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RCFossils posted a topic in Member CollectionsKottixerxes belongs to a fascinating group of problematic arthropods named Euthycarcinoidea. The current thinking is that they are marine cousins distantly related to insects and myriapods. When Schram first described Kottixerxes in 1971, the Euthycarcinoidea were only know from 2 Triassic aged sites in Germany and Australia. At the time it was described, Kottixerxes was the oldest known Euthycarcinoid. Since that time, Euthycarcinoidea have been found in strata dating back to the Cambrian. In fact there is evidence from a site in Wisconsin that Euthycarcinoids may have been the first creature with the ability to walk on land. Trackways and body fossils have been found that suggest they may have made brief trips out of the water for feeding and possibly egg laying. Based on gut contents, Kottixerxes was a bottom dwelling detritus feeding organism. Kottixerxes is one of the rarest Arthropods found in the marine portion of the Mazon Creek deposit. In 1985, A faunal study was done by Gordon Baird, John Anderson and others to try and determine relative abundance of different Mazon Creek fauna. Using a small army of volunteers, they collected and split nearly 230,000 concretions from the Essex portion of the deposit. Approximately 145,000 of these were “duds”. The other 85,000 were identified and recorded to determine rarity. Out of these 85,000, 2 specimens of Kottixerxes were found making up approximately .002% of the fauna found. The specimen shown may be the finest and largest ever collected. Schram was able to locate nine specimens for his original description. Most are poorly preserved as the carapace must have been quite thin. The largest from his study measured 4 centimeters. They normal average between 2 and 3. This specimen measures slightly over 7 centimeters and is the largest that I am aware of.