TIME FILE: Morrison Formation - Wyoming, 153 million years ago

"The fragile land of the Allosaurus"
(based on the Morrison Formation)

Description
The overall climate was dry, like a modern grassland sans the grass. Flowering plants have yet to evolve, leaving ferns and horsetails to dominate the earthy landscape.

Geography
Sundance Sea, an extension of the Arctic, bordered the north and a massive desert to the south that we know existed due to aeolian processes, with dunes and one massive salt pan called Lake T'oo'dichi' evident from siltstone deposits.

Features
Swampy lowlands, lakes, rivers and floodplains

Rock Type
Mudstone, sandstone, siltstone and limestone

Fossilisation Extent
Found mostly in green siltstone and lower sandstone layers, in former rivers and floodplains, ideal for fossilisation.
 
Animals
Theropods – Allosaurus, Torvosaurus, Ceratosaurus, Marshosaurus, Strokesosaurus, Ornitholestes, Tanycolagreus
Sauropods – Diplodocus, Camarasaurus, Brontosaurus, Apatosaurus, Barosaurus, Supersaurus, Brachiosaurus, Suuwassea, Haplocanthosaurus
Ornithopods – Camptosaurus, Dryosaurus, Othnielosaurus
Heterodontosaurids – Fruitadens
Ankylosaurids – Gargoyleosaurus, Mymoorapelta
Stegosaurids – Stegosaurus, Hesperosaurus
Pterosaurs – Mesadactylus, Harpactognathus
Crurotarsans – Amphicotylus, Hallopus, Fruitachampsa, Hoplosuchus
Lizards and Snakes – Dorsetisaurus, Diablophis
Sphenodonts – Eilenodon
Choristodera – Ctenigenys
Turtles – Glyptops
Amphibians – Rhadinosteus, Iridotriton
Fish – Ceratodus, Morrolepis, Leptolepis, Hulettia
Mammals – Triconolestes, Docodon, Glirodon, Dryolestes, Tinodon
Other – Termites, Crayfish, Clams, Dragonflies, Scorpions, Millipedes, Dung Beetles, Snails, Slugs, Jellyfish, Wasps, Flies
 
Plants
Conifers, ginkgos, cycads, Tree ferns and horsetails

Most plants were riparian, living near the river and other water sources like lakes. Only tough conifers and ferns could live away from direct sources of hydration.