Witnessing floral evolution: a case study from Barakar formation in Lajkura colliery, Ib-river coalfield, Mahanadi Basin, India

ABSTRACT

Signatures for evolutionary trends have been observed in various glossopterid elements ora recovered from a single stratigraphic succession of Barakar Formation (Artinskian-Kungurian) of Lajkura Colliery, Ib River Coalfield. Significant variations in morphographic characters pertaining mainly to the non-existence/existence of midrib and venation pattern occurring in various species from older to younger horizons reveal two distinct assemblage zones. Assemblage zone–I (oldest, I^st horizon) consists of leaf genera- Noeggerathiopsis, Cordaites, Euryphyllum, Kawizophyllum, Buriadia, Gangamopteris, and Glossopteris whereas Assemblage zone-II (2^nd, 3^rd and 4^th horizons) consists of leaf genera Palaeovittaria, Raniganjia, Bengalia, Ginkgoites and Glossopteris. Barring few overlapping Glossopteris species all four horizons have their distinct sets of Glossopteris species. A gradual shift of Glossopteris species with narrow-mesh forms having evanescent and thin midribs in the I^st horizon to broad and middle-mesh forms with thick midribs in the youngest 4^th horizon, through middle-mesh forms with moderately thick midribs in 2^nd and 3^rd horizons has been noticed. The occurrence of distinct sets of taxa in successive coal seams demonstrates a characteristic pattern of floral distribution suggesting evolution in glossopterids, and prevalence of some specific climatic conditions during the deposition of these coal seams influencing origin and development of such distinct set of species.

KEYWORDS:

• Cordaitalean taxa
• emergence of midrib
• floristic evolution
• glossopterids
• ib-River Coalfield
• permian

Acknowledgments

The authors are greatly indebted to the Director, Birbal Sahni Institute of Palaeosciences, Lucknow (RDCC/25/2020-21) and Vice Chancellor, Sambalpur University, Sambalpur for permitting us to publish this paper and for providing necessary research facilities.

Disclosure statement

We don’t have any conflict of interests.