Transcript Chapter 12
Chapter 12 Paleozoic Life History: Invertebrates Burgess Shale • Diorama of the environment and biota – of the Phyllopod bed of the Burgess Shale, • British Columbia, Canada Burgess Shale Soft-Bodied Fossils • On August 30 and 31, 1909, – Charles D. Walcott, • geologist and head of the Smithsonian Institution, – discovered the first soft-bodied fossils – from the Burgess Shale, – a discovery of immense importance in deciphering the early history of life • Walcott and his collecting party split open numerous blocks of shale, – many of which yielded the impressions – of a number of soft-bodied organisms – beautifully preserved on bedding planes Thousands of Fossil Specimens • Walcott returned to the site the following summer – and located the shale stratum – that was the source of his fossil-bearing rocks – in the steep slope above the trail • He quarried the site – and shipped back – thousands of fossil specimens – to the United States National Museum of Natural History, – where he later catalogued and studied them More Complete Picture of a Middle Cambrian Community • The importance of Walcott's discovery – is that it allowed geologists a rare glimpse into a world previously almost unknown – that of the soft-bodied animals that lived some 530 million years ago • The beautifully preserved fossils – – – – from the Burgess Shale present a much more complete picture of a Middle Cambrian community than deposits containing only fossils of the hard parts of organisms Sixty Percent Soft-Bodied • In fact, 60% of the total fossil assemblage – of more than 100 genera is composed of softbodied animals, – a percentage comparable to present-day marine communities • What conditions led to the remarkable preservation of the Burgess Shale fauna? • The site of deposition of the Burgess Shale – was located at the base of a steep submarine escarpment Reason for the Preservation • The animals – – – – whose exquisitely preserved fossil remains are found in the Burgess Shale lived in and on mud banks that formed along the top of this escarpment • Periodically, this unstable area – would slump and slide down the escarpment – as a turbidity current • At the base, the mud and animals carried with it – were deposited in a deep-water anaerobic environment devoid of life Carbonaceous Impressions • In such an environment, – bacterial degradation did not destroy the buried animals – and they were compressed by the weight of the overlying sediments – and eventually preserved as carbonaceous impressions Study of Paleozoic Life • We will examine the history of Paleozoic life – as a system of interconnected biologic and geologic events • Evolution and plate tectonics – are the forces that drove this system • The opening and closing of ocean basins, – – – – – transgressions and regressions of epeiric seas, the formation of mountain ranges, and the changing positions of the continents had a profound effect on the evolution of the marine and terrestrial communities Tremendous Biologic Change • A time of tremendous biologic change – began with the appearance of skeletonized animals – near the Precambrian-Cambrian boundary • Following this event, marine invertebrates – began a period of adaptive radiation and evolution – during which the Paleozoic marine invertebrate community greatly diversified • Indeed, the history of the Paleozoic marine invertebrate community – was one of diversification and extinction, – culminating at the end of the Paleozoic Era – in the greatest mass extinction in Earth history The Cambrian Explosion • At the beginning of the Paleozoic Era, – animals with skeletons – appeared rather abruptly in the fossil record • In fact, their appearance is described – as an explosive development – of new types of animals – and is referred to as – the "Cambrian explosion" by most scientists The Cambrian Explosion • This sudden and rapid appearance – of new animals in the fossil record – is rapid, however, only in the context of geologic time, – having taken place over millions of years – during the Early Cambrian Period Not a Recent Discovery • Early geologists observed – that the remains of skeletonized animals – appeared rather abruptly in the fossil record • Charles Darwin addressed this problem – – – – – in On the Origin of Species and observed that, without a convincing explanation, such an event was difficult to reconcile with his newly expounded evolutionary theory Sharp Contrast • The sudden appearance of shelled animals – during the Early Cambrian – contrasts sharply with the biota living – during the preceding Proterozoic Eon • Up until the evolution of the Ediacaran fauna, – Earth was populated primarily – by single-celled organisms • The Ediacaran fauna, • which is found on all continents except Antarctica, – consists primarily of multicelled soft-bodied organisms