The tempo of cetacean cranial evolution

Area of Science:

• Paleontology
• Evolutionary Biology
• Comparative Anatomy

Background:

• Cetacean evolution showcases an extreme adaptive transition from terrestrial mammals to fully aquatic life.
• Cranial anatomy, including feeding, respiratory, and sensory structures, underwent significant modifications during this transition.

Purpose of the Study:

• To quantify cranial morphological changes throughout cetacean evolution using 3D geometric morphometrics.
• To identify key periods and drivers of rapid cranial evolution in whales and dolphins.

Main Methods:

• A high-density, 3D geometric morphometric analysis was performed on 201 living and extinct cetacean species.
• Evolutionary rates and disparity were analyzed across cetacean suborders and geological time periods.

Main Results:

• Cetacean suborders occupy distinct cranial morphospace areas, with extinct taxa bridging ancestral and modern forms.
• Three major periods of rapid cranial evolution were identified: early Eocene archaeocetes, late Eocene mysticete/odontocete divergence, and Miocene odontocete diversification.
• Archaeocetes exhibited fast rates but low disparity; odontocetes showed high disparity; mysticetes evolved slowest, especially in the Neogene.

Conclusions:

• Cranial evolution in cetaceans was driven by distinct bursts of diversification, influenced by factors like diet and echolocation.
• Diet and echolocation significantly impacted cranial shape, disparity, and evolutionary tempo, alongside habitat, size, and feeding strategies.