A Most Interesting Problem by Jeremy DeSilva

Author:Jeremy DeSilva
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2020-09-02T00:00:00+00:00

Primate Relationships Today

More than 500 species of living primates, belonging to more than eighty genera, are known to science today. Both these numbers have recently been increasing. Geneticists and field biologists continue to refine their knowledge of the diversity of natural populations in many parts of the world, identifying species that remained unrecognized in the past. Natural geographic ranges of primates include parts of Africa, Asia, Europe, and North and South America, as well as island Southeast Asia, Japan, Taiwan, and Madagascar. Evidence of relationships from DNA has helped to establish the pattern of branching as well as the approximate times that different groups diverged from one another.10 Fossil evidence has added to this picture, providing a hard record of the first appearances of many primate groups, as well as documenting their arrival in various parts of the world.

The last common ancestors of today’s primates lived shortly after the beginning of the Paleogene period, some 66 million years ago. Living and fossil primates share many traits that are the legacy of these common ancestors. Binocular vision, grasping hands with opposable thumbs, and broad fingertips with nails instead of claws are shared by primates as diverse as humans and galagos. These traits are adaptations that enabled the common ancestors of all primates to thrive in trees.

Like other mammals, primates emerged from the shadows after the extinction of dinosaurs, rapidly diversifying into a multiplicity of forms. Several families of these early primates evolved during the Paleocene and Eocene, before 35 million years ago, and became extinct in later time periods. Fossils from western North America, China and Southeast Asia, Europe, and North Africa document these early primates. Geneticists can examine their emergence only indirectly, through the DNA similarities of their living descendants. Still, genetic evidence has allowed for estimation of the times when living groups diverged and has overturned many ideas about relationships that were based on fossils and anatomy of living primates.

The two deepest branches of living primates are a good example of the interplay of these areas of evidence. Modern scientists recognize these deepest primate branches as the Strepsirrhini and Haplorhini, the names describing the forms of their noses. The moist-nosed strepsirrhines include lemurs, lorises, and galagos, while the haplorhines are the tarsiers, monkeys, and apes, including humans. During the past thirty years, this deepest split in the tree has become near universally accepted, but earlier scientists had different views about the deepest branches. Nearly all agreed that lemurs and lorises share a common heritage, reflected in traits such as a “toilet claw” and a “tooth comb” of closely packed lower incisor teeth, both used in grooming the fur. Scientists also agreed that monkeys, apes, and humans are a natural branch, historically known as “anthropoid primates” and today classified as Simiiformes. Paleontologists trace these two groups back to two successful and diverse groups during the Eocene, the lemur-like adapids (Adapidae) and the tarsier-like omomyids (Omomyidae).

This primary division, between strepsirrhine and haplorhine primates, hinges on the placement of tarsiers—small nocturnal primates from the Philippines, Sulawesi, and other islands of Southeast Asia.

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