• Volume 34, Issue 5

November 2009,   pages  647-823

• Foreword

• Divergence time estimates of mammals from molecular clocks and fossils: Relevance of new fossil finds from India

This paper presents a brief review of recent advances in the classification of mammals at higher levels using fossils and molecular clocks. It also discusses latest fossil discoveries from the Cretaceous – Eocene (66–55 m.y.) rocks of India and their relevance to our current understanding of placental mammal origins and diversifications.

• Growth patterns of fossil vertebrates as deduced from bone microstructure: case studies from India

Bone microstructure is affected by ontogeny, phylogeny, biomechanics and environments. These aspects of life history of an extinct animal, especially its growth patterns, may be assessed as fossil bone generally maintains its histological integrity. Recent studies on the bone histology of fossil vertebrates from India encompass different types of temnospondyls and dicynodonts from different Permian and Triassic horizons. The examined taxa show that they had distinct bone histology and varied growth patterns. The Early Triassic trematosaurids had an overall fast growth, which contrasts with that of the Middle and Late Triassic temnospondyl taxa examined. The dicynodonts on the other hand, were characterized by an overall fast growth with periodic interruptions, variable growth rates dependent on ontogeny and indeterminate growth strategy. A comparative study encompassing several neotherapsid genera including the dicynodonts shows significant evolutionary trends towards determinate growth strategy and reduced developmental plasticity.

• The origin and early evolution of whales: macroevolution documented on the Indian Subcontinent

The origin of whales (order Cetacea) from a four-footed land animal is one of the best understood examples of macroevolutionary change. This evolutionary transition has been substantially elucidated by fossil finds from the Indian subcontinent in the past decade and a half. Here, we review the first steps of whale evolution, i.e. the transition from a land mammal to obligate marine predators, documented by the Eocene cetacean families of the Indian subcontinent: Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, and Basilosauridae, as well as their artiodactyl sister group, the Raoellidae. We also discuss the influence that the excellent fossil record has on the study of the evolution of organ systems, in particular the locomotor and hearing systems.

• The Out-of-India hypothesis: What do molecules suggest?

The remarkable geological and evolutionary history of peninsular India has generated much interest in the patterns and processes that might have shaped the current distributions of its endemic biota. In this regard the Out-of-India” hypothesis, which proposes that rafting peninsular India carried Gondwanan forms to Asia after the break-up of Gondwana super continent, has gained prominence. Here we have reviewed molecular studies undertaken on a range of taxa of supposedly Gondwanan origin to better understand the Out-of-India scenario. This re-evaluation of published molecular studies indicates that there is mounting evidence supporting Out-of-India scenario for various Asian taxa. Nevertheless, in many studies the evidence is inconclusive due to lack of information on the age of relevant nodes. Studies also indicate that not all Gondwanan forms of peninsular India dispersed out of India. Many of these ancient lineages are confined to peninsular India and therefore are relict Gondwanan lineages. Additionally, for some taxa an Into India” rather than Out-of-India” scenario better explains their current distribution. To identify the Out-of-India” component of Asian biota it is imperative that we understand the complex biogeographical history of India. To this end, we propose three oversimplified yet explicit phylogenetic predictions. These predictions can be tested through the use of molecular phylogenetic tools in conjunction with palaeontological and geological data.

• Tree ring imprints of long-term changes in climate in western Himalaya, Indi

Tree-ring analyses from semi-arid to arid regions in western Himalaya show immense potential for developing millennia long climate records. Millennium and longer ring-width chronologies of Himalayan pencil juniper (Juniperus polycarpos), Himalayan pencil cedar (Cedrus deodara) and Chilgoza pine (Pinus gerardiana) have been developed from different sites in western Himalaya. Studies conducted so far on various conifer species indicate strong precipitation signatures in ring-width measurement series. The paucity of weather records from stations close to tree-ring sampling sites poses difficulty in calibrating tree-ring data against climate data especially precipitation for its strong spatial variability in mountain regions. However, for the existence of strong coherence in temperature, even in data from distant stations, more robust temperature reconstructions representing regional and hemispheric signatures have been developed. Tree-ring records from the region indicate multi-century warm and cool anomalies consistent with the Medieval Warm Period and Little Ice Age anomalies.

