ZOO503 Zoogeography and Paleontology Past Paper PDF

MUHAMMAD IMRAN Topic no 1 to 80 mid term and 81 to 165 final term syllabus ZOO503 Zoogeography and Paleontology 1 Paleontology as a science: Paleontology in the modern world Paleontology as a science Paleontology in the modern world What is Paleontology? The branch of science concerned with fossil animals and plants. It is the study of fossils to determine organisms' evolution & ecology. The Word Originates from Greek “palaios-old”, “ontos-creature" “logos-study" and Paleontology lies on the border between Biology and Geology. The fossils are present in the layers of earth and on the different areas of the earth. This is why the geology is of great importance in studying paleontology. Use of Paleontology 1. Origin of life: In the modern world the paleontology is being used for studying origin of life. Paleontology is study of old creatures and we further go in the past we can infer how the life originated in the first place. People want to know where life came from, where humans came from, where the Earth and universe came from. These have been questions in philosophy, religion and science for thousands of years and paleontologists have a key role. Despite the spectacular progress of paleontology, earth sciences and astronomy over the last two centuries, many people with fundamentalist religious beliefs deny all natural explanations of origins – these debates are clearly seen as hugely important. 2. Curiosity about different worlds How different environment give rise to different organisms. We can speculate about how a life form could evolve in a world which is different from our world. Science fiction and fantasy novels allow us to think about worlds that are different from what we see around us. Another way is to study paleontology – there were plants and animals in the past that were quite unlike any modern organism. Just imagine land animals 10 times the size of elephants, a world with higher oxygen levels than today and dragonflies the size of seagulls, a world with only microbes, or a time when two or three different species of humans lived in Africa! 3. Climate and biodiversity change Thinking people, and now even politicians, are concerned about climate change and the future of life on Earth. Much can be learned by studying the modern world, but key evidence about likely future changes over hundreds or thousands of years comes from studies of what has happened in the past. For example, 250 million years ago, the Earth went through a phase of substantial global warming, a drop in oxygen levels and acid rain, and 95% of species died out might this be relevant to current debates about the future? 4. The shape of evolution The tree of life is a powerful and all-embracing concept – the idea that all species living and extinct are related to each other and their relationships may be represented by a great branching tree that links us all back to a single species somewhere deep in the Precambrian. MUHAMMAD IMRAN 1 Biologists want to know how many species there are on the Earth today, how life became so diverse, and the nature and rates of diversifications and extinctions. It is impossible to understand these great patterns of evolution from studies of living organisms alone. 5. Extinction Fossils show us that extinction is a normal phenomenon: no species lasts forever. Without the fossil record, we might imagine that extinctions have been caused mainly by human interactions. 6. Dating rocks Biostratigraphy, the use of fossils in dating rocks, is a powerful tool for understanding deep time, and it is widely used in scientific studies, as well as by commercial geologists who seek oil and mineral deposits. Radiometric dating provides precise dates in millions of years for rock samples, but this technological approach only works with certain kinds of rocks. Fossils are very much at the core of modern stratigraphy, both for economic and industrial applications and as the basis of our understanding of Earth’s history at local and global scales. 2 Paleontology as a science: What is Science? Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe. From Latin scientia, meaning "knowledge” Science is supposed to be about reality, about hard facts, calculations and proof. In mathematics, and many areas of physics, this might be true. In natural sciences, there have been two main approaches 1. Induction 2. deduction Induction Sir Francis Bacon: The enquirer might hope to see common patterns among the observations, and these common patterns would point to an explanation, or law of nature. Deduction Aristotle : A series of observations point to an inevitable Outcome “All men are mortal. Socrates is a man. Therefore Socrates is mortal.” Mathematics and in detective work. Hypotheticodeductive method Karl Popper “Proof is impossible” Scientists set up the hypotheses hypothesis testing; They seek to refute, or disprove, hypotheses rather than to prove them. A good Hypothesis 1. hypotheses should be sensible and testable 2. Speculation vs. “Informed deduction” 3. Should be based on observable facts, not the fantasy. Paradigm shifts Thomas Kuhn: science shuttles between so-called times of normal science and times of scientific revolution. Scientific revolutions, or paradigm shifts, are when a whole new idea invades an area of science. An Example of Paradigm shift The paper by Luis Alvarez and colleagues (1980). The Earth had been hit by a meteorite 65 million years ago, caused the extinction of the dinosaurs and other groups. MUHAMMAD IMRAN 2 Paleontology rendition in Popular culture Jurassic Park and Walking with Dinosaurs The slow evolution of reconstructions of ancient life over the centuries reflects the growth of paleontology as a discipline. 3 Paleontology as a science: Steps to understanding Steps to understanding 1. Earliest fossil finds 2. Fossils as magical stones. 3. Fossils as fossils 4. The idea of extinction 5. The vastness of geological time Earliest fossil finds Prehistoric peoples picked up and used them as Ornaments Early Greeks, Xenophanes (576–480 bce) and Herodotus(484–426) Fossils as magical stones Roman and medieval times Fossil sharks’ teeth were known as glossopetrae worn as amulets The idea of vis plastica The work of Johann Beringer Fossils as fossils The genius of Leonardo da Vinci Nicolaus Steno, true nature of glossopetrae Robert Hooke, descriptions of Fossils using a crude microscope Magical explanations of fossils were debunked The idea of extinction Robert Hooke was one of the first to hint at the idea of extinction William Hunter (1768): “American incognitum” Reality of extinction: French natural scientist Georges Cuvier Cuvier : father of comparative anatomy The vastness of geological time Sedimentary rocks and their contained fossils document the history of long spans of time. Naming of the geological periods and eras : 1820s and 1830s Stratigraphy is an understanding of geologic time Until the late 18th century, scientists accepted calculations from the Bible that the Earth was only 6000– 8000 years old by dissecting the head of a huge modern shark. 4 Paleontology as a science: Fossils and evolution Fossil & Evolution: 1. Progressionism and Evolution 2. Darwinian evolution People want to know where life came from, where humans came from, where the Earth and universe came from. These have been questions in philosophy, religion and science for thousands of years and paleontologists have a key role (seepp. 117–20). Despite the spectacular progress of paleontology, earth sciences and astronomy over the last two centuries, many people with fundamentalist religious beliefs deny all natural explanations of origins – these debates are clearly seen as hugely important. MUHAMMAD IMRAN 3 1. Progressionism and Evolution Limited Knowledge of the fossil record in the 1820s and 1830s. Paleontologists debated whether there was a progression from simple organisms in the most ancient rocks to more complex forms later. Charles Lyell (1797– 1875), was an antiprogressionist. Charles Lyell (1797–1875), was an antiprogressionist. He believed that the fossil record showed no evidence of long-term, one way change, but rather cycles of change. He would not have been surprised to find evidence of human fossils in the Silurian, or for dinosaurs to come back at some time in the future if the conditions were right. Progressionism (Orthogenesis) was linked to the idea of evolution. The work of Comte de Buffon (1707–1788) and JeanBaptiste Lamarck (1744–1829). Lamarck s’ idea of “Great Chain of Being” or the Scala naturae. “All organisms were linked in time by a unidirectional ladder, from simplest at the bottom to most complex at the top” 1. Darwinian evolution Charles Darwin (1809–1882), developed the theory of evolution by natural selection in the 1830s. Abandoning the usual belief that species were fixed and unchanging. Idea of evolution by common descent, that all species today had evolved from other species in the past. The problem: how the variation within species could be harnessed to produce evolutionary change? Ideas of Thomas Malthus (1766–1834). Survival of the fittest through adaptations, Book “On the Origin of Species (1859)” “Modern synthesis” Modern genetics early in the 20th century. Amalgamation of Genetics with “natural history” (systematics, ecology, paleontology). Establishment of Darwinian evolution by natural selection. 5 Paleontology as a science: Paleontology today Palenotology Today: 1. Dinosaurs and fossil humans 2. Evidence of earliest life 3. Macroevolution 4. Paleontological research Dinosaurs and fossil humans: 19th century paleontology: “Archaeopteryx”, true “missing link” predicted by Darwin only 2 years before. Incomplete remains of Neandertal man in 1856 Archaeopteryx lithographica, Specimen displayed at the Museum für Naturkunde in Berlin. MUHAMMAD IMRAN 4 Evidence of earliest life: Older, simpler, forms of life were recognized after 1960 by the use of advanced microscopic techniques, and some aspects of the first 3000 million years of the history of life are now understood. Extraordinary progress in understanding the earliest stages in the evolution of life. Cambrian fossils Precambrian fossils In 1947, the first soft-bodied Ediacaran fossils were found in Australia. Macroevolution: Rates of evolution, the nature of speciation , the timing and extent of mass extinctions the diversification of life, other topics that involve long time scales. Paleontological research: Done by paid professionals, by amateur enthusiasts, amateurs are not paid to work as palaeontologists, collaborations between different sciences is the key. Most paleontological research is more mundane. 