DINOSAUR TRACKSITES OF THE PALUXY RIVER (GLEN ROSE FORMATION, LOWER CRETACEOUS), DINOSAUR VALLEY STATE PARK, SOMERVELL COUNTY, TEXAS

In 1940 R.T. Bird of the American Museum of Natural History (New York) collected segments of trackways of an herbivorous sauropod and a carnivorous theropod from a tracksite in the bed (Glen Rose Formation) of the Paluxy River, in what is now Dinosaur Valley State Park. However, Bird left undocumented thousands of other dinosaur footprints in several other Paluxy tracksites. In 2008 and 2009 we carried out fieldwork to create detailed photomosaics of extant Paluxy tracksites, using GIS technology to combine these with historic maps and photographs of older tracksites. In addition, photographs, tracings, and measurements were made of individual footprints and trackways at numerous tracksites.

Although there are multiple tracklayers, the largest number and most spectacular footprints occur in a thick (ca. 20-25 cm) "main " tracklayer that is also densely dotted by vertical invertebrate burrows. The diversity of dinosaur footprint morphotypes is limited to tracks of the quadrupedal sauropods, and the far more numerous tridactyl prints, most or all of which were probably made by theropods. Some tridactyl prints show beautiful morphological details that are readily interpretable in terms of trackmaker foot structure, but more commonly the prints are distorted, with variably collapsed toe marks. Some tridactyl prints include long "heel" impressions.

Beyond documenting ichnological diversity, our project seeks to estimate the minimum number of individual dinosaurs recorded by the Paluxy tracksites. Are there patterns in the orientation, distribution, and association of trackways that suggest group behavior on the part of either sauropods or theropods? Can we support/refute Bird’s hypothesis that one or more of the theropods was pursuing one or more of the sauropods? The Paluxy tracksites constitute one of the world’s largest concentrations of dinosaur footprints. Our research will facilitate systematic comparison of Glen Rose dinosaur tracks with those from other footprint faunas, and will shed new light on the movements and behavior of the great reptiles.