New Palaeogene primate basicrania and the definition of the order Primates

Area of Science:

• Paleontology
• Comparative Anatomy
• Primate Evolution

Background:

• The posterior basicranium is crucial for defining the order Primates.
• Two key features: absence of a major vascular foramen and petrosal development of the auditory bulla, are widely cited.
• However, these features are not consistently present in archaic primates (plesiadapiforms).

Purpose of the Study:

• To re-evaluate the diagnostic criteria for the order Primates.
• To assess the phylogenetic position of plesiadapiforms within primate evolution.
• To investigate the validity of basicranial specializations in defining primates.

Main Methods:

• Comparative anatomical analysis of fossil primate basicrania.
• Examination of vascular foramen presence and auditory bulla development in plesiadapiforms and other mammals.
• Phylogenetic and stratigraphic analyses to determine evolutionary relationships.

Main Results:

• The cited basicranial specializations are not universally present in undoubted primates or plesiadapiforms.
• Plesiadapiforms exhibit mixed traits, with some resembling 'euprimates' (primates of modern aspect) in cheek teeth and postcranium.
• Phylogenetic placement of plesiadapiforms is uncertain due to lack of unique defining features.

Conclusions:

• The order Primates cannot be clearly defined by unique basicranial specializations.
• Stratigraphic and phenetic evidence suggests plesiadapiforms are likely antecedents to euprimates.
• Systematic arrangements should emphasize adaptive grades over unsubstantiated clades.