Significant relationships noted between mean premonsoon temperature over the western Himalaya and ENSO features endorse utility of climate records from western Himalayan region in understanding long-term climate variability and attribution of anthropogenic impact.

• Deccan volcanism, the KT mass extinction and dinosaurs

Recent advances in Deccan volcanic studies indicate three volcanic phases with the phase-1 at 67.5 Ma followed by a 2 m.y. period of quiescence. Phase-2 marks the main Deccan volcanic eruptions in Chron 29r near the end of the Maastrichtian and accounts for ∼80% of the entire 3500 m thick Deccan lava pile. At least four of the world’s longest lava flows spanning 1000 km across India and out into the Gulf of Bengal mark phase-2. The final phase-3 was smaller, coincided with the early Danian Chron 29n and also witnessed several of the longest lava flows.

The KT boundary and mass extinction was first discovered based on planktic foraminifera from shallow marine intertrappean sediments exposed in Rajahmundry quarries between the longest lava flows of the main volcanic phase-2 and smaller phase-3. At this locality early Danian (zone P1a) planktic foraminiferal assemblages directly overlie the top of phase-2 eruptions and indicate that the masse extinction coincided with the end of this volcanic phase. Planktic foraminiferal assemblages also mark the KT boundary in intertrappean sediments at Jhilmili, Chhindwara, where freshwater to estuarine conditions prevailed during the early Danian and indicate the presence of a marine seaway across India at KT time.

Dinosaur bones, nesting sites with complete eggs and abundant eggshells are known from central India surrounding the hypothesized seaway through the Narmada-Tapti rift zone. A Maastrichtian age is generally assigned to these dinosaur remains. Age control may now be improved based on marine microfossils from sequences deposited in the seaway and correlating these strata to nearby terrestrial sequences with dinosaur remains.

• India at the cross-roads of human evolution

The Indian palaeoanthropological record, although patchy at the moment, is improving rapidly with every new find. This broad review attempts to provide an account of

• the Late Miocene fossil apes and their gradual disappearance due to ecological shift from forest dominated to grassland dominated ecosystem around 9–8 Ma ago,
• the Pliocene immigration/evolution of possible hominids and associated fauna,
• the Pleistocene record of fossil hominins, associated fauna and artifacts, and
• the Holocene time of permanent settlements and the genetic data from various human cultural groups within India.

Around 13 Ma ago (late Middle Miocene) Siwalik forests saw the emergence of an orangutan-like primate Sivapithecus. By 8 Ma, this genus disappeared from the Siwalik region as its habitat started shrinking due to increased aridity influenced by global cooling and monsoon intensification. A contemporary and a close relative of Sivapithecus, Gigantopithecus (Indopithecus), the largest ape that ever-lived, made its first appearance at around 9 Ma. Other smaller primates that were pene-contemporaneous with these apes were Pliopithecus (Dendropithecus), Indraloris, Sivaladapis and Palaeotupia. The Late Pliocene and Early Pleistocene witnessed northern hemisphere glaciations, followed by the spread of arid conditions on a global scale, setting the stage for hominids to explore Savanahastan”. With the prominent expansion of grassland environments from East Africa to China and Indonesia in the Pliocene, monkeys and baboons dispersed into the Indian subcontinent from Africa along with other mammals. Though debated, there are several claims of the presence of early hominins in this part of the world during the Late Pliocene, based primarily on the recovery of Palaeolithic tools. Fossils of our own ancestor and one of the first globe-trotters, early Homo erectus, has been documented from the Early Pleistocene of East Africa, Western Asia and Southeast Asia, thus indirectly pointing towards Indian subcontinent as a possible migration corridor between these regions. The only definite pre-Homo sapiens fossil hominin remains come from the Central Narmada Valley and are thought to be of Middle to late Pleistocene age, and the cranium has been shown to be closely linked to archaic Homo sapiens/H. heidelbergensis of Europe. Around ∼74,000 yrs ago, a super volcanic eruption in Sumatra caused the deposition of Youngest Toba Tephra, that covered large parts of the Indian peninsula. Just around this time anatomically-and-behaviorally modern humans or Homo sapiens possibly arrived into India as evidenced by the so called Middle and Upper Palaeolithic assemblages and associated symbolic evidence. The available genetic data reveals that the gene pool to which modern Indians races belong was extremely diverse and had variable mixed links with both European and Asian populations.

