Jurassic Museum of Asturias display in separate cabinets. In the Pre-Mesozoic hall, the exhibits relate to the time from the creation of the Earth 4500 million years ago to the Palaeozoic age, 251 million years ago with displays of first organisms on the Earth, evolution process of fossils and their dating, classification of the vertebrates and their inherited relations, deterioration and extinction of nearly 95% of these systems by end of the Palaeozoic period. In the hall representing the Cretaceous period, which is the last period of the Mesozoic era from 145 to 66 million years ago, the displays relate to the biological and
Sea urchin with just six species known from the Permian period. Only two lineages survived this period's massive extinction and into the Triassic: the genus "Miocidaris", which gave rise to modern cidaroida (pencil urchins), and the ancestor that gave rise to the euechinoids. By the upper Triassic, their numbers increased again. Cidaroids have changed very little since the Late Triassic, and are the only Paleozoic echinoid group to have survived. The euechinoids diversified into new lineages in the Jurassic and Cretaceous periods, and from them emerged the first irregular echinoids (the Atelostomata) during the early Jurassic. Some echinoids, such as "Micraster" in