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For over a decade the Chihuahuan Desert has been considered as a hotspot of biodiversity. The diverse aquatic ecosystems, especially, are (and were) rich in mollusk species. The dunes of the Comarca Lagunera, Coahuila, Mexico, are of major importance due to the well-preserved remains of animals and plants in a paleolake that covered a vast area in the region. This paper is the first report of the paleolimnological investigations of the Paleolake Irritila ecosystems in northern Mexico. We determined more than 28 species of gastropods, bivalves, ostracods, algae and one aquatic plant. The dunes contain one of the richest and most diverse fauna of the late Quaternary of northern Mexico. The fossils indicate a permanent but shallow lake with moderate salinity and alkalinity (pH) higher than 8.5, most likely around 10. Most of the mollusks are distributed outside Mexico and restricted to northern latitudes (northern United States and Canada). Several of them are endemic to the southern United States (Florida, Nevada, and Texas). For the first time in North America, using the local fauna and flora preserved in dune sediments, we try to reconstruct the paleoenvironmental conditions in northern Mexico during the late Quaternary.