Soft-Bodied Organisms • Microscopic calcareous tubes, • presumably housing worm-like suspension feeding organisms, – have also been found at some localities • In addition, trails and burrows, • which represent the activities of worms • and other sluglike animals – are also found associated – with Ediacaran faunas throughout the world • The trails and burrows – are similar to those made by present-day softbodied organisms Time Between Fauna • Until recently, it appeared that – a fairly long time period existed – between the extinction of the Ediacaran fauna – and the evolution of the first Cambrian fossils • That gap has been considerably narrowed – in recent years with the discovery – of new Proterozoic fossiliferous localities – that continue right to the base of the Cambrian Hotly Debated Topic • Nonetheless, the cause of the sudden appearance – of so many different animal phyla – during the Early Cambrian – is still a hotly debated topic • Newly developed molecular techniques – – – – that allow evolutionary biologists to compare the similarity of molecular sequences of the same gene from different species is being applied to the phylogeny of many organisms Early Invertebrate History • In addition, new fossil sites – and detailed stratigraphic studies – are shedding light – on the early history and ancestry – of the various invertebrate phyla Triggering Mechanism • The Cambrian explosion – probably had its roots firmly planted in the Proterozoic • However, the mechanism – that triggered this event is still unknown and – was likely a combination of factors, • both biological and geological • For example, geologic evidence – indicates Earth was glaciated – one or more times during the Proterozoic, – followed by global warming during the Cambrian Hypotheses for Shell Development • These global environmental changes – may have stimulated evolution – and contributed to the Cambrian explosion • A change in ocean chemistry may have favored – the evolution of a mineralized skeleton • Skeletonized forms may have been a response – to the evolution of predators • Recent work on Hox genes, which are • sequences of genes that control the development of individual regions of the body, – – – – shows that the basic body plans for all animals was apparently established by the end of the Cambrian explosion, and was only slightly modified since then Major Event in Earth's History • Whatever the ultimate cause of the Cambrian explosion, – – – – the appearance of a skeletonized fauna and the rapid diversification of that fauna during the Early Cambrian was a major event in life history The Emergence of a Shelly Fauna • The earliest organisms with hard parts – are Proterozoic calcareous tubes – found associated with Ediacaran faunas – from several locations throughout the world • These are followed by other microscopic skeletonized fossils – from the Early Cambrian – and the appearance of large skeletonized animals – during the Cambrian explosion Lower Cambrian Shelly Fossil • A conical sclerite* of Lapworthella from Australia * a piece of armor covering – This specimen is several millimeters in size Lower Cambrian Shelly Fossil • Archaeooides, an enigmatic spherical fossil from the Mackenzie Mountains, Northwest Territories, Canada – This specimen is several millimeters in size Why Skeletons? • Along with the question of – why did animals appear so suddenly in the fossil record – is the equally intriguing one of – why they initially acquired skeletons – and what selective advantage this provided • A variety of explanations – about why marine organisms evolved skeletons – have been proposed, – but none is completely satisfactory or universally accepted Advantages of an Exoskeleton • The formation of an exoskeleton confers many advantages on an organism: (1) It provides protection against ultraviolet radiation, allowing animals to move into shallower waters; (2) it helps prevent drying out in an intertidal environment (3) A supporting skeleton allows an increase in size and provides a place for attachment of muscles; (4) it provides protection against predators Advantages of an Exoskeleton • Recent evidence of actual fossils of predators – – – and specimens of damaged prey, as well as antipredatory adaptations in some animals, indicates that the impact of predation during the Cambrian was great Cambrian Predator • Reconstruction of Anamalocaris – a predator from the Early and Middle Cambrian – is shown feeding on Opabinia • It was 45 cm long and probably – used its gripping appendages to carry food to its circular mouth Wounded Trilobite • Wounds to the body of the trilobite Olenellus robsonensis – The wounds have healed, demonstrating that they occurred when the animal was alive and were not inflicted on an empty shell Advantages of an Exoskeleton • With predators playing an important role – – – – – in the Cambrian marine ecosystem, any mechanism or feature that protected an animal would certainly be advantageous and confer an adaptive advantage to the organism It Is Unknown Why Organisms Evolved Mineralized Skeletons • There currently is no clear answer about – why marine organisms evolved mineralized skeletons – during the Cambrian explosion and shortly thereafter • They undoubtedly evolved – because of a variety of biologic and environmental factors Mineralized Skeletons Were Successful • Whatever the reason, – – – – the acquisition of a mineralized skeleton was a major evolutionary innovation allowing invertebrates to successfully occupy a wide variety of marine habitats Paleozoic Invertebrate Marine Life • Having considered the origin, differentiation, and evolution – – – – of the Precambrian-Cambrian marine biota, we now examine the changes that occurred in the marine invertebrate community during the Paleozoic Era Marine Invertebrate Communities • Rather than focusing on – the history of each invertebrate phylum, – we will survey the evolution – of the marine invertebrate communities through time, – concentrating on the major features and changes that took place • To do that, we need to briefly examine – – – – the nature and structure of living marine communities so that we can make a reasonable interpretation of the fossil record The Present Marine Ecosystem • In analyzing the present-day marine ecosystem, – we must look at where organisms live, – how they get around, – as well as how they feed • Organisms that live in the water column – above the seafloor – are called pelagic • They can be divided into two main groups: – the floaters, or plankton, – and the swimmers, or nekton Plankton • Plankton are mostly passive and go where currents carry them – Plant plankton • such as diatoms, dinoflagellates, and various algae, – are called phytoplankton and are mostly microscopic – Animal plankton are called zooplankton and are also mostly microscopic • Examples of zooplankton include foraminifera, radiolarians, and jellyfish Nekton • The nekton are swimmers – and are mainly vertebrates • such as fish; – the invertebrate nekton • include cephalopods Benthos • Organisms that live – on or in the seafloor make up the benthos • They can be characterized – as epifauna (animals) or epiflora (plants), • for those that live on the seafloor, – or as infauna, • which are animals living in and moving through the sediments Sessile and Mobile • The benthos can be further divided – into those organisms that stay in one place, – called sessile, – and those that move around on or in the seafloor, – called mobile Marine Ecosystem • Where and how animals and plants live in the marine ecosystem Plankton: Sessile epiflora: Nekton: fish cephalopod seaweed Jelly fish Sessile epifauna: Benthos: g-m bivalve coral crinoid Marine Ecosystem Infauna: worm, bivalve Mobile epifauna: gastropod, starfish Feeding Strategies • The feeding strategies of organisms – are also important in terms of their relationships – with other organisms in the marine ecosystem • There are basically four feeding groups: – suspension-feeding animals remove or consume microscopic plants and animals as well as dissolved nutrients from the water; – herbivores are plant eaters; – carnivore-scavengers are meat eaters; – and sediment-deposit feeders ingest sediment and extract the nutrients from it Marine Ecosystem coral crinoid bivalve Suspension feeders: Marine Ecosystem worm sedimentdeposit feeder Herbivores: gastropod Carnivores-scavengers: starfish An Organism's Place • We can define an organism's place – in the marine ecosystem – by where it lives – and how it eats • For example, an articulate brachiopod – is a benthonic, – epifaunal suspension feeder, • whereas a cephalopod – is a nektonic carnivore Trophic Levels • An ecosystem includes several trophic levels, – which are tiers of food production and consumption – within a feeding hierarchy • The feeding hierarchy – and hence energy flow – in an ecosystem comprise – a food web of complex interrelationships among • the producers, • consumers, • and decomposers Primary Producers • The primary producers, or autotrophs, – are those organisms that manufacture their own food • Virtually all marine primary producers are phytoplankton • Feeding on the primary producers – are the primary consumers, which are mostly suspension feeders Other Consumers • Secondary consumers feed on – the primary consumers, – and thus are predators, while tertiary consumers, which are also predators, feed on the secondary consumers • Besides the producers and consumers, – there are also transformers and decomposers • These are bacteria that break down the dead organisms – that have not been consumed – into organic compounds that are then recycled Marine Food Web • Showing the