Ontogenetic allometry and scaling in catarrhine crania

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Primatology

Background:

• Ontogenetic scaling is often used to explain cranial morphological differences between related taxa of varying sizes.
• This hypothesis suggests shape changes are byproducts of size changes, not under direct selection.
• Previous studies, often using bivariate methods, show discrepancies regarding the prevalence and mechanisms of ontogenetic scaling in primates.

Purpose of the Study:

• To investigate if size divergence (ontogenetic scaling) primarily drives cranial shape differences in closely related catarrhines.
• To evaluate the hypothesis of size as a primary driver of evolutionary change in catarrhine crania.
• To explore the role of direct selection on cranial shape versus size-driven allometry.

Main Methods:

• Utilized a large, comparative ontogenetic sample of catarrhines.
• Employed geometric morphometric methods for detailed shape analysis.
• Applied multivariate statistical tests to assess allometric patterns and evolutionary pathways.

Main Results:

• Observed significant variation in ontogenetic allometry patterns across different catarrhine taxa.
• Found that ontogenetic scaling sensu stricto does not typically account for the majority of morphological differences.
• Demonstrated that large and small taxa within clades are generally not simple scaled variants of each other.

Conclusions:

• Ontogenetic scaling is not the primary explanation for most cranial shape differences in catarrhines.
• The diversity of ontogenetic pathways suggests that selection often acts directly on cranial shape.
• Cranial evolution in catarrhines is influenced by factors beyond simple size increase or decrease.