Plesiadapiforms, the Archaic Primates

Plesiadapiforms: Archaic Primates

• Plesiadapiforms emerged during the Paleocene epoch.
• They are considered archaic primates, exhibiting some but not all primate features.
• The term "plesiadapiform" means "almost adapiform," indicating resemblances in molar teeth to some adapiforms (adapoids), which are later-appearing true primates.
• Molar teeth are frequently the first-discovered remains due to better fossilization of enamel, leading early paleontologists to initially link plesiadapiforms to primates based on dental similarities.
• Significant morphological differences between plesiadapiforms and euprimates (true primates) became apparent with the discovery of more skeletal parts.
• Key differences include:
  • Unusual anterior teeth.
  • Digits with claws instead of nails in most species.
  • Absence of a postorbital bar (characteristic of extant strepsirrhines) or septum (found in haplorhines).
  • Unclear formation of the auditory bulla by the petrosal bone in many specimens.
• Despite these differences, there are reasons to include plesiadapiforms within the Order Primates, supported by new skeletal material.