A review of the early Cambrian tubiform fossil Anabarites: taxonomy and spatiotemporal distribution
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Abstract:
The tubiform fossil Anabarites, characterized by triradial symmetry, is a common component of early Cambrian small shelly fossils (SSFs). Although its record may extend into terminal Ediacaran strata, typical species such as Anabarites trisulcatus first appear at the base of the Cambrian Fortunian and serve as key index fossils for the Anabarites trisulcatus-Protohertzina anabarica Assemblage Zone of the lower Fortunian in South China. Owing to extensive synonymy problems, this study reevaluates the status of all 41 species previously assigned to the genus Anabarites. Through a comprehensive analysis of diagnostic characters, including tubular morphology, development of longitudinal grooves, and variability in growth angles, we propose a revised classification scheme recognizing 14 accepted species. Spatiotemporal distribution analysis further reveals three distinct evolutionary stages: occurrence, diversification, and decline. The genus underwent its initial radiation in the Fortunian Age, reaching peak species diversity and maximal geographic distribution by the late Fortunian. A pronounced decline began in Cambrian Stage 2, marked by reduced abundance and contracted geographic range. This genus gradually went extinct during Stages 3–4, with occurrences restricted to a single region. Evolutionary trends in morphology show a clear shift from simple to more complex forms over time: tubular symmetry transitions from triradial to hexaradial, longitudinal surface grooves deepen progressively, and development of growth lines becomes increasingly pronounced.
