DINOSAURIA AND ASSOCIATED VERTEBRATE FAUNA OF THE LATE CRETACEOUS CHRONISTER SITE OF SOUTHEAST MISSOURI

The late Cretaceous (Campanian) Chronister site of Southeastern Missouri stands unique as the only known locality in the state that contains Mesozoic terrestrial vertebrate remains. Fossils occur within a clay that shows considerable soft sediment deformation due to the close proximity of a normal fault, on whose downthrown block it has been preserved. The environment of deposition as indicated by faunal and stratigraphic evidence, is a body of fresh water that was predominately low energy with occasional influxes of higher turbulence as indicated by a prominent gravel zone. This may represent a backwater, wetland, or oxbow lake. Allocthonous boulders of Paleozoic rocks in the clay are probably associated with faulting, but evidence suggests that parts of the deposit may also represent debris flows. Abundance of bone is highly variable, but in some parts of the deposit is high enough to constitute a “bone bed.” Many bones have been damaged by stresses that accompanied deposition, tectonic sediment deformation, and some are crushed which could be due to compaction or bioturbation. Some bones show evidence of predation or scavenging. The fauna includes three types of dinosaur which have been positively identified: Hypsibema missouriensis, which is considered to be a hadrosaur of uncertain affinities, an undetermined genus of tyrannosaurid, and an undetermined genus of dromaeosaurid. More problematic is the assignment of a single phalange to an undetermined genus of ornithomimid. The deposit also contains aquatic vertebrates such as: crocodilians, Leidyosuchus sp., turtles (the most common faunal element), Adocus punctatus and Naomichelys speciosa, a sirenian amphibian, Habrosaurus sp., and several fish including: Lepisosteus sp. (gar), and an Amiid (bowfin). Current excavation by the Missouri Ozark Dinosaur Project Inc., is being conducted under an enclosure to keep out water, and utilizes a 60 square meter hanging grid to facilitate detailed mapping and taphonomic record keeping.