Conservatism and adaptability during squirrel radiation: what is mandible shape telling us?

Area of Science:

• Evolutionary Biology
• Comparative Anatomy
• Paleontology

Background:

• Morphological diversity within taxa is shaped by functional adaptation and phylogenetic constraints.
• Squirrels (Sciuridae) are a diverse rodent family with a well-established phylogenetic framework.

Purpose of the Study:

• To investigate the interplay between functional adaptation and phylogeny in shaping squirrel mandible morphology.
• To identify key ecological factors driving mandible shape variation in squirrels.

Main Methods:

• Landmark-based geometric morphometrics applied to extant squirrel mandibles.
• Comparative phylogenetic analysis integrating morphological data with evolutionary relationships.
• Dietary reconstruction for fossil squirrels from the Eocene.

Main Results:

• Mandible shape is significantly predicted by dietary specialization and locomotion.
• A strong phylogenetic signal is evident across the squirrel family and major clades.
• The Callosciurinae subfamily exhibits notable adaptations linked to diverse ecological niches.
• Early fossil squirrels (Eocene) specialized in nuts and seeds, suggesting skull evolution wasn't solely diet-driven.

Conclusions:

• Phylogeny plays a crucial role in squirrel mandible morphology, indicating a conservative evolutionary history.
• Functional adaptations, particularly related to diet, have occurred within this conserved framework.
• The evolution of skull morphology in squirrels may not be directly tied to dietary shifts.
• Specific adaptations in Callosciurinae highlight their radiation into varied Asian forest ecosystems.