The Jurassic in Northeast region, Mexico |
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Paleontology and geologyIn the Early Jurassic, the eastern part of Northeastern Mexico was above sea level and the continental margin ran down the center of the country. The land was covered in forests, swamps, and lakes, which were filled with a wide variety of animals, including fish and early mammals. There were also many reptiles, such as crocodilians, pterosaurs, theropod and sauropod dinosaurs, sphenodontians (some of which may have been venomous), and mammal-like reptiles called tritylodontids. Subduction in the west along the edge of the continent continued to generate substantial volcanism. Huge blocks of granite pushed up under older rocks, and volcanoes spewed lava and ash over the land and sea. The Gulf of Mexico opened up, and by the end of the period, shallow seas flooded the east. In some areas, the seas were so shallow that water evaporated, leaving behind deposits of salt and gypsum. In deeper areas, rudist bivalves built up reefs, which were home to foraminifera, sponges, corals, gastropods, echinoids, bryozoans, algae, and other bivalves, as well as ammonites, ichthyosaurs, and pliosaurs. |
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