OPPORTUNISTIC ECOMORPHS OR ICARUS POPULATIONS? INTERPRETING ASSEMBLAGES OF DIMINUTIVE BRACHIOPODS ASSOCIATED WITH A DEVONIAN TURNOVER EVENT
Diminutive assemblages of Allanella have long been recognized and explanations for their formation have included paedomorphosis and juvenile mortality, among others. Determining the cause of these assemblages has been stymied by preservational differences between facies, and the inability of linear measurements to morphologically differentiate specimens from different populations and at different ontogenetic stages. Simple linear measurements of shell width to length fail to distinguish any allometric trends among specimens within nearshore facies that would be usable in interpreting the diminutive fauna. What previously has been interpreted as an example of ecophenotypic variation (i.e., adaptation to dysoxic soft substrates), may be indistinguishable morphologically from an Icarus population: an assemblage of juveniles killed while dispersing into stressful fringe environments. Eigenshape analysis is now being employed to look for morphological variation missed by traditional linear morphometric techniques.