Major Ecological and Geographic Patterns in the Evolution of Colubroid Snakes

Fifty characters of colubroid snakes were analyzed phyletically. Relative frequencies of occurrence of character states was the principal criterion in deciding derivativeness of states, with the colubrid subsample serving as the out-group. Although the characters were chosen with respect to variation among the venomous hollow-fanged taxa (Viperidae, Elapidae, Hydrophiidae), here we have principally examined the distribution of character states among colubrid taxa. In the colubrids there are distinctive ecological and geographic patterns of relative derivativeness (measured as the proportion of characters in derived states). Terrestrial snakes are more generally primitive, burrowers most derived. Aquatic, arboreal and subterrestrial snakes are intermediate. The Neotropical and Holarctic colubrid snakes are more primitive than those of tropical Africa and the Orient. These data can be reconciled with the meagre fossil record, suggesting that (1) there may have been pre-Miocene tropicopolitan colubrid stocks, possibly of tropical American origin, (2) the Old Northern element of Holarctic ophidian faunas originated from tropical Asian stocks, adapted to and spread with Arcto-tertiary floras. The rear-fanged colubrids in the three major tropic areas may be largely parallel developments from a preadaptive largetoothed condition. Similar adaptive radiation patterns are apparent in the front-fanged elapid-hydrophiid line and among rear-fanged colubrids and viperids. The geographic distributions suggest that evolutionary events in the Colubroidea and particularly in the elapids date to the Cretaceous and reflect Pangaean fragmentation. Phyletic character analysis appears to offer a relatively effective method of uncovering morphological, ecological and geographic evolutionary sequences.