Life7e-Fig-22-17-0 Evolutionary Faunas Paleozoic Fauna Paleozoic fauna Historical Geology Ordovician Life Ecological Complexity •Major events in the evolution of land plants –The Devonian Period was a time of rapid evolution for the land plants Plant Evolution 2561_tble1302 – –the appearance of leaves –and emergence of seeds The Early Ordovician was a time of adaptive radiation of many faunal groups, following the mass extinction of trilobites and nautiloids at end of Cambrian. Increase in diversity from 150 families -> 400 families Important Groups of Paleozoic Invertebrates •Porifera – Sponges •Cnidaria – Corals (Rugosa and Tabulata) •Bryozoa – Moss animals •Brachiopoda – Lamp shells (Articulata and Inarticulata) •Arthropoda – Trilobites, Crustaceans, Insects •Mollusca – Snails, Bivalves, Cephalopods •Echinoderms – Crinoids and Blastoids •Foraminifers – mainly in Devonian • EARLY PALEOZOIC LIFE Foraminifera First appeared in the Cambrian Survive to present Unicellular Organisms (Protistans) forams cambrian foram platysolenites Platysolenites, a Cambrian foram Agglutinated form Calcareous skeleton Nanicella – middle to late Devonian Late Frasnian – Eogeinitzina, Eonodosaria Late Famennian - Quasiendothyra EARLY PALEOZOIC LIFE Radiolaria First appeared in the Cambrian, more abundant in mid-Paleozoic Survive to present Have a siliceous skeleton Unicellular Organisms (Protistans) radslineup In Paleozoic only Nasselaria. Rock-forming role in the Devonian – radiolarites. E.g. Ponikev Formation Arthropoda Trilobita Trilobites (extinct) Crustacea Shrimp, lobsters, crabs, ostracods, crayfish Chelicerata - klepítkatci Spiders, scorpions, Merostomata Insects, centipedes, and millipedes Trilobites Still abundant and stratigraphically important. Second and last prime in early Devonian, since middle Devonian on retreat Uralichas – 75 cm, world largest trilobite Selenopeltis Selenopeltis Ordovician Selenopeltis province - Perigondwama lgUralichas tri_asaphus_platyurus Asaphus Asaphus province - Baltica Ordovician Aulacopleurus Aulacopleura konincki, Silur 58 Phacops trilo.10.0014.jpg (57694 bytes) Reedops DEVONIAN Odontochile hausmani Odontochile . Odontochile formosa. Arthropoda Trilobita Trilobites (extinct) Crustacea Shrimp, lobsters, crabs, ostracods, crayfish Chelicerata - klepítkatci Spiders, scorpions, Merostomata Insects, centipedes, and millipedes Crustacea Arthropoda Ostracodes Look like beans Segmented body enclosed in CaCO3 and chitin carapace Marine and freshwater Useful in biostratigraphy Early Cambrian to Recent ostracod3 ostracod ostracod2 Ostracodes Since Ordovician diversification of ostracodes •Eoleperditia fabulites Conrad •Middle Ordovician, Rutherford Co., Tennessee •Shells are bivalved, small (1 to 10 mm) and oval •Recrystallization Ostracodes Branchiopoda (lupenonožci) je skupina primárně sladkovodních korýšů - devon First Decapoda (shrimps - krevety) in the late Devonian Chelicerata Arthropoda Eurypterids Swimming or crawling arthropods Some up to 3 m in length Ordovician to Permian Mostly Silurian and Devonian Eurypterid_live eurypterid Eurypterus(B) Mixopterus Merostromata – top predators Pterygotus, 2.3 m, also fresh water Eurypterus – 10 cm Abundant Silurian-mid Devonian Ancestors of scorpions, first scorpions Silurian F-gigantocharinus R-gigantocarinus Gigantocharinus -7mm Arachnids Silurian, Devonian taxon links 934e0b694b0152a5813a2dda98ca20bc In contrast, fossils of the earliest known true insects are known from later on in the Devonian period. However, reinterpretation of a fragmentary insect fossil from the important early Devonian Rhynie cherts of Scotland shows that the enigmatic Rhyniognatha hirsti was not only a true insect, but relatively derived — that is it had been around long enough to have accumulated some uniquely insect-like features. Although only the mandibles are preserved, it is possible that they once belonged to a winged insect. In any case, the fossil shows that the origin of insects was much earlier than previously thought. The discovery suggests that insects almost certainly evolved in the Silurian Period, some 438-408 million years ago. First insects - Silurian collembola Insects – Apterygota (Colembola Chvostoskoci) Insect evolution: Six legs good Primitive insect-like creatures called springtails were among the earliest known animals to colonize the land, early in the Devonian period almost 400 million years ago. New light shed on the oldest insect MICHAEL S. ENGEL & DAVID A. GRIMALDI Nature 427, 627–630 (2004); doi:10.1038/nature02291 taxon links Brachiopods Diversification of articulates, dominant group sof benthos Brachiopods Ordovician-There was an enormous radiation of brachiopods. Brachiopod abundance through geologic time bracspin Max bar width equals 200 genera Brachiopods strophmn Strophomena Stringocephalus1_2 Stringocephalus Gastropoda Gastropods - they appear in the Cambrian but are not abundant until the Late Paleozoic. gastropod sm1 Platyceras Cardiola Cardiola coruncopiae Bivalve Panenka. Panenka Bivalves BIVALVES tentaculite-3 Tentaculites Tentaculite limestones and shales - Devonian CLASS: Cephalopoda- This class of the order Molluska is divided