Oligocene vertebrate footprints from the Lower Red Formation, Central Iran

Abstract

The Lower Red Formation (LRF) in Central Iran consists of the alternation of red-brown terrigenous sediments, marls and evaporites with basalt intercalations, exposed under the Chattian-Burdigalian Qom Formation and deposited on Eocene volcaniclastic sediments. The LRF is considered Rupelian in age. In the Deh Nar area, between Qom and Kashan cities, the LRF includes a basal conglomerate, alternations of brown-red sandstone and shale, colored marls with evaporite diapirs and top eroded red sandstone, with dark gray and green basalt lava intercalations. These sedimentary rocks are deposited in fluvial and playa environments, influenced by volcanic activities. Lower sandstone layers of the LRF in Deh Nar contain numerous vertebrate footprints, mostly preserved as convex hyporeliefs. Bird footprints are identified as Ardeipeda egretta, Aviadactyla vialovi, Avipeda phoenix and Gruipeda dominguensis. Small bird footprints are attributed to small, incumbent anisodactyl shoreline birds, such as sandpipers, and the larger of them to Gruiformes and Ciconiiformes, such as Ardeidae and Ciconiidae. Mammal footprints include Dehnaripus incognitus ign. nov. and isp. nov., Lophiopus isp., Moropopus elongatus, Moropopus kashanensis isp. nov., Platykopus stuartjohnstoni, and Zanclonychopus isp. Dehnaripus incognitus is large circular manus and pes imprints; usually, they show unorganized, large, radial surface wrinkles and their digital or metatarsal/ metacarpal imprints are ambiguous. Moropopus kashanensis is tridactyl mammal pes and manus imprints and is distinguished by sharp, claw-like imprints in lateral digits of the manus from Moropopus elongatus. Most probably, the mammal tridactyl footprints of Deh Nar made by three toed, medium- to large sized terrestrial herbivores perissodactyls such as Tapiroidea. Platykopus and Zanclonychopus, however, were remained by large carnivores such as Amphicyonidae or Ursidae. Trackmakers of footprints in the LRF of Deh Nar area lived under hot and dry conditions of terrestrial and evaporitic environments, after cool and dry conditions of the Early Oligocene.