Christian A. Meyer

Megatracksites, popularly known as ‘dinosaur Freeways’ are regionally extensive, stratigraphically restricted track-bearing sequences mainly associated with coastal plain facies, but in rarer cases with fluvio-lacustrine palaeoenvironments. Nine convincing, dinosaur-dominated examples are reported from the Mesozoic of North America, Europe, Africa and Central Asia, with a tenth tetrapod-dominated example reported from the Permian. Some, like the Moab Megatracksite (Utah) are labelled as Type 1 and restricted to ‘single surfaces’ or units only c . <1.0 m thick. Others (Type 2) represent relatively thin track-bearing packages ( c. 1.0– c. 10.0 m in thickness). Type 3 megatracksites represent imprecisely correlated, laterally extensive track-bearing facies. Most Type 1 and 2 examples including a Permian, four Jurassic and three Cretaceous examples display genetic sequence stratigraphic similarities, mainly associated with transgressive marginal marine facies. A Triassic megatracksite from Colorado and Utah is associated with a terrestrial fluvio-lacustrine system, and another from Spain is a lacustrine example. Type 1 megatracksites are defined by correlating multiple tracksites (assemblages) in stratigraphically restricted zones, across distances of c. 10 km– c. 100 km or more. Tetrapod megatracksites, ichnocoenoses and ichnofacies are all large-scale ichnological phenomena, which despite variability and different definitions can be integrated to various degrees. Because sequence stratigraphic, sedimentological and ichnological studies often proceed along separate, specialist lines a more integrated approach to the study of sedimentary geology and tetrapod ichnology is advocated in areas where megatracksites have been reported.