Convergent evolution of anthropoid-like adaptations in Eocene adapiform primates

Area of Science:

• Paleoprimatology
• Primate Evolution
• Fossil Record Analysis

Background:

• Adapiform primates, common in the Eocene, are debated as either stem Strepsirrhini (lemur-like) or stem anthropoids (higher primates).
• The discovery of Darwinius fueled debate about adapiforms' role in early anthropoid evolution.
• Previous phylogenetic analyses have yielded conflicting placements for adapiforms within the primate order.

Purpose of the Study:

• To describe the dentition and jaw of a new large-bodied adapiform, Afradapis, from the late Eocene of Egypt.
• To re-evaluate the phylogenetic position of adapiforms using a comprehensive morphological dataset.
• To investigate the evolutionary relationship between adapiforms and early anthropoids.

Main Methods:

• Detailed morphological analysis of the complete dentition and jaw of Afradapis.
• Phylogenetic analysis incorporating 360 morphological features from 117 primate taxa, including fossil and extant species.
• Comparative analysis of dental and gnathic features between Afradapis, other adapiforms, and early anthropoids.

Main Results:

• Afradapis exhibits derived dental and gnathic features convergent with later anthropoid primates.
• Phylogenetic analysis robustly places adapiforms as sister taxa to crown Strepsirrhini, excluding them from Haplorhini (Tarsius-Anthropoidea clade) and stem anthropoids.
• Afradapis and Darwinius belong to a extinct clade of caenopithecine adapiforms, indicating no direct descendants.

Conclusions:

• The specialized features shared between some adapiforms and anthropoids represent evolutionary convergences, not shared ancestry.
• Afradapis, the largest non-anthropoid primate from Afro-Arabia, highlights significant Eocene prosimian diversity.
• Ecological competition between adapiforms and higher primates may have influenced the early evolution of stem and crown Anthropoidea in Afro-Arabia.