1014


Journal of Paleontology


Figure 8. Variation in the outline (length/width) and profile (thickness/width) of A. tarimensis n. sp. from the Kuruktag Platform in northwestern China in comparison with A. zhejiangensis from the JCY area in South China. The r2 values are indicated for respective linear regression lines. Both species share a similar outline, but are significantly different in lateral profile.


Figure 9. Variation in number of ribs in the sulcus at the anterior of A. tarimensis n. sp. and A. zhejiangensis as shown in a frequency plot (left) and figured specimens (right). Both A. tarimensis n. sp. shells are from the same population, collection AFT-X 400; A. tarimensis n. sp. shells are also shown in Figure 5 in full.


only one rib within the ventral sulcus that corresponds to two ribs on the dorsal fold that are separated by a median groove and the shells have a more rounded outline in comparison to the subcircular to subpentagonal Altaethyrella.


Morphological variation within Altaethyrella tarimensis n. sp. —As in other species of Altaethyrella, there is considerable intraspecific variation in A. tarimensis n. sp. in terms of: shell size, shell shape, number of ribs in the ventral sulcus and dorsal fold, and degree of asymmetry.


The collection contains shells of a range of sizes and shell


shapes. Shell length, for example, varies from 7mmto 17.9mm, or a difference of 256% (see Tables 1–3). To illustrate the variability of shell shape, shell length/width and thickness/width were plotted as proxies for shell outline and convexity, respectively, independent of shell size (Fig. 8), producing a linear trend indicative of a single morphospecies. The r2 values from linear regression in both cases are near 0.80, indicating a clear trend, but the scatter of individual datapoints reveals some variability.


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