THE CROCODYLOMORPHA AT AND BETWEEN GEOLOGICAL BOUNDARIES - THE BADEN-POWELL APPROACH TO CHANGE

Although the Crocodylomorpha spans a time period of over 200 million y ears, none of its notable morphological transitions appear 'to coincid e with major geological boundaries. The Crocodylomorpha originated bef ore the extinction event at the end of the Carnian Stage (Late Triassi c), concomitant with a shift of locomotor pattern from bipedal erect p osture to quadrupedal erect posture. With the successive divergence of the Sphenosuchia and Protosuchia the majority of features of the exta nt Crocodylia became established before the end of the Triassic. The M esoeucrocodylia may have arisen in the early part of the Early Jurassi c. The adoption of a more sprawling posture in the Longirostrine Taxa of the Mesoeucrocodylia was associated with a change of way of life fr om terrestrial to aquatic, probably immediately after the extinction e vent at the end of the Pliensbachian Stage (Jurassic). The Eusuchia ar ose in the Early Cretaceous, being characterized mainly by a complete bony secondary palate and the procoely of all vertebrae. The three ext ant clades most probably all arose before the Cretaceous-Tertiary boun dary. Thus, the patterns of cladogenesis and diversification within th e Crocodylomorpha indicate that, at least as currently understood, the se taxa were prepared for the major environmental and biotic events th at occurred during their history. Baden-Powell's motto of ''be prepare d'' (Maynard 1946), taken from his own initials, appears to be an adeq uate descriptor of the history of the Crocodylomorpha,