August 31 , 2016

The Rhynchocephalia (tuataras) are an ancient lineage of lepidosaurian reptiles. Today, they are only represented by a single genus, but the clade was diverse taxonomically and ecologically during the Mesozoic. One of the most important Mesozoic units that have yielded rhynchocephalians are the Late Jurassic laminated limestones of southern Germany. These layers are especially noteworthy as they usually contain complete skeletons and not only isolated elements, as it is the case with most other Mesozoic rhynchocephalian localities. Unfortunately, however, the taxonomy of the rhynchocephalians from these units has not been satisfactorily established so far, which hampers studies of their evolutionary importance. From the Late Kimmeridgian limestones of Schamhaupten, Bavaria, a single, complete specimen of a rhynchocephalian has been reported so far. This specimen has been identified as Leptosaurus pulchellus, thus accepting the proposed synonymy of the genera Kallimodon (with the type species Kallimodon pulchellus) and Leptosaurus (type species Leptosaurus neptunius). Detailed comparisons between the specimen from Schamhaupten with the type specimen of Kallimodon pulchellus and published descriptions of Leptosaurus neptunius resulted in the recognition of important differences, however. Differences to the type of Kallimodon pulchellus include the morphology of the maxillary teeth, the phalangeal formula of the manus, and the shape of the posterior process of the second sacral rib. An important difference with the type of Leptosaurus neptunius is the higher number of premaxillary teeth in the specimen from Schamhaupten (four versus two), despite a significantly larger body size, whereas there is rather a tendency to reduce the number of premaxillary teeth through fusion during ontogeny in rhynchocephalians. Thus, these differences indicate that the specimen from Schamhaupten can neither be referred to Kallimodon pulchellus, nor to Leptosaurus neptunius, indicating that rhynchocephalian diversity in the Late Jurassic of southern Germany was higher than currently recognized. However, a formal description of this specimen as a new taxon has to await a thorough revision of all of the available materials (and thus an evaluation of all proposed taxa) from these deposits.

Oliver W. M. Rauhut & Adriana López-Arbarello (2015)

Zur Taxonomie der Brückenechse aus dem oberen Jura von Schamhaupten. [On the taxonomy of rhynchocephalians from the Late Jurassic of Schamhaupten]

Archaeopteryx 33: 1-11