DECIPHERING THEROPOD-DOMINATED COMMUNITIES IN LATEST TRIASSIC ICHNOFOSSIL ASSEMBLAGES (NEWARK BASIN, NJ)

The sudden explosion of dinosaur diversity at the end of the Triassic is a key transition in their rise to ecological dominance through the remainder of the Mesozoic. At several sites in the Newark Basin, abundant theropod footprints directly underlie the oldest lavas of the massive Central Atlantic Magmatic Province (CAMP). In combination with magnetostratigraphy, U-Pb geochronology and astrochronological dating, this level is tightly constrained to within 10 kyr after the end-Triassic Extinction (201.564 Ma) (1,2). Within the myriad footprints displaying clear pedal morphology, many exhibit intermediate sizes and shapes that make classification into traditional ichnogenera and species difficult. Here, we analyze the relative proportions and interdigital-divarication to test two opposing hypotheses withing an allometric conceptual framework: 1) The intermediate footprints represent juveniles of larger, previously known species, suggesting a monospecific dinosaurian community populated by active sub-adult theropods; 2) The anomalous footprints represent multiple, new and previously described, species co-inhabiting a diverse post extinction environment Providing new evidence for an earlier than expected initial pulse of dinosaurian adaptive radiation. Although paleontological data are frequently limited by temporal averaging, the presence of so many footprints at these few sites in a time interval constrained to less than 20 kyr suggests evolutionary change is not a major source of diversity within this dataset, and rather, the assemblage represents a snapshot in time.

1. 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. J. Blackburn et al., Zircon U-Pb geochronology links the end-Triassic extinction with the Central Atlantic Magmatic Province. Science 340, 941–945 (2013).