Early Cambrian lobopodian sclerites and associated fossils from Kazakhstan

Abstract

A low diversity fossil assemblage dominated by Mongolitubulus spines, from the Early Cambrian Geres Member of the Shabakhty Formation at Koksu, Malyi Karatau, Kazakhstan, enables identification of its sclerite variability within the scleritome. No other sclerotised structures could be matched with the spines, indicating that these were the only sclerotised part of the body and were periodically shed. The prominent spines of Mongolitubulus have a scale–like external ornamentation and fibrous internal structure. Possibly they armed the body of a lobopodian similar to Xenusion. The Mongolitubulus spines belong to a series of Cambrian phosphatic fossils, the other end members of which are sclerites of Microdictyon, the second most abundant component of the Koksu assemblage. The latter superficially resemble schizochroal trilobite eyes, but in life covered the dorso–lateral sides of the body segments, as is evident from complete specimens from the Chinese Chengjiang locality. A pair of sclerites of Microdictyon, representing uncompleted exuviation, from Koksu show that each hole originally contained a non–phosphatised lenticular body. This makes a compound eye nature of the Microdictyon sclerites likely, and even their homology with arthropod eyes cannot be excluded.