A LACUSTRINE LATE JURASSIC FLORA IN THE MORRISON FORMATION

The Morrison Formation is famous for its wealth of dinosaur fossils and rich uranium deposits, yet little is known about its flora. In fact, as a whole, the Late Jurassic flora of the North America is poorly understood. Previous studies of Kimmerdigian and Tithonian plant fossils from the Southwest US demonstrate two ecosystems: the first, a forest rich in conifers, horsetails, ferns, and cycads and the second a “savannah” filled with herbaceous ferns filling in the same ecological niche as grasses. A recently discovered fossil locality southwest of Colorado Springs shines light on a new ecosystem within the Morrsion Formation. The sedimentology and stratigraphy of the Temple Canyon section demonstrates that the deposit ranges from fluvial to deltaic to lacustrine. In the lacustrine beds, the presence of limestone and alternating mudstone to very fine sand layers indicates little clastic input. The deltaic and lacustrine facies contain well-preserved leaf, fish, vertebrate and insect fossils, which together show a heterogeneous and diverse ecosystem. Specifically, the plants indicate an environment full of bryophytes, ferns, ginkgophytes, horsetails, cycads and bennettites, which segregate taphonomically. In the low energy lake beds, whole leaves of gingkophytes, cycads and bennettites are common; in the higher energy deltaic beds, the flora is more often fragmentary and consists of low lying plants, such as bryophytes and ferns. This demonstrates the influence of taphonomy on ecosystem reconstruction in the Jurassic.