6 Fossils in time and space Early paleontologists did not know these things, and so they tried to pack the whole of the history of life into a relatively short span of time, visualizing trilobites or dinosaurs inhabiting a world that was much as it is today. The Earth is old, and the distribution of continents and oceans has changed radically over time. Past: History of life into a relatively short span of time Life on Earth: Evolving for up to 4 billion years Complex story of fossil groups coming and going Continents moving from place to place How to Study fossils in time and space: Development of geographic and temporal frameworks. Accurate and reliable enough to chart the distributions of fossil organisms through time and space. Paleogeographers and Stratigraphers are equipped with a range of computer-based hightech methods. Models describing the distributions of the continents, oceans and their biotas throughout geological time. Use of Fossils information: Fossils information is also useful in Geology. Allows the tectonic history of mountain ranges to be reconstructed. Helps in identifying the levels of thermal maturity of rocks. The gas and oil windows in hydrocarbon exploration. 7 Fossils in time and space: Frameworks Rock stratigraphy : A rock stratigraphy is the essential framework that paleontologists use to accurately locate fossil collections in both temporal and spatial frameworks. Leonardo’s legacy: The origin of modern stratigraphy: Leonardo da Vinci and his drawings. da Vinci portrayed a clear sequence of laterally continuous, horizontal strata showing the concept of superposition MUHAMMAD IMRAN 5 Steno’s Work: Nicolaus Steno: Established the simple fact that older rocks are overlain by younger rocks if the sequence has not been inverted law of superposition of strata (The law of superposition is an axiom that forms one of the bases of the sciences of geology, archaeology, and other fields dealing with geological stratigraphy. In its plainest form, it states that in undeformed stratigraphic sequences, the oldest strata will be at the bottom of the sequence). The principle of original horizontality: "Strata either perpendicular to the horizon or inclined to the horizon were at one time parallel to the horizon"; The principle of lateral continuity: "Material forming any stratum were continuous over the surface of the Earth unless some other solid bodies stood in the way" The principle of cross-cutting relationships: "If a body or discontinuity cuts across a stratum, it must have formed after that stratum. Types of Stratigraphy: 1. Lithology (Lithostratigraphy) 2. Fossils (Biostratigraphy) 3. Tectonic units, such as thrust sheets (Tectonostratigraphy) 4. Magnetic polarity (Magnetostratigraphy), 5. Chemical compositions (Chemostratigraphy) 6. Discontinuities (Allostratigraphy), 7. Seismic data (Seismic stratigraphy) 8. Depositional trends (Cyclo- and sequence stratigraphies) 8 Fossils in time and space: lithostratigraphy Early geologists thought the Earth was very young. Scottish scientist James Hutton (1726–1797) chellenged. “no vestige of a beginning,– no prospect of an end”. “ruins of an earlier world” Gaia hypothesis and Modern Concept: Gaia hypothesis: Earth as a living organism in equilibrium with its biosphere. Modern Concept: Earth as a dynamic and changing system, Lithostratigraphy: All aspects of stratigraphy start from the rocks themselves. The order and succession of rocks is called lithostratigraphy. Building blocks for any study of biological and geological change through time. Successions of rock are often divided by gaps or unconformities. A stratigraphy is required to monitor biological and geological changes through time and underpins the whole basis of Earth history. The Permian through Jurassic strata of the Colorado Plateau area of southeastern Utah demonstrate the principles of stratigraphy. Stratigraphic unit: A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, paleontologic features. It is fundamental Unit of Lithostratigraphy. Lithostratigraphic units are bodies of rocks, bedded or unbedded. Lithostratigraphic units: 1. A bed, is a lithologically distinct layer within a member or formation and is the smallest recognizable stratigraphic unit. 2. A member is a more local lithologic development, usually part of a formation 3. The formation, a rock unit that can be mapped and recognized across country 4. A succession of contiguous formations with common characteristics is called a group 5. Groups themselves may comprise a supergroup 9 Fossils in time and space: Use of fossils: discovery of biostratigraphy (Part 1) Early Palaeontologists: Work of William Smith in Britain “Assemblages of fossils in different layers”. William Smith: Trilobite- Dominated assemblages in England and Wales area. MUHAMMAD IMRAN 6 Georges Cuvier (Anatomist) and Alexandre Brongniart in France (Mollusck expert). Cuvier and Brongniart: Comparison of different strata in Paris basin and supposed Biological catastrophs in between. The Work of John Phillips: Formally defined the three great eras separated by extinction events. Paleozoic (“ancient life”) Mesozoic (“middle life”) Cenozoic (“recent life”) Precise biotic and morphological changes along phylogenetic lineages. Accurate correlation using a wide variety of fossil organisms Biostratigraphy: the means of correlation: Biostratigraphy is the establishment of fossil based successions and their use in stratigraphic correlation. Measurements of the stratigraphic ranges of fossils, or assemblages of fossils, form the basis for the definition of biozones. Biozones: The main operational units of a biostratigraphy. The known range of a zone fossil is the time between its first and last appearances in a specific rock section, 1. First appearance datum (FAD) 2. Last appearance datum (LAD) Establishment of biozones. Quantitative techniques to understand the relationships between rock thickness and time, and to make links from locality to locality. 10 Fossils in time and space: Use of fossils: discovery of biostratigraphy (Part 2) The fossil record is rarely complete. Only a small percentage of potential fossils are ever preserved. Stratigraphic ranges can also be influenced by the Signor–Lipps effect. Signor–Lipps effect “Since the fossil record of organisms is never complete, neither the first nor the last organism in a given taxon will be recorded as a fossil” Many different animal and plants are used in biostratigraphic correlation. Graptolites (1 myr) and Ammonites (25 kyr) are the best known and most reliable zone macrofossils. Microfossil groups: conodonts, dinoflagellates, foraminiferans and plant spores used in petroleum exploration. Comprise of small samples, drill cores and chippings. Microfossil groups many groups are widespread and rapidly evolving. Drawback: Techniques used to extract them from rocks are specialized, like acid digestion and thin sections. Chronostratigraphy: “The branch of geology concerned with establishing the absolute ages of strata.” Dividing up geological time. Chronostratigraphy or global standard stratigraphy. Most fundamental of all stratigraphic concepts Sequence stratigraphy MUHAMMAD IMRAN 7 “Sequence Stratigraphy is a branch of geology that attempts to subdivide and link sedimentary deposits into unconformity bound units on a variety of scales.” Cyclostratigraphy Finding the rhythm. Cyclostratigraphy is the study of astronomically forced climate cycles within sedimentary successions. Geologic time scale System of chronological dating that relates geological strata (stratigraphy) to time. Used to describe the timing and relationships of events that have occurred during Earth's history. 11 Fossils in time and space : Paleobiogeography All living organisms have a defined geographic range. The ranges may be large or small, and controlled by a variety of factors including climate and latitude. Early Biogeographists: Charles Darwin (Galápagos islands ) and Alfred Russel Wallace (East Indies). Recognized the reality of biogeographic provinces. Philip Sclater and Alfred Russel Wallace. The Earth today can be divided into six main provinces (Nearctic, Palearctic, Neotropical, Ethiopian, Oriental and Australasian). Early 1900s, the German scientist Alfred Wegener suggested that the continents moved across the Earth’s surface on a liquid core, suggesting that continents could in fact drift. Computerized paleogeographic systems: Our understanding of plate movements has been greatly advanced. Paleomap Project taking the Earth far into the future as well as deep into the past. Faunal and floral barriers: Barriers of various types have partitioned biogeographic provinces through time. The work of Gaylord Simpson: George G. Simpson Three passages Corridors (open at all times) Filters (allowed restricted Access) Sweepstake routes (opened only occasionally) Barriers Continental settings: mountain ranges, inland seas or even rain forests. Marine faunas: wide expanses of deep ocean, swift ocean currents or land. Isthmus of Panama MUHAMMAD IMRAN 8 Barrier for some organisms may provide a corridor for others. The emergence of the Isthmus of Panama (3 Mya) Connected North and South America Separated the Atlantic and Pacific oceans. 12 Fossils in time and space : Island Paleobiogeography Island biogeography Modern oceans are littered with islands. The biogeography of modern islands is complex and it is hard to apply models based on modern islands to ancient examples. Island biogeography is the study of the species composition and species richness on islands. Island biogeography is a study aimed at establishing and explaining the factors that affect species diversity of a specific community. Most islands are isolated from the mainland, and they are important powerhouses of speciation. Moving island complexes: the cross-latitude transfer of evolving animals and plants may have acted as “Noah’s arks”. Example: The transit of India from Gondwana to Asia Island biotas (faunas and floras) are often diverse, with many endemic species and commonly with evidence that these species came originally from one or more source continents. Galápagos, or Aldabra, have become important sites for biologists to watch “evolution in action”. It is difficult to understand the role of such islands through geological time By their very nature, being short lived and located in tectonically active areas. They are quickly lost and often destroyed. 