Abstract
Nummulites with reticulate septal filaments stratigraphically span from the Bartonian to the Rupelian Stages. The size of the proloculus of the megalospheric forms of reticulate species helped recognise N. fabianii – N. fichteli lineage in western Tethys. Unlike the species of this lineage, N. ptukhiani, described from Armenia, is characterised by an unusually large proloculus. A possibly second lineage of reticulate species comprising N. ptukhiani is recently reported from Lutetian – Bartonian succession of Tanzania. The present study examines reticulate species from palaeogeographically adjacent Bartonian succession of Kutch. The statistical analysis of the biometric data suggests the presence of three distinct species, referred to Nummulites ptukhiani, N. aff. hormoensis and N. acutus. The reticulation starts developing in N. acutus that ranges from P13 to P14 in its type locality, Kutch. We infer that Nummulites ptukhiani and N. aff. hormoensis possibly evolved from N. acutus in Zone P14. A binary tree model based on Classification and Regression Tree is proposed to statistically discriminate the three reticulate species.
Highlights
In the planispirally coiled foraminiferal genus Nummulites the septa continue over the lateral surfaces of the test as septal filaments
The N. garganicus – N. hormoensis – N. fabianii – N. fichteli – N. bormidiensis lineage is well established in the western Tethys (Less & Özcan, 2012)
Three species of reticulate Nummulites are recognised in the Bartonian succession of Kutch
Summary
In the planispirally coiled foraminiferal genus Nummulites the septa continue over the lateral surfaces of the test as septal filaments. The proloculii of the reported N. hormoensis and N. fichteli are two times that of the respective species in the western Tethys (Table 1) Does it imply that (i) the eastern Tethys developed an independent lineage of reticulate Nummulites and, (ii) there are multiple lineages evolving contemporaneously in a region? Reticulate; surface smooth Reticulate; apical mamelon (polar plug) Sinuous septal filaments in A forms but crude reticulate structure reported in B forms; coarse, spirally arranged granules; Reticulate; surface smooth Reticulate; no pustules Primitive reticulation; no pustules, sometimes small polar pillars Reticulate; no pustules or polar plug Reticulate; raised polar plug Reticulate; small pustules near polar region; no polar plug Primitive reticulations at periphery; small granules, pillars in polar region They belong to Fulra Limestone of Bartonian age, referred by Samanta (1970) to Zones Orbulinoides beckmanni – Truncorotaloides rohri (P13-P14). Saraswati and Sabnis (2006) discussed the methodology of CART and its application in the taxonomy of Nummulites
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