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Notes on Graphical Methods of Recording the Dimensions of Ammonites

Published online by Cambridge University Press:  01 May 2009

C. H. Waddington
C. H. Waddington
Affiliation:
Sedgwick Museum, Cambridge.
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Summary

(1) When the diameter of the umbilicus of an ammonite is plotted against the diameter of the whole shell, or the whorl-thickness plotted against the whorl-height, the curves obtained are very commonly straight lines for the greater part of their courses.

(2) If, as is usually the case, these lines do not pass through the origin, the formula for the ammonite spiral is of the form r + c = eβθ and not r = eβθ.

(3) If the straight lines do not pass through the origin, it is useless to express one dimension as a percentage of the other and compare these percentages in different shells.

(4) There is no way of foreseeing, before the measurements are made, whether the dimensions of a species will plot accurately on a single curve or whether they will show a considerable amount of scatter. If, however, they do fall accurately on a single curve, this fact is an argument for the validity of the species, and the curve is a useful aid in the identification of other specimens.

Type
Original Articles
Information
Geological Magazine , Volume 66 , Issue 4 , April 1929 , pp. 180 - 186
Copyright
Copyright © Cambridge University Press 1929

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References

page 180 note 1 Buckman, S. S., Yorkshire Type Ammonites, vol. ii, 1913, p.viiiGoogle Scholar

page 182 note 1 Neaverson, E., Amm. Up. Kimm. Clay, Liverpool Univ. Press, 1925. p. 17 et seq.Google Scholar

page 182 note 2 Ilovaisky, D., Amm. Jur. Sup. du pays de Liapine, Ouv. Sect. Gèol. Soc. Imp. Amis de Sci. Nat. de Moscou, 1917.Google Scholar

page 182 note 3 Buckman, S. S., loc. cit., vol. v, 1924, P. 13 et seq.Google Scholar

page 183 note 1 This method is only useful when the two groups of shells can be separated by characters other than their dimensions, but it is only under these circumstances that the problem is likely to arise.

page 183 note 2 Fisher, R. A., Statistical Methods for Research Workers, p. 117.Google Scholar

page 183 note 3 The differences between these two groups will be fully dealt with in a future publication.

page 185 note 1 Brinkmann, R., “Statistisch-phylogenetische Untersuchungen an Ammoniten,” Zeits. für Ind. Abst. u. Vererbungslehre, Suppl. Bd. 1, 1928; p. 496;Google Scholar and, by the same author, “Statistisch-Biostratigraphische Untersuchungen an mitteljurassischen Ammoniten über Artbegriff und Stammesentwicklung,” Abh. d. Ges. d. Wiss. zu Göttingen, N.F., Bd. xiii, 3, 1929.Google Scholar

page 185 note 2 This is Neumann's “conchospiral”. See Thompson, D'Arcy W., On Growth and Form, p. 531 et seq., and references given tbere.Google Scholar

page 186 note 1 See note 2, p. 185.