Jurassic Period

Marine Biology of the Jurassic Period The Jurassic period is known as one of the most interesting periods of time in earth’s history, mainly for the awe-inspiring creatures many of which have gone extinct, the most remarkable being the dinosaurs. Life in the ocean during this time was also extremely diversified and amazing for the creatures it beheld. The Jurassic occurred from 199.6 to 145.5 million years ago, following the Triassic Period and preceding the Cretaceous Period within the Mesozoic Era. The supercontinent of Pangea began to drift apart during this time. Right before the Jurassic period began, a major extinction event occurred wiping out much of the life on earth. The events that unfolded afterwards gave life to a new planet.

Almost 23% of all families, 48% of all genera (20% of marine families and 55% of marine genera) and 70% to 75% of all species went extinct (Beaz). Although the cause of this mass extinction is debatable, many speculate that global warming was the killer. Because Pangea was breaking up into Laurasia and Gondwanaland, there was widespread volcanic activity caused by the rifting, increasing atmospheric carbon dioxide. The massive release of this greenhouse gas increased global air temperatures and resulted in acidified oceans along with rising sea levels. If this is the case, the life in the ocean would have died at a significant rate. Many families of brachiopods, gastropods, bivalves, and marine reptiles became extinct (Rafferty). An important trace fossil known as the phylloceratid ammonoid was able to survive, and they gave rise to the explosive radiation of cephalopods later in the Jurassic Period, as well as evolved into many different forms during the later Cretaceous (End Triassic Extinction). This extinction event ranks fourth in severity of the five major extinction events over geologic history

Cartilaginous and bony fishes were abundant. Large fishes and marine reptiles were common; the largest bony fish ever to live existed at this time called the Leedsichthys, coming in at a mindboggling size. Estimates of the size of this fish range from 20 to 27 meters and mass from 20 to 50 tons (Owen). This species is the largest bony fish ever to have ever existed and swam in what is now near England. Jurassic pliosaurs are some of the largest carnivorous reptiles ever discovered, even rivaling Tyrannosaurus which lived during the Cretaceous Period, although the pliosaurs was not a dinosaur but distant cousins of modern turtles ranging from 4 to 15 meters. The ichthyosaurs were at their height, sharing the oceans with the plesiosaurs, huge marine reptiles covering the globe. The Jurassic Period of our earth’s history was one of great change. It began with a major extinction even, bounced back, and was yet again the victim of an extinction event. The Jurassic was a flourishing time of new species adapting, changing, and modernizing to suit the ever-changing world they