UPDATES OF THE TAPHONOMY OF DINOSAUR LAKE (AARON SCOTT SITE, MORRISON FORMATION, JURASSIC) OF UTAH

A rich accumulation of vertebrate remains accumulated along the margin of a large lake during the Late Jurassic. The accumulation of these vertebrates was the result of a moderate drought, which attracted animals to remaining large watering holes. Material at the site includes dinosaurs, including a Diplodocid, Allosaurus, Ceratosaurus, an ornithopod as well as an abundant and diverse microfauna. Microfauna include turtle and crocodile, supporting a lacustrine environment.

Exposure of the bone-bearing horizon is dominated by a large, partially articulated Diplodocid skeleton. Most of the cervical vertebrae are present and articulated, as well as most of the caudal vertebrae. Other elements include a tibia and fibula, isolated podial elements, teeth and an associated skull. Associated with this partial skeleton are numerous isolated skeletal elements and Allosaurus teeth. The majority of bones in the quarry, aside from the sauropod skeleton, are fragmented.

Fragmented and disarticulated bones are randomly oriented in the quarry, suggesting little or no reworking of the bones by current. This is supported by the fine grain size of the sediments in the quarry. The fragmented and disarticulated nature of most of the bones supports a drought scenario, where animals congregated around the lake and died along the shores, possibly due to stress from the drought, predator attacks or natural causes. Trampling by later animals and reworking by wave activity along the shore would have further broken up the bones. The Diplodocid likely died relatively soon before burial, as evidenced by the partial articulation of the vertebral elements – bones which are held together by strong ligaments and tendons that decay more slowly than muscle tissue. It is possible that this animal was killed by an Allosaurus, as suggested by the large association of broken Allosaurus teeth in association with the skeleton.