The Patagonian Telmatobiid Fauna of the Volcanic Somuncura Plateau of Argentina

Abstract

The Late Tertiary basaltic rocks of the Patagonian Meseta of Somuncura, Rio Negro, Argentina, extend for about 15,000 square km north of 42° South Latitude, approximately 60 miles from the Atlantic coast. It is a flat stepparian landscape of some 1200-1400 m elevation in which many temporary clay-lagoons are scattered. Small rocky streams filter from the basaltic uplands towards the lower slopes of the Meseta, about 700-500 m. The fauna of such an isolated environment is very peculiar and a high rate of endemic forms can be emphasized. Two new species of telmatobiid frogs are reported: <i>Telmatobius reverberii</i> from the clay-lagoons of the stepparian uplands, and <i>Telmatobius somuncurensis</i> from the lower rocky streams. Adults and tadpoles of <i>Telmatobius reverberii</i> are described; this form has morphological and ecological affinities with the smaller <i>Telmatobius praebasalticus</i> of the volcanic lagoons of Neuquen, near the Southern Argentine Cordilleras. Certain characteristics of <i>Telmatobius somuncurensis</i> are discussed, such as the uncommon everted cloaca and the similarity between the upper and lower rounded structures of its iris and the upper "meniscus” of the iris of the east-Brazilian Cyclorhamphus. Probable biogeographic relationships and a tentative evolutionary history of these ancient leptodactylid stocks are discussed.