Do Bony Orbit Dimensions Predict Diel Activity Pattern in Sciurid Rodents?

Area of Science:

• Paleontology
• Comparative Anatomy
• Animal Ecology

Background:

• Diel activity patterns (DAP) are crucial for understanding animal ecology but challenging to determine in the fossil record.
• Previous methods relied on eyeball or scleral ring dimensions, which are often not preserved.
• Bony orbit dimensions are a potential proxy for DAP, especially for mammals lacking scleral rings.

Purpose of the Study:

• To investigate the predictive power of orbit and cranial measurements for determining DAP in sciurids (rodents).
• To evaluate quantitative methods, including phylogenetic flexible discriminant analysis, classification trees, and logistic regression, for DAP prediction.
• To assess the feasibility of using bony orbit dimensions for DAP inference in extinct mammals.

Main Methods:

• Analysis of orbit and cranial dimensions in extant sciurids with known DAPs.
• Application of phylogenetic flexible discriminant analysis, classification trees, and logistic regression.
• Utilized methods that do not require a priori DAP assignment, mimicking fossil data scenarios.

Main Results:

• Nocturnal and non-nocturnal sciurids were differentiated with over 80% accuracy using orbit and cranial measurements.
• Phylogenetic factors can influence DAP prediction accuracy.
• Distinguishing crepuscular species from nocturnal and diurnal ones proved significantly more difficult.

Conclusions:

• Orbit and cranial measurements, analyzed quantitatively and phylogenetically, offer viable options for predicting DAP in the fossil record.
• These methods are particularly valuable for inferring DAP in mammals and nonmammalian synapsids.
• Phylogenetic context is essential for robust DAP predictions from fossil skeletal remains.