The legs of ostriches (Struthio) and moas (Pachyornis)

✍ Scribed by R. McNeill Alexander

• Publisher: Springer
• Year: 1985
• Tongue: English
• Weight: 419 KB
• Volume: 34
• Category: Article
• ISSN: 0001-5342
• DOI: 10.1007/bf00046782

✦ Synopsis

Ostriches were filmed running at maximum speed, and forces on the feet were calculated. Measurements were made of the principal structures in the legs of an ostrich. Hence peak stresses in muscles, tendons and bones were calculated. They lay within the range of stresses calculated for strenuous activities of other vertebrates. The ostrich makes substantial savings of energy in running, by elastic storage in stretched tendons.

Pachyornis was a flightless bird, much heavier than ostriches and with massively thick leg bones. These bones are shorter than predicted for its estimated body mass, by extrapolation from allometric equations for flying birds. An attempt is made to calculate the stresses that acted in the leg bones in running, for all possible patterns of leg movement. The stresses were probably rather low, unless Pachyornis was capable of running fast.

It is argued that the optimum factor of safety for moa leg bones may have been exceptionally high, as a consequence of the absence of predators.

]. THE QUESTIONS The investigations described in this paper posed two main questions.

(i) What stresses act in the bones, tendons and muscles of the legs of an ostrich (Struthio camelus) when it runs fast [9]? This question asked for facts, not explanations, but it was hoped that the answers would help us to understand the structure of ostriches.

(ii) Why were the leg bones of moas such as Pachyornis so thick, in comparison with ostriches [2,3] ? This question seeks an explanation. Why did selection in moas favour leg bones so different from those of ostriches? 2. OSTRICHES Fast running was chosen as the normal activity likely to impose the largest loads on the legs. Larger forces may occur in falls and other accidents, but are not predictable. It was decided to study wild ostriches