'' can be considered a sexually dimorphic species. Specifically, ''C. torresi'' lower canines clearly demonstrate sexual dimorphism in having a male/female
anine
is a Traditional animation, hand-drawn and computer animation, computer-generated animation originating from Japan. Outside Japan and in English, ''anime'' refers specifically to animation produced in Japan. However, , in Japan and in Ja ...
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'' 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
Big or BIG may refer to:
* Big, of great size or degree
Film and television
* ''Big'' (film), a 1988 fantasy-comedy film starring Tom Hanks
* ''Big'', a 2023 Taiwanese children's film starring Van Fan and Chie Tanaka
* ''Big!'', a Discovery C ...
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
Notharctidae is an extinct family (biology), family of Adapiformes, adapiform primates found primarily in North America and Europe.
Classification
*Family Notharctidae
**Subfamily Asiadapinae
**Subfamily Cercamoniinae
**Subfamily Notharctinae
...
. 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
In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...