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GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



the oblique facet for the tibia on the top of the astragalus. This denotes greater activity and 

 freedom of movement than is displayed by the slow climbing opossums. This primitive arboreal 

 placental stage by adaptive radiation probably gave rise to the various orders of terrestrial unguiculate 

 and ungulate placentals most of which were already well differentiated at the opening of the Paleocene 

 record. 



(5) Upper Cretaceous. (Predicated from indirect anatomical and palseontological evidence.) 

 Primitive tupaioid or pre-Primate stage, represented by more or less specialized descendants (Plesiadapidse, 

 Mixodectidse) in the Paleocene and Lower Eocene. Beginning of advanced arboreal specializations. 

 Phalanges elongate and slender, but claws retained. Pads and friction ridges essentially as in lemuroids, 

 but terminal digital pads not so much expanded. The animals leap actively among the branches. 



(6) Paleocene (?) and Lower Eocene. Primitive lemuroid stage, described in preceding pages. 

 Distinguished from (5) by the still more advanced specializations for grasping, leaping, and perching. 

 Hallux strongly divergent, with very large process for attachment of peroneus longus muscle. Finger 

 tips, ungual phalanges and nails more or less expanded. Phalanges elongate, heads of metapodials ball- 

 like. The animals leap actively among the branches but do not sit altogether upright. Notharctinse, 

 Adapinse and their Paleocene ancestors. This central type probably gave rise to the following branches: 



(7 A) Lower Eocene to Recent. Hopping arboreal types with elongate astragalus and cuboid. 

 Tarsioids, Galagininse. 



(7B) Oligocene (?) to Recent. Far-leaping arboreal lemurs finally with very long hands and 

 feet and extreme specializations for grasping and perching: Lemuridse, Indrisidae. Chiromys in limb 

 structure is merely a specialized member of this group. 



(7C) Oligocene (?) to Recent. Lethargic clinging lemuroids with secondarily shortened tarsus: 

 Lorisinae. 



{7D) Pleistocene to Recent. Gigantic lemurs with very stout and secondarily shortened Umb 

 bones and large hands and feet: Megaladapis. 



{7E). Eocene or Oligocene to Recent. Very agile climbing and running monkeys using the 

 hands as such rather than as mere clinging organs. Entepicondylar foramen often lost, humerus with 

 long cylindrical shaft, low crests and spherical head. Third trochanter of femur reduced or absent: 

 primitive Cebidae and undiscovered Eocene ancestors of the catarrhine primates. In this stage the 

 specializations for leaping and grasping become overlaid by specializations for running lightly on the 

 branches and for sitting upright. This stage gives rise to: 



(8A) Miocene (?) to Recent. Small squirrel-like forms, using the secondarily compressed nails 

 as claws in climbing: Hapalidae. 



(8B) Oligocene (?) and Miocene to Recent. Subterrestrial, cursorial and more or less quad- 

 rupedal types: baboons. 



(8C) Miocene (?) to Recent. Thumbless, narrow-handed types, using the hands both as hooks 

 and as feet. Tail long, more or less prehensile: Ateles, Colobus. 



(8D) Upper (?) Eocene. Brachiating acrobatic types, sitting upright; tail vestigial; perfected 

 supination of fore limb; thumbs more or less opposable: Ancestral man-anthropoid stock. From this 

 stage was derived: 



(9A) Miocene to Recent. Extremely long-limbed brachiating anthropoid types: orang, gibbon. 

 (9B) Oligocene (?). Subterrestrial semi-erect anthropoids with moderately long arms and shorter 

 legs; astragalus and calcaneum of subhuman type; entocuneiform retaining saddle-shaped articulation 



