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Research Article SOFT–BODIED EDIACARAN METAZOANS AND Available Online at http://www.recentscientific.com International Journal of CODEN: IJRSFP (USA) Recent Scientific International Journal of Recent Scientific Research Research Vol. 11, Issue, 07 (B), pp. 39177-39191, July, 2020 ISSN: 0976-3031 DOI: 10.24327/IJRSR Research Article SOFT–BODIED EDIACARAN METAZOANS AND ICHNOFOSSILS FROM THE MARWAR SUPERGROUP, WESTERN RAJASTHAN: EMERGENCE OF EARLIEST MULTICELLULAR, COMPLEX MEGASCOPIC ANIMAL LIFE Purnima Srivastava Centre of Advanced Study in Geology, Lucknow University, Lucknow, 226020 DOI: http://dx.doi.org/10.24327/ijrsr.2020.1107.5457 ARTICLE INFO ABSTRACT Article History: Well preserved ediacaran fossils have earlier been discovered from the basal part of the Marwar Supergroup, western Rajasthan. The assemblage reported till date comprised of medusoids and Received 06th April, 2020 microbial mats only. Ediacaran assemblage with fronds viz. Charniodiscus and trace fossils are Received in revised form 14th reported for the first time from the Jodhpur Sandstone formation of the Marwar Supergroup. In May, 2020 Jodhpur assemblage, discs of variable sizes and morphological structures are associated with un- Accepted 23rd June, 2020 oriented, haphazardly distributed mesh of irregular bodies comparable to algae. These discs exhibit a Published online 28th July, 2020 wide size range from a few millimeters to 75 centimeters in diameter. Exceptionally large size of the discs in present assemblage represents largest discs reported so far from any Ediacaran assemblage. Key Words: Although, larger medusoid discs have been reported from USA, but they are from the Middle Ediacaran, Marwar Supergroup, Metazoans, Cambrian and even younger rocks. Presence of microbial mats and weed-like structures with well Multicellular preserved hold fasts and horizontal rhizome like structures in association with some of these large- sized discs support their animal affinity, which probably feed on this weed- like vegetations. This association also support their benthic habitat. Unlike general trend of sudden increase in size of organisms in Ediacaran period and further decrease in size during Cambrian, these discs continued increasing in size in Cambrian also. Palaeoecological distribution of such well preserved morphologies are certainly an indication of ecosystem, where algal blooms enhabited the Ediacaran organisms represented by medusoid discs and possibly serve as their food. Moderately diverse Ediacaran body fossils, traces, burrows and giant sized algal fossils occur sporadically in Jodhpur Sandstone Formation, which are well exposed in open mines in and around Sur Sagar and Artiya Kalan area of Jodhpur district (see Srivastava, 2012-c and 2013, 2015). Here in this paper we deal only with Ediacaran metazoan body fossils (impressions) and ichnofossils. Copyright © Purnima Srivastava, 2020, this is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original work is properly cited. INTRODUCTION related to modern jellyfish and corals, representing first megascopic animals known in fossil record. In recent years The Ediacaran period was a distinctive stage of biological these fossils have been compared with plants, giant single- evolution and Ediacaran fossils represent the earliest known celled organisms and even a failed evolutionary experiment macroscopic and complex life forms on the planet earth. They completely separated from all known kingdoms of life occur in various parts of world for which more than thirty (Seilacher, 1992). Most of the Ediacaran fossils are preserved species have been identified so far. Reconstruction of as casts and molds in relatively coarse siliciclastic sedimentary biological evolution in the fossil records, only reflect the wide rocks (Narbonne, 2005). Their unusual morphology resulted in expansion of metazoans with a mineralized skeleton. However various interpretations regarding their affinities like lichens, the timing of appearance and early radiation of extant high rank which covered much of the earth during Precambrian times taxa is still a matter of debate for many reasons. The possible (Retallack, 1994), fungus-like organisms (Peterson et al., absence of skeletons in majority of Vendian organisms may be 2003), prokaryotes (Steiner and Reitner, 2001), stem or crown- one of them (Serezhnikova, 2014). Ediacaran fossils are group animals (Glaessener, 1984; Conway Morris, 1993; considered the black holes of palaeontology so inscrutable, Fedonkin and Waggoner, 1997) or vendobionts that are which swallow up every theory thrown at them. Conventionally different from animals (Seilacher, 1992). Problem of large-size they have been interpreted as the impressions left by