Paleontology and geologyIn the Triassic, the supercontinent Pangea began to rift apart, and as the crust stretched and thinned in the northeastern part of this region, some areas dropped down into basins while others were pushed up. In the west, shallow to deep inland seas extended out into the open ocean until the Late Triassic when subduction began along the continental margin in the center of modern Mexico. Volcanic island chains approached from the west and slices of oceanic crust were pushed up against the continent, including some of the deposits in the western part of this region. The shallow to deep marine waters of the Triassic were home to many different animals, including crinoids, corals, sponges, brachiopods, bivalves, gastropods, hydrozoans. Some of these animals built up reefs around which ammonites and ichthyosaurs swam. On land, floodplains and deltas were covered by many different kinds of plants, which are preserved as individual fossils and layers of coal among the sandstones, mudstones and conglomerates deposited in these environments. Some Triassic rocks have been eroded away and others are buried below the surface, but a few exposures can be found in the west and smaller ones may appear in other areas on more detailed maps. |