• Deep-sea palaeoceanography of the Maldives Islands (ODP Hole 716A), equatorial Indian Ocean during MIS 12–6

Deep-sea benthic foraminifera, planktic foraminifer Globigerina bulloides and pteropods have been quantitatively analysed in 451 samples from Ocean Drilling Program (ODP) Hole 716A, to understand both surface and deep-sea palaeoceanographic changes in the equatorial Indian Ocean basin during the late Quaternary (∼444–151 Kyrs). Benthic foraminifera were analysed from > 125 𝜇m size fraction whereas Globigerina bulloides and pteropods were analysed from > 150 𝜇m size fraction. Factor analysis of most dominant benthic foraminiferal species over the studied time span made it possible to identify three biofacies characterizing distinct deep-sea environmental settings at Hole 716A. The environmental interpretation of each species is based on the ecology of recent deep-sea benthic foraminifera. The faunal record indicates fluctuating deep-sea conditions including changes in surface productivity, organic food supply and deep-sea oxygenation linked to changing wind intensities. These changes are pronounced on glacial-interglacial time scales driven by summer monsoon winds.

• The evolution and distribution of life in the Precambrian eon-Global perspective and the Indian record

The discovery of Precambrian microfossils in 1954 opened a new vista of investigations in the field of evolution of life. Although the Precambrian encompasses 87% of the earth’s history, the pace of organismal evolution was quite slow. The life forms as categorised today in the three principal domains viz. the Bacteria, the Archaea and the Eucarya evolved during this period. In this paper, we review the advancements made in the Precambrian palaeontology and its contribution in understanding the evolution of life forms on earth. These studies have enriched the data base on the Precambrian life. Most of the direct evidence includes fossil prokaryotes, protists, advanced algal fossils, acritarchs, and the indirect evidence is represented by the stromatolites, trace fossils and geochemical fossils signatures. The Precambrian fossils are preserved in the form of compressions, impressions, and permineralized and biomineralized remains.

• Evidence of Late Palaeocene-Early Eocene equatorial rain forest refugia in southern Western Ghats, India

Equatorial rain forests that maintain a balance between speciation and extinction are hot-spots for studies of biodiversity. Western Ghats in southern India have gained attention due to high tropical biodiversity and endemism in their southern most area. We attempted to track the affinities of the pollen flora of the endemic plants of Western Ghat area within the fossil palynoflora of late Palaeocene-early Eocene (∼55–50 Ma) sedimentary deposits of western and northeastern Indian region. The study shows striking similarity of extant pollen with twenty eight most common fossil pollen taxa of the early Palaeogene. Widespread occurrences of coal and lignite deposits during early Palaeogene provide evidence of existence of well diversified rain forest community and swampy vegetation in the coastal low lying areas all along the western and northeastern margins of the Indian subcontinent. Prevalence of excessive humid climate during this period has been seen as a result of equatorial positioning of Indian subcontinent, superimposed by a long term global warming phase (PETM and EECO) during the early Palaeogene. The study presents clear evidence that highly diversified equatorial rain forest vegetation once widespread in the Indian subcontinent during early Palaeogene times, are now restricted in a small area as a refugia in the southernmost part of the Western Ghat area. High precipitation and shorter periods of dry months seem to have provided suitable environment to sustain lineages of ancient tropical vegetation in this area of Western Ghats in spite of dramatic climatic changes subsequent to the post India-Asia collision and during the Quaternary and Recent times.

