Integration, phylogeny, and the hominid cranial base.

Area of Science:

• Paleoanthropology
• Evolutionary Biology
• Comparative Anatomy

Background:

• Phylogenetic analyses often assume character independence, potentially overlooking complex evolutionary relationships.
• Basicranial morphology in catarrhine primates and early hominids provides a unique dataset for investigating character integration.
• Understanding morphological integration is crucial for accurate reconstruction of evolutionary histories.

Purpose of the Study:

• To assess the impact of morphological integration on phylogenetic analyses of early hominids.
• To determine if basicranial features exhibit functional or structural relationships that violate phylogenetic independence.
• To integrate findings on morphological integration into cladistic analyses for improved accuracy.

Main Methods:

• Factor analysis was employed to test hypotheses about functional and structural relationships among basicranial characters.
• Characters identified as integrated were grouped into complexes and treated as single units in cladistic analysis.
• Cladistic analyses were performed on early hominid data, comparing results with and without accounting for integration.

Main Results:

• Factor analysis suggested potential structural relationships between five basicranial features and relative brain size in hominoids.
• The degree of morphological integration varied, with some characters potentially integrated while others remained independent.
• Treating integrated features as complexes significantly altered the phylogenetic placement of *Australopithecus africanus*.

Conclusions:

• Morphological integration patterns must be carefully considered in all morphology-based cladistic analyses.
• Failure to account for integration can bias phylogenetic reconstructions, as seen in analyses of early hominids.
• Hypotheses of integration require rigorous testing before being applied in phylogenetic analyses to avoid introducing new biases.