Physiological constraints on body size distributions in Crocodyliformes

Area of Science:

• Paleontology
• Evolutionary Biology
• Physiology

Background:

• Modern crocodylians represent a small fraction of the diverse Crocodyliformes.
• Fossil crocodyliforms exhibited extreme variations, including terrestrial and marine forms.

Purpose of the Study:

• To analyze how marine habitats influenced body size evolution in Crocodyliformes.
• To identify selective pressures driving body size changes in different crocodyliform habitats.

Main Methods:

• Compiled a database of body sizes for 264 fossil and modern crocodyliform species.
• Included species from terrestrial, semi-aquatic, and marine environments.
• Quantified body size evolution, selection strength, and variance across habitats.

Main Results:

• Marine habitat invasions correlated with increased body size, stronger selection, and reduced size variance.
• Semi-aquatic habitat invasions did not show similar body size evolutionary patterns.
• Thermoregulation and lung capacity models explained larger minimum and average body sizes in marine species.

Conclusions:

• Physiological constraints, such as thermoregulation and lung capacity, are key drivers of body size evolution in marine crocodyliforms.
• Allometric scaling may impose shared constraints on maximum body size across Crocodyliformes.
• Body size patterns are primarily shaped by physiological limitations rather than ecological factors.