Chakpaktas Formation (also known as the Chakpaktas svita) is a geological formation in eastern Kazakstan, as well as being the lowest fossil-bearing strata of the Zaysan Depression. The formation is aged to the Arshantan Asian Land Animal Age which correlates to between the upper Ypresian and lower Lutetian.[1][2]
The Chakpaktas formation is made up of 29 meters of deposits with the sediment transitioning from mudstone to sandstone around midway through.[3] It contains interbedding of quartz and pebbles at the lower parts of the deposit.[4]The mammal localities of the formation can only be found in the southeastern part of the basin which falls in between the Kalmakpay Mountain and Kendyrlyk River.[5]
A more terrestrial crocodilian, the genus is of questionable validity as some species have been moved to other genera.[8] It is not completely known where the material attributed to the species is found, though it is most likely to have come from the Chakpaktas Formation.[4]
A hyrachyid known from a fairly complete skull,larger than other species within the genus like E. tianshanicus. It was orginally described as the genus Subhyrachyus.[9]
An isectolophidperissodactyl that helped to confirm the correlation between the Arshantan and Bridgerian land animal ages. The animal lacked the postcanine diastema seen in most ungulates.[1]
Kazakhstan