| Autor: |
GILI, EULÀLIA, SKELTON, PETER W., BOVER-ARNAL, TELM, PASCUAL-CEBRIAN, ENRIC, SALAS, RAMON |
| Předmět: |
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| Zdroj: |
Lethaia; Dec2023, Vol. 56 Issue 4, p1-18, 18p |
| Abstrakt: |
A morphometric analysis has been carried out on 140 specimens of the polyconitid rudist, Polyconites hadriani Skelton et al. from the Aptian carbonate platforms of the western Maestrat Basin, eastern Iberia, in order to compare the shapes of shells from platform-top to uppermost slope (pl) facies with those from nearby slope (sl) deposits. Comparisons between shells from these two palaeoenvironmental settings yielded the following results: (1) sl shells reached significantly larger sizes than pl shells (using commissural diameters as proxies for size), while no significant differences were found between the commissural diameters of lower and upper Aptian sl specimens; (2) relative growth of the dorso-ventral, and antero-posterior commissural diameters did not deviate significantly from isometry in either setting; (3) but in pl shells, radial growth of the attached valve's ventral margin was positively allometric relative both to commissural size and to radial growth of the dorsal margin, which had the effect of causing the commissural plane to tilt upwards ventrally during growth, in the manner of flat oysters; and (4) in sl shells, by contrast, radial growth of the ventral margin relative to the other variates did not deviate significantly from isometry, so the commissure was evenly raised during growth - with the exception of some crowded specimens, which did show some upward tilting of the ventral margin. These subtle differences of shell shape arising between coeval and contiguous populations are interpreted to reflect ecophenotypic variation in a single species resulting from adaptive plasticity of growth in response to differing conditions in the two settings. Although previous morphometric studies of other rudist taxa have focused on identifying intraspecific variation, most notably in relation to phyletic size increase, this is the first to apply the approach specifically to the recognition of ecophenotypic variation in a rudist species. A critical eye thus needs to be cast over the huge historical legacy of rudist 'species' arbitrarily distinguished on typological criteria. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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