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References: GRZEGORZ PACYNA and DANUTA ZDEBSKA (2012) Carboniferous plants preserved within sideritic nodules – a remarkable state of preservation providing a wealth of information. Acta Palaeobotanica 52(2): 247–269, 2012.

Palaeoxyris is now thought to be the shark egg morphotype of the family Hybodontoidae. Quote from Fischer & Kogan (2008): "Based on the size differentiation and frequency of two Palaeoxyris species and different hybodont shark remains from the Stephanian lacustrine Wettin strata of the Saale Basin, Germany, SCHNEIDER (1986) was able to assign both egg capsules to their putative producers (P. helicteroides to Lissodus lacustris and P. carbonaria to Limnoselache [Sphenacanthus SOLER-GIJÓN, 1997] vicinalis; this attribution was confirmed by GEBHARDT, 1988) (Fig. 5), which occurred in the same strata but in different sedimentary facies. The capsules were mainly found in fluviatile-palustrine deposits, whereas skeletal remains were restricted to pelagic lacustrine sediments. So it seemed plausible that both hybodont shark species used the shore area of the lake for spawning." Lit.: Jan Fischer & Ilja Kogan (2008) Elasmobranch egg capsules Palaeoxyris, Fayolia and Vetacapsula as subject of palaeontological research – an annotated bibliography. Freiberger Forschungshefte, C 528, pp75-91