First report of Sphenothallus Hall, 1847 from the lower Cambrian of North China

Sphenothallus is a tubular organism that is one of the most widely distributed and longest-ranging genera through the Palaeozoic. Despite its apparent cosmopolitan distribution, the genus has never been reported from North China. New specimens of Sphenothallus sp. have been discovered in the upper part of the Houjiashan and base of the Mantou formations (early to middle Age 4, Epoch 2, Cambrian) in Jiangsu Province, North China. The specimens are small tubes (up to 5 mm long) and have typical Sphenothallus characteristics, such as a multilayered lamellar structure, and subcircular to elliptical transverse cross-section with a pair of longitudinal thickenings situated at the widest diameter. Our material shows that both the rate of apertural expansion and the curvature of the tubes are significantly larger in early growth stages than in the later growth stages. As the diameter of the aperture increases, the transverse cross-section of the Sphenothallus sp. tube changes from subcircular at the proximal end to elliptical or lenticular at the distal end, and its wall thickness changes from uniform to thickening longitudinally. The discovery of Sphenothallus sp. from the North China Platform represents an extension of its palaeogeographic range during the Cambrian.