Populations of eight species of charophyte gyrogonites from the Morrison formation (Jurassic), Front Range area, Colorado, collected in successive samples in six measured sections, show differences in average size, variation in size, and in tightness of spiralling. These differences, the same kind as are found among Recent charaphyte subspecies, are suggestive of genetic changes resulting from evolution. The relative abundance of species in samples is apparently controlled by ecological conditions similar to those operative in distributing Recent Charophyta.

The proposed correlation of the six sections is based on population characteristics of the more abundant species, Aclistochara bransoni Peck, Praechara symmetrica Peck, and Latochara Latitruncata (Peck).