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The Zoogeography of the Crocodilia
William D. Sill
Vol. 1968, No. 1 (Mar. 15, 1968), pp. 76-88
Stable URL: http://www.jstor.org/stable/1441553
Page Count: 13
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The order Crocodilia probably came into existence during the Middle Triassic, arising from a primitive thecodont lineage. The primitive members of the order are known only from a few specimens, apparently of two groups, the earliest of which is found in South America. Knowledge of the Crocodilia during the early and middle Jurassic is practically non-existent, but this interval of time marked the rise of a number of independent groups, highly varied but with many common characters, forming the suborder Mesosuchia (possibly an artificial group). In the late Cretaceous a further expansion of the Crocodilia took place, that of the Eusuchia. This expansion continued into the warm early part of the Tertiary and became greatly reduced with the cooling which began during the later part of this period. The present distribution is a relict of the early Tertiary radiation. Crocodiles are sensitive to climatic fluctuation and their distribution correlates well with the climatic changes of the Tertiary as represented by fossil floras. The endemic groups of crocodiles present in South America and Africa indicate that these continents were isolated for long periods of time.