Determination of the causes of the Permian -Triassic boundary(PTB) biotic crisis is hindered primarily by the diachronous nature ofthe used PTB. poor stratigraphic control of compared Upper Permianand Lower Triassic faunas. espec ially in cont inental biotopes. poorknowledge of the lower and middle Scythian faunas from m. https://unitedssports.shop/product-category/bike-parts-fork-parts/