The Cretaceous ammonite Eopachydiscus and the origin of the Pachydiscidae

Volume / Part: 26 / 3
Publication Date: July 1983
Page(s): 655 - 662
Authored By: W. J. Kennedy, C. W. Wright and G. R. Chancellor

£1.00

Eopachydiscus Wright, 1955 is confirmed as the earliest, Upper Albian representative of the Pachydiscidae, derived in all probability from a bullate member of the Beaudanticeratinae and giving rise to the Cenomanian-Coniacian Lewesiceras Spath, 1939. Nuclei of Eopachydiscus are ribbed, tuberculate, and constricted, showing even at this stage and date typical pachydiscid ornament; the evolution of Lewesiceras simply involved retention of these features into middle growth. The suggestion that the Pachydiscidae arose from Arrhaphoceras Whitehouse, 1927 of the Hoplitinae is discounted on morphological, stratigraphical, and biogeographical grounds.

Palaeontology - Volume 26 Part 3 Pages 655-662

Palaeontology - Volume 26 Part 3 Pages 655-662

Citations

KENNEDY, W. J., WRIGHT, C. W., CHANCELLOR, G. R. 1983. The Cretaceous ammonite Eopachydiscus and the origin of the Pachydiscidae. Palaeontology, 26, 3, 655–662.