Abstract

CZAJA, Alexander et al. Fossil freshwater gastropods from northern Mexico - A case of a “silent” local extirpation, with the description of a new species. Bol. Soc. Geol. Mex [online]. 2019, vol.71, n.3, pp.609-629.  Epub Dec 06, 2019. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2019v71n3a2.

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 are 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. The study site contains subfossil (Late Holocene) deposits of the Laguna District, a small area in Coahuila and Durango. Here we describe a new species and report several new records of subfossil 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 from 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 anthropogenic activities. The results show that especially hydrobiid 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 Cuatrociénegas Basin. The same imperilment that led to local extirpation in the area of study still threatens the freshwater snail communities of the Cuatrociénegas valley.

Keywords : Paleobiology; extirpation; gastropods; freshwater; loss of habitat.

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