1. de Bary, A. Die Erscheinung der Symbiose. Vortrag auf der Versammlung der Naturforschung und Ärtze zu Cassel. Verlag von Karl J. Trubner, Strassburg. pp. 1–30 (1879).
2. Sapp, J. The dynamics of symbiosis: an historical overview. Can. J. Botany 82, 1046–1056 (2004).
3. Zapalski, M. K. Is absence of proof a proof of absence? Pal., Pal., Pal. 302, 484–488 (2011).
4. Alexander, R. R. & Brett, C. E. Symposium on Paleozoic epibionts: Introduction. Hist. Biology 4, 151–153 (1990).
5. Wang, H., Zhang, Z., Holmer, L. E., Hu, S., Wang, X. & Li, G. Peduncular attached secondary tiering acrotretoid brachiopods from the Chengjiang fauna: Implications for the ecological expansion of brachiopods during the Cambrian explosion. Pal., Pal., Pal. 323, 60–67 (2012).