|Case study 5 - Heterochrony in a fossil rhynchosaur reptile|
Data file: rhynch.dat
Heterochrony involves differences in the timing of developmental processes; thus detailed, preferably statistical, analyses of ontogenetic series are of considerable value in unravelling and identifying the track and mode of heterochronic trends in phylogeny. The rhynchosaur reptiles were abundant and widespread during the mid and early late Triassic. Benton & Kirkpatrick (1989) have studied heterochrony in the rhynchosaur Scaphonyx.
|Two growth stages of the rhynchosaur Scaphonyx (from Benton & Kirkpatrick 1989, text-fig. 10 with permission from the Palaeontological Association).|
Nine measurements were made (in mm) on a small sample (N=13) of the rhynchosaur Scaphonyx fischeri: SKULL, SKULW, ORBIT, FRONW, FRONL, PARW, PARL, UTLEN and UTWID.
|Location of measurements on the skull of Scaphonyx (from Benton & Kirkpatrick 1989, text-fig. 3 with permission from the Palaeontological Association).|
Investigate the parametric and non-parametric mutual correlations of the variates. Try the Rho/Tau correlation (non-parametric) on pairs of variates at a time, and then try 'Correlation' (parametric) on the whole data matrix. Discuss the strength of correlation between variates in this sample.
More information about linear regression can be found in the manual.
Benton & Kirkpatrick (1989) used some of the allometric trends in their sample to illustrate a peramorphic evolutionary cline towards a broader skull type (for example SKULL vs. FRONW and PARW). Does your study support these conclusions?
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