The Size of the Largest Land Animal

• Main Author: J. E. I. Hokkanen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1985
• Subjects: Blue whale
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.63.3969; http://www.miketaylor.org.uk//dino/hokkanen/Size-Hokkanen.pdf

The upper mass limit to terrestrial animals is studied using physical arguments and allometric laws for bone and muscle strength and animal locomotion. The limit is suggested to lie between 10 5 and 10 6 kg. A possibility for a still higher mass, in case of new adaptations, is not excluded. 1. Qualitative Mass Limits Since Galilei (1637) it has been claimed that the 100-ton blue whale can reach its size only because of the supportive aid of water. Land animals of similar weight would be crushed by the earth’s gravitational field. Recent measurements of land mammals and dinosaurs, with some help from elementary physics, can be used in evaluation of the upper limit to their mass. FIG. 1. An animal of mass M and leg bone diameter D. For the kind of animals on land we know, a maximum weight necessarily exists. Let us examine, for the sake of simplicity, the case of the one-legged animal in Fig. 1. The force Mg due to the animal’s mass M acting on a bone of diameter D and cross-sectional area A loads it in axial compression σ σ = (Mg/A)∝(M/D 2) (1) ∝ Denoting proportionality (g is the gravitational acceleration). Suppose our animal grows while keeping its shape unaltered. Constant shape means M ∝ D 3, because D grows just like any other linear