Evolutionary prospection in Globorotalia menardii

 

In practice we use menardiform globorotalids for the study of evolution. In the figure to the left the low frequency portion of the density distribution of G. menardii, is shown for DSDP Site 502 (Caribbean Sea). Density means here the relative number of specimens per grid-cell, whereby each grid-cell is spanned by units in direction of the spiral height of the shell (red axis), units in direction of the length of the shell in axial view (green axis) and units of geological time (blue axis).

 

The axes are normalized to units between o and 1 in oder to better represent the pattern. The orange "carrot" illustrates stasis in smaller forms in the lower 2/3 of the time span. Only in the upper third, G. menardii has developed large forms, which is during and after the closure of the Isthmus of Panama. The blue axis covers a time span from 8 Ma to 0 Ma.

 

The red axis extends from 0 to 675 micrometers (spiral height), and the green axis from 0 to 1550 micrometers (axial length). The yellow plane, that cuts the density distribution at a value of about 0.2 (corresponding to an age of about 1.6 Ma), shows the internal structure of the "carrot" by lines, that contour frequencies of specimens in the morphospace of shell-width versus shell-length at that time.

 

 

Click here for launching a rotating animation of the carrot diagram.

Click here for launching a pulsing animation of the carrot, showing

the distribution at various values of density (specimens per grid-cell).

For a full presentation of methods see Knappertsbusch and Mary (2012).

 

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