Mukhopadhyay, S. K. (2017). Neonummulites gen. nov., representing a phylogenetic link between evolute and involute nummulitines. Micropaleontology. 62(5): 365-383.

335534

Mukhopadhyay, S. K.

2017

62(5): 365-383

Publication

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A new genus Neonummulites gen. nov. and its two new species - Neonummulites depressa sp. nov. and Neonummulites granuli sp. nov.- are designated and described from the middle Eocene succession of Gujarat India.With planispiral coiling, undivided simple chambers andmarginal cord, the new genus belongs to the subfamily Nummulitinae. It is conspicuous in axial section by evolute chambers and evolute whorl walls during the premature stage and involute chambers and involute whorl walls at the mature stage. The commonly occurring change from involute to evolute coiling is considered a generic feature in the subfamily, and in this regard, a change of coiling from evolute to involute during ontogeny is given due importance as a generic feature. With the absence of transverse trabeculae in the polar area, the premature part possesses some distinctive characters of evolute Operculina whereas with trabeculae, septal filaments and moderately thickmarginal cord in the extra-polar area, themature part resembles involute Nummulites. The successive development of the features of evolute and involute nummulitines during the ontogeny suggests Neonummulites gen. nov. possibly represents a phylogenetic link between the two principal genera. Of its two recognized species, Neonummulites depressa sp. nov. is distinct with thin discoidal smooth test having a mild depression on the one side, andwith inflated lenticular test Neonummulites granuli sp. nov. is distinct with heavy polar granulations.

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