All-time giants: The largest animals and their problems

The largest known swimming, walking and flying animals are all vertebrates. They include the blue whale (up to 190 tonnes), the largest sauropod dinos aurs (probably about 80 tonnes) and two flying animals estimated to have ha d masses of at least 75 kg, the pterosaur Quetzalcoatlus and the bird Argen tavis. Even larger sizes might be physically possible, but may not have bee n attained because problems associated with size may make excessively large animals competitively inferior. These problems are discussed with frequent reference to basic consequences of geometric similarity (areas are proport ional to the squares of lengths and volumes to the cubes) and to the empiri cal rule that metabolic rates of similar animals tend to be proportional to (body mass)(0.75). Excessively large animals would be liable to overheat, both in water and on land. Larger animals tend to have fewer individuals in each species, suggesting the possibility that the largest whales and dinos aurs approach the limits of size above which numbers would be unlikely to b e large enough for long term viability. Even the largest dinosaurs seem to have been well able to support their weight on land. Flying animal size may have been limited more by the problem of taking off than by the power requ irement for flight. The largest swimming animals are filter feeders and the largest land animals were herbivores, so neither are at the top of a long food chain.