In vertebrates, embryos and juveniles have large heads relative to their overall body

Chapter 1, Problem 89

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In vertebrates, embryos and juveniles have large heads relative to their overall body size. As the animal grows older, proportions change; for instance, the ratio of skull length to body length diminishes. That this is the case not only for living vertebrates, but also for fossil vertebrates, is shown by the following example: Ichthyosaurs are a group of marine reptiles that appeared in the early Triassic and died out well before the end of the Cretaceous.1 They were fish shaped and comparable in size to dolphins. In a study of 20 fossil skeletons, the following allometric relationship between skull length S (measured in cm) and backbone length B (measured in cm) was found: S = 1.162B0.93 (a) Choose suitable transformations of S and B so that the resulting relationship is linear. Plot the transformed relationship, and find the slope and the y-intercept. (b) Explain why the allometric equation confirms that juveniles had relatively large heads. (: Compute the ratio of S to B for a number of different values of Bsay, 10 cm, 100 cm, 500 cmand compare.)