Pattern and Instability in the Evolving Premaxilla of Boine Snakes

Morphological evidence indicates that within the snake familyBoidae the subfamily Pythoninae is ancestral to the Boinae.The python-boa transition in evolution involves a peculiar rotationof the premaxillary bone. During rotation the ventral processof the premaxilla, the processus palatini, is largely obliteratedbut reconstituted in later Boinae. There exist indications thatthe pattern of the processus palatini is less controlled orstable in boine snakes than in pythonines. Pattern instabilitycan be the result of several factors which include relaxed selectionfor precise form and a disruption in the developmental foundationof the feature which has not fully been reversed. These possiblefactors, though fundamentally different, need not exclude eachother. It is surmised that the pattern instability in boinesis related, at least in part, to the disruption of a morphogeneticparadigm affecting premaxillary shape.