Clade-specific evolutionary diversification along ontogenetic major axes in avian limb skeleton

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Developmental biology

Background:

• Avian limb skeleton proportions are linked to locomotor specializations.
• Phylogenetic signals suggest historical factors influence avian limb evolution.
• Ontogenetic integration may bias evolutionary trajectories.

Purpose of the Study:

• To investigate the role of ontogenetic integration in shaping avian limb evolution.
• To compare evolutionary diversification patterns with postnatal ontogenetic trajectories in six avian families.
• To explore how developmental pathways influence limb bone evolution.

Main Methods:

• Morphometric analyses of six limb bones (humerus, ulna, carpometacarpus, femur, tibiotarsus, tarsometatarsus).
• Examination of 2641 avian specimens, including ontogenetic series and published data.
• Comparison of evolutionary diversification patterns with clade-specific ontogenetic trajectories.

Main Results:

• Ontogenetic trajectories of limb bone proportions vary significantly among avian families.
• Evolutionary diversification of the avian limb skeleton is anisotropic.
• Key axes of evolutionary diversification correlate with clade-specific ontogenetic trajectories.

Conclusions:

• Developmental processes (ontogeny) bias the direction of evolutionary change in the avian limb skeleton.
• Clade-specific ontogenetic trajectories help explain peculiar avian diversification patterns, such as long legs in Ardeidae and flightlessness in Anatidae.
• Ontogenetic integration plays a crucial role in the evolutionary variability of avian limb morphology.