Early Jurassic Kayenta Formation from the Dinosaur Collector

   update 102912

201 million years ago, about 50% of all terrestrial vertebrate families were wiped out at the end of the Triassic.  Plants also exhibit a low diversity, dominated by primitive conifers.  The new flora favored high browsing herbivores like the prosauropods.  The first large theropods appear.  The theories for the extinction include a possible meteor strike, but no conclusive evidence has been put forward.  The Late Triassic witnessed a series of extinctions that marked the change from low browsing aeteosaurs and dicynodonts preyed on by archosaurs, to the high browsing prosauropods and large theropods. This has been used as an argument that dinosaurs out-competed the earlier forms. It also possible they were the lucky survivors of the extinction that allowed them to diversify and fill the vacant niches. The Late Triassic had several waves of extinctions. The final one at the Triassic–Jurassic boundary happened in less than 10,000 years and marks the boundary between the Triassic and Jurassic periods. There is some evidence for meteor strikes and volcanism but the cause is not proven. The climate changes with arid bands spreading through previously wet areas possibly caused by a change in the earth’s rotational tilt at least half of the species now known to have been living on Earth at that time went extinct. Ecological niches were cleared out, allowing the dinosaurs to assume the dominant roles. This event occured just before Pangaea started to break apart. The climate was warm and moister than during the Triassic. During the Early Jurassic a global flora spreads. Equatorial groups like cycadiods, cycads and primitive conifers, along with ferns, became more important components of the southern Gondwanan flora. Gingkoes and Czekanowskiales are more common in the north and the Araucaria (monkey puzzle) in the south. Dinosaurs dominate the large land vertebrates and mammals are the most important small vertebrates.  Pangaea the world continent begins to break up.

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Considering the Early Jurassic lasts for 25 my we do not have a lot of information about the dinosaurs from that time. Large plant eater and medium plant eater roles were dominated by prosauropods and rare primative sauropods able to browse higher in the canopy. Ornithischian dinosaurs are small to medium fabrosaurs, heterdontosaurs and the armored sclediosaurs most feeding below three feet. Dilophosaurs become the large carnivores. Scrappy finds of large carnivores are wide spread and some have been tentively indentifed as tenaturans. The small carnivores look like their Triassic ancestors.

The best known formations from North America are the Kayenta Formation and Navajo Sandstone. We have Dilophosaurus, small coelophysoid, prosauropods, armored dinosaurs and small ornithisians. Fossils for of smaller forms are much less common than tracks would indicate.

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The Lufeng Series of China has a crested theropod like Dilophosaurus, prosauropods, sauropods and armored dinosaurs.

In Britian the Lower Lias and Oxford Clay give a range of scrappy and indeterminate theropods and ornithiscians with the best example of Scliediosaurus. Scliediosaurus is also found int he American Southwest.

Kota Formation in India gives us the best early sauropods.

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