Paleobiogeographic distribution of Testudinata and neosuchian Crocodyliformes in the Morrison Formation (Upper Jurassic) of North America: Evidence of habitat zonation?

Abstract

Nearly 150 occurrences of turtles and neosuchian crocodyliforms in the Upper Jurassic Morrison Formation indicate that, by number of localities and number of specimens, both are preferentially preserved off the Colorado Plateau in deposits in the eastern and northern parts of the Morrison basin, suggesting that these latter areas contained wetter paleoenvironments and either were more populated with these semi-aquatic taxa or more frequently preserved their remains, compared with areas to the south and west. Cursorial crocodylomorphs occur at more sites and in greater numbers on the Colorado Plateau than to the east and north, but this pattern is only significant by number of specimens. Previous suggestions of wetter paleoenvironmental conditions on floodplains distal to the southwestern source areas on the Colorado Plateau, or western source areas for northern outcrops, based on geological and microvertebrate data, seem to be borne out by these data from semi-aquatic mesovertebrates.