| Sumario: | Brachiopods are common in the lower and middle parts of the early Mississippian (Osagean) Vicente Guerrero Formation that is mainly a fine-grained quartz arenite found in the Ciudad Victoria area, Tamaulipas, northeastern Mexico. This shallow marine brachiopod fauna includes several spire-bearers: Lamellosathyris lamellosa, Cleiothyridina cf. tenuilineata, Camarophorella sp., Alispirifer tamaulipensis n. sp., Tylothyris? sp., Torynifer pseudolineatus, Syringothyris cf. typa, Syringothyris? sp., and Punctospirifer sp. Similar assemblages have been found in Osagean rocks of the Santiago Formation, Oaxaca, southeastern Mexico, and in several coeval formations in the USA: Arizona, Arkansas, Illinois, Ohio, and Texas. North American biogeographic affinities are suggested for these Mississippian faunas of northeastern Mexico. These contrast markedly with the Late Silurian situation, where the Tamaulipas material has Old World Realm, rather than North American, biogeographic affinities. This supports the interpretation that northeastern Mexico was an integral part of North America by the Mississippian, but not in the Late Silurian.
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