• Biomechanical aspects of bone microstructure in vertebrates: potential approach to palaeontological investigations

Biomechanical or biophysical principles can be applied to study biological structures in their modern or fossil form. Bone is an important tissue in paleontological studies as it is a commonly preserved element in most fossil vertebrates, and can often allow its microstructures such as lacuna and canaliculi to be studied in detail. In this context, the principles of Fluid Mechanics and Scaling Laws have been previously applied to enhance the understanding of bone microarchitecture and their implications for the evolution of hydraulic structures to transport fluid. It has been shown that the microstructure of bone has evolved to maintain efficient transport between the nutrient supply and cells, the living components of the tissue. Application of the principle of minimal expenditure of energy to this analysis shows that the path distance comprising five or six lamellar regions represents an effective limit for fluid and solute transport between the nutrient supply and cells; beyond this threshold, hydraulic resistance in the network increases and additional energy expenditure is necessary for further transportation. This suggests an optimization of the size of the bone’s building blocks (such as osteon or trabecular thickness) to meet the metabolic demand concomitant to minimal expenditure of energy. This biomechanical aspect of bone microstructure is corroborated from the ratio of osteon to Haversian canal diameters and scaling constants of several mammals considered in this study. This aspect of vertebrate bone microstructure and physiology may provide a basis of understanding of the form and function relationship in both extinct and extant taxa.

• Palynoflora from Deccan volcano-sedimentary sequence (Cretaceous-Palaeogene transition) of central India: implications for spatio-temporal correlation

The sedimentary beds associated with Deccan Continental Flood Basalt (DCFB) sequences exposed in the volcanic subprovinces of Jabalpur-Mandla-Chhindwara (JMC) regions of Madhya Pradesh and Nand-Dongargaon (N-D) basin and the adjoining areas to the west in Yeotmal-Nanded in Maharashtra were studied for their palynofloral analysis. The sediments were characterized palynologically and changes in the palynoflora are observed at different stratigraphic levels in a number of sections including several new intertrappean localities recorded in recent years. For the purpose of effective correlation of different subprovinces, palynofloras of some of the previously studied intertrappeans are also reviewed. Our studies suggest that before the start of the Deccan volcanic activity, the palynoflora found in the Lameta sediments, was dominated by gymnosperms-angiosperm association. The plant canopy consisted mainly of gymnosperms (Conifers and Podocarpaceae) whereas, the understory members were mostly of palms and herbs (Poaceae and Asteraceae). The eruption of Deccan volcanic flows severely affected the existing floral association and proved fatal for the well established plant community. The immediately overlying sediments associated with the earliest volcanic flows are dominated by pteridophytes and angiosperm taxa (Azolla cretacea, Aquilapollenites bengalensis, Ariadnaesporites sp., Gabonisporis vigourouxii and Triporoletes reticulatus). Higher up in the stratigraphic sequence, similar forms continued with simultaneous appearance of new taxa including Scabrastephanocolpites spp. At still higher stratigraphic levels, abundance of fungi especially the mycorrhizal fungi, concurrent with sharp decline in pollen/spore recovery was observed. In the culminating phase (i.e. Palaeocene) of Deccan volcanic history a new palynofloral assemblage of typical Palaeocene taxa (Dandotiaspora dilata, D. pseudoauriculata, D. plicata, Spinizonocolpites echinatus, Matanomadhiasulcites sp., and Lakiapollis ovatus) was encountered.

• # Journal of Biosciences

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