relationships – – – – among the producers, consumers, and decomposers When the System Changes • When we look at the marine realm today, – we see a complex organization of organisms – interrelated by trophic interactions – and affected by changes in the physical environment • When one part of the system changes, – the whole structure changes, – sometimes almost insignificantly, – other times catastrophically Changing Marine Ecosystem • As we examine the evolution of the Paleozoic marine ecosystem, – keep in mind how geologic and evolutionary changes – can have a significant impact on its composition and structure Changing Marine Ecosystem • For example, the major transgressions onto the craton – opened up vast areas of shallow seas – that could be inhabited • The movement of continents – affected oceanic circulation patterns – and caused environmental changes Cambrian Marine Community • The Cambrian Period was a time – during which many new body plans evolved – and animals moved into new niches • As might be expected, the Cambrian – witnessed a higher percentage of such experiments – than any other period of geologic history Cambrian Skeletonized Life • Although almost all the major invertebrate phyla – evolved during the Cambrian Period – many were represented by only a few species • While trace fossils are common – and echinoderms diverse, • the organisms that comprised the majority of Cambrian skeletonized life were – trilobites, – inarticulate brachiopods, – and archaeocyathids Cambrian Marine Community • Floating jellyfish, swimming arthropods, benthonic sponges, and scavenging trilobites Reconstruction Trilobites • Trilobites were – by far the most conspicuous element – of the Cambrian marine invertebrate community – and made up about half of the total fauna • Trilobites were – – – – benthonic mobile sediment-deposit feeders that crawled or swam along the seafloor Trilobites • They first appeared in the Early Cambrian, – – – – – – rapidly diversified, reached their maximum diversity in the Late Cambrian, and then suffered mass extinctions near the end of the Cambrian from which they never fully recovered • As yet no consensus exists on what caused the trilobite extinctions Trilobite Extinctions • A combination of factors were likely involved in the extinctions, – including a possible reduction of shelf space, – increased competition, – and a rise in predators • It has also been suggested – – – – that a cooling of the seas may have played a role, particularly for the extinctions that took place at the end of the Ordovician Period Cambrian Brachiopods • Cambrian brachiopods – were mostly primitive types called inarticulates • They secreted a chitinophosphate shell, – composed of the organic compound chitin – combined with calcium phosphate • Inarticulate brachiopods – also lacked a tooth-and-socket-arrangement – along the hinge line of their shells Articulate Brachiopods • The articulate brachiopods, – – – – which have a tooth-and-socket arrangement, were also present but did not become abundant until the Ordovician Period Archaeocyathids • The third major group of Cambrian organisms – were the archaeocyathids • These organisms – – – – – were benthonic sessile suspension feeders that constructed reeflike structure at the beginning of the Cambrian Archaeocyathids went extinct at the end of the Cambrian Cambrian Reeflike Structure • Restoration of a Cambrian reeflike structure built by archeocyathids Other Cambrian Fauna • The rest of the Cambrian fauna – – – – consisted of representatives of the other major phyla, including many organisms that were short-lived evolutionary experiments Primitive Echinoderm • Helicoplacus was a primitive echinoderm – that became extinct 20 million years after its first appearance about 510 million years ago – and was a representative of one of several short-lived echinoderm classes – Such organisms illustrate the “experimental” nature of the Cambrian invertebrate fauna The Burgess Shale Biota • No discussion of Cambrian life – would be complete without mentioning – one of the best examples – of a preserved soft bodied fauna and flora, • the Burgess Shale biota • As the Sauk Sea transgressed – from the Cordilleran shelf – onto the western edge of the craton • Early Cambrian sands were covered – by Middle Cambrian black muds – that allowed a diverse soft-bodied benthic community to be preserved Soft-Bodied Animals and Plants • These fossils were discovered in 1909 by Charles Walcott – near Field, British Columbia • They represent one of the most significant fossil finds of the 20th century – because they consist of impressions of soft-bodied animals and plants – which are rarely preserved in the fossil record Rare Preservation: Burgess Shale • Ottoia, a carnivorous worm Rare Preservation: Burgess Shale • Wiwaxia, a scaly armored sluglike creature