Age: Early Cretaceous (100 mya)
The importance of the Tlayua fossils is the perfect preservation of the skeleton and other mineralised elements such as fish scales and spicules; but most important is the preservation of soft tissue of some specimens that has allowed anatomical studies. It is also important to mention the abundance (more than 5000 specimens so far) and the diversity of taxonomic groups of animals and plants.
Animal groups include foraminifera, sponges, gorgonids, bivalves, gastropods, belemnites (Neohibolie), ammonites of the genera Hystoceras, Mortoniceras and Anisoceras. The echinoderms are represented by the families Asteroidea, Ophiuroidea, Equinoidea and Holothuroidea. Crinoids, annelids, arthropods and also numerous specimens of the arachnid Atocalis ranulfoi (reported for the first time in Mexico) and the anispoterus Ixtahua benjamini.
As for the vertebrates, a small but very diverse fauna of reptiles has been recovered and studied by Victor Hugo Reynoso (1998), including turtles, pleurosaurs, sphenodonts, lizards, crocodiles and pterosaurs. The most common vertebrates and the most common fossils are the fishes.