13 Fossils in time and space : Fossils in fold belts “One bad fossil is worth a good working hypothesis” Rudolf Trümpy, an eminent Alpine geologist. FOLD BELTS A fold and thrust belt is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. FOSSILS IN FOLD BELTS Fossils from the deformed zones of mountain belts. They are usually poorly preserved. Metamorphosed and tectonized. We can reassemble ancient mountain belts and trace the origins of their jumbled structure using paleontological data. Fossils in fold belts can be of great value to structural geologists in understanding the rates and timing of tectonic events. A fossil that was originally symmetric, but now squeezed, or stretched. The precise evidence of the magnitude of the tectonic forces on it Example is the “Delabole butterfly” In fact, the wide-hinged fossils are “Spiriferide brachiopods” MUHAMMAD IMRAN 9 Hughes and Jell (1992): Techniques to unstrain Cambrian trilobites from Kashmir, distorted by earth movements during the uplift of the Himalayan mountain belt The investigation of thermal maturation is now a routine petroleum exploration technique. A number of groups of microfossils change color with changing paleotemperature. 14 Taphonomy and the quality of the fossil record Taphonomy “Taphonomy is the paleontological study includes all the processes that occur after the death of an organism and before its fossilization in the rock”. Plants and animals with hard tissues are most frequently preserved in the fossil record. Soft tissues usually decay rapidly, but rapid burial or early mineralization may prevent decay. Physical and chemical processes during transport and compaction damage hard tissues. Plants preserve as permineralized tissues, coalified compressions and cemented casts. Physical and chemical processes during transport and compaction damage hard tissues. Plants preserve as permineralized tissues, coalified compressions and cemented casts. Many of the analytic approaches used by taphonomists are also used by forensic scientists. Both observe the state of decay of remains. Measurement of the chemistry of the bone. Assessment of the rare earth elements (scandium, yttrium and the 15 lanthanides) to help pinpoint the time of death. Archeologist and Paleontologists both use these techniques Fossil Record Quality of the fossil record? Fidelity and quality of the fossil record. Can paleontologists trust their patchy fossil finds to understand large-scale patterns of evolution? Paleontologists should be careful when they attempt to reconstruct a whole plant or animal, and try to understand its biomechanics, when they have just a few bones or bits of twigs. Care is required in seeking to understand patterns of diversity change and evolution when many fossil species are missing. Diverse opinions and arguments in favour and against the fossil records. 15 Taphonomy and the quality of the fossil record : Fossil preservation (Part 1) Fossilization Sometimes a plant or an animal dies ends up as a fossil. There are several stages that normally occur in the transition from a dead body to a fossil. In rare cases, soft parts may be preserved, and these examples of exceptional preservation are crucially important in reconstructing past life. “Lagerstätten” Transition to fossil 1. Decay of the soft tissues of the plant or animal. 2. Transport and breakage of hard tissues. 3. Burial and modification of the hard tissues. Two kinds of fossils 1. Body fossils: the partial or complete remains of plants or animals 2. Trace fossils: the remains of the activity of ancient organisms, such as burrows and tracks. Decay When large animals feed on dead plant or animal tissues, the process is termed scavenging. When microbes, such as fungi or bacteria, transform tissues of the dead organism, the process is termed decay Factors controlling Decay Oxygen Microbial nutrients Temperature pH Example of Neolithic and younger “bog bodies” of northern Europe MUHAMMAD IMRAN 10 Volatiles and Refractories Soft parts of animals are made from volatiles, forms of carbon that break down readily. Refractories are the organic carbons much less liable to break down, such as cellulose. Mineralization Early mineralization of soft tissues depends on three factors: 1. Rate of burial 2. Organic content 3. Salinity Physical and chemical effects occurring after burial, are termed as Diagenesis Conservation traps Obrution deposits: sedimentation rates are so rapid that carcasses are buried virtually instantly Amber: fossilised resin Mineralization Types Mineralization of soft tissues occurs in three ways 1. Permineralization 2. Formation of mineral coats 3. Formation of tissue casts and shells 16 Taphonomy and the quality of the fossil record : Fossil preservation (Part 2) Breakage and transport Several processes of breakage 1. Physical: disarticulation, fragmentation, abrasion 2. Chemical: bioerosion, corrosion, dissolution 3. Disarticulation: Skeletons that are made from several parts may become disarticulated, separated into their component parts. After scavenging or decay of connective tissue 4. Fragmentation: Skeletons may also become fragmented. Individual shells, bones or pieces of woody tissue break up into smaller pieces usually along lines of weakness 5. Abrasion: Shells, bones and wood may be abraded by physical grinding and polishing against each other and against other sedimentary grains. 6. Bioerosion: The removal of skeletal materials by boring organisms such as sponges, algae and bivalves. Shells, bones and wood may undergo bioerosion 7. Corrosion and Dissolution: Before and after burial, skeletal materials are commonly corroded and dissolved by chemical action, i.e. by weak acidic waters Burial and Modifications The remains are typically buried after scavenging, decay, breakage and transport. Sediment is washed or blown over the remains, and the specimen becomes deeply buried. During and after burial, the specimen may undergo physical and chemical change Addition of CaCO3 is called Carbonate concretion Coprolites are phosphtised. Plant Preservation: Through petrification or cellular permineralization 1. Coal balls 2. Coalified compression 3. Cementation 4. Direct preservation of hard parts MUHAMMAD IMRAN 11 17 Taphonomy and the quality of the fossil record : Quality of the fossil record Incompleteness of the fossil record Charles Darwin “imperfection of the geological record” In 1972, David Raup explained all the factors that make the fossil record incomplete Anatomic filters Organisms are likely to be preserved only if they have hard parts, a skeleton of some kind. Entirely soft- bodied organisms, such as worms and jellyfish, are only preserved in rare cases Biological filters Behavior and population size matter Common organisms such as rats are more likely to be fossilized than rare ones such as pandas Shorter life span of rats Ecological filters Where an organism lives matters. Animals that live in shallow seas, or plants that live around lakes and rivers, are more likely to be buried under sediment Flying animals Sedimentary filters Some environments are typically sites of deposition, and organisms are more likely to be buried there. Mountainside or a beach VS a shallow lagoon or a lake Preservation filters Once the organism is buried in sediment, the chemical conditions must be right for the hard parts to survive. The destruction of bones or shells by acidic waters. worn and damaged by physical movement. Diagenetic filters After a rock has formed, the rock may be transformed by the passage of mineralizing waters Either enhancing the fossils, by replacing biomolecules with mineral molecules, or destroying the fossil Metamorphic filters Over millions of years, the fossiliferous rock might be baked or subjected to high pressure. In these kinds of metamorphic fossils may survive these terrible indignities, or they may be destroyed. Vertical movement filters Burial means the rock has been covered by younger rock. Tectonic movements must subsequently raise the fossiliferous rock to the Earth’s surface, or the fossil remains forever buried and unseen. Human filters: Fossils are seen and collected by a human being. The fossil has to be registered in a museum as part of collective human paleontological knowledge. Individual amateur collections wasted Sampling and reality The fossil record give us a good outline of the key events in the history of life. Understanding the history of life with the help of the fossils (small remnant of what once existed)is a big question 18 Paleoecology and paleoclimates Fossil organisms provide fundamental evidence of evolution. They also allow the reconstruction of ancient animal and plant communities. Paleoecologists The functions of single fossil organisms (paleoautecology). The composition and structure of fossil communities MUHAMMAD IMRAN 12 (paleosynecology The Paleoecology of fossil organisms Described in terms of life strategies and trophic modes together with their habitats. All fossil organisms interacted with other fossil organisms. Described in terms of life strategies and trophic modes together with their habitats. All fossil organisms interacted with other fossil organisms. The Paleoecology Analysis Populations and paleocommunities may be analyzed with a range of statistical techniques. Evolutionary Paleoecology Charts the changing structure and composition of Paleocommunities through time.Ecological events can be ranked in importance. Paleoclimates Described on the basis of climatically-sensitive biotas and sediments together with stable isotopes. Climate has been an important factor in driving evolutionary change at a number of different levels. Feedback loops and Gaia Hypothesis Feedback loops between organisms and their environments indicate that the Gaia hypothesis is a useful model for some of geological time. 19 Paleoecology and paleoclimates : Paleoecology (Part 1) Study of the life and times of fossil organisms, the lifestyles of individual animals and plants together with their relationships to each other and their surrounding environment. Speculation Element of speculation has prompted some paleontologists to exclude paleoecology from mainstream science Solution Emerging numerical and statistical techniques can help us frame and test hypotheses. Paleoecology is actually not very different from other sciences. Two main areas Paleoautecology is the study of the ecology of a single organism Paleosynecology looks at communities or associations of organisms. Fidelity The similarity of a death assemblage to its living counterpart, its fidelity. Measurements of biomass and taxonomic composition Structure of Community Numerical abundance and diversity are not the best estimates. Counts of stable adult populations are the most realistic monitors of community structure. A census of an extraordinarily preserved Lagerstätte deposit can help in the estimation of the Taphonomic loss. The degree of breakage with the attitude of fossils in sediments is useful to separate autochthonous (in place) from allochthonous (transported) assemblages. The -Coenoses The living assemblage, or biocoenosis, is transformed into a thanetocoenosis after death and decay. Taphocoenosis is the end product that is finally preserved 20 Paleoecology and paleoclimates : Paleoecology (Part 2) Population Populations are the building blocks of communities. A population is a naturally occurring assemblage of plants and animals that live in the same place at the same time and regularly interbreed. MUHAMMAD IMRAN 13 Ecosystem “All the populations of species living in association” Keystone species help shape the ecosystem and that can trigger large-scale changes if they disappear. E.g A classic keystone species is the elephant Incumbent Species Incumbent species can occupy the same ecological niche for many millions of years, adding stability to many ecosystems. E.g Dinosaurs and mammals Habitat and Niche Fossil organisms can be classified in terms of Habitat, where they live.