whose affinities remain controversial Rare Preservation: Burgess Shale • Hallucigenia, a velvet worm Rare Preservation: Burgess Shale • Waptia, an anthropod Rarely Preserved Organisms • This discovery therefore – – – – provides us with a valuable glimpse of rarely preserved organisms as well as the soft-part anatomy of many extinct groups Reinterpretation • In recent years, the reconstruction, classification, and interpretation – – – – of many of the Burgess Shale fossils have undergone a major change that has led to new theories and explanations of the Cambrian explosion of life • Recall that during the Neoproterozoic multicellular organisms evolved, – and shortly thereafter animals with hard parts – made their first appearance Basic Body Plans • These were followed by – an explosion of invertebrate groups – during the Cambrian, – many of which are now extinct • These Cambrian organisms – represent the rootstock – and basic body plans – from which all present-day invertebrates evolved How Many Phyla? • The question that paleontologists are still debating is – How many phyla arose during the Cambrian? – At the center of that debate are the Burgess Shale fossils • For years, most paleontologists – – – – placed the bulk of the Burgess Shale organisms into existing phyla, with only a few assigned to phyla that are now extinct Cambrian Phyla • Thus, the phyla of the Cambrian world – were viewed as being essentially the same in number – as the phyla of the present-day world, – but with fewer species in each phylum • According to this view, the history of life – has been simply a gradual increase in the diversity of species – within each phylum through time • The number of basic body plans – has therefore remained more or less constant – since the initial radiation of multicelled organisms Explosion of Varied Lifeforms • This view, however, has been challenged – by other paleontologists – who think that the initial explosion of varied lifeforms in the Cambrian – was promptly followed by a short period of experimentation – and then extinction of many phyla • The richness and diversity of modern life-forms – are the result of repeated variations of the basic body plans – that survived the Cambrian extinctions Strangeness of the Burgess Shale Biota • In other words, life was much more diverse – in terms of phyla – during the Cambrian – than it is today • The reason members of the Burgess Shale biota – – – – look so strange to us is that no living organisms possess their basic body plan, and therefore many of them have been reassigned into new phyla Reassignment to Extant Phyla • Discoveries of Cambrian fossils – at localities such as Sirius Passet, Greenland, and Yunnan, China, – have resulted in reassignment – of some Burgess Shale specimens back into extant phyla • If these reassignments to known phyla prove to be correct, – then no massive extinction event followed the Cambrian explosion, – and life has gradually increased in diversity through time No Clear Answer to This Debate • Currently, there is no clear answer to this debate, – and the outcome will probably be decided – as more fossil discoveries are made Ordovician Marine Community • A major transgression that began – during the Middle Ordovician (Tippecanoe sequence) – resulted in widespread inundation of the craton • This vast epeiric sea, – which experienced a uniformly warm climate during this time, – opened numerous new marine habitats – that were soon filled by a variety of organisms Striking Changes in Ordovician • Both sedimentation patterns and fauna – underwent striking changes – from the Cambrian to the Ordovician, • Whereas the Cambrian invertebrate community – was dominated by trilobites, inarticulate brachiopods, and archaeocyathids, • the Ordovician was characterized – by the adaptive radiation of many other animal phyla, • such as articulate brachiopods, bryozoans, and corals – with a consequent dramatic increase – in the diversity of the total shelly fauna Middle Ordovician Seafloor Fauna • Recreation of a Middle Ordovician seafloor fauna with cephalopods, crinoids, colonial corals, trilobites, and brachiopods Acritarchs • The Ordovician was also a time – of increased diversity and abundance – of the acritarchs • organic-walled phytoplankton of unknown affinity – – – – which were the major phytoplankton group of the Paleozoic Era and the primary food source of the suspension feeders Upper Ordovician Acritarch • Acritarch from the Upper Ordovician Sylvan Shale, Oklahoma • Acritarchs are organic-walled phytoplankton – and were the primary food source for suspension feeders during the Paleozoic Era Upper Ordovician Acritarch • Acritarch from the Upper Ordovician Sylvan Shale, Oklahoma Reef Builders • During the Cambrian, archaeocyathids – were the main builders of reeflike structures, – but beginning