Vertebrate Footprints from the Miocene Upper Red Formation, Shokorchi Area, Zanjan Province, NW Iran

Abstract

Bird, carnivore, and artiodactyl mammal footprints were found in the Miocene Upper Red Formation in the Shokorchi area, west Zanjan, NW Iran. The Upper Red Formation section (about 50 m thick) to the east of Shokorchi village is mainly composed of marls and hard, thin- to thick-bedded sandstone layers. Sinuous ripple marks, mud cracks, and raindrop prints are common on the bedding planes, and flute casts and ripple marks show north-northwest to south-southeast paleocurrent directions. The bird tracks include digitigrade tridactyl footprints without hallux or metatarsus imprints and are assigned to Iranipeda, Antarctichnus and Avipeda isp. These bird tracks were made mainly by charadriiform birds such as sandpipers or snipes and large birds such as cranes. Mammal tracks include carnivore footprints with manus and pes imprints. The manus imprints are better preserved than the pes imprints and are semiplantigrade with five short digits. Digit V is clearly distinct from digits I-IV. The tips of manus digit traces are rounded without claw marks. The pes imprints are poorly preserved as a rounded or oval shape with no digit imprints and only one or two depressions in the mid to front parts of pes imprints. It seems that these footprints belonged to a carnivore in which the forefeet supported most of the animal's weight. These imprints determined as Platykopus ilycalcator and were made by large ursid. Artiodactyl footprints vary from wedge to rounded rectangular or heart shaped. Digits III and IV imprints are distinct with interungual ridges in the median or posterior region. The artiodactyl footprints are Pecoripeda (Gazellipeda) gazella, and because of the high density of tracks, distinguishing pes and manus imprints are impossible. These may have been made by a herd of artiodactyls that traversed a broad area.

Keywords:

• Trace fossils
• Miocene
• footprints
• Upper Red Formation
• Iran