This specimen of sponge is in the form of a cylinder with a large opening on the top of its body interpreted here as osculum (Fig. 3, Plate 1, Fig. 3). There are numerous small pores or ostia in the wall of the cylinder and inside the cylinder is a body cavity (large central cavity) or spongocoel (Paragastrc cavity). Ostia open in this spongocoel and permit entry of water in this cavity, which exits through osculum. The present specimens show radial symmetry and simplest type of (Ascon types) canal system.
Almost all sponges are provided with a skeleton embedded in mesenchymes. The mineralized skeleton is absent. Instead a reticulation made by interlacing of spongin fibers or hard mucus like sol to rather stiff gel is present.
5. Early Evolution of Life and Its Evidences from the Lesser Himalaya
The oldest known record of life on Earth is bacteria described by Walsh (1992), Westall (1999, 2006) and Westall et al. (2001, 2006) from Early Archean Onverwacht Group (3.3-3.5 Ga), South Africa. The oldest well preserved stromatolites have been recorded in 3.5 Ga old Warrawoona Group sedimentary rocks in Western Australia. Schopf (1968, 1983, 1993) and Schopf and Klein (1992) have discussed the global occurrence of Archaean and Proterozoic microfossils and their significance. The Laser Raman Spectroscpic study and 3D imagery of the oldest Archaean and the Proterozoic microfossils confirm the presence of kerogen in high concentration (Schopf et al., 2008).
The Meso-Neoproterozoic microbial diversification has been recorded from all continents and the microfossils are preserved in early diagenetic silicified carbonates Table 1). The Deoban Limestone is a well developed carbonate buildup in the Lesser Himalaya of northern India near Mussoorie (Fig. 1). It has been assigned Meso-Neoproterozoic age on the basis of Riphean stromatolite assemblage Conophyton garganicum, Kussiella kussiensis, Colonnella columnaris and Baicalia nova (Tewari, 1989, 1993a, 2002, 2007). Deoban and Buxa cherts show highly diversified microbial assemblage in the Meso-Neoproterozoic of the Lesser Himalaya in India and its global distribution is shown in Table 1. Twenty species belonging to eleven genera of coccoid forms are Myxococcoides minor, M. inor-nata, Huronispora psilata, H. microreticulata, Eoentophysalis belcherensis, E. magna, E. cumulus, Glenobotrydion aenigmatis, G. majorinum, Tetraphycus major, T. conjunc-tum, Melasmatosphaera media, M. parva, Gloeodiniopsis lamellosa, G. gregaria, G. sp., Globophycus rugosum, Sphaerophycus parvum, Eosynechococcus isolatus and Caryosphaeroides pristina (Shukla et al., 1987; Tewari, 1989, 2001b, 2002, 2004; Kumar and Srivastava, 1992). Five genera and eight species of filamentous forms have been recorded by Shukla et al., 1987; Tewari, 1989, 2001b, 2002 and Kumar and Srivastava (1992). These are Eomycetopsis robusta, E. filiformis, E. siberiensis, Gunflintia minuta, G. grandis, Biocatenoides sp., Oscillatoriopsis sp. and Siphonophycus kestron. The above named twenty eight species are recorded in the Deoban assemblage, whereas the maximum number of common species is known from Bitter Springs Formation of Australia (900 Ma, Table 1). According to Hofmann (1976) Glenobotrydion, Myxococcoides, Globophycus, Caryospheroides, and Melasmatosphaera possibly represent the degradational variants. Tiwari et al. (2000) and Tewari (2002) have reported isolated hexactinellid and monaxon sponge spicule and calcified algae Epiphyton sp. and Renalcis sp. from the
Gangolihat Dolomite (eastern extension of Deoban Limestone in the Uttaranchal Lesser Himalaya) which suggest Neoproterozoic age for the Gangolihat Dolomite.
Vendotaenid algae from the Lower Krol Formation of the Lesser Himalaya (a new genus Krolotaenia gnilovskayi) was established and subsequently the genus Tyrasotaenia and Vendotaenia have been recorded from the Nainital Syncline (Tewari, 1993b, 1999b). Hofmann (1992) regarded some carbonaceous megascopic ribbon shaped remains as algae (metaphyte) affinities of Neoproterozoic age. Schopf et al. (1973) described Vendotaenia as a multicellular macroscopic benthic metaphyte. The Vendotaenids are also recorded from the Sinian System (Late Proterozoic) of China and this eukaryotic algae has a global distribution. Ediacaran life diversified in the Terminal Proterozoic and includes soft bodied metazoans (coelenterates-medu-soid, frondoid forms) and trace fossils. These evolved after the Varangian glaciation and are well known from the Ediacara type locality in Australia. These have been recorded from China, Eurasia, India and Wernecke and Mackenzie mountains of Canada (Glaessener, 1984; Narbonne and Hofmann, 1987; Hofmann, 1992; Walter, 1989; Mathur and Shankar, 1989; Shankar and Mathur, 1992; Shankar et al., 1997; Tewari, 1992, 1996, 2001b, 2004, 2007). The oldest pre Ediacaran fauna has been recorded from the intertillite beds of Windermere Supergroup, Mackenzie Mountains, Canada (Hofmann et al., 1990).
In India, the Ediacaran assemblage has been recorded from the Upper Krol Formation of the Lesser Himalaya (Fig. 1). The assemblage includes the soft bodied metazoans Cyclomedusa davidi, Charniodiscus sp. fronds and disc, Kimberella cf. quadrata, Zolotytsia biserialis Fedonkin and Conomedusites lobatus Glaessener and Wade (Shanker and Mathur, 1992; Tewari, 1992, 1996, 2004, 2007).
The recovered organic-walled microfossils comprise of 36 taxa of cyanobacterial, acritarchs and VSM. In which 17 taxa of cyanobacteria belong to Chroococcaceae, Nostocaceae and Oscillatoriaceae, 18 taxa of Acritarchs belong to Sphaeromorphida, Scaphomorphida and Sphaerohystrichomorphida subgroups and one VSM (Vase shaped microfossils now considered testate amoebae) are present. The recovered assemblage compares well with the known Late Neoproterozoic assemblages from other parts of the world (see Table 1).
The cyanobacteria is the most tolerant and primitive group and has remained morphologically unchanged since Archaean. The filamentous and coc-coidal forms recorded here are known from the shales, bedded chert and cherti-fied stromatolites of Archaean to recent sediments exposed in different part of the world, viz. Africa, Australia, Canada, China, India, Spitsbergen, Svalbard and thus, these forms do not have any stratigraphic significance. However, the helically coiled morphology, as shown by Obruchevella has wide spread occurrence in Upper Riphean - Early Cambrian sediments (Yakschin, 1989; Sergeev, 1989;
Knoll, 1992; Wang et al., 1983; Yin and Gao, 1993; Yin et al., 2003; Srivastava and Kumar, 2003). Though, there are records of Obruchevella even from older sediments viz from Archaean and late Palaeoproterozoic to Mesoproterozoic, this form is generally considered marker for Vendian. Morhologically close form Volyniella valdaica with coiled morphology reported here is known from the sediments belonging to Vendian age of Russian platform.
The acritarchs show morphological changes through time and hence have been used as stratigraphic markers (Timofeev, 1966; Downie, 1984; Timofeev, 1973; Jankauskas, 1989; Vidal and Ford, 1985; Knoll, 1992b; Zang and Walter, 1992; Jenkins et al., 1992; Butterfield and Rainbird, 1998; Yin, 1985; Spjeldnaes, 1963; Germs, 1995; Xio et al., 1997; Tewari and Knoll, 1994; Maithy and Babu, 1997; Weiss, 1989; Knoll, 1996). The large size acanthomorph acritarchs along with lei-opshaerids are present in the early Vendian and these large forms disappear near the advent of the Ediacara fauna (Knoll, 1992; Zang and Walter, 1989). The size of the acanthomorphs reduces in younger sediments till we get dominence of small forms in the late Vendian (Volkova, 1968; Jankauskas, 1989). The acanthomorphs in the present assemblage, which include Trachysphaeridium; Micrhystridium; Baltisphaeridium; Archaeohystrichosphaeridium; Vandalosphaeridium; Trachystrichosphaera; Gorgonisphaeridium; Meghystrichosphae-rium; Navifusa are generally of small size indicating late Vendian affinity. The comparision of the present assembalages with other known assembalages of the world shows close comparison with the Terminal Proterozoic - Cambrian assembalages described from Canada, China, Australia, Greenland, Spitsbergen Russia and Svalbard (Table 1) Thus, the overall analysis of the recovered assemblage indicates late Vendian age for Buxa Dolomites.
The carbon and oxygen isotopic ratios of the Buxa Dolomite from Subansiri, Chillipam and Dedza areas of the Arunachal Lesser Himalaya suggest that these signatures are of Neoproterozoic (Vendian) age and represent pristine marine environment (Tewari, 2002, 2003; Tewari and Sial, 2007). The carbon isotope ratios are significantly positive and quite consistent with 513 C (carbonate carbon) values ranging from +3.7%o to +5.4%o (PDB). The Oxygen-isotope data also shows remarkable consistency with the 518O value fluctuating within a narrow range between -8.9%° and -7.2%o (PDB). The Buxa Dolomite of the Arunachal Lesser Himalaya can be correlated with the Vendian Krol Formation of the Uttaranchal Lesser Himalaya on the basis of the very high positive carbon iso-topic ratios and the present palaeobiological assemblage. The Doushantuo carbonates (Terminal Neoproterozoic) of the Yangtze Platform, South China also display very high carbon isotopic ratios identical to Krol- Buxa signatures of the Himalaya and were deposited after the global Neoproterozoic low latitude glacial event (Tewari, 2003, 2004, 2007).
A major event in the diversity of fossil algae and unicellular eukarya is recorded in 1.2-1.0 Ga old rocks (Knoll, 1985). The Meso-Neoproterozoic and Terminal Proterozoic succession of the Lesser Himalaya in the northern India shows excellent preservation of the highly diversified microbial assemblages.
The microbiota of the Deoban cherts and the Bitter Springs Formation of Central Australia (Schopf, 1968) are remarkably similar.
The Terminal Proterozoic diversification of life that led to the radiation of animals and plants occurred between 0.59 and 0.53 billion years ago on Earth. The prokaryotic to eukaryotic evolution and diversification of life on Earth, palaeoclimatic events of Neoproterozoic snowball Earth and the extinction and further emergence of highly organized life after Varanger (Blainian) glaciation can also be used as a possible model for the search of extraterrestrial life (astrobiological research). The stromatolites can also be used in the search for past life on Mars and elsewhere in the universe (Tewari, 1998, 2001b). In summary it is possible that the early life (4-3.8 Ga) must have been preserved on Mars as compared to Earth. Planet Earth has undergone Archaean Proterozoic plate tectonics and earliest life forms must have been destroyed or not preserved due to very high grade metamorphism (Tewari, 1999). Westall and Southam (2006) have also interpreted that the first life forms may exist on a planet (most probably Mars) where plate tectonics has not destroyed the early primitive evidence of life. The southern Highlands of Mars is the potential area for astrobiological research.
The author is grateful to Professor Joseph Seckback, Hebrew University Jerusalem, Israel for his constant encouragement. Professor J.W Schopf, University of California, Los Angeles, USA is thanked for discussions on Proterozoic microfossils and their Laser Raman Spectroscopy during my visit to UCLA as a Visiting Scientist in 2007. Professor Julian Chela Flores, I.C.T.P., Trieste, Italy is thanked for discussions about the astrobiological implications of the microfossils and origin of life. Dr. F. Westall, Director, Centre de Biophysique Moleculaire, CNRS, Orleans, France and another anonymous reviewer have reviewed the manuscript critically and thanked for the valuable suggestions. Dr. Maud M. Walsh, Louisiana State University, USA is thanked for suggestions to improve the chapter. Dr. B.R. Arora, Director, Wadia Institute of Himalayan Geology, Dehra Dun, Uttarakhand, India is thanked for the facilities and permission to publish the paper. Girish Chauhan ably typed the article.
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Biodata of Burns P. Brendan and his group authors of the chapter "Stromatolites"
Dr. Burns P. Brendan is a Senior Lecturer in Microbiology and Fellow of the Australian Research Council. He completed his Ph.D. in 1999 and from here was awarded a highly prestigious Alexander von Humboldt Fellowship and conducted a post-doc in Munich, Germany from 2000-2001. Dr. Brendan was then awarded an ARC Fellowship to return to UNSW in 2002. Since then he has led research on the Shark Bay stromatolites, complex geomicrobial communities that are analogues of the very earliest evidence of life on Earth. Using these ancient life forms as blueprints, Brendan has also consulted with NASA to better focus efforts on the search for signals that may help in the detection of life on other planets. His research has been recognised with the award of the Eureka Prize for Interdisciplinary Scientific Research (2005), ASM Research Trust Fellowship (2001), Kanagawa Museum of Natural History Award (2003), Japan Society for the Promotion of Science Invitation Fellowship (2004), and the Australia Institute of Political Science Tall Poppy Award (2005). Brendan has over 40 peer-reviewed publications, 5 book chapters, plus over 50 conference proceedings. Brendan has also demonstrated a real commitment to communicating science to the general public with numerous radio and print articles, involvement in film projects, and an invitation showcase his research at the 2005 World Expo in Japan, an event that had over 20 million attendees.
E-mail: [email protected]
Professor Dr. Brett A. Neilan is head of the UNSW Cyanobacteria Research Laboratory and co-director of the Australian Centre for Astrobiology. He received a Ph.D. in 1995 from UNSW and has held Postdoctoral positions at Stanford (NASA Fellow) and Humboldt University Berlin (Alexander von Humboldt Fellow). Since 1998 he has been a Fellow of the Australian Research Council at UNSW. He is considered to be one of the world's leaders in the genetics of toxic cyanobacteria. The results of his basic research and his other work on the evolution of cyanobacteria has revolutionised an entire field of environmental science. He is also engaged in "molecular bioprospecting", which has led him to study the secondary metabolism of microorganisms from unique environments, such as Antarctica and the hypersaline coasts of Shark Bay in Western Australia. He has been awarded the Australian Academy of Science Fenner Medal in 2004 and the Eureka Prize for Scientific Research in 2001 and 2005.
E-mail: [email protected]
Malcolm R. Walter is Professor of Astrobiology at UNSW in Sydney, Director of the Australian Centre for Astrobiology based at that university, and Director of M. R. Walter Pty Ltd. He received his Ph.D. in 1970 and has worked for 35 years
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