in the Middle Ordovician – bryozoans, stromatoporoids, and tabulate and rugose corals – assumed that role • Many of these reefs – – – – were small patch reefs similar in size to those of the Cambrian but of a different composition, whereas others were quite large Suspension Feeders Dominated Reefs • As with present-day reefs, – Ordovician reefs exhibited a high diversity of organisms – and were dominated by suspension feeders Biostratigraphic Correlation • Three Ordovician fossil groups – have proved to be particularly useful – for biostratigraphic correlation • the articulate brachiopods, • graptolites, • and conodonts • The articulate brachiopods, – – – – present since the Cambrian, began a period of major diversification in the shallow-water marine environment during the Ordovician Brachiopods Brachiopods • Brachiopods became a conspicuous element – of the invertebrate fauna – during the Ordovician – and in succeeding Paleozoic periods Graptolites • Most graptolites were – planktonic animals carried about by ocean currents • Because most graptolites were planktonic – and most individual species existed for less than a million years, – graptolites are excellent guide fossils • They were especially abundant – during the Ordovician and Silurian periods • Graptolites are most commonly found in black shales – preserved as carbonaceous impressions Graptolites Conodonts • Conodonts are a group – of well-known, small tooth-like fossils – composed of the mineral apatite • (calcium phosphate) – the same mineral that composes bone • Although conodonts have been known for more than 150 years, – their affinity has been the subject of debate – until the discovery of the conodont animal in 1983 Conodonts • Conodonts are microscopic tooth-like fossils • Cahabagnathus sweeti, Copenhagen Formation – Middle Ordovician, Monitor Range, Nevada Conodonts • Conodonts are microscopic toothlike fossils • Scolopodus, sp., Shingle Limestone, – Shingle Pass, Nevada Conodonts • The conodont animal – preserved as a carbonized impression 40mm x 2 mm – in the Lower Carboniferous Granton Shrimp Bed in Edinburgh, Scotland Conodont Animal • Several specimens of carbonized impressions – – – – – of the conodont animal from Lower Carboniferous rocks of Scotland reveal that it is a member of a group of primitive jawless animals assigned to the phylum Chordata • Study of the specimens – indicates that the conodont animal – was probably an elongate swimming organism Excellent Guide Fossils • The wide distribution – and short stratigraphic range of individual conodont species – make them excellent fossils – for biostratigraphic zonation and correlation Mass Extinctions • The end of the Ordovician – was a time of mass extinctions in the marine realm • More than 100 families of marine invertebrates became extinct, • and in North America alone, – approximately one-half of the brachiopods and bryozoans died out • What caused such an event? – – – – Many geologists think these extinctions were the result of the extensive glaciation that occurred in Gondwana at the end of the Ordovician Period Silurian and Devonian Marine Communities • The mass extinction at the end of the Ordovician – was followed by rediversification – and recovery of many of the decimated groups • Brachiopods, bryozoans, gastropods, bivalves, corals, crinoids, and graptolites – were just some of the groups that rediversified – during the Silurian Massive Reef Builders • Recall that the Silurian and Devonian – were times of major reef building • While most of the Silurian radiations of invertebrates – represented repopulation of niches, • organic reef builders diversified in new ways, – building massive reefs – larger than any produced – during the Cambrian or Ordovician Repopulation • This repopulation – – – – – – was probably caused in part to renewed transgressions over the craton, and although a major drop in sea level occurred at the end of the Silurian, the Middle Paleozoic sea level was generally high Silurian and Devonian Reefs • The Silurian and Devonian reefs – were dominated by – tabulate and colonial rugose corals and stromatoporoids • While the fauna of these Silurian and Devonian reefs – – – – was somewhat different from that of earlier reefs and reef-like structures, the general composition and structure are the same as in present-day reefs Middle Devonian Reef • Reconstruction of a Middle Devonian reef from the Great Lakes area – with corals, cephalopods, trilobites, crinoids, and brachiopods Eurypterids and Ammonoids • The Silurian and Devonian periods – were also the time when eurypterids • arthropods with scorpion-like bodies and impressive pincers – were abundant, especially in brackish and freshwater habitats • Ammonoids, – a subclass of the cephalopods, – evolved from nautiloids – during the Early Devonian and rapidly diversified