Shell Area–To-Volume Ratio in Ammonoids

GRECO, ANDRES; PARENT, HORACIO; BEJAS, MATIAS

PALEONTOLOGICAL RESEARCH

PALAEONTOLOGICAL SOC JAPAN

Año: 2020 vol. 24 p. 216 - 225

1342-8144

The external area-to-volume ratio of the ammonite shell has been held to be related to morphology but never evaluated quantitatively. A dimensionless ratio, the Vogel number, was computed for large samples of Devonian to Cretaceous ammonites with a new method based on the ADA-model. The estimated ratios range from 2.4 to 3.4. The highest values are exhibited by uncoiled serpenticone ammonites, lowering in the sequence serpenticone-oxycone-spherocone. It is shown that the area-to-volume relationships are controlled by the involution (degree of overlapping) and the relative width of whorl section. The typical evolutionary trends serpenticone?spherocone and/or serpenticone?oxycone, broadly documented through the history of the Ammonoidea, could have been driven, at least in part, by the lowering of the area-to-volume ratio.