(their address) Niche, their lifestyle (their occupation). Marine Sediments The majority of fossil animals have been found in marine sediments Occupy a wide range of depths and conditions. Photic zone is the depth of water penetrated by light Marine Variety of Life Marine environments host a variety of lifestyles. The upper surface waters are rich in floating plankton, and nektonic organisms swim at various levels in the water Marine Sediments Benthos are the beasts that live in or on the seabed Mobile nektobenthos, scuttle across the seafloor the fixed or sessile benthos are fixed Infaunal organisms live beneath the sediment–water interface Epifaunal organisms live above it The sediment–water interface Guilds Guilds are groups of functionally similar organisms occurring together in a community. Megaguild Megaguilds are a range of adaptive strategies based on a combination of life position (e.g. shallow, active, infaunal burrower) 21 Paleoecology and paleoclimates : Paleoclimates The study of changes in climate taken on the scale of the entire history of Earth. Uses the methods from the Earth and life sciences Paleoclimatology It obtains data from previously preserved things such as rocks, sediments, ice sheets, tree rings, corals, shells, and microfossils. The Climate change in life history Last 600 million years. Earth has oscillated at least five times between icehouse and greenhouse conditions. Spending most of the time in greenhouse climates Five climate zones 1. Humid Tropical (no winters and average temperatures above 18°C) 2. Dry subtropical (evaporation exceeds precipitation) 3. Warm temperate (mild winters) 4. Cool temperate (severe winters) 5. Polar (no summers and temperatures below 10°C MUHAMMAD IMRAN 14 Identification of climate zones A range of geological and paleontological criteria has helped identify climatic zones through time. calcretes (soils rich in calcium carbonate) and evaporites (evaporated salts) help identify dry, arid climates Dropstones (stones that plummet from the bottoms of melting icebergs into seabed sediments) and Tillites (rocks and sand left behind by an advancing glacier) indicate polar conditions. Trends of climate change Short term trends Long term trends Consequences for evolution Biological Feedback and Gaia Hypothesis 22 Macroevolution and the tree of life Evolution by natural selection Evolution by natural selection is a core scientific model that was set out by Darwin. It has been confirmed again and again in every branch of Biology. Intelligent design Creationists attempts to promote their religious beliefs, such as “intelligent design” or belief in a flat Earth, are not testable and therefore are not science. Speciation Speciation often occurs by the establishment of a barrier, and the isolation of part of a previously interbreeding population. Evolution Evolution takes place both within Species lineages (phyletic gradualism) at the time of speciation (punctuated equilibrium) Tree of Life The evolution of life may be represented by a single branching phylogenetic tree. Cladistics is a method of reconstructing phylogeny based on the identification of shared derived characters (homologies). Evolution Molecular sequencing provides additional evidence for reconstructing and dating the tree of life. DNA has been extracted from fossils such as woolly mammoths, but not from truly ancient fossils 23 Macroevolution and the tree of life : Evolution by natural selection Early Evolutionists Darwin laid the framework for Evolutionary Biology 150 years ago. No one has yet falsified Darwin’s theory of evolution by natural selection On The Origins of Species (1859) Tree of Life Darwin: life had diversified to millions of species by the continued splitting of species from a common stem. Explained for the first time the meaning of the natural hierarchy of life. Macroevolution Paleontological aspects of evolution, such as the tree of life and studies of processes over thousands and millions of years, are sometimes called macroevolution (“big evolution”) MUHAMMAD IMRAN 15 Microevolution (“small evolution”) are all the smaller-scale and shorter-term processes studied by biologists and geneticists in the laboratory or in the field. Darwin’s Quest of the Truth The Voyage of HMS Beagle Observation of Diversity of life Evidence for relationship in time and space Awareness of Fossil record Malthus’ work Principle of Natural Selection “Only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated.” Natural Selection 1. Nearly all species produce far more young than can survive to adulthood (Malthus’principle) 2. The young that survive tend to be those best adapted to survive. 3. Characters are inherited from parent to offspring, so the characters that ensure survival will tend to be passed on. 4. These survival characteristics will increase generation by generation. 24 Macroevolution and the tree of life : Evolution and the fossil record Species: Species consist of many highly variable individuals, often divided into geographically restricted populations and races. Homo sapiens: Single specie Biological Species’ Concept “A species consists of all individuals that naturally breed together and that produce viable offspring” Humans Wolves and Dogs Birds and Frogs Gene pool of Local populations Local populations may be isolated from other populations of the same species, and with a subtly different gene pool, the overall array of genetic material in all the individuals within the population. Gene flow The cohesion of a species is maintained over its natural range by processes of gene flow. The occasional wandering of individuals from one area to another, which interbreed with members of neighboring populations. Gene flow: interbreeding with members of neighboring populations. Speciation “The process of splitting of a population to form two species is speciation”. The allopatric (“other homeland”) model The geographic model (based on the establishment of geographic barriers) The Reasons for Speciation 1. Each population, or set of populations, would start out with a different gene pool. 2. Selection pressures would be different, perhaps only subtly, on either side of the barrier. Models of Speciation 1. The Phyletic Gradualism Model: Phyletic gradualism, where evolution takes place in the lineages, and speciation is a side effect of that evolution MUHAMMAD IMRAN 16 2. Punctuated Equilibrium Model: Where most evolution is associated with speciation events, and lineages show little evolution (stasis). 25 Macroevolution and the tree of life : The tree of life Tree Thinking: ✓ Darwin was the first to picture evolution as a great branching tree. ✓ “Which species of ape is closest to humans – the gorilla or chimp?” ✓ Putting together complete trees of all species ✓ Scala Naturae: the ladder of life. ✓ Ladder go from lower to higher, simple to complex ✓ Tree of life: Splits and Branches ✓ Tree is a better analogy for life Cladistics In Cladistics, we reconstruct the Life’s Hierarchy. The true patterns of Relationship among the organisms. Similarities and Differences among organisms Phylogenetically informative characters Good characters are phylogenetically informative, that is, indicative of the true phylogeny. These characters identify the clads. Phylogenetically uninformative characters fall into two main categories: Convergences Plesiomorphies 1. Convergence Convergence in evolution is when features, or organisms, evolve to look the same perhaps because they live the same way. 2. Plesiomorphies Plesiomorphies are characters that are shared by the organisms of interest, but also by other groups. Monophyletic Groups These are groups that had a single origin and include all the descendants of that common ancestor. Psittaciformes, the parrots, long been identified as real and distinct from all others by naturalists Non Natural Groups Clades are distinguished from two kinds of non-natural groups: Paraphyletic groups Polyphyletic groups 26 Macroevolution and the tree of life : Cladistics Early Scientists Willi Hennig (1913–1976), an eminent German entomologist, stressed the need to develop a new, more objective method in systematics, which has come to be called cladistics. Cladistics The fundamental aim of cladistics is to identify clades, and so to discover, or reconstruct, the tree of life. Patterns of relationships are shown as branching diagrams, or cladograms MUHAMMAD IMRAN 17 Nodes The most closely related species are joined most closely. The branches in the cladogram join at branching points, or nodes, each of which marks the base of a clade Apomorphies Hennig called the phylogenetically informative characters “Apomorphies” or derived characters. Apomorphies are features that arose once only in evolution. Synapomorphies “Apomorphies” shared by two or more species are termed synapomorphies. Synapomorphies of Order Psittaciformes include the deep, hooked beak and the unusual foot. Older distinctions “Homology” and “Analogy” Vertebrate Limbs Wing of bird, paddle of whale arm of human are the same. Homologs. Peddles of whales and seals Molecular Revolution Birth of Molecular Biology 1950s and 1960s. Comparisons of molecules allow analysts to do two things: 1. To draw up trees of relationships 2. To estimate time. Dendrograms Trees of relationships can be based on a comparison of the amount of difference between protein sequences, and a bestfitting dendrogram, or branching diagram, is drawn. Molecular Clocks Time estimation comes from the concept of the molecular clock. The amount of difference in the fine structure of a protein is proportional to the time since they last shared a common ancestor. Nucleic Acids The nucleic acid sequences must be aligned, that is matched, so that the code of a particular gene in one species is lined up with the same sequence in another species. 