Multiple paths to morphological diversification during the origin of amniotes.

Area of Science:

• Evolutionary Biology
• Paleontology
• Comparative Anatomy

Background:

• Early terrestrial vertebrates, known as amniotes, exemplify adaptive radiation after colonizing land.
• Dietary diversification and associated craniomandibular/dental adaptations followed terrestrialization.
• Limited studies on early amniote morphological evolution leave questions about their radiation dynamics.

Purpose of the Study:

• To quantify evolutionary rates and constraints in the amniote feeding apparatus during diversification.
• To investigate the morphological evolution of early amniotes using novel analyses.
• To understand the drivers of phenotypic diversity in early amniote radiations.

Main Methods:

• Novel analyses of discrete characters were employed.
• Quantification of variation in evolutionary rates and constraints.
• Examination of craniomandibular and dental adaptations.

Main Results:

• Evidence suggests an initial burst of high anatomical change rates that decelerated over time.
• Morphological evolution became saturated, with later diversity not driven by increased rates.
• Independent origins of herbivory in different groups led to distinctive, group-specific morphologies.

Conclusions:

• Plant-animal interactions were crucial in structuring the early amniote radiation.
• Variation in evolutionary modes, not just rates, shaped phenotypic divergence.
• The study highlights diverse pathways of morphological evolution during a major terrestrial radiation.