Silurian Brackish Water Community • Restoration of a Silurian brackish water scene – near Buffalo New York – with algae, eurypterids, gastropods, worms, and shrimp Ammonoids • Ammonoids are excellent guide fossils – – – – for the Devonian through Cretaceous periods with their distinctive suture patterns, short stratigraphic ranges, and widespread distribution Ammonoid Cephalopod • A late Devonian ammonoid cephalopod – from Erfoud, Morocco – The distinctive suture pattern, short stratigraphic range, and wide geographic distribution make ammonoids excellent guide fossils Another Mass Extinction • Another mass extinction – occurred near the end of the Devonian – and resulted in a worldwide near-total collapse – of the massive reef communities • On land, however, the seedless vascular plants – were seemingly unaffected, • Thus, extinctions at this time – were most extensive among marine life, – particularly in the reef and pelagic communities Global Cooling • The demise of the Middle Paleozoic reef communities – highlights the geographic aspects – of the Late Devonian mass extinction • The tropical groups were most severely affected; – in contrast, the higher latitude communities were seemingly little affected • Apparently, an episode of global cooling – was largely responsible for the extinctions – near the end of the Devonian Actors in Extinctions • During such a cooling, – the disappearance of tropical conditions – would have had a severe effect on reef – and other warm-water organisms • Cool-water species, on the other hand, – could have simply migrated toward the equator • The closing of the Iapetus Ocean – – – – and the orogenic events of the Late Devonian undoubtedly also played a role in these extinctions by reducing the area of shallow shelf environments where many marine invertebrates lived Carboniferous and Permian Marine Communities • The Carboniferous invertebrate marine community – – – – – responded to the Late Devonian extinctions in much the same way as the Silurian invertebrate marine community responded to the Late Ordovician extinctions that is, by renewed adaptive radiation and rediversification Rapid Recovery • The brachiopods and ammonoids – quickly recovered – and again assumed important ecological roles, – while other groups, such as the lacy bryozoans and crinoids, – reached their greatest diversity during the Carboniferous • With the decline – of stromatoporoids and tabulate and rugose corals, – large organic reefs virtually disappeared – and were replaced by small patch reefs Mississippian Patch Reefs • These patch reefs were dominated – by crinoids, blastoids, lacy bryozoans, brachiopods, and calcareous algae – and flourished during the Late Paleozoic • In addition, bryozoans and crinoids – contributed large amounts of skeletal debris – to the formation of the vast bedded limestones – that constitute the majority of Mississippian sedimentary rocks Mississippian Marine Life • Based on a fossil site in the Upper Mississippian at Crawfordville, Indiana • Invertebrate animals shown include – blastoids – crinoids – lacy bryozoans – brachiopods – small corals Restricted Permian Marine Faunas • The Permian invertebrate marine faunas – – – – – resembled Carboniferous faunas, but were not as widely distributed because of the restricted size of the shallow seas on the cratons and the reduced shelf space along the continental margins Permian Period • Paleogeography of North America during the Permian Period Productids • The spiny and odd-shaped productids – – – – dominated the brachiopod assemblage and constituted an important part of the reef complexes that formed in the Texas region during the Permian Permian Patch-Reef Community • From Glass Mountains of West Texas – including algae, productid brachiopods, cephalopods, sponges, and corals Fusulinids • The fusulinids • spindle-shaped foraminifera – – – – which first evolved during the Late Mississippian and greatly diversified during the Pennsylvanian, experienced a further diversification during the Permian Fusulinid • Fusulinids are spindleshaped, benthonic foraminifera that are excellent guide fossils for the Pennsylvanian and Permian periods Fusulinids Are Important Guide Fossils • Because of their – abundance, diversity, and worldwide occurrence, – fusulinids are important guide fossils – for Pennsylvanian and Permian strata • Bryozoans, sponges, and some types of calcareous algae – also were common elements of the Permian invertebrate fauna Mass Extinctions • Throughout geologic history – various plant and animal species have become extinct • Extinction is a common feature of the fossil record, – and the rate of extinction through time has fluctuated only slightly. – Just as new species evolve, – others become extinct. Mass Extinctions • There have been however, – brief intervals in the geologic