Palaeobiology of Palaeozoic medusiform stem group echinoderms.

No Thumbnail Available
Change log
Friend, Duncan 

The morphological details of both external and internal anatomy of a group of Palaeozoic fossil medusiform animals are described with the aid of text-figures and plates with explanatory drawings. This fossil group had a worldwide distribution with a stratigraphic range from the Lower Cambrian to the Upper Devonian and includes the following taxa:- Eldonia ludwigi Walcott 1911, E. eumorphus sp. nov., Rotadiscus grandis Sun and Hou 1987, Discophylluni peltatum Hall 1847, D. mirabile Chapman 1926, D. cryptophya (Clarke) 1900. Newly recognised anatomical structures for E. ludwigi include c.30, internal, radially-arranged, bifurcating lobes, a coelomic sac surrounding the alimentary canal, internal structures assumed to represent gonads and c.4 oral tentacles. E. eumorphus has c.44 internal bifurcating lobes associated with rows of pores on the ventral surface, which form a possible respiratory system. R. granclis has a possibly mineralised dorsal surface, rows of pores on the ventral surface and a tentacular appendage with arm-like extensions. Discophylluni 1s characterised by an ornamented dorsal surface with rows of elaborate pores. The nomenclature 1s revised, anatomical reconstructions are presented and modes of life in terms of feeding and benthic versus pelagic existence are discussed. It is concluded that this group, the Discophylla (equivalent in status to a new class), lies within the stem group Echinodermata. As a consequence, current understanding of the early evolution of the Echinodermata, especially with respect to internal anatomy, is questioned . A number of medusiforrn fossils, not studied in detail as part of this work, are discussed and tentatively assigned to the Discophylla.


This thesis is not available on this repository until the author agrees to make it public. If you are the author of this thesis and would like to make your work openly available, please contact us:

Cambridge University Library can make a copy of this work available only for the purposes of private study and non-commercial research. Copies should not be shared or saved in any shared facilities. Copyright over the content of these works is with their authors. Theses from the Library collection are considered unpublished works and according to UK legislation quoting from them is not allowed without permission from their author.

If you can commit to these terms, please complete the request form which you can find through this link:

Please note that print copies of theses may be available for consultation in the Cambridge University Library's Manuscript reading room. Admission details are at

Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge