acaran fossils all over world, which is distinctly visible in discs of present assemblage. The Ediacaran period can be characterized as a time of explosive development of medusoids and coelentrates [23]. However, scarcity of Ediacaran fossils in exceptionally preserved Cambrian biota, like Burgess Shale [24] points their extinction or the ecological restriction [25].

Noncarbonaceous discs from the Jodhpur Sandstone in Sursagar and Artiya Kalan areas occur on bedding surface and exhibit flexible to rigid structures. They exhibit remarkable variation in morphology and ascribed to different biologic affinities of plant and animal kingdom. Although taphonomic interplay between the flexibility, related to decay rate and surrounding sediments followed by the degree of post burial compressions may result in

Figure 6. Noncarbonaceous discs from the Jodhpur Sandstone in Sursagar area. For Scale, coins of rupee one and two have been given, Two rupee coin measures 2.7 cm and one rupee coin measures 2.5 cm. Marker pen and gel pen given in Figure A = 14 cm and pen given in Figure C = 14 cm. (A), (B), (E) Aspidella, Disc with prominently preserved inner circular body; (C), (F) Heimalora, Disc with tentacles or processes radiating from the periphery of the disc; (D) Cyclomedusa, Circular disc with radiating and concentric markings; (G) Unidentified Elliptical disc with inner circular body and outer sheath-like structure.

variable morphological features of the fossils. Discs acquiring different shapes exhibit oval, ellipsoidal, egg shaped, circular, semi circular, elongated structure, with or without an intracellular mass of variable dimensions and shapes, discs with single, double or triple lamellated outer sheath like structures (Figure 6(G)). It seems that some of these structures are the result of taphonomic effect on organisms of possibly single biologic affinity. Although morphologies exhibited by most of the fossils in present assemblage are so prominent, consistent and repetitive, hence supporting the original characters. A degree of genetic variability can be expected within any taxon, and this may be compounded by preservational or taphonomic factors affecting the Jodhpur Ediacara fossils. Plasticity in morphology was present to a greater degree in the earliest, simple flora or fauna, where the genetic mechanisms may have been unable to replicate body form faithfully [26].

Specimens exhibiting morphologies comparable with discs of Chuaria (without carbonaceous matter), division stages and budding like structures as described in organic walled acritarchs like Germinosphaera and higher fungi support the plant affinity. At the same time specimens exhibiting four fold symmetry: a characteristic feature of Scyphozoans or Jellyfish and specimens resembling ephyra stage and dispersal stages-like features (Figure 4(D)), specimens comparable with Aspidella, Cyclomedusa, Heimalora Beltanelliformis (the most primitive organisms among Precambrian metazoans, occurring with Arumberia and microbial mats) in present assemblage, support animal affinity and suggest an ecological relationship between plants and animals.

6. Conclusions

In present assemblage, Ediacaran discs from the Jodhpur Sandstone exhibiting variable morphologies may be facets of preservation, hence some of these forms can be categorized among synonyms and variation in morphology is simply taphonomic or preservational. Since most of the Ediacaran discs in present assemblage are preserved on bedding surface, the interplay between rigidity and flexibility of organisms, related to process of decay and nature of surrounding sediments, followed by compressions or deformation after burial resulted in visible morphologies. At the same time prominent features consistently and repetitively exhibited by a number of discoidal specimens of present assemblage are undoubtedly generic features of variable affinities. It is therefore inferred that variation in morphology of Ediacaran discs from the Jodhpur Sandstone is governed by both taphonomy as well as biological diversity among plant and animal communities, prevailing at the time of host rock sedimentation.

Globally the discoidal fossils probably account for the majority of fossils in Fermuse Formation of Newfoundland and similar assemblage from the Norway, Long Mynd Group, England and Wales. Discs in Mistaken Point have been inferred as hold fasts. Present assemblage along with other complex assemblages from the South Australia and White Sea of Russia also unequivocally contain more than one biological construction responsible for the discoidal structures.

On the basis of Ediacaran fossils reported from the Jodhpur Group and Bhander Group (Vindhyan Supergroup) exposed in Madhya Pradesh and Rajasthan, both the groups can be correlated biostratigraphically, which was supported by earlier workers also [27]. It has also been inferred earlier that during Ediacaran period, both the Basins were linked with each other through Himalayas [11].

7. Acknowledgements

The author is thankful to the Head, Centre of Advanced Study in Geology, Lucknow University, India, for providing basic facilities to carry out this research. She is indebted to Dr. R. Bali for his help during the course of investigation. Financial assistance from DST, New Delhi in form of a WOS-A project no SR/OY/WOS-A/ES-20/ 2008 is thankfully acknowledged.

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