The Late Triassic lepidosaur fauna from Hallau, North-Eastern Switzerland, and a new 'basal' rhynchocephalian Deltadectes elvetica gen. et sp. nov.

The Late Triassic vertebrate assemblages from Hallau, Switzerland, have been collected since 1915 and include sharks, bony fish (actinopterygians and lungfish), amphibians and archosau- riformes (a phytosaur and the dinosaur Plateosaurus). Many of the microtetrapods, including the haramyid and morganucodontid mammaliamorphs, are well known but the lepidosaurian reptiles have not been figured or described in any detail. We address that gap here reporting four distinct taxa in the 20th century collections made by Bernhard Peyer and emil Schutz. We describe a new basal rhynchocephalian, Deltadectes elvetica gen. et. sp. nov., which is of Gephyrosaurus-type grade rather than a sphenodontian. All the lepidosaurs in the fauna have teeth showing little or no replacement including a suppressed pleurodont and/or pleuracrodont dentition or acrodonty. A Diphydontosaurus- like sphenodontian is present and we record Paleollanosaurus,previously only known from the type locality in Texas U. S. A., together with an acrodont rhynchocephalian of uncertain affinities. The Hal- lau basal rhynchocephalians add further insight into the Norian-Rhaetian lepidosaur faunas found in Europe and North America by providing important new information, particularly to our knowledge of non-sphenodontian rhynchocephalians.