FROM THE TOMB OF THE FIRST STEGOSAURUS: A PRELIMINARY REPORT ON A STEGOSAUR-RICH TRACK ASSEMBLAGE FROM LAKES' QUARRY 5, MORRISON FORMATION OF MORRISON, COLORADO

Arthur Lakes removed giant Late Jurassic dinosaurs from his Quarry 5 sandstone, excavated in 1877-78 at Morrison, Colorado. This quarry is famous for producing the type specimen for the genus Stegosaurus (S. armatus, Yale Peabody Museum specimen 1850). Neither Lakes nor subsequent investigators reported footprints from the Quarry 5 sandstone. We have examined bedding surfaces on the talus blocks of the Quarry 5 left along the roadway at Morrison. The blocks preserved an ichnofauna unusually rich in stegosaurs, adult and juvenile, plus sauropods, juvenile and adult, theropods, ornithopods, lepidosaurs, and possible badger-sized mammal.

During the 1930’s the Alameda road was built across the hogback ridge where the Quarry 5 sandstone outcropped. Road-building activity displaced bone-bearing boulders which then were parbuckeled onto the shoulder of the road. In 2005, a roadside safety girder was scheduled to be installed on the shoulder of Alameda Parkway, and Morrison Museum staff collected and moved to the museum in January of 2005.

Locating tracks was done in two ways: strong, oblique lighting and high resolution latex peels. This process revealed diminutive tracks, including three tiny theropod tracks only 16 millimeters long (measured from the anterior extent of the third digit to the posteriormost extent of the track). Track identification began with an analysis of manual and pedal skeletons when possible, in conjunction with a review of published inchnotaxa.

The most common track morphotype from Quarry 5 ichnofacies range are wider medio-laterally than deep anterio-posteriorly, tridactyl with blunt digits ending in squared, hoof-like claws. Combined, these characters point to the pes of a single genus: Stegosaurus. Stegosaurus-morphotype tracks range in size from hatchling (estimated body mass 3kg) to adult animals (estimated body mass 6-8 tons). One talus block demonstrates adult stegosaur pedal track partially crushing a juvenile Stegosaurus-morphotype track, implying social behavior amongst juvenile and adult stegosaurs.

As with the bone sample from Quarry 5, the ichnofauna suggests an atypical Morrison Formation ichnofauna, enriched in stegosaurs. The Quarry 5 ichnofauna also provides insight into habitat preference and social behavior amongst stegosaurs.