Age of the Dinosaurs

The period of time that the dinosaurs lived in is called the Mesozoic (Middle Life) Era. It started after the great mass extinction at the end of the Permian that wiped out 90% of marine and 70 % of terrestrial life on Earth, 252.2 million years ago (Benton, 2005). The era is split into three periods: the Triassic (252.2-201.3 MYA), the Jurassic (201.3-145 MYA) and the Cretaceous (145-66 MYA). The era ended with the mass extinction that wiped out the non-avian dinosaurs as well as other large prehistoric reptiles like the pterosaurs and the mosasaurs. In this post, we will look at an overview of the three periods.

Dinosaurs appeared towards the end of the Triassic. The world was very different to today. There were forests of conifers, cycads and horsetails that grew near water. Ferns grew over the ground. There was no grass and no flowering plants. Early crocodiles such as Protosuchus (First Crocodile) (Brown, 1934) lived mostly on land. Mammals appeared but they were small and insignificant at this point. Bizarre lizard-like reptiles like Kuehneosaurus (Kuehn's Lizard) (Robinson, 1962) glided from branch to branch chasing insects. Other lizard-like reptiles like Clevosaurus (Gloucestershire Lizard) (Swinton, 1939) scurried along the ground. Dinosaurs of this time were primitive and precursors to the later, more famous descendants, for example, Plateosaurus (Flat Lizard) (Meyer, 1837) was an ancestor of the great sauropods and Procompsognathus (Before Delicate Jaw) (Fraas, 1913) paved the way for the awe-inspiring carnivorous theropods.

The Jurassic is when things really got exciting. The giant sauropod dinosaurs such as Apatosaurus (Deceptive Lizard) (Marsh, 1877) and Brachiosaurus (Arm Lizard) (Riggs, 1903) were the dominant herbivores. The earliest birds, such as Archaeopteryx (Ancient Wing) (Meyer, 1861) evolved. The earliest described dinosaur Megalosaurus (Great Lizard) (Buckland, 1824) attacked the peaceful plant-eaters such as the early stegosaur Dacentrurus (Spiky Tail) (Lucas, 1902). Conifers, cycads, horsetails and tree ferns were some of the plants that grew at the time and were eaten by dinosaurs like Cetiosaurus (Whale Lizard) (Owen, 1842). Pterosaurs such as Rhamphocephalus (Beak Head) (Seeley, 1880) soared overhead. Mammals were still relatively small and insignificant.

The Cretaceous is when the dinosaurs reached their heyday. Whilst ferns, horsetails, conifers and cycads continued to dominate the landscape, the first flowering plants such as magnolias and roses flourished. The giant sauropods declined as bigger, badder predators such as Tyrannosaurus (Tyrant Lizard) (Osborn, 1905) and Albertosaurus (Alberta Lizard) (Osborn, 1905) appeared and were replaced with ornithopods like Iguanodon (Iguana Tooth) (Mantell, 1825). Birds, the only dinosaurs to survive to the present day, diversified during the Cretaceous, sharing the skies with giant toothless pterosaurs. Well-known dinosaurs like Triceratops (Three-Horned Face) (Marsh, 1889) lived alongside large herds of hadrosaurs like Corythosaurus (Helmeted Lizard) (Brown, 1914) and Parasaurolophus (Near Lizard Crest) (Parks, 1922). Fast-running meat-eaters like Troodon (Wounding Tooth) (Leidy, 1856) emerged. Mammals became bigger, about the size of a badger, and became dangerous - with one Repenomamus (Reptile Mammal) (Li et al., 2000) known to have eaten dinosaurs! (Hu et al., 2005)

And that is a very basic outline of the Mesozoic Era. Next time, we'll take a look at the landscape of Earth during this time. However, coming up next will be something completely unrelated to dinosaurs. 

See also:
More dinosaurs
Geochronology
Life before the Dinosaurs

References
Benton, M. (2005) When Life Nearly Died: The Greatest Mass Extinction of all Time, London: Thames and Hudson

Brown, B. (1914) 'Corythosaurus casuarius, a new crested dinosaur from the Belly River Cretaceous, with provisional classification of the family Trachodontidae', Bulletin of the American Museum of Natural History, 33, pp. 559-565

Brown, B. (1934) 'A change of names', Science, 79 (2039), p. 80

Buckland, W. (1824) 'Notice on the Megalosaurus or great Fossil Lizard of Stonesfield', Transactions of the Geological Society of London, 2 (1), pp. 390-396

Fraas, E. (1913) 'Die neuesten Dinosaurierfunde in der schwäbischen Trias [The newest dinosaur finds in the Swabian Trias]', Naturwissenschaften, 1 (45), pp. 1097-1100

Hu, Y., Meng, J., Wang, Y. and Li, C. (2005) 'Large Mesozoic mammals fed on young dinosaurs', Nature, 433 (7022), pp. 149-152

Leidy, J. (1856) 'Notice of remains of extinct reptiles and fishes, discovered by Dr. F. V. Hayden in the badlands of the Judith River, Nebraska Territory', Proceedings of the Academy of Natural Sciences of Philadelphia, 8, pp. 72-73

Li, J., Wang, Y., Wang, Y. and Li, C. (2000) 'A new family of primitive mammal from the Mesozoic of western Liaoning, China', Chinese Science Bulletin, 46 (9), pp. 782-785

Lucas, F. (1902) 'Paleontological notes. The generic name Omosaurus: A new generic name for Stegosaurus marshi', Science, 16 (402), p. 435

Mantell, G. (1825) 'Notice on the Iguanodon, a newly discovered fossil reptile, from the sandstone of Tilgate forest, in Sussex', Philosophical Transactions of the Royal Society, 115, pp. 179-186

Marsh, O. (1877) 'Notice on some new dinosaurian reptiles from the Jurassic Formation', American Journal of Science, 3 (14), pp. 514-516

Marsh, O. (1889) 'Notice of gigantic horned Dinosauria from the Cretaceous', American Journal of Science, 38, pp. 173-175

Meyer, H. (1837) 'Mittheilungen, an Professor Bronn gerichtet [Communications, sent to Professor Bronn], Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde, 1837, pp. 314-317

Meyer, H. (1861) Archaeopteryx litographica (Vogel-Feder) und Pterodactylus von Solenhofen

Osborn, H. (1905) 'Tyrannosaurus and other Cretaceous carnivorous dinosaurs', Bulletin of the American Museum of Natural History, 21 (14), pp. 259-265

Owen, R. (1842) 'Report on British Fossil reptiles, Pt. II', Reports of the British Association for the Advancement of Science, 11, pp. 60-204

Parks, W. (1922) 'Parasaurolophus walkeri, a new genus and species of crested trachodont dinosaur', University of Toronto Studies, Geology Series, 13, pp. 1-12

Riggs, E. (1903) 'Brachiosaurus altithorax, the largest known dinosaur', American Journal of Science, 4 (15), pp. 299-306

Robinson, P. (1962) 'Gliding lizards from the upper Keuper of Great Britain', Proceedings of the Geological Society of London, 1601, pp. 137-146

Seeley, H. (1880) 'On the Rhamphocephalus prestwichi, Seeley, an ornithosaurian from the Stonesfield Slate of Kineton', Quarterly Journal of the Geological Society, 36, pp. 27-30

Swinton, W. (1939) 'A new Triassic rhynchocephalian from Gloucestershire', Annals and Magazine of Natural History: Zoology, Biology and Geology, 4, pp. 591-594