Possible Functional Significance of the Reduction of Cartilage Bone

Abstract

IN a recent article on the evolution of vertebrates, D. M. S. Watson¹ takes into consideration a number of anatomical features of recent and fossil animals, showing that the overwhelming majority of them can be easily understood as the results of functional adaptations. Watson underlines, however, the importance of a major evolutionary trend in lower vertebrates, consisting in the gradual loss of cartilage bone in the skeleton and the growing importance of the membrane bones. This trend can be followed in many groups of fishes and amphibians. It is difficult, however, to find for it an adaptive significance. Watson writes (p. 58): “I have been able to find no advantage that an animal can obtain by a reduction in the amount of cartilage bone”, and further: “these basal changes … are not of such a character that it is at present possible to explain their occurrence as an adaptation and hence their appearance as a result of natural selection”.