Environmental Context of Triassic-Jurassic Lagerstätten in Newark Supergroup Rift Basins, Eastern North America, with Special Reference to Footprint Assemblages

Triassic-Jurassic Lagerstätten in eastern North America record biotic and environmental changes that set the stage for the era of dinosaurian ecological dominance that lasted 136 million years. This paper describes the morphologic, systematic, stratigraphic, temporal, and environmental context of these extraordinary fossil assemblages within strata of the vast, paleotropical eastern North American Newark Supergroup. Formed during the initial rifting of the supercontinent of Pangea, these mostly lacustrine and fluvial deposits combine a super-abundance of tetrapod footprints, particularly those of dinosaurs, with a physical stratigraphy that reflects orbitally paced climate cyclicity, which in turn provides a high-resolution stratigraphy for most of the record. Some Newarkian footprint Lagerstätten are exceptional, displaying detailed scale patterns, associated body impressions, and, plausibly, feather homologues. These strata contain other Lagerstätten that yield superbly preserved insects, fishes, and reptiles. More conventional assemblages of skeletal remains, tracks, fishes, and plants also abound. Most Lagerstätten and other assemblages occur in sedimentary cycles that reflect the expansion and contraction of perennial lakes in monsoonal climates. Newark Supergroup faunal and floral assemblages, and the strata they come from, document consequential events during the early Mesozoic, most notably those surrounding the continental end-Triassic mass extinction and the ensuing Jurassic recovery.