Youngibelus

Youngibelus tubularis and Y. levis are two species from Toarcian aged rocks in Yorkshire. It has been suggested that these two species are actually morphs of the same species. The divergence in morphology occurs in the gerontic stage of development, characterised by differences in the rostrum. In Y. levis, the rostrum thickens, whilst in Y. tubularis, an epirostrum develops. Peter Doyle proposed that the epirostrum developed as either a counterbalance for a sexual adaptation, or for display in courtship.^[2]

• Riegraf, W. (1980). "Revision der Belemniten des Schwäbischen Jura. Teil 7". Palaeontographica Abteilung A (in German). 169 (4–6): 128–206.
• Simpson, M. (1855). The Fossils of the Yorkshire Lias Described from Nature. Whitby & London. pp. 256 pp.{{cite book}}: CS1 maint: location missing publisher (link)
• Young, G.; Bird, J. (1822). A Geological Survey of the Yorkshire Coast. Whitby: Clark. pp. 335 pp.

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