27 Fossil form and function Fossil species Fossil species are identified according to their external form; this is termed the morphological species concept. Variations in form include normal levels of individual variation The other types of variations in the forms of the fossils include ✓ Geographic distribution ✓ Sexual dimorphism ✓ Different growth stages ✓ ecophenotypic variation Allometry Fossil species may show allometry, or changes in relative proportions during growth; Specific organs may show positive (grow faster) or negative (grow slower) allometry. Development and Phylogeny The development of an organism may give some evidence about phylogeny. Changes in developmental rates and timing (heterochrony) may affect evolution. The New “Evo-Devo” Perspective Shows how certain developmental genes control fundamental aspects of form. MUHAMMAD IMRAN 18 ✓ Symmetry ✓ Front–back orientation ✓ Segmentation ✓ Limb form Inferring function from ancient organisms: Is difficult ✓ Various methods of doing this: ✓ Comparison with modern analogs ✓ Biomechanical testing ✓ Circumstantial evidence Modern analogs Modern analogs may provide exact parallels with some fossil organisms. More often they provide only principles or rules. Biomechanical models May be used to assess how the design of an ancient organism matches the hypothetical forces acting on it. May be used to assess how the design of an ancient organism matches the hypothetical forces acting on it. Models of locomotion are easy to produce. Circumstantial evidence, such as 1. The enclosing rocks 2. Associated fossils 3. Trace fossils and 4. Close study of the fossils themselves can add considerable information on fossil function. 28 Fossil form and function : Growth and form (part 1) Evolution and Form: Darwin gave us an evolutionary view of form. He was astonished by the variety of external appearances, by their wonderful adaptations to life. Forms: The form, or external appearance, of any microbe, plant or animal is shaped by evolution. Wings for flight Longs beak and tongue of humming bird Sexual selection Sexual selection is the set of evolutionary processes that depend on interactions between the sexes. Example: The astonishing tails and colors of male birds Adaptations: Plants and animals have adaptations that function in the context of both natural and sexual selection. An adaptation is an aspect of form that performs a physical or behavioral function. Importance of Form: The form of fossils is important for three reasons 1. Form is the only evidence we have in fossils for identifying species and wider relationships 2. Form can tell us about behavior and ecology 3. The study of changes in form through time informs us about evolution Recognizing ancient species Paleontologists use the morphological species concept. Statistical observations define the mean or average characteristics in specie. MUHAMMAD IMRAN 19 29 Fossil form and function : Growth and form Variations Within the Species Within a species, there may be a range of morphologies ❖ Individual variation ❖ The stuff of natural selection, as Darwin stressed. ❖ Geographic variation and physical differences between populations or subspecies in different parts of the overall species range. ❖ Sexual dimorphism, in which males and females may show different sizes, and different specialized features (horns, antlers, tail feathers). E.g Sexual dimorphism in ammonites, the Jurassic Kosmoceras. The larger shell was probably the female, the smaller the male. (Courtesy of Jim Kennedy and Peter Skelton.) ❖ Growth stages, where there may be quite different larval and adult stages, or where body form alters during growth ❖ Ecophenotypic effects, Where local ecological conditions affect the form of an organism during its lifetime Allometry Changes in form during growth are common. Think of human growth: babies have relatively large heads and eyes, and small limbs. If measurements of the variable parts are scaled against a standard measure of the animal, it is evident that the proportions change as the animal grows older E.g: Adult female Ichthyosaurus from the Lower Jurassic of Somerset, England, showing an embryo that has just been born (arrow), and detail of the curled embryo. (Courtesy of Makoto Manabe.) Allometric Growth The ratio of eye diameter to body length diminishes as the animal approaches adulthood. This is an example of allometric (“different measure”) growth. Isometric Growth If there is no change in proportions during growth, the feature is said to show isometric (“same measure”) growth. Biological Scaling Principle: MUHAMMAD IMRAN 20 Some organs and functions relate to the mass of an animal (a three-dimensional measure) others relate to body length or body outline (one- and two-dimensional measures). 30 Fossil form and function : Evolution and development Ontogeny and Phylogeny Biologists have long sought a link between ontogeny (development) and phylogeny (evolutionary history). Biogenetic Law In 1866, Ernst Haeckel, a German evolutionist, announced his Biogenetic Law, that “ontogeny recapitulates phylogeny”. Ernst Haeckel’s idea was that the sequence of embryonic stages mimicked the past evolutionary history of an animal. Von Baer’s Law: A parallel between the sequence of development, and a cladogram. In human development embryo passes through the major nodes of the cladogram of vertebrates. The synapomorphies of vertebrates appear first, then those of tetrapods, then those of amniotes, then those of mammals, of primates, and of the species Homo sapiens last. Development and Phylogeny : Three other aspects of development throw light on phylogeny Atavisms Vestigial structures Patterns of Development Atavisms: Certain developmental abnormalities called atavisms, or throwbacks, show former stages of evolution, such as human babies with small tails or excessive hair E.g: Hints of ancestry in modern animals. Extra toes in a horse; normal horse leg (left), extra toes (right). The vestigial hip girdle and hindlimb of a whale; the rudimentary limb is the rudiment of a hindlimb that functioned 50 Ma. Developmental Genes Widely shared among organisms. Since the 1980s a major new research field “evodevo” (short for evolution–development). Most famous developmental genes are the homeobox genes. MUHAMMAD IMRAN 21 Determine aspects of form Symmetry Anteroposterior orientation Limb differentiation 31 Mass extinctions and biodiversity loss Introduction Mass Extinctions During mass extinctions, 20–90% of species were wiped out; these include a broad range of organisms, and the events appear to have happened rapidly. It is difficult to study mass extinctions in the Precambrian There have been a Neoproterozoic event between the Ediacaran and Early Cambrian faunas. The “big five” Phanerozoic mass extinctions occurred in the End-Ordovician Late Devonian End-Permian End-Triassic End-Cretaceous The end-Permian mass extinction was the largest of all time Probably caused massive volcanic eruptions, leading to acid rain and global anoxia. The end-Cretaceous mass extinction has been most studied, and it was probably caused by a major impact on the Earth. Smaller-scale extinction events include the loss of mammals at the end of the Pleistocene, perhaps the result of climate change and human hunting. Recovery from Mass Extinctions Takes a long time First, some unusual disaster taxa that cope well in harsh conditions Gives way to the longer-lived taxa that rebuild normal ecosystems Major Concern Today MUHAMMAD IMRAN 22 Calculated species loss as high as during any mass extinction of the past. The severity of the current extinction episode is still debated. 32 Mass extinctions and biodiversity loss : Mass extinctions Extinction Extinction, is now a key theme in discussions about the future The dodo is perhaps the most iconic of icons An icon of human carelessness rather than of avian extinction. An image of a dodo from another era. Lewis Carroll introduced the dodo as a kindly and wise old gentleman in Alice Through the Looking Glass, although at the time most people probably regarded the dodo as rather foolish. Driven to extinction in the 17th century by overhunting, the dodo is now an image of human thoughtlessness. The most spectacular extinctions are known as mass extinctions Times when a large cross-section of species died out rather rapidly. Extinctions Events There may have been only five or six mass extinctions throughout the known history of life, although there were many extinction events, Study of Mass Extinctions From the 1980s Wide interdisciplinary links Stratigraphy Geochemistry Climate modeling Ecology Conservation Astronomy The study of mass extinctions involves careful hypothesis testing at all levels, from the broadest scale to the narrowest Back ground Extinctions Extinction happens all the time Species have a natural duration of few million years and so they live for a time and then disappear Features of Mass Extinction More than 30% of plants and animals of the time. MUHAMMAD IMRAN 23 The extinct organisms spanned a broad range of ecologies The extinctions were worldwide covering most continents and ocean basins. The extinctions all happened within a relatively short time The level of extinction stands out as considerably higher than the background extinction level. 33 Mass extinctions and biodiversity loss : Mass extinctions (continued) Mass Extinctions Paleontologists talk about the “big five” mass extinctions of the last 540 myr The Phanerozoic, and the current extinction crisis is sometimes called the “sixth extinction”. Mass extinctions through the past 600 myr. Major: 50% of families and up to 96% of species Intermediate: global in extent, and involved losses of 20% of families and 75–85% of species. Minor mass extinctions: causing losses of 10% of families and up to 50% of species Patterns and Timings Good-quality fossil records indicate a variety of patterns of extinction The rock record can be misleading Gradual extinctions might look catastrophic Signor–Lipps effect Paleontologists will never find the very last fossil of a species. Signor and Lipps showed how this backward smearing now termed the Signor–Lipps effect MUHAMMAD IMRAN 24 Selectivity and mass extinctions The second defining character of mass extinctions was that they should be ecologically catholic There should be little evidence of selectivity. Periodicity of mass extinctions Fundamental debate has been whether each event had its own unique causes, or whether a unifying principle linking all mass extinctions might be found The idea of periodicity of impacts was reawakened by Rohde and Muller (2005) who argued for a 62 myr periodicity in mass extinction 34 Mass extinctions and biodiversity loss : The “big five” mass The “big five” or the “big three”? There is some debate about whether there were five or three mass extinctions. Key points about three of the five events. 