Dinosaur tracks from the Jurassic Shemshak Group in the Central Alborz Mountains (Northern Iran)

Abstract

Abstract The Shemshak Group includes alternating layers of coal-bearing shale and siliciclastic sediments in the Baladeh area in the central Alborz Mountains of northern Iran. A diverse and abundant Jurassic dinosaur footprint assemblage is now recognized in the group, which is Toarcian to Bajocian in age in the northern Baladeh. This is the first report of a diverse dinosaur ichnoassemblage from Iran that includes the footprints of sauropods. These tracks can be assigned to three groups of trackmakers: theropods, ornithopods and sauropods. Those of theropods are typically tridactyl in shape, their trackways reflecting bipedal movement. Theropod footprints are very abundant in both northern and western Baladeh. The studied theropod tracks themselves are divided into three major dimensional groups. The medium sized footprints (footprint length, 11-15 cm) are abundant and have a stride length, digit and pace angles like the coelurosaurs footprints and trackway. Theropod footprints were identified as similar to Schizograllator otariensis, Talmontopus tersi and Wildeichnus isp. Ornithopod footprints are tridactyl with rounded and thick toes and belong to bipeds. Some didactyl imprints were also observed. Skin imprints were well preserved in these footprints. The ornithopod tracks resemble Jiayinosorupus johnsoni, as well as Velociraptorichnus sichuanensis for didactyl footprints. Sauropod footprints found in the western part of Baladeh are assigned here to Eosauropus isp., which are pentadactyl pes imprints of a quadruped. The assemblage from Iran resembles similar associations from eastern Asia.