Sinemurian in the context of "Pliensbachian"

The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau area of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Originally suggested as being Sinemurian-Pliensbachian, but more recent dating of detrital zircons has yielded a depositional age of 183.7 ± 2.7 Ma, thus a Pliensbachian-Toarcian age is more likely. A previous depth work recovered a solid "Carixian" (Lower-Middle Pliensbachian) age from measurements done in the Tenney Canyon. More recent works have provided varied datations for the layers, with samples from Colorado and Arizona suggesting 197.0±1.5-195.2±5.5 Ma (Middle Sinemurian), while the topmost section is likely Toarcian or close in age, maybe even recovering terrestrial deposits coeval with the Toarcian Oceanic Anoxic Event. This last age assignation also correlated the Toarcian Vulcanism on the west Cordilleran Magmatic Arc, as the number of grains from this event correlate with the silt content in the sandstones of the upper layers.

This rock formation is particularly prominent in southeastern Utah, where it is seen in the main attractions of a number of national parks and monuments. These include Zion National Park, Capitol Reef National Park, the San Rafael Swell, and Canyonlands National Park.

Massospondylus (/ˌmæsoʊˈspɒndɪləs/ MASS-oh-spon-di-lus) is a genus of sauropodomorph dinosaur from the Early Jurassic of southern Africa. It was described by Richard Owen in 1854 from remains discovered in South Africa, and is thus one of the first dinosaurs to have been named. The name Massospondylus means 'longer vertebra', alluding to what Owen identified as tail vertebrae; these vertebrae are now known to be from the neck. Although the original fossils were destroyed in London during a bombing raid in World War II, a plethora of specimens have since been assigned to the genus, making it one of the best-known sauropodomorphs from the Early Jurassic. The genus lived during the Hettangian, Sinemurian, and Pliensbachian ages, which lasted from ca. 201 to 184 million years ago. Most fossils come from the upper Elliot and Clarens formations of South Africa and Lesotho, but the genus is also found in the Forest Sandstone and the Mpandi Formation of Zimbabwe. Material from the US, India, and Argentina was previously assigned to the genus, but the US and Argentinian specimens are now assigned to their own genera (Sarahsaurus and Adeopapposaurus). Because of their great abundance, Massospondylus fossils have been used to date rocks, and a biozone, the Massospondylus Range Zone, is named after the genus.

Two species are considered valid: the type species M. carinatus, as well as M. kaalae, which was named in 2009 and is known from a single skull. Six other species have been named during the past 150 years but are no longer recognised. Originally, Massospondylus and similar dinosaurs have been regarded as theropods, but are now classified as basal ("early diverging") members of Sauropodomorpha. This group also includes sauropods. Within sauropodomorphs, Massospondylus is often classified in the family Massospondylidae. The genus was 4–6 metres (13–20 ft) long, with a long neck and tail, a small head, and a slender body. It is distinguished from related genera by the very elongated vertebrae of the front portion of the neck, amongst other features. Although Massospondylus was long depicted as quadrupedal (four-legged), it is now considered to have been bipedal (two-legged).