Abstract

The fossil trackway Pteraichnus saltwashensis Stokes 1957, from the Morrison Formation of Arizona, originally attributed to a pterodactyloid pterosaur, is reassessed. We conclude that this assignment was incorrect because: 1, Pteraichnus has five toes on the manus (all pterosaurs have four); and 2, pterosaurs did not walk quadrupedally. However, trackways similar in detail to the poorly preserved Pteraichnus can be simulated experimentally by a small caiman, and we suggest that Pteraichnus could have been made by a crocodilian. Experimental work on trackways, coupled with considerations of limb kinematics and substrate conditions, will permit the most robust inferences about paleoichnologic trackmakers, and will thus maximize the utility of fossil footprint data.--Modified journal abstract.

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