Palaeoecology of the Morrison Formation, Upper Jurassic, western USA
The Morrison Formation is a suite of rocks that were deposited by rivers and on flood plains between about 157 and 147 million years ago in what is now western North America. The Morrison flood plains were home to many of the most iconic dinosaurs, including Stegosaurus, Diplodocus, Allosaurus and Brontosaurus. Although dinosaur fossils have been collected in the Morrison for nearly 150 years, many are highly fragmentary, few are known from complete specimens, and there is much we still do not understand about ecosystems and dinosaur palaeobiology at the time. The fauna of the Morrison Formation has generally been considered homogenous across the 1.2 million square kilometres of its outcrop. At least 12 distinct species of sauropod inhabited the Morrison floodplains, and an enduring question relates to how an apparently semi-arid to seasonally wet environment could be home to such diversity and volume of large herbivorous animals.
This question remains to be answered, but two possibilities are emerging. One is that the Morrison rocks are not contemporaneous across their outcrop area. Recent efforts to produce a stratigraphic framework for the formation have suggested that not all of the dinosaurs were living at the same time. Alternatively, there is an increasing body of evidence to suggest that the fauna of the Morrison was geographically segregated, possibly due to climatic preferences. The rare stegosaur Hesperosaurus is only found in the north of the Morrison basin, while Stegosaurus is only found in the south. The vast outcrop area and excellent fossil record of the Morrison Formation provide an unparalleled insight into the world of the Late Jurassic, and give us an unprecedented opportunity to investigate evolution and ecology in a drastically different climatic setting than our own.
Biography Dr. Susannah Maidment
Dr. Susannah Maidment is a dinosaur researcher and curator of fossil archosaurs at the Natural History Museum. Her work focuses on the palaeobiology of the bird hipped dinosaurs, bias in the fossil record, and the geological context of dinosaur ecosystems. Susannah has published more than 60 papers in the international peer-reviewed literature, and appears fairly regularly in the media talking about dinosaurs. Susannah was one of National Geographic UK’s Women of Impact in 2019. In 2016 she was awarded the Geological Society of London’s Lyell Fund and in 2017 the Palaeontological Association’s Hodson Award, both for notable contributions to palaeontology. Susannah has a PhD in vertebrate palaeontology from the University of Cambridge, and prior to working at the NHM, she was a Research Fellow at Imperial College London and a postdoctoral researcher at the Natural History Museum.