The haplorrhines, the "dry-nosed" primates, are members of the Haplorrhini clade: the prosimian tarsiers and all of the true simians (the monkeys and the apes, including humans).

The omomyids are an extinct group of prosimians, believed to be more closely related to the tarsiers than to any strepsirrhines, and are considered the most primitive haplorrhines.

Haplorrhines are considered to be less primitive than the strepsirrhines, the other suborder of primates. Their upper lip is not directly connected to their lip or gum, allowing a large range of facial expressions. Their brain to body ratio is significantly greater than the haplorrhines, and their primary sense is vision. Most species are diurnal (the exceptions being the tarsiers and the night monkeys) and have color vision. Their hands and feet are more generally adapted, with specialization only for locomotion, such as the hooked hands common to gibbons and orangutans, or the human bipedal feet.

All of the simians have a single chabered uterus; tarsiers have a bicornate uterus like the strepsirrhines. Most species have single births, although twins and triplets are common for marmosets and tamarins. Despite similar gestation periods, haplorrhine newborns are relatively much larger than strepsirrhine newborns, but have a longer dependence period on their other. This difference in size and dependence is creditted to the increased complexity of their behavior and natural history.

Classification and evolution

Haplorrhini and its sister clade, Strepsirrhini ("wet-nosed" primates), parted ways about 63 million years ago. The first division within the haplorrhines is the tarsier family Tarsiidae standing alone in infraorder Tarsiiformes. This split happened about 58 million years ago, a short time from an evolutionary perspective. This could be why the prosimian tarsiers used to be grouped with the rest of the strepsirrhines.

The remaining clade is the infraorder Simiiformes (formerly Anthropoidea), which is made up of the Platyrrhini (the New World monkeys) and Catarrhini (the Old World monkeys, apes, and humans). The New World monkeys split from the Old World about 40 mya, while the apes diverged about 25 mya.

• ORDER PRIMATES
  • Suborder Strepsirrhini: non-tarsier prosimians
  • Suborder Haplorrhini: tarsiers, monkeys and apes
    • Infraorder Tarsiiformes
      • Family Tarsiidae: tarsiers
    • Infraorder Simiiformes
      • Platyrrhini: New World monkeys
        • Family Cebidae: marmosets, tamarins, capuchins and squirrel monkeys
        • Family Nyctipithecidae: night monkeys, owl monkeys, douroucoulis
        • Family Pitheciidae: titis, sakis and uakaris
        • Family Atelidae: howler, spider and woolly monkeys
      • Catarrhini
        • Superfamily Cercopithecoidea
          • Family Cercopithecidae: Old World monkeys
        • Superfamily Hominoidea
          • Family Hylobatidae: gibbons
          • Family Hominidae: great apes and humans

References

• Primate Taxonomy (Smithsonian Institute Press, 2001), Colin Groves (ISBN 156098872X)
• Primates in Question (Smithsonian Institute Press, 2003), Robert W. Shumaker & Benjamin B. Beck (ISBN 1-58834-176-3)