Morphological variability and paleoecology of the Late Ordovician Parastrophina from eastern Canada and the Tarim Basin, Northwest China

Bivariate and multivariate analyses of well-preserved specimens of four species of the Ordovician–Silurian brachiopod genus Parastrophina from eastern North America, the Tarim Basin of Northwest China, and Kazakhstan revealed that the subelliptical shells of Parastrophina hemiplicata from southern Ontario are less globose than the subpentagonal shells of Parastrophina tarimensis n. sp. from the Tarim Basin. Parastrophina minor from Baffin Island has a subelliptical outline, similar to P. hemiplicata, but is more globose than the specimens from southern Ontario, although this increased globosity was due partly to increased convexity of ventral valve. Three specimens of Parastrophina iliana from Kazakhstan show features between the extreme forms of P. hemiplicata and P. tarimensis. These differences may be related to different paleoenvironmental settings — an enlarged dorsal valve in P. tarimensis would enable the development of larger lophophores at maturity for feeding and gas exchange in the generally low-energy, shallow-water carbonate mound settings in the paleoequatorially located Tarim Basin and Kazakhstan terranes, whereas a wider outline would increase stability on the high-energy, storm-influenced, flat-bottom substrates in the epeiric seas of southern Ontario, which was located in the subtropics during the Late Ordovician.