Fossil freshwater gastropods from northern Mexico - A case of a "silent" local extirpation, with the description of a new species

The decline of freshwater species diversity is a worldwide phenomenon but it is especially pronounced in arid regions such as in the Chihuahuan Desert of Coahuila and Durango, Northern Mexico. There are few historical data on the distribution but no data on extinctions of Mexican freshwater gastropods. In such cases, paleontological data can be very helpful and :we often the only way to document past distributions and local extinction or extirpation events. This new paleoecological approach, called Conservation Paleobiology, can provide important perspectives in favor of conservation of recent analogue ecosystems. he study site contains subfossil (Late Holocene) deposits of the Languna District, a small area in Coahuila and Durango. Here we describe a new species and report several new records of subfbssil cochliopid, hydrobid, planorbid and neritid gastropods. Most of these species (and some genera' have not been known as fossil from Mexico and all of them disappeared in very recent times. Together with data horn our former paleomalacological studies, we present herein an example of a "silent" local extirpation in northern Mexico that began in the Middle Holocene. This loss of species apparently increased rapidly in the second half of the 20th century. Of 32 species of freshwater snails present in the area of study through the Holocene only four (12.5%) are still extant At least 24 (75.0%) of them disappeared from the area in the 20th century due to habitat loss caused by antluopogenic activities. "The results show that especially hydmbiid species with small geographic ranges (local endemics) are highly sensitive and vulnerable to such extirpation events. In this study area the extirpation of freshwater snails happened silently (unrecorded) while at the same time some two hundred kilometers farther north, one of the greatest recent hotspots of gastropods diversity in North America remained in the Cuatrocienegas Basin. The same imperilment that led to local extirpation in the area of study still threatens the freshwater snail communities of the Cuatrocienegas valley.