San Juan Raya is a town located on the border between Puebla and Oaxaca, in the Tehuacán-Cuicatlán Biosphere Reserve. It has only 200 inhabitants, but it has a museum that exhibits fossils of invertebrates that once lived in the region and with a program of paleontological ecotourism.
The fossil reserve includes an extraordinary collection of traces of vertebrates, including those of pterosaurs and those of a theropod dinosaur.
In the desert where San Juan Raya is located, at the beginning of the 19th century, two Belgian naturalists named Nyst and Galeotti, who first introduced the first fossils of marine snails in 1836.
But it was not until the 20th century that Mexican geologists and paleontologists began studies of the invertebrate fauna that inhabited this place 110 million years ago, during the early Cretaceous.
At that time this place was part of a shallow sea, with well-oxygenated and warm waters, called sea of Tethys (named thus in honor of the sea goddess of the Greek mythology). Their conditions allowed the development of environments similar to the current reef inhabited by sponges, corals, mollusks, worms, sea urchins and abundant microscopic organisms.