Eurypterid setae and cuticle fragments from the Ora Formation (Upper Devonian) of Iraq

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Eurypterid setae and fragments of cuticle are encountered in palynological samples from different areas in Gondwana. In the literature published in the past seven decades, eurypterid remains are recorded as a part of Paleozoic palynological assemblages without giving significance to their biostratigraphic potential. This is because of the absence of a taxonomical classification that allows tracking the occurrence of similar specimens from different samples and regions. In the present study, a rich assemblage of eurypterids is found in the Devonian Ora Formation in Akkas-3 well in Iraq. The assemblage includes isolated setae and cuticular sheets that still have attached setae. The detached setae show great variation in dimensions including the seta length, base width and length/width ratios. This is in addition to other important morphological characteristics such as segmentation and flexible ends. The cuticular sheets in contrast hold many setae that are identical in shape and size. The observation of cuticular sheets that hold many identical setae is an indication that individual eurypterids produce certain classes of similar setae. This is the basis that can be used to establish taxonomy for the setae after accumulation of more extensive studies. The taxonomy will facilitate the tracking of the setae throughout successive sampling interval and biostratigraphic classification. At least 23 types of setae are documented throughout the studied samples in Ora Formation with some stratigraphical variations documented for five of them. The results of this study established the basis for taxonomic nomenclature for eurypterid remains that may be of benefit to biostratigraphic studies in the Paleozoic in Gondwana. The main morphological characteristics of the eurypterid cuticles and setae recorded in the present study are compared to those from other parts of Gondwana. The morphological differences and similarities are documented. The samples are also rich in spores and other terrigenous organic matter with the complete absence of marine palynomorphs. This indicates the deposition in a fresh water environment.