1. End-Ordovician mass extinction 445 Ma Substantial turnovers occurred among marine faunas. Reef-building animals, brachiopods, echinoderms, ostracodes trilobites died out Major Climatic changes, Tropical-type reefs and their rich faunas lived around the shores of North America that then lay around the equator. Southern glaciation and lowering sea levels globally 2. Late Devonian mass extinction A succession of extinction pulses 380 to 360 Ma. The cephalopods were decimated. Causes: A major cooling phase associated with anoxia or an extraterrestrial impact 3. The End Permian/ Permo-Triassic (PT) The end-Permian, or Permo-Triassic, extinction was the most devastating of all time. Less understood than KT event. The peak of eruptions by the Siberian Traps was dated at 251 Ma, matching precisely the date of the PT boundary. Environmental changes studies of stable isotopes (oxygen, carbon) in those rock sections revealed a common story of environmental turmoil. 35 Mass extinctions and biodiversity loss : The Cretaceous-Tertiary event MUHAMMAD IMRAN 25 4. The end-Triassic mass extinction The fourth of the big five mass extinctions A marine mass extinction event at, or close to, the Triassic- Jurassic boundary, 200 Ma Anoxia and global warming due to Volcanic eruptions 5. The End-Cretaceous/ Cretaceous-Tertiary (KT) events The KT event Intense scrutiny since 1980: Reasonable theories (global climate change, change in plants, impact, plate tectonic movements, sealevel change) June 1980, paper in Science by Luis Alvarez and colleagues. 10 km meteorite (asteroid) had hit the Earth. The impact threw up a great cloud of dust that encircled the globe An unusual clay band right at the KT boundary, within a succession of marine limestones Iridium spike: where the iridium content shot up from normal background levels MUHAMMAD IMRAN 26 Alvarez Predictions: 150KM crater, 10 KM Diameter of Meteorite 1991, Crater was identified in Chicxulub in Mexico Catastrophic Extinction in plants, lower level of pollens, sudden loss of angiosperms and replacement with ferns. Progressive return to Microflora Another Alternative The gradualist model: Extinctions occurred over long intervals of time as a result of climatic changes On land, subtropical lush habitats with dinosaurs gave way to strongly seasonal, temperate, conifer- dominated habitats with mammals Third school of Thought Volcanic activity: The Deccan Traps in India represent a vast outpouring of lava that occurred over the 2–3 myr spanning the KT boundary 36 The origin of life RNA world: By fusion of organic molecules in the first billion years after the formation of the Earth. Self-replicating RNA “RNA world” The Origin of Life Photosynthesis by a group of bacteria, called cyanobacteria, generated molecular oxygen (O2). The atmosphere became oxygenated Three great domains By gene sequencing of modern organisms, Bacteria, Archaea and Eucarya The first two are prokaryotes, the last eukaryotes The Earliest Fossils Bacteria in rocks up to 3.2 Ga, indicated by stromatolites. Structures built by alternating algal mats and sediment layers Cellular Organism Cellular fossils 3.5 Ga are highly controversial. The first widely accepted cellular fossils date from 2.5 Ga Origin of Eukarya Lipids Biomarkers, evidence for cyanobacteria and eukaryotes 2.7 Ga. The oldest eukaryotes, 1.9 Ga Origin of Sexes Red algae from 1.2 Ga show that sex had originated. They show mitosis, but also meiosis, which is unique to sexual reproduction Origin of Multicellularity Together with sex came multicellularity. The possession of many, often specialized, cells, first seen in 1.2 Ga red algae 37 The origin of life : Scientific Methods Scientific models Some of them now rejected by the evidence. Others still available as potentially valid hypotheses: Spontaneous generation Inorganic model Extraterrestrial origins Biochemical model Hydrothermal model MUHAMMAD IMRAN 27 Spontaneous generation Medieval scholars Organisms sprang into life directly from nonliving matter Pasteur, 1861 Meat in airtight containers: maggots did not appear The inorganic model Complex organic molecules arose gradually on a pre-existing, non-organic replication platform Silicate crystals Graham Cairns-Smith of Glasgow University, 2007 not conclusive Extraterrestrial Model: The building blocks for life were seeded on Earth from outer space Simple organic molecules in meteorites called carbonaceous chondrites Panspermia 1996, David McKay Biochemical Model 1920s, independently Russian biochemist, A. I. Oparin British evolutionary biologist, J. B. S. Haldane Life could have arisen through a series of organic chemical reactions that produced ever more complex biochemical structures Biochemical theory of Origin of Life The biochemical theory for the origin of life, as proposed by Oparin and Haldane in the 1920s. Biochemists have achieved steps 1–3 in the laboratory, but scientists have so far failed to create life. Hydrothermal Model Modification to the Oparin–Haldane biochemical model MUHAMMAD IMRAN 28 The last universal common ancestor of life (LUCA) was a hyperthermophile, a simple organism that lived in unusually hot conditions. Seawater mixes with molten magma and emerges as superheated steam, with the sulfur in it now concentrated as sulfide Emerging hot-water plume black Black smokers 38 The origin of life: Testing the Biochemical Method Stanley Miller In 1953, then a student at the University of Chicago, made a model of the Precambrian atmosphere and ocean in a laboratory glass vessel. Exposed a mixture of water, nitrogen, carbon monoxide and nitrogen to electric sparks, to mimic lightning, found a brownish sludge in the bottle after a few days. Brownish Sludge Contained sugars, amino acids and nucleotides. Researchers consider the mixture of gases that Miller used was strongly chemically reducing Further Experiments In 1950s and 1960s led to the production of polypeptides, polysaccharides and other larger organic molecules Protocells of Sidney Fox FSU, Succeeded in creating cell-like structures, in which a soup of organic molecules became enclosed in a membrane. Didn’t survive for long 39 The origin of life: RNA World Precellular Life The transition from non-living to living. No a single Step. Widely accepted view “RNA World” RNA RNA, or ribonucleic acid, is one of the nucleic acids and it has key roles in protein synthesis. The genetic code. There are several different forms of RNA RNA the Precursor In 1968, Francis Crick suggested that RNA was the first genetic molecule. RNA has unique property of acting both as a gene and an enzyme. RNA could act as a precursor of life RNA World Walter Gilbert first used the term “RNA world” in 1986. The first evidence. Sidney Altman and Thomas Cech. Ribozyme An RNA that could edit out unnecessary parts of the message it carried before delivering it to the ribosome. Cech called his discovery a ribozyme Chasing Evidence Since 1990, Jack Szostak and colleagues argued that the first RNA molecules on the prebiotic (“before life”) Earth were assembled from nucleotides dissolved in rock pools RNA Replicase One RNA acted as a Template and another Enzyme. Combine as an RNA replicase. Szostak and colleagues proposed a second precellular structure, “A self-replicating vesicle” MUHAMMAD IMRAN 29 Protocell A membrane-bound structure composed mainly of lipids that self-replicates. The RNA replicase entered a self- replicating vesicle. RNA replicase to function efficiently The model behind “RNA world”, where an RNA replicase and a self-replicating membrane-bound vesicle combine to form a protocell 40 The origin of life : Evidence for the origin of life The Early Precambrian world The Precambrian is divided into Hadean eon Archaean eon Proterozoic eon Hadean Eon spans from the origin of the Earth, 4.57 to about 4 Ga Precambrian world Beginning of the Hadean. Temperatures on surface were too high. The crust was too unstable for any form of carbonbased life to exist Cooling of Earth As the Earth’s surface cooled, the lithosphere, its rocky crust, began to differentiate as a cooler upper layer above the underlying asthenosphere. Oldest Rocks The oldest rocks are from Canada and are dated at 3.8–4 Ga, and some mineral grains from Australia have even been dated to 4.4 Ga The Archaean Eon Lasted from about 4 to 2.5 Ga. The oldest sedimentary rocks from the Isua Group in Greenland, dated at 3.8–3.7 Ga. Rosing and Frei (2004), Reported values of δ13C in organic matter from the Isua Group rocks that match those of modern living organic matter. The Great Oxygenation Event The Proterozoic Eon, from 2.5 Ga to 542 Ma. 2.4 Ga, atm oxygen levels rose to one-hundredth or one-tenth of modern levels A Second Rise of Oxygen Around 0.8–0.6 Ga is indicated by increased levels of marine sulfate. The two rises in oxygen levels, at the beginning and end of the Proterozoic MUHAMMAD IMRAN 30 41 The origin of life: Life diversifies: eukaryotes Eukaryote Characters Evidence about the earliest evolution of the three domains is scant Nucleus: DNA in chromosomes Cell organelles Endosymbiotic Theory Margulis: 1970s. Prokaryote consumed, or was invaded by, prokaryotes. Two species evolved together in a mutually beneficial way. Basal Eukaryotes The oldest eukaryote is controversial Lipid biomarkers indicate that eukaryotes were around at least by 2.7 Ga The oldest eukaryote fossil may be Grypania, a coiled, spaghetti-like organism that has been reported from rocks as old as 1.85 Ga MUHAMMAD IMRAN 31 Multicellularity and sex True multicellular organisms arose only among the eukaryotes. Allowed plants and animals to become large (kelp, reach lengths of tens of meters). Sexual reproduction involves the exchange of gametes (sperms and eggs) between organisms Bangiomorpha One of the oldest multicellular organisms/eukaryote is Bangiomorpha 1.2 Ga. Multicellular and a member of a modern group that engages in sex. 42 Protists : Protista: introduction Micropaleontology A multidisciplinary science, focused on the study of microorganisms or the microscopic parts of larger organisms. Prokaryotes Unicellular microbes lacking nuclei and organelles, include the carbonate producing cyanobacteria Promoted an oxygen-rich atmosphere Protists Unicellular organisms with nuclei, a variety of organisms with external protective coverings (tests and cysts) Kingdoms Protozoa and Chromista Fossilized Protists Split into Organic (acritarchs, dinoflagellates, chitinozoans), Calcareous (coccolithophores, foraminiferans) Siliceous (diatoms, radiolarians) Foraminifera MUHAMMAD IMRAN 32 Single-celled animal-like protozoans Contain both benthic and planktonic form With chitinous, agglutinated tests throughout the Phanerozoic Rock Formers Radiolarians: animal-like protozoans with siliceous tests, Diatoms: plant-like protozoans with silicic skeletons Both important rock formers. 