Metaphyte and Metazoan fossils from Precambrian sediments of India: a critique

Abstract

Evidences of multicellular life from the Indian Precambrian sediments have been reviewed. Their nature, morphology, biogenecity and syngenecity are evaluated in the light of associated evidences. The published records have been grouped under 13 categories, viz., Archaeocyatha, Chuaria·Tawuia group, frordoid forms, Hyolithoides, Longfengshania, medusoids, metaphytic algae, Sekwia excentrica, shelly forms, spiral forms, trace fossils, trilobitoid and eurypteroid and enigmatic group. Contrary to the world-wide records of multicellular organisms only at the Terminal-Precambrian (≈600 Ma), some of the Indian reports are 1,000-2,500 Ma old. This older antiquity needs proper explanation. In the present review after reassessment, all the records have been classed as true fossil, non-fossil and dubiofossil. In few cases, it has not been possible to comment upon the structure reported due to non-availability of specimen and poor photographic reproduction in print, such records have been grouped separately without any comments.

In several cases synaeresis and mud cracks have been described as trace fossils. Sedimentary structures have also been described as Sekwia, Longfengshania, Cyclomedusa, Archaeocyatha, Dasycladaceae algae, Epiphyton, lamellibranchs and such other forms Some records though of undoubted biogenic nature, viz., Katnia singhi and Vindhyavasinia misrai and Ajaicicyatha (from Krol sediments) need reassessment concerning their taxonomic affinity.

The oldest authentic biogenic structures in this review are considered to be about 1,000 Ma old. These records of metaphytes and metazoans-Ramapuraea vindhyanensis, vendotaenid forms, trace fossils, megascopic spiral algal forms and Chuaria·Tawuia assemblage, are mostly from the base of Kaimur and top of Semri groups. Trace fossils from Bhander Limestone of Vindhyan Supergroup; a metaphytic alga Renalcis from the Calc-Zone of Pithoragarh, and frondoid forms, trace fossils as well as small shelly fauna from the Krol-Tal sequence belonging to younger sediments of probable Vendian-Tommotion age are authentic records.

The multicellular plants and animals undoubtedly proliferated during the Vendian, but there are a few authentic exceptional records of multicellular life prior to 600 Ma from India. Similar earlier records are also known from China and Canada. These records are important in understanding the antiquity of multicellular life.