Volumetric versus Element-scaling Mass Estimation and Its Application to Permo-Triassic Tetrapods.

Area of Science:

• Paleobiology
• Biomechanics
• Comparative Anatomy

Background:

• Accurate body mass estimation is crucial in paleobiology for understanding physiology, biomechanics, and ecology.
• Current methods include whole-body volumetric models and individual element-scaling (e.g., bones, teeth), with debates on their relative accuracy and precision.

Purpose of the Study:

• To develop and validate a whole-body volumetric model using minimum convex hulls (MCHs) for estimating body mass across diverse taxa and sizes.
• To compare the accuracy and precision of the MCH model against traditional stylopodial (limb bone) scaling methods.
• To investigate the influence of differential skeletal scaling between reptiles and mammals on body mass estimation.

Main Methods:

• Developed a predictive body mass model using minimum convex hulls (MCHs) applied to a broad range of animal sizes (127 g - 2735 kg).
• Compared MCH model estimations with published data from stylopodial-scaling methods.
• Analyzed differential scaling of stylopodial circumference and length in reptiles and mammals.
• Applied both MCH and stylopodial-scaling methods to a sample of 12 Permo-Triassic tetrapods.

Main Results:

• The MCH volumetric model demonstrated superior accuracy and precision in body mass estimation compared to stylopodial-scaling.
• Differential scaling of limb bone dimensions between reptiles and mammals explains overestimation of reptile mass by mammalian-weighted models.
• Stylopodial-scaling consistently overestimated body mass in Permo-Triassic tetrapods due to their more robust bones.
• MCH models revealed that relative body proportions influence the center of mass position differently across mammals, crocodylians, and extinct tetrapods.

Conclusions:

• Whole-body volumetric approaches, like MCH modeling, are more reliable for estimating body mass, particularly for extinct species or those with unique anatomies.
• Element-scaling methods can be inaccurate when applied to taxa outside the original dataset's scope due to differing anatomical proportions.
• MCH models offer additional benefits, including the ability to measure inertial properties and explore constraints on the center of mass.