A review and reappraisal of the specific gravities of present and past multicellular organisms, with an emphasis on tetrapods

Abstract

The density, or specific gravity (SG), of organisms has numerous important implications for their form, function, ecology, and other facets of beings living and dead, and it is especially necessary to apply SG values that are as accurate as practical when estimating their masses which is itself a critical aspect of living things. Yet a comprehensive review and analysis of this notable subject of anatomy has never been conducted and published. This is such an effort, being as extensive as possible with the data on hand, bolstered by some additional observations, and new work focusing on extinct animals who densities are least unknown: pterosaurs and dinosaurs with extensive pneumatic complexes, including the most sophisticated effort to date for a sauropod. Often difficult to determine even via direct observation, techniques for obtaining the best possible SG data are explained and utilized, including observations of floating animals. Neutral specific gravity (NSG) is proposed as the most important value for tetrapods with respiratory tracts of fluctuating volume. SGs of organisms range from 0.08 to 2.6, plant tissues from 0.08 to 1.39, and vertebrates from about 0.75 (some giant pterosaurs) to 1.2 (those with heavy armor and/or skeletons). Tetrapod NSGs tend to be somewhat higher than widely thought, especially those theropod and sauropod dinosaurs and pterosaurs with air‐sacs because respiratory system volume is usually measured at maximum inhalation in birds. Also discussed is evidence that the ratio of the mass of skeletons relative to total body mass has not been properly assayed in the past.

Quantifying avian inertial properties using calibrated computed tomography

“…For example, voxels containing several tissue types, including air (such as feather shafts and vanes), yield a density that is a weighted average of all the materials (including air) present within the voxel. This inclusion of air in the volume measurements influences average calculated density measurement and is why other studies focusing on density measurement have removed the feathers ( Larramendi et al, 2021 ).…”

The extinct shark Otodus megalodon was a transoceanic superpredator: Inferences from 3D modeling

“…To calculate the model polygonal mesh’s body mass ( M ), we combined V with density ( D ), as performed in previous studies ( 1 , 3 , 4 ). The density of sharks is widely accepted as being only slightly higher than that of seawater ( 43 , 72 ). In pelagic sharks, this has been found to be an average of around 1060 kg/m 3 ( 32 ).…”

“…We also calculated the volume of each prey by dividing its body mass (kilograms) by the approximate density of water (1000 kg/m 3 ) and converting from cubic meters to liters. This volume was then multiplied by 1.025 to account for the specific gravity of sea water ( 72 ). The results were compared against the stomach volume calculated for the O. megalodon model to determine whether this shark could have entirely consumed each taxon.…”

Observations on Paleospecies Determination, With Additional Data on Tyrannosaurus Including Its Highly Divergent Species Specific Supraorbital Display Ornaments That Give T. rex a New and Unique Life Appearance

“…Skulls are illustrated by direct tracings of photographs and technical illustrations. Procedures for producing high fidelity profile-skeletals and using them to estimate body masses for tyrannosaurids and other tetrapods are detailed in Paul (1988Paul ( , 1997Paul ( , 2016Paul ( , 2019Larramendi et al 2021).…”