POST-EXTINCTION, TETRAPOD ICHNOECOLOGY OF THE LATEST TRIASSIC (NEWARK BASIN, NJ, USA): DAWN OF THE JURASSIC WORLD

Exemplary tetrapod ichnofossils from the uppermost Passaic Formation (Latest Rhaetian) provide direct evidence of transitional ecosystems between the end-Triassic extinction and the beginning of the Jurassic. Analysis of the ichnoecological community at the site reveals a low diversity assemblage of small lepidosauromorphs, theropods, and crocodylomorphs that thrived in the Newark Rift Basin at sites just before eruption the oldest Newark Basin lavas of the giant Central Atlantic Magmatic Province (CAMP). This level is constrained to within 10kyr after the end-Triassic extinction (201.564 Ma), based on astrochronology, magnetostratigraphy, and U-Pb geochronology (1, 2). Paleobiologically important taxa at the site include a new ichnospecies of Rhynchosauroides differing from other members of the ichnogenus in autopod emplacement patterns and scale morphology. Its presence at these sites provides links between the phylogenetically diverse and morphologically disparate sauropsid communities of the late Triassic, and their more limited presence through the subsequent Phanerozoic. One ichnospecies, Batrachopus dewyeii, represents an abundant small crocodylomorph. Theropod ichnospecies at the site include abundant Jurassic-aspect tracks ranging in size from Grallator to Eubrontes giganteus. Despite there being many tracks from multiple sites, there is no hint of uniquely Triassic forms. Quantitative measurements taken via photogrammetry provide major benefits in allowing clear morphological description and specific rapid comparison to other ichnofossils. The composition of this assemblage is consistent with a model in which insulated dinosaurs and burrowing abilities of smaller reptiles were critical for survival of volcanic winters caused by eruption of the CAMP (3).

1. P. E. Olsen et al., in 88th Annual, New York State Geological Field Conference, Guidebook, Geologic Diversity in the New York Metropolitan Area, A. E. Gates, Ed. (Rutgers University, Newark and Hofstra University, Newark, New Jersey, 2016), pp. 190–274.
2. T. J. Blackburn et al., Zircon U-Pb geochronology links the end-Triassic extinction with the Central Atlantic Magmatic Province. Science 340, 941–945 (2013).
3. P. E. Olsen et al., Arctic Ice and the Ecological Rise of the Dinosaurs. Science 8, eabo6342, 1 July 2022, (2022).