PALEOECOLOGY OF PTEROSAURS FROM THE LOWER MORRISON FORMATION IN CENTRAL WYOMING

The Alcova region is replete with pterosaur tracks and trackways including the type specimen, Pteraichnus stokesi. With the abundant material available, quantitative analysis on diversity, behavior and taphonomy as well as ontogeny studies can be made. This information can be used to describe the paleoecology of the Lower Morrison Formation with respect to pterosaurs. The pterosaur tracks are found in two distinct lithologic layers representing two unique environments. The Windy Hill Member, which contains the majority of the tracks, is described as a classic nearshore facies complete with oolitic and glauconitic sandstone and well developed small scale ripple marks. Above the Windy Hill in the lower Lake Como Member, the tracks are found in sediments reminiscent of overbank and fluvial deposits. The results of this study show that there is a very low diversity in the fauna with only 1 or 2 pterosaur species present. However, there is a high diversity in track size, which is interpreted as evidence of various age groups. The behavior, as expressed by the trackways, is consistent within a given environment. In the Windy Hill Member, tracks and trackways suggest the animals were simply traveling from one place to another by either walking or swimming. There is very little deviation in the direction of travel and relative stride length. In the Lake Como Member, the tracks demonstrate a different behavioral pattern. Here the tracks show no preferred direction of travel and the stride patterns are random or not present suggesting that the track makers were staying in the area. Along with these tracks are impressions of plant debris, worm burrows and dinosaurian footprints.