The Upper Jurassic, commonly called the Late Jurassic, is the final epoch of the Jurassic Period in the geologic timescale. It extends from about 163.5 million years ago to roughly 145 million years ago and precedes the Lower Cretaceous. In stratigraphic usage the term "Upper" often appears in rock descriptions while "Late" is more common in time-rock contexts; both names denote the same interval in chronostratigraphy.
Subdivisions and stratigraphy
The epoch is conventionally divided into three stages: Oxfordian, Kimmeridgian and Tithonian. These stages are characterized by distinctive fossil assemblages—especially ammonites—that permit global correlation of sediments. Geologists and paleontologists use these subdivisions to date rock units and reconstruct ancient environments across different continents of the Jurassic.
Climate and paleogeography
During the Upper Jurassic the supercontinent Pangaea continued to fragment, widening shallow seaways and creating new coastlines. Sea levels were relatively high and climates were generally warm with reduced polar ice, producing humid to semi-arid regions depending on latitude and local topography. These conditions promoted extensive carbonate deposition and the formation of reef and lagoonal facies.
Life and ecosystems
Life in the Upper Jurassic included diverse terrestrial and marine communities. On land, large sauropod dinosaurs (long-necked herbivores), stegosaurs and medium- to large-bodied theropods were common. Early birds and a variety of pterosaurs occupied aerial niches. In the seas, ammonites, plesiosaurs, pliosaurs and abundant bony fishes thrived, while some groups such as ichthyosaurs were declining in diversity.
Notable fossil sites and importance
Fossil-bearing formations from this epoch have yielded iconic specimens and have been crucial for understanding Mesozoic life. Examples include lagoonal limestones and terrestrial beds that preserve articulated skeletons and early bird fossils. Upper Jurassic rocks also serve as source and reservoir units for hydrocarbons in several basins and provide clay, limestone and building stone used regionally.
Key distinctions of the interval include the evolution and radiation of giant sauropods, prolific ammonite biostratigraphy, and faunal turnovers that set the stage for changes seen in the ensuing Cretaceous. For further reading see regional stratigraphic syntheses and paleontological surveys (research summaries, textbooks).