Morphology and paleoecology of the late Ediacaran tubular fossil Conotubus hemiannulatus from the Gaojiashan Lagerstätte of southern Shaanxi Province, South China

Conotubus hemiannulatus Zhang and Lin 1986 is a phylogenetically problematic tubular fossil that is only known from the late Ediacaran (ca. 551–541 Ma) Gaojiashan Lagerstätte in southern Shaanxi Province, South China. It is a cm-sized conical tube that tapers adapically from an aperture to a rounded apex. The tube consists of a series of nested cylindrical-to-funnel-shaped tube walls (cylinders hereafter). This conotubular construction of nested cylinders is similar to that of the late Ediacaran fossil Cloudina. Integrated morphological, taphonomic, and paleoecological data suggest that C. hemiannulatus occupied an epibenthic life-mode, with the apex anchoring to muddy substrate and the aperture extending upwards into the water column. It was probably a suspension-feeding organism. This soft bottom dweller employed specialized paleoecological strategies to rejuvenate and self-right the tubes after being subjected to sediment obrution, indicating strong burial-resistant capabilities. The tube likely provided space for the living organism, with successively larger cylinders added episodically to accommodate growth. Currently available evidence suggests that C. hemiannulatus likely had non-biomineralized tubes, and, although potentially closely related to Cloudina, its phylogenetic affinity remains unresolved.