Evolutionary and Systematic Significance of Crocodilian Nesting Habits

Abstract

DIFFERENT species of crocodilians build one of two kinds of nest. For example, the Nile crocodile (Crocodylus niloticus) lays its eggs in a simple hole in the earth, usually sand or loose gravel, which is then covered over with the excavated material to the level of the surrounding ground^1–6, whereas the American alligator (Alligator mississippiensis) constructs a mound of vegetation, cleared from the surrounding area, in which it lays its eggs^7–13. Schmidt¹⁴ suggested that nesting habits might be indicative of relationship, but his idea failed to gain acceptance. One reason for this might be the belief, most recently expressed in an authoritative monograph in 1953¹⁵, that the differences in nesting habits are not sharp but instead show all possible intermediate stages. In pursuing Schmidt's idea, however, I have reviewed nearly all the literature on crocodilian nesting habits (summarized in Table 1) and conclude that there are absolute differences in these nesting habits and, as I hope to show, these differences are also closely correlated with the evolution and systematics of the group.