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Nasrollah Abbassi

Abbassi, N., Alimohammadian, H., Shakeri., S., Broumand, A., and Brouman, S. 
Aptian small dinosaur footprints from the Tirgan Formation, Kopet-Dagh region, northeast Iran

Numerous dinosaur footprints are reported from the Cretaceous of Iran for the first time. These footprints are small and they have been discovered in the one of uppermost layers of the Tirgan Formation (Neocomian–Aptian), Gelian section, south Shirvan, Northeast Iran. The Tirgan Formation comprises Orbitolina-bearing bioclastic and oolitic limestones (200 m), which were deposited in the tidal flat to shallow marine environments of a carbonate ramp. Footprints were impressed in the subaerial conditions of an intertidal environment. Based on microfossils and stratigraphic position, they are Aptian in age. Most footprints are weathered and remained as indistinct holes, but five distinctive trackways are distinguishable. One of the trackways belongs to small sauropod with a narrow gauge. The means of pes footprint length and footprint width are 27.8 cm and 37.7 cm, respectively. Means of footprint length and footprint width of the manus in this trackway are 14.1 cm and 19.3 cm. Well preserved plantigrade stegosaurs footprints are circular to ellipsoidal in outline and include tridactyl pes and tetraductyl manus imprints. The means of footprint length and footprint width equal 15.5 cm and 12.8 cm in the pes and 6.4 cm and 10.3 in the manus. These stegosaur footprints as are assigned to Deltapodus isp. Abundant, small, quadrupedal ornithopod footprints (footprint length of pes and manus equals 13.0 cm and 9.7 cm; footprint width of pes and manus equals 18.4 and 15.0 cm) are attributable to Caririchnium and Ornithopodichnus, though they have a lower footprint length/footprint width ratio than the well-known ichnospecies of these ichnotaxa. It seems that, dwarfism of the Tirgan Formation’s dinosaur track-makers was due to the position of the Iranian microplate in northern part of Tethys, which is explainable by the island rule.    



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