up into 7 subclasses SUBCLASSES: •NAUTILOIDEA-These were the first cephalopods to appear in the fossil record. They appeared in the Late Cambrian and quickly expanded. The only surviving Nautiloidea are members of the genus Nautilus (picture in heading of page). The members of the subclass Nautiloidea have orthoconic or coiled shells. Many of the straight Nautiloidea secreted deposits in their older chambers to make their shells neutrally bouyant. For more information on this subclass see this page. •AMMONOIDEA- Their shells are tightly spiraled with complex sutures. Like the bactritoids, they have have a bulbous protoconch and a marginal siphuncle. They entered the fossil record in the Devonian and left in the Cretaceous at the famous K/T boundary. •COLEOIDEA- The common Cephalopoda of today, which include squids, octopuses, and cuttlefish. They have either internal shells or no shell at all. Coleoidea differ from other cephalopods by having only one pair of gills and one pair of nephridia (kidneys); all other cephalopods have 2 pairs of both gills and nephridia. Coleoidea entered the fossil record during the Devonian and are still around today. Endoceras Fossil Nautiloidea Endoceras Ordovician Endoceras – 3,5m Silurian Orthocera limestones azammc02c Lituites littuus, an odd nautiloid fossil from the Ordovician of China. Devonreef Reconstruction of the Silurian sea Trilobite_IMG_0124_lg Silurian Orthoceras limestone Ammonites Ammonites First occurrence in Pragian ammonite-fig4 603az Clymenia sk-suture.jpg (8669 bytes) Coleoidea-dvoužábří pijlinktvis2 Devonian Eoteuthis – první sepie Alloteuthis Ordovicianlife Ordovician reefs First True Reefs The phylum Bryozoa is a diverse one with approximately 4000 living species known, and almost four times that amount are found in the fossil record (Levin, 1999). These "moss animals" are often mistaken for corals due to their structural similarities but bryozoans have a much more complex anatomy. Bryozoans are also mistaken for plants, hence the term 'moss animal'. Bryozoans (sometimes referred to as Entoprocta and Ectoprocta) are microscopic sea animals that live in colonial structures that are much larger than the individual animal. Because these structures are usually composed of secreted calcite, they commonly form fossils. title illustration title illustration title illustration Skip Taxon Links Bryozoa Moss Animals, Sea Mats, Stenolaemata - Cyclostomata Fenestrata Cryptostomata Cystoporata Trepostomata Gymnolaemata - Ctenostomata Cheilostomata Phylactolaemata Bryozoan Classification - Class Stenolaemata Marine bryozoans with tubular zooids with calcified walls. Lophophore is protruded by action of annular muscles. Includes five sub-groups: •Trepostomata: Colonies generally robust; dendroid, encrusting, or massive. (Ordovician - Triassic) •Cystoporata: Colonies robust or delicate. (Ordovician - Triassic) •Cryptostomata: Colonies typically delicate; foliate or dendroid. (Ordovician - Permian) •Fenestrata: Colonies typically delicate; reticulate (net-like) or pinnate. (Ordovician - Triassic) •Tubuliporata, or Cyclostomata (Ordovician - Recent) Historical Geology The Paleozoic Fauna Fossil Bryozoans Fossil fenestrate bryozoans Prasopora sp. Hallopora sp. Archimedes sp. poriferafr Porifera Family Tree Stromatoporoids Sponge-like, grew in sheet-like calcareous layers. Dominant reef builders, Ordovician Period through the Devonian Period, a period of about 100 million years. stroma Stromatoporoids were marine colonial forms with a calcareous skeleton. They were important contributors to reef building during the Silurian and Devonian. Their relationship to other creatures is uncertain but they show some affinities with Porifera. They consist of calcareous layers which, when weathered, show a charecteristic contour line pattern as seen in the specimen above. Amphipora floatstone in peloidal line mud matrix; note common stylolites" Upper Devonian Leduc Formation Alberta Alternate click to enlarge EARLY PALEOZOIC LIFE Metazoan Invertebrates Phylum Porifera (sponges) Silurian sil sil Astylospongia Caryospongia EARLY PALEOZOIC LIFE Phylum Porifera (sponges) SPICULES Metazoan Invertebrates sponge spicules Spicules – Composed of Silica EARLY PALEOZOIC LIFE Phylum Porifera (sponges) SPICULES Metazoan Invertebrates sponge spicules Spicules – Composed of Calcium carbonate Cnidaria – Rugosa (solitary) •Rugosa are an extinct group of corals that were abundant in Middle Ordovician to Late Permian •Solitary rugosans are often referred to as "horn corals" •Rugosa can also be colonial •extinct at the end of the Permian, about 245 million years ago rugosa Cnidaria – Rugosa (solitary) •Cystiphyllum conifollis •Solitary Rugose coral •Middle Devonian, Ontario, Canada •Recrystallization • Cystiphyllum Cnidaria – Rugosa (colonial) •Arachnophyllum pentagonum Goldfuss •Colonial rugose coral •Middle Silurian, Kentucky •Silica replacement • Arachnophyllum Petoskey Stones – recrystallized colonial Devonian rugose corals petoskey_upclose ptstone Tabulata (Tabulate Corals) Ranged from Ordovician to Permian Major reef formers, Silurian and Devonian reefs Always colonial EARLY PALEOZOIC LIFE Metazoan Invