TRIASSIC RECORDS OF THE DINOSAUR FOOTPRINT ICHNOGENUS EUBRONTES

Eubrontes is a large (length pes impression > 25 cm) grallatorid, bipedal, functionally tridactyl track with a relatively short digit III and a broad pes of a theropod dinosaur. Since the 1970s, many workers have considered the lowest occurrence (LO) of Eubrontes to mark the base of the Jurassic, largely based on its stratigraphic distribution in the Newark Supergroup of eastern North America. However, theropods large enough (> 5 m body length) to make Eubrontes tracks (e.g., Liliensternus, Gojirasaurus) are known from Upper Triassic body fossils, and there are several well documented Late Triassic records of Eubrontes (Eubrontes-size grallatorids) in Australia, Africa and Europe: (1) Blackstone Formation, Queensland, Australia; (2) Lower Elliot Formation, Lesotho, South Africa, (3) Keuper, d'Anduze, France; (4) ?Upper Keuper Rhaetian Sandstone, Germany; (5) Höganäs Formation, Scania, Sweden; (6) Tomanová Formation of the Polish-Slovak borderland; (7) Diavel Formation, Swiss Alps; (8) Mercia Mudstone Group, Great Britain; (9) Flemingfjord Formation, Greenland. Furthermore, the palynological change equated to the Triassic-Jurassic boundary in the Newark Supergroup does not correlate to the Triassic-Jurassic boundary in marine strata. The latter boundary is above the oldest Newark basalts, so it is above the pollen change and the LO of Eubrontes. This means that the LO of Eubrontes in the Newark predates the beginning of the Jurassic; it is probably a Rhaetian datum. Indeed, Eubrontes may even have older records in the Newark, such as its possible occurrence at the Culpeper Crushed Stone Quarry in Virginia, which is in the Norian Balls Bluff Siltstone. If the LO of Eubrontes actually is a biological event (not just a facies artifact), then its large theropod trackmaker has a markedly diachronous Late Triassic first appearance. It appears first in the Carnian of Australia, then in the Norian-Rhaetian of Africa and Europe and finally in the Rhaetian of eastern North America. The stratigraphic distribution of Eubrontes thus falsifies the idea of “ecological release” enabling large theropods to diversify following a putative end-Triassic extinction.