Fossil freshwater gastropods from northern Mexico – A case of a “silent” local extirpation, with the description of a new species

The freshwater snails (Mollusca: Gastropoda) of Mexico: updated checklist, endemicity hotspots, threats and conservation status

“…All 5 interacting threats affect the freshwater ecosystems of the 3 hotspots. An special case in the transition area between hotspots A and B in northern Mexico with dramatic declines in diversity of freshwater gastropods was recently reported by Czaja, Covich et al (2019). The impacts occurred mainly during the 20 th Century and were so catastrophic that we can now call the region a "ghost" center of endemism (in the sense of Contreras-MacBaeth et al [2014]), where 84% of the gastropod species of the springs and marshes in the area of Viesca was extirpated within a short time.…”

“…This may be a result of the relatively short time in which these systems have been fragmented, and this seems to be confirmed by paleomalacological studies in the northern part of Mexico, where several locally restricted endemics had much wider distributions, and the now separate hotspots A and B in the middle Holocene were once connected (Czaja, Estrada-Rodríguez et al, 2014;Czaja, Estrada-Rodríguez, Romero-Méndez & Orona-Espino, 2017;Czaja, Estrada-Rodríguez, Romero-Méndez, Estrada-Arellano et al, 2017;Czaja, Estrada-Rodríguez, Romero-Méndez, Ávila-Rodríguez et al, 2017;Czaja, Palacios-Fest et al, 2014). The final division of the originally united region into the 2 present-day hotspots probably occurred in the latest Holocene, or even in historical times (Czaja, Covich et al, 2019). These transitional regions between the current hotspots support a uniform gastropod fauna of a small set of ubiquitous species, mainly planorbids and physids, known from many other similarly affected regions of the world (Neubauer et al, 2015).…”

A remarkable new genus and species of subterranean freshwater snail from a recently dried-up spring of Viesca, Coahuila, Northern Mexico

“…1). Like most of the other 15 springs near Viesca, this spring began to dry up during the drought of 1958-59, but the area remained a partial wetland until the late 1990s (Czaja et al 2015(Czaja et al , 2019a. The shells were found in superficial spring deposits a few meters at the outlet of a cave.…”

“…Many stygobiotic gastropods inhabit a diversity of subterranean habitats that are nearto-completely inaccessible to humans, such as the hyporheic or phreatic zones of an aquifer system. In Mexico, the majority of the species have been discovered from these less accessible habitat types through opportunistic sampling of the groundwater saturated, interstitial spaces within the sediment of surface streams or from groundwater discharge in wells or small springs (Hershler 1985;Czaja et al 2019a). This inaccessibility to extant populations and low probability of discovering stygobiotic gastropods in vivo has led to many taxonomic descriptions worldwide (whether later found extant or extinct) relying solely on empty shells (Georgiev 2013;Grego et al 2017;Quiñonero-Salgado and Rolán 2017;Hofman et al 2018;Czaja et al 2019b).…”

“…This fossil scarcity is likely owing to the usually narrow geographic distributions of stygobiotic gastropods, along with their extremely small size that does not typically exceed two millimeters (Gladstone et al 2021). However, these small stygobiont fossils may be more likely obtained from sites that have gone through recent environmental change, such as the springs in Viesca, Mexico that dried up in the second half of the 20 th century (Czaja et al 2017(Czaja et al , 2019a.…”