T223 Topics in Paleoecology: Predation/Biotic Interactions, Fidelity/Taphonomy, and Community Ecology/Whole Organism Paleoecology III

Wednesday, 7 November 2012
8:00 AM - 12:00 PM
217D

A REALLY CRAPPY TALK: FECAL VOLUME AND BODY SIZE IN BIRDS, MAMMALS AND DINOSAURS

Paper number: T223-8
Program: Technical Sessions
Time: 9:45 AM – 10:00 AM

Authors

Abstract

Turd size and body size are significantly correlated in 97 species of extant birds and mammals. We measured fecal volume in 11 species from zoos, farms and pets and estimated fecal volume of 86 species from handbooks on scat identification. Body mass and trophic group were assigned based on the University of Michigan Animal Diversity Web (http://animaldiversity.ummz.umich.edu). Turd volume and body mass were log-transformed. Body size varies over six orders of magnitude, from the deer mouse to the African elephant. For all 97 species, r2 = 0.569; for all mammals (N= 81), r2 = 0.584; for birds (N=16), r2= 0.725. Slopes of the linear regression vary from 0.588 (carnivorous mammals) to 1.113 (ruminant herbivores). Slopes near 1.0 indicate that fecal volume increases in proportion to increases in body volume. Slopes significantly less than one (carnivorous mammals and birds) indicate either more frequent defecations per unit time, an increase in fecal density with increasing body mass (increasing digestive efficiency), an increase in the nutritive value of the food, or some combination of these factors.

The all-species regression predicts, with a minimum extrapolation of size, a turd size for tyrannosaurs similar to that of the known tyrannosaurid coprolites analyzed by Chin and others. Extrapolation of the turd size-body size relationship of birds to that of a 6,300 kg tyrannosaurid predicts a turd size similar to that of known coprolites. The turd size-body size relationship in carnivorous mammals predicts a tyrannosaurid turd much smaller than that of the known coprolites. Tyrannosaurid prey or digestion may have been unlike those of extant carnivorous mammals.

So how big was the biggest terrestrial turd of all time? Sauropods were the largest dinosaurs but their turds are poorly known. Unbridled extrapolation of the turd size-body size relationship of birds to the 74,000 kg estimated mass of the largest sauropod dinosaur, Argentinosaurus huinculensis, yields an estimated turd volume of 15 liters.