ABSTRACT
As the number and types of reptiles gradually decreased, mammals began to compete for the vacated habitat. One group of early mammals—the plesiadapiformes—was among the most diverse and abundant groups during the Paleocene. Some authorities believe the ancestral primate, or primate precursor, was a plesiadapiform or was behaving in ways similar to the plesiadapiformes. The earliest true primates—the adapids and omomyids—were prosimians and appeared about 55 mya. These small animals possessed all the characteristics that define modern primates including postorbital bars, larger brains, reduced snouts, orbital convergence, grasping hands and feet, and claws rather than nails. Some early primates adapted to the ground and became extinct after about 10 million years. Others ascended the trees, where they fared better. The trees probably offered a refuge zone where competition was less intense but living more complicated. Early primates were forced to adapt to a strange new world, a new dimension of life among the dense foliage, branches, and canopies of the forest.