past • during which mass extinctions have eliminated – large numbers of species. • Extinctions of this magnitude – could only occur due to radical changes – in the environment – on a regional or global scale Common Themes • When we examine different mass extinctions – of the geologic past • several common themes stand out • Mass extinctions typically have affected – life in both sea and on land • Tropical organisms – particularly in the marine realm – are apparently more affected • Some animal groups repeatedly experience – mass extinctions. Mass Extinctions • We when examine mass extinctions – for the past 650 million years, • we see the first extinction event – involved only acritarchs. • Several extinction events – occurred during the Cambrian – and only affected marine invertebrates • particularly trilobites. Paleozoic Mass Extinctions • Three other marine mass extinctions took place during the Paleozoic Era: – End of the Ordovician • involving many invertebrates – Near the end of the Devonian • affecting major barrier reef-building organisms • and primitive armored fish – End of the Permian • the most severe • about 90% of all marine invertebrate species and • more than 65% of all land animals became extinct Mesozoic Mass Extinctions • The Mesozoic Era experienced several mass extinctions – The most devastating occurring – at the end of the Cretaceous, – when almost all large animals • dinosaurs, flying reptiles, seagoing animals – became extinct. • Many scientists think the terminal Cretaceous mass extinction – was caused by a meteorite impact Cenozoic Mass Extinctions • Several mass extinctions occurred during the Cenozoic Era: – The most severe was at the end of the Eocene Epoch – and is correlated with global cooling – and climate change. • The most recent extinction event – occurred near the end of the Pleistocene Epoch. Gradual Events • Although many scientists think of marine mass extinctions – as sudden events from a geologic perspective • they were gradual from a human perspective, – occurring over hundreds of thousands – and even millions of years • Furthermore, many geologists think – that climate changes, rather than a single catastrophic event – were primarily responsible – particularly at the marine realm • Evidence of glacial episodes – and other signs of climate change – such as global warming • have been correlated with extinction events – in the fossil record Permian Mass Extinction • The greatest recorded mass extinction – to affect Earth – occurred at the end of the Permian Period. • Roughly 50% of all marine vertebrates families – and about 90% of all marine invertebrate species – became extinct Phanerozoic Diversity • Diversity for marine invertebrate and vertebrate families – 3 episodes of Paleozoic mass extinctions are visible – with the greatest occurring at the end of the Permian Period Casualties • Fusulinids, rugose and tabulate corals, several bryozoan and brachiopod orders, – as well as trilobites and blastoids – did not survive the end of the Permian • All of these groups – had been very successful during the Paleozoic Era • In addition, more than 65% of all amphibians and reptiles, – as well as nearly 33% of insects on land also became extinct Permian Mass Extinction • What caused such a crisis – for both marine and land-dwelling organisms? • Various hypotheses have been proposed, – but no completely satisfactory answer – has yet been found • Because the extinction event extended over – millions of years, – a meteorite impact can be reasonably discounted. Permian Mass Extinction • A reduction in shelf space due to the formation of Pangaea, – and a widespread marine regression – can also be rejected • By the end of the Permian, most continental collisions – had already taken place – before the mass extinctions began in earnest. • The widespread glaciation that took place in the Carboniferous – was already waning in the Permian Anoxic Waters • Currently, many scientists think – – – – that an episode of deep-sea anoxia and increased CO2 levels resulted in a highly stratified ocean during the Late Permian. • There was little circulation – of oxygen-rich surface waters – into the deep ocean. – Stagnant waters also covered the shelf region. • There is also evidence – of increased global warming – during the Late Permian, – which would contribute to a stratified global ocean Carbon Dioxide • During this time, widespread volcanic eruptions – – – – – and continental fissure eruptions also took place, further releasing additional carbon dioxide into the atmosphere and contributing to increased climatic instability and ecological collapse • By the end of the Permian, – a near collapse of both the marine and terrestrial ecosystem had occurred. • Probably an combination of interconnected and related geologic and biologic events – was responsible