The earliest known fossils confidently classified as tapeworms have been dated to , after being found in coprolites (fossilised faeces) from an elasmobranch. Putative older fossils include a ribbon-shaped, bilaterally symmetrical organism named Rugosusivitta orthogonia from the Early Cambrian of China, brownish bodies on the bedding planes reported from the Late Ordovician (Katian) Vauréal Formation (Canada) by Knaust & Desrochers (2019), tentatively interpreted as turbellarians (though the authors cautioned that they might ultimately turn out to be fossils of acoelomorphs or nemerteans) and circlets of fossil hooks preserved with placoderm and acanthodian fossils from the Devonian of Latvia, at least some of which might represent parasitic monogeneans.
The earliest known fossils confidently classified as tapeworms have been dated to  after being found in coprolites (fossilised faeces) from an elasmobranch. Putative older fossils include a ribbon-shaped, bilaterally symmetrical organism named Rugosusivitta orthogonia from the Early Cambrian of China, brownish bodies on the bedding planes reported from the Late Ordovician (Katian) Vauréal Formation (Canada) by Knaust & Desrochers (2019), tentatively interpreted as turbellarians (though the authors cautioned that they might ultimately turn out to be fossils of acoelomorphs or nemerteans) and circlets of fossil hooks preserved with placoderm and acanthodian fossils from the Devonian of Latvia at least some of which might represent parasitic monogeneans.