animals *Corresponding author: Purnima Srivastava Centre of Advanced Study in Geology, Lucknow University, Lucknow,226020 International Journal of Recent Scientific Research Vol. 11, Issue, 07 (B), pp. 39177-39191, July, 2020 of ediacarans in Precambrian time is explained by Seilacher as Geological Setting bodies of Ediacaran organisms was comprised of fluid-filled The Marwar Supergroup was previously known as Trans compartments just like an air-mattress. Among quilted body Aravalli-Vindhyans where sedimentary rocks occurring on structures, a large surface area was maintained across which western side of NE-SW trending Aravalli Ranges in parts of nutrients and gasses could diffuse. These organisms must have Bikaner, Churu, Ganganagar, Jaisalmer, Jodhpur, Nagaur and absorbed nutrients from sea-water or harbored symbiotic Pali districts of Rajasthan. Khan (1971) designated these rocks microbes that provided nourishment through photo synthesis or as Marwar Superroup and gave the startigraphic succession. chemosynthesis. Absence of proper mouth and anal structures The supergroup is further divided into three groups, in in Ediacaran fossils also favor the plant affinity to some extent, stratigraphic order these are; Jodhpur, Bilara and Nagaur where photosynthetic ability could explain puzzling aspect. Groups (Pareek, 1984). The rocks of Jodhpur Group show The uncertainity of taxonomic position of these organisms has overlapping relationship with the Malani volcanics (Paliwal, led to different opinions on their place in the evolution. Despite 1998).which is dated as 779- 681 Ma (Rathore et al. 1999). The conflicting theories and reconstructions, some Ediacaran taxa Jodhpur Group is further divided into three formations; these are unanimously assigned to basal group of metazoa are Pokran Boulder Beds, Sonia Sandstone Formation and (Glaessner, 1984; Fedonkin 1985; Seilacher et al., 2003, Girbhakhar Formation. Chauhan et al., 2004, merged the Sonia Fedonkin et al., 2007; Xiao & Laflamme, 2009). Their views Sonia and Girbhakhar Sandstone Formations and named them are not in contrast with present day palaeontological and Jodhpur Sandstone Formation (Fig 2). Ediacaran fossils have molecular genetic reviews, according to which most been reported from the outcrops of Jodhpur Sandtone exposed Phanerozoic animal phyla formed in the late Precambrian in numerous quarries at and around Sur Sagar and Artiya Kalan (although very little evidence is provided by the fossil record). areas of Jodhpur district (Fig. 1). The rocks are least disturbed, It is also believed that in Cambrian, animals became diversified almost horizontal and exhibit well preserved sedimentary and many bilaterian taxa acquired skeletons (Erwin et al., structures like ripple marks of various scales and alignments, 2011). Very recently well preserved ediacaran fossils have been cross bedding, internal primary sedimentary structures, range discovered from the basal part of the Marwar Supergroup, from trough cross bedding, small-scale cross beddings etc. western Rajasthan (Raghav et al., 2005, Kumar et al., 2009, Lithology at Artiya Kalan, chocolate brown sandstone Kumar and Pandey, 2009, Srivastava, 2012 a,b,c). The interbedded with siltstone, shale and conglomeratic sandstone assemblage reported till date comprised of medusoids and and at Sur Sagar can be represented by coarse to fine grained microbial mats only. Ediacaran assemblage with fronds viz. brick red siliciclastic sandstone (Fig. 2-a,b respectively). Charniodiscus and trace fossils are reported for the first time from the Jodhpur Sandstone Formation of the Marwar Supergroup. In Jodhpur assemblage, discs of variable sizes and morphological structures are associated with un-oriented, haphazardly distributed mesh of irregular bodies comparable to algae. These discs exhibit a wide size range from a few millimeters to 75 centimeters in diameter. Exceptionally large size of the discs in present assemblage represents largest discs reported so far from any Ediacaran assemblage. Although, larger medusoid discs have been reported from USA, but they are from the Middle Cambrian and even younger rocks. Presence of microbial mats and weed-like structures with well preserved hold fasts and horizontal rhizome like structures in association with some of these large-sized discs support their animal affinity, which probably feed on this weed- like vegetations. This association also support their benthic habitat. Unlike general trend of sudden increase in size of organisms in Ediacaran period and further decrease in size during Cambrian, these discs continued increasing in size in Cambrian also. Palaeoecological distribution of such well preserved morphologies are certainly an indication
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