Hyloidichnus bifurcatus Gilmore, 1927 and Limnopus heterodactylus (King, 1845) from the Early Permian of Southern Alps (N Italy): A New Equilibrium in the Ichnofauna

Abstract

Studies on Early Permian tetrapod ichnofauna emphasized the scarcity of forms from Italian sites. A revision work on the entire collections revealed the presence of Hyloidichnus bifurcatus Gilmore, 1927 and Limnopus heterodactylus (King, 1845). The ichnoassociation now lists seven ichnogenera: Amphisauropus, Batrachichnus, Dromopus, Erpetopus, Hyloidichnus, Limnopus, Varanopus. These new data enlarge the ichnoceonosis, adding tracks of medium-size captorhinomorphs (Hyloidichnus) and temnospondyls (Limnopus) to the Italian ichnofauna, previously characterized by scarcity of predators and amphibians. Radiometric ages give a strong age constraint to the ichnoassociation (Early Kungurian), allowing useful correlations to contemporary successions all over the world. The main difference is the absence of Ichniotherium and Dimetropus, and this could have a stratigraphic or paleoenvironmental significance. The fauna is similar in two main basins, Collio and Orobic. It differs solely in the proportions between ichnotaxa, with a predominance of areoscelid traces (Dromopus) in the Collio Basin and of captorhinomorph traces (Erpetopus, Varanopus, Hyloidichnus) in the Orobic Basin. This datum could reflect slightly different environments, seasonal in the Collio Basin (alluvial plain) and more arid in the Orobic Basin (playa-like). The lack of some forms in smaller basins of the Athesian Volcanic Complex is probably due to a bias.

Keywords:

• Ichnoassociation
• Hyloidichnus
• Limnopus
• Early Permian

ACKNOWLEDGEMENTS

We would like to thank Sebastian Voigt (Urweltmuseum GEOSKOP, Germany) and Spencer Lucas (New Mexico Museum of Natural History and Science, Albuquerque, New Mexico) for the helpful suggestions on determinations and for revising the manuscript. We are also grateful to Linda Riti of Paleontological Museum “La Sapienza” of Rome, Dr. Paolo Schirolli of Natural History Museum of Brescia, Dr.ssa Anna Paganoni of Natural History Museum “Enrico Caffi” of Bergamo, Dr.ssa Gabriella Bianchi of Natural History Museum of Morbegno, Dr. Giuseppe Santi of University of Pavia and Dr. Cristiano Dal Sasso of Natural History Museum of Milan for the access to the collections.

This study is part of the project “The Permian-Triassic ecological crisis in the Dolomites: extinction and recovery dynamics in Terrestrial Ecosystems” financed by the Promotion of Educational Policies, University and Research Department of the Autonomous Province of Bolzano – South Tyrol.