PALEOECOLOGY OF A CRETACEOUS COASTAL ECOSYSTEM; ARCHOSAURS THAT LIVED WITH FOREST FIRES, AN EXAMPLE FROM THE WOODBINE FORMATION, NORTH TEXAS

The Arlington Archosaur Site (AAS) is a diverse fossil locality from the Cretaceous (95 Mya) Woodbine Formation of North Central Texas. The paleoenvironment is a coastal, delta plain system from the southeastern interior seaway. The site preserves components of a coastal ecosystem within a 2m section consisting of a peat bed containing numerous, well preserved fossil turtle, crocodile (adult and juvenile), dinosaur and logs. Overlying the peat is a fossil horizon containing remains of vertebrates in a mudstone that demonstrates early pedogenesis from an inundated delta plain paleosol. The vertebrates occurring within this horizon include dinosaur (ornithopod), crocodile, turtle and lungfish. The dinosaurs recovered to date include a large herbivorous ornithopod and at least two theropods. All of these animals lived along a coastal plain that was beset with wildfires.

The AAS preserves a uniquely excellent record of wildfires from the Cenomanian represented by three distinct forest fire (FF) beds. The first FF bed is a charcoal conglomerate that lies beneath the primary vertebrate bearing fossil horizon. The charcoal conglomerate contains numerous charcoal and fossil wood fragments (1-4cm length) bound in a Fe rich sand. The 2^nd FF bed occurs in a paleosol bed, within concretions that contain charcoal fragments and several large burned tree stumps and roots. Concretion formation is indicative of seasonal dryness, and the burned stumps are evidence of wildfires. FF bed 3occurs in mid-section above FF bed 2 and is interpreted as a debris flow, as it is a sand rich charcoal bed with mixed conglomeratic interclasts. The FF horizons occur below, within and above the vertebrate fossil horizons. Periodic forest fires are therefore thought to have been an influential part of the AAS coastal ecosystem.