Micromorphic brachiopods from the early Permian (Kungurian) of Hidalgo, Mexico. Stratigraphic, paleoenvironmental and paleobiogeographic significance

This work describes for the first time a fauna of micromorphic brachiopods from Mexico. The biota comprises Permian species of the order Productida: Dyoros (Dyoros) extensiformis, Quadrochonetes girtyi, Rugaria hessensis, Fimbrinia ovata, as well as a productid indeterminate. The samples were located in the Calnali 2 section, belonging to the Tuzancoa Formation. The Kungurian (upper Cisuralian) relative age of the section was established by employing brachiopods, which were associated with bivalves, crinoids, trilobites, and bryozoans. The rocks with invertebrates are interbedded with strata bear plant remains. Sedimentological traits and preservation of brachiopods and associated fauna suggest that the marine community was deposited in a subtidal shallow and restricted environment with very low energy and continuous terrigenous input. On the other hand, the productid indeterminate is the largest brachiopod and displays the worst preservation, with evident traits suggesting that it was transported from a faraway region of the coast. Given that all taxa were previously identified in different units of Texas, considered a region where the Grandian Province was extended, it can be proposed that brachiopods of the Tuzancoa Formation also belonged to the same province. Thus, apart from New Mexico and Texas (USA), Huehuetenango (Guatemala), Palmarito (Venezuela), and Coahuila and Chiapas (Mexico), also Hidalgo's early Permian fauna could be included in the same biotic province.