43 Protists: Kingdom Protista Kingdom Protista Single-celled organisms with nuclei and organelles Autotrophs Heterotrophs The Protista is a convenient grouping but it is not well defined Subdividing the diversity of protists is equally problematic On the basis of Trophism Phylogenetic Mode of locomotion Flagellates and Amoebans The First Protists Heterotrophs, but chloroplasts were acquired separately in at least six lineages, producing autotrophs, Lost secondarily even more often Groups with microfossil records are widely scattered across the diversity of protists Modern molecular genetic and cytologic research 44 Protists : Protozoa Protozoa Neither animal nor plant, but single-celled eukaryotes that show animal characteristics such as motility and heterotrophy. Able to form cysts. Foraminifera Foraminifera are shelled & heterotrophic, Phanerozoic sedimentary rocks, Considerable bio stratigraphic and paleoenvironment-al value. Radiolaria The radiolarians are marine, unicellular, planktonic protists with delicate skeletons. Usually composed of a framework of opaline silica. Origin in the Mid Cambrian or earlier, became common in the Ordovician. Often found in deep-sea cherts associated with major subduction zones. Radiolarian cherts commonly occur in oceanic facies preserved in mountain belts, associated with ophiolites, origins and destruction of ancient ocean systems Acritarchs A mixed bag of entirely fossil, hollow, organic-walled microfossils that are impossible to classify. The acritarchs are probably polyphyletic Dinoflagellates The dinoflagellates, or “whirling whips”, comprise a group of microscopic algae with organic-walled cysts. Dinoflagellate biomarkers have been identified in Upper Proterozoic and Cambrian rocks. A number of Paleozoic acritarch taxa may in fact be dinoflagellates Ciliophora Consist of some 8000 species of single-celled organisms that swim by beating cilia. Tithonian (Upper Jurassic) to the Albian (Middle Cretaceous) MUHAMMAD IMRAN 33 45 Protists : Chromista Chromistans A paraphyletic group of eukaryotes that usually contains chloroplasts with chlorophyll c. Chlorophyll c is absent from all known plant groups. The group includes various algae, the coccolithophores and the diatoms. Primary producers, functioning as part of the phytoplankton Nannoplankton Defined as plankton less than 63 μm across, the smallest standard mesh size for sieves. Includes organic-walled and siliceous forms Coccolithophores Dominant members of the fossil calcareous nannoplankton, and calcareous plates, Coccoliths. Dominate nannofossil assemblages, Calcareous nannoplankton. Appeared: Late Triassic Increased: Jurassic and Cretaceous Reaching an acme of diversity: Late Cretaceous Severely affected: KT mass extinction Radiated: Early Paleogene and throughout the Cenozoic Extremely abundant: Modern oceans 46 Protists : Chromista Diatoms Diatoms Unicellular autotrophs that are included among the Chrysophyte algae characterized by large green- brown chloroplasts. Both individuals and loosely integrated colonies. Saline to freshwater. The Centrales – prefer marine environments; The Pennales –more common in freshwater lakes Diatom frustules, Endospores: preserved in fossil record Range of temperatures. Common: Antarctic plankton. First diverse floras: mid-Cretaceous,10 families from Aptian rocks. 100 genera of centric diatoms: the Upper Cretaceous. The first pennate diatoms appeared during Paleogene colonizing freshwater for the first time. The group reached an acme during the Miocene. MUHAMMAD IMRAN 34 47 Origin of the metazoans Fossil evidence Few basic body plans have appeared in the fossil record, most animals have triploblastic architecture. Three fundamental body layers. Molecular Data Show three main groupings of animals: Deuterostomes Spiralians Ecdysozoans Spiralians and Ecdysozoans: the protostomes. Three Groups The deuterostomes (echinoderm–hemichordate–chordate group) The Spiralians (mollusk–annelid–brachiopod–bryozoans group) The ecdysozoans (arthropod–nematode–priapulid plus other taxa group) Five lines of evidence Body fossils Trace fossils fossil embryos The mol. Clock Biomarkers Suggest metazoans originated before Ediacaran 600 Ma Coincidence or Design Snowball Earth by coincidence or design was a pivotal event in metazoan history; bilaterians evolved after the Marinoan glaciation. The First Metazoans Probably similar to the demosponges, occurring first before the Ediacaran The Ediacaran Biota A soft-bodied assemblage of uncertain affinities Reaching its acme: the Late Proterozoic Earliest ecosystem having large, multicellular organisms Cambrian Explosion The Cambrian explosion generated a range of new body plans during a relatively short time interval. Ordovician Radiation Marked by accelerations in diversification at the family, genus and species levels along with complexity in marine communities. 48 Origin of the metazoans : Origins Precambrian life Evidence of metazoan body and trace fossils. The investigation of minute fossil embryos. Carefully calibrated molecular clocks. Biomarkers MUHAMMAD IMRAN 35 Metazoan Life Molecular data suggest metazoans have been around for at least 600 myr. During which time as many as 35 separate phyla have evolved. Recalibrated molecular clocks. Animal origins be tracked back only to the Ediacaran, when there was also a sudden rise in oxygen levels in the deep ocean Body Fossil Evidence Earliest metazoans occur in Ediacara biota 600–550 Ma. Significant Proterozoic record for the cnidarians and sponges Trace Fossil Evidence The oldest locomotory trace fossils are from about 550 Ma northwest Russia. Fecal strings from rocks some 600 Ma suggesting. Digestive system Embryo Fossil Evidence Best studied example: Doushantuo Formation, South China 580 Ma. Earliest body fossil evidence for metazoan life Molecular Evidence Molecular clock, the metazoan clade excluding the sponges and cnidarians, has been placed at anywhere between 900 and 570 Ma Biomarker Evidenc Biomarkers, essentially the biochemical fingerprints of life. BMs associated with metazoan demosponges from rocks older than the Ediacaran 49 Origin of the metazoans : Invertebrate body and skeletal plans Invertebrate Body & Skeletal Plans Body plans are usually defined by the number and type of enveloping walls of tissue together with the presence or absence of a Celom. The first metazoans were multicellular with one main cell type & peripheral collar cells or choanocytes, with a whip or flagellum. The Parazoan Body Plan Seen in sponges, characterized by cells organized in two layers separated by jelly-like material punctuated by so- called wandering cells or amoebocytes The Diploblastic Body Plan Cnidarians and the ctenophorans. Two layers are separated by acellular mesogloea an outer ectoderm an inner endoderm The Triploblastic Body Plan Seen in most other animal. Has three layers of tissues from the outside in: the ectoderm, mesoderm and endoderm. Bilateral Symmetry Defines the bilaterians. The development of the celom or body cavity characterizes Most of the animal groups found as fossils Skeleton The skeleton is an integral part of the body plan of an animal, providing support, protection and attachment for muscles Hydraulic Skeleton Many animals such as the soft-bodied mollusks (slugs) possess a hydraulic skeleton in which the movement of fluid provides support Rigid Skeletons Mineralized material may be external (exoskeleton) in the case of most invertebrates Internal (endoskeleton) structures, in the case of a few mollusks MUHAMMAD IMRAN 36 Skeleton Growth Growth is accommodated in a number of ways. Most invertebrate skeletons grow by the addition of new material, a process termed accretion. Arthropods, however, grow by periodic bursts between intervals of ecdysis or molting 50 Origin of the metazoans : Classifications and Relationships Classification Based on purely morphological data and embryology has problems. Difficulties in establishing homologous characters and homoplasy Basal Eumetazoans The demosponges and calcisponges are the simplest animals. The cnidarians are the most basal eumetazoans Three Groups Three robust bilaterian groupings are recognized mainly on molecular data Ecdysozoans, Spiralians Deuterostomes Protostomes Ecdysozoans, spiralians comprise the protostomes. “First mouth” mouth develops directly from the blastopore. By cell growth and migration` Deuterostomes “Second mouth” however, have a mouth arising from a secondary opening. True blastopore develops as anus. Echinoderm– Hemichordate-Chordate Larval Types Invertebrate larvae are occasionally identified in the fossil record. More advanced preparatory and high-tech investigative techniques Nauplius larva: crustaceans Planula: cnidarians Trochophore larva: mollusks and the polychaetes Shelled veliger: mollusks Evolutionary Faunas 51 Origin of the The three great evolutionary faunas of Phanerozoic, Cambrian, Paleozoic modern Developed during last 550 myr. The Ediacara biota, Faunas during metazoans : Four key Cambrian explosion & Ordovician radiation set the scene for life on our planet. faunas Ediacara Biota The Ediacaran biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms that lived during the Ediacaran Period (ca. 635–542 Mya) First impressions of soft-bodied organisms Upper Proterozoic rocks of Namibia In the Pound Quartzite In the Ediacara Hills, north of Adelaide Shallow-water siliciclastic sediments Soft-bodied, with high SA/V ratios Radial or bilateral symmetries Extinct about 550 Ma MUHAMMAD IMRAN 37 Cambrian Explosion Cambrian radiation Relatively short span event 20my 541 million years ago Most major animal phyla appeared Generated many entirely new and spectacular body plans. Sequential appearance of successively more complex metazoans. Phylogenetic analysis shows metazoans evolved monophyletically from flagellated colonial protists similar to modern choanoflagellates. 52 Origin of the metazoans : Ordovician Radiation Ordovician Radiation Great Ordovician biodiversification event (GOBE), Evolutionary radiation of animal life during the Ordovician Period, 40 my after the CE. Followed a series of Cambrian–Ordovician Extinction events Fauna went on to dominate the Palaeozoic Marine diversity increased The majority of “Paleozoic” taxa were derived from Cambrian stocks Interplay of many geological and ecological factors likely produced the diversification Ordovician diversification generated witnessed a staggering increase in biodiversity at the family, genus and species levels. E.g. The Ordovician Seafloor, The Cambrian Seafloor 53 Origin of the metazoans : Soft-bodied invertebrates Inadequate Fossil Record Out of 25 or so commonly recognized animal phyla fewer than nine (35%) have an adequate fossil record A number of larger soft-bodied phyla lack a preservable skeleton Soft-bodied forms are preserved in fossil Lagerstätten Significance of the diverse worm-like animals at the Precambrian–Cambrian boundary and the postulated origins of some major clades MUHAMMAD IMRAN 38 Burgess Shale Burgess Shale and other exceptionally preserved faunas suggests that many of these soft-bodied groups dominated certain marine paleocommunities Platydendron The platyhelminths or the flatworms are bilateral animals. Platydendron from the Middle Cambrian Burgess Shale has been ascribed to the platyhelminthes Polychaetes A diverse polychaete fauna has been described from the Burgess Shale. Even contains Canada spinosa. Similar to some living polychaetes. Paddle worms: most complete fossil record. Record is enhanced by the relatively common preservation of elements of the phosphatic jaw: scolecodonts 54 The basal metazoans: sponges and corals Parazoa Parazoans are metazoans composed of multicellular complexes with few cell types and lack variation in tissue or organs. I.e. The sponges (Phylum Porifera). Two groups, the Porifera and the Cnidaria, form the basal parts of the metazoan tree, diverging during Neoproterozoic. Important parts of the planet’s reef ecosystems Sponges Sponges are filter-feeding members of the sessile benthos. Contains a variety of grades of functional organization. Sponge reefs dominated: Phanerozoic. Calcareous grades. Siliceous sponges were important reef builders: Mesozoic Stromatoporoids A grade of organization within the Porifera with a secondary calcareous skeleton. Important in reefs during the midPaleozoic and mid-Mesozoic Archaeocyaths Cambrian organisms of sponge grade Mainly solitary Developed branching, modular growth Successfully built reefs in unstable environments Cnidarians The simplest of the higher metazoans with a radial diploblastic body plan and stinging cells or cnidoblasts. Sea anemones, jellyfish and hydra along with Corals Reef-Type Structures Reef-type structures were already present in the Late Precambrian hosting large, robust, colonial organisms. Reef development through time has waxed and waned. Dominated at different times by different groups of reef-building organisms MUHAMMAD IMRAN 39 Coloniality Evolved many times. One hypothesis suggests that a Precambrian colonial organism may have been a source for the bilaterians 55 The basal metazoans: sponges and corals : Porifera Porifera: Dr Robert Grant “Porifera is a unique group in its own right”. Unique porous structure and cellular body plan, lack true tissues. Most lack symmetry, true differentiated tissues, and organs, although their cells, like those of the protists, can switch function Skeleton Sponges are skeletal organisms. Skeletons are composed of a colloidal jelly or spongin Chamber Organization Three levels 1. Ascon: Sacs with a single chamber lined by flagellate cells 2. Sycon: a number of simple chambers with a single central paragaster. 3. Leucon: most common where a series of sycon chambers access a large central paragaster Stromatoporoidea Common in the fossil record from the Ordovician through the Devonian. Especially abundant in the Silurian and Devonian. These invertebrates were important reef-formers throughout the Paleozoic and the Late Mesozoic Archaeocyatha “Ancient cups” are one of only a few major animal groups that are entirely extinct. Reef-building marine organisms of warm tropical and subtropical waters. Lived during the early (lower) Cambrian Period. It is believed that the center of the Archaeocyatha origin are now located in East Siberia 56 The basal metazoans: sponges and corals : Cnidaria The Cnidarians “Nettle-bearers”. Include the Sea anemones, jelly fish, corals. The least complex of the true metazoans (eumetazoans). Few tissue types in a radial plan. Although there are no specialized organs and only a few tissue types, they are more complex than the parazoans. Two basic life strategies Polyps: sessile Medusae: swim, MUHAMMAD IMRAN 40 Medusoids and polyps appear different, they are essentially same inverted structures. Cnidarian life cycles generalized view of the life of the hydrozoan Obelia, alternating between the conspicuous polyp and medusa stages Class Hydrozoa Polymorphic forms. Undivided enteron, solid tentacles, colonies. Chondrophora oldest cnidarians. Ediacaran to Recent Class Scyphozoa Jellyfish, Lagerstätten. The extinct Conulata. Appeared in Cambrian. Extinct in Mid Triassic. Ediacaran to Recent Class Anthozoa Marine, sessile, colonial forms. Mobile planula larvae. Octocorallia class includes corals, sea anemones. Produce spicules microfossils. Ediacaran to Recent Class Cubozoa The sea wasps and box jellyfish. Both medusae and polyps. Restricted to tropical and subtropical latitudes. Carboniferous to Recent Corals Most diverse and most threatened ecosystems. The coral reef. Shallow-water coral reefs in zone extending 30° north and south of equator. 30m or 18 °C 57 Spiralians 1: lophophorates The Spiralians Morphologically diverse clade of protostome animals Molluscs Annelids Platyhelminths and other taxa Lophophores Lophophores, a filamentous feeding organ. Three spiralian invertebrate groups Brachiopods Bryozoans Phoronids Brachiopods Twin-valved shellfish, Lophophore and a pedicle, Linguliformeans: organophosphatic shells Craniiformeans & rhynchonelliformeans: calcareous shells Paleozoic Communities Orthides and Strophomenides. Rhynchonellides and Terebratulides were in Lower-diversity post-Paleozoic brachiopod assemblages. Brachiopods dominated the filter-feeding benthos of the Paleozoic. Never fully recovered during the endPermian mass extinction Living Brachiopods Living brachiopods are relatively rare, occupying mostly cryptic and deep-water habitats. Bryozoans Colonial invertebrates with Lophophores. Displaying marked non-genetic variation across a wide range of environments Stenolaemata Dominated Paleozoic bryozoan faunas. Only the cyclostomes surviving the combined effects of the end-Permian and endTriassic mass extinctions. Stenolaemata are a class of marine bryozoans. This class originated in the Ordovician, and members still live today. All extant species are in the order Cyclostomatida MUHAMMAD IMRAN 41 Cyclostomes Cyclostomes continued to decline after the end-Cretaceous extinction event. Cheilostomes radiated to dominate Cenozoic assemblages 58 Spiralians 1: lophophorates : Brachiopoda Brachiopoda Most successful invertebrate phyla Appeared: Early Cambrian Diversified: Paleozoic Dominate the low-level, suspension feeding benthos Morphology The brachiopod soft parts are enclosed by two morphologically different shells or valves with variety of muscles. The ventral or pedicle valve is larger Distribution in time Cambrian MUHAMMAD IMRAN 42 Paleozoic Modern brachiopod faunas, Fundamentally different. A dominance of different orders Cambrian Faunas Dominated by a range of non-articulated groups with groups of disparate articulated taxa Chileides Naukatides Obolellides etc Ordovician Radiation Deltidiodont, Orthides and Strophomenides First evolved: Early Ordovician island complexes Dominated the shelf benthos & basis of the Paleozoic brachiopod fauna. 59 Spiralians 1: lophophorates : Five extinction events Brachiopoda Five Main Extinctions The brachiopods experienced five main extinction events. Followed by recoveries and radiations of varying magnitudes The End-Ordovician Event Occurred in two phases, glaciation & loss of almost 80% of brachiopod families. Decline of deltidiodont groups. Dominance of the spiriferides pentamerides Late Devonian events Climate change. Removed the Atrypides & Pentamerides. Severely affected Orthides & Strophomenides. Spiriferides & Rhynchonellides survived in deeper-water environment Carboniferous Era Intervals of spectacular experimentation. Mimicked corals or developed extravagant clusters of spines. Reduced shells, presenting soft tissues to outside environment. End-Permian Mass Extinction Demise of over 90% of brachiopod species, disaster taxa including lingulids, later diversified within a few clades dominated by the rhynchonellides and terebratulides End-Triassic Event Removed the majority of the remaining spiriferides and the last strophomenides. Dominance of Rhynchonellide and terebratulide groups Modern Brachiopods Exhibit a remarkable range of adaptations based on a simple body plan and a well defined role in the fixed, low- level benthos. 60 Spiralians 1: lophophorates : Bryozoa Bryozoans All species are colonial. Skeletons fragment easily after death, least well-known invertebrates, 6000 living & 16,000 fossil species, marine. Superficially resembling the corals and hydroids, “Moss animals”, Filter feeders, Sieve food particles using a retractable lophophore. The genus Bowerbankia is a relatively simple Bryozoan. Useful for illustrating the general anatomy of bryozoan zooids. E.g A Gymnolaemate. Morphology Each living zooid is enclosed by a body wall/cystid. The lophophore, with its beating cilia, A ring of 10 tentacles direct food to mouth leading into a U shaped gut. Egestion: anus MUHAMMAD IMRAN 43 Oldest Bryozoans Occur in the Tremadocian Stage of the Lower Ordovician. Primitive, soft-bodied bryozoans existed during the Cambrian but have not been fossilized. Stenolaemata dominated Paleozoic bryozoan faunas. Genera such as Monticulipora, Prasopora and Parvohallopora are typical of Ordovician assemblages. Cheilostomes, Polymorphic zooids, appeared during the Late Jurassic; Common in the Late Cretaceous and Paleogene of the Baltic and Denmark. Brachiopods and Bryozoans Members of the filter-feeding Paleozoic evolutionary fauna. Brachiopods a minor part of the Recent marine fauna but bryozoans continue to flourish 61 Spiralians 2: mollusks Mollusks The Phylum Mollusca can be traced back to at least the Late Precambrian, when Kimberella probably fed on algae in Ediacaran communities Early Mollusks Characterized by some short-lived, unusual forms Molluskan features: mantle, mineralized shell and radula Members of the small shelly fauna Bivalves Characterized by a huge variety of shell shapes, dentitions and muscle scars Adapted for a wide range of life strategies in marine and some freshwater environments Gastropods Most gastropods undergo torsion in early life; they have a single shell, often coiled. The group adapted to a wide range of environments from marine to terrestrial. Cephalopods The most advanced mollusks, with a head, senses and a nervous system Nautiloids, Ammonoids and the Coleoids Carnivorous Mollusks During the Mesozoic developed a number of protective strategies Robust armor Deep infaunal life Multiformity of shape and color Annelid worms Annelid worms were a sister group to the mollusks Their jaws, the scolecodonts, are relatively common in Paleozoic faunas 62 Spiralians 2: mollusks : Mollusks: introduction Phylum Mollusca MUHAMMAD IMRAN 44 The Phylum Mollusca includes The slugs, snails, squids, cuttlefish and octopuses All manner of marine shellfish such as clams, mussels and oysters The most common marine animals today, Occupy wide range of habitats Abyssal depths of the oceans and intertidal mudflats Forests, lakes and rivers. Mollusks are usually Unsegmented Soft-bodied animals With a body plan based on four features Four Features 1. The head contains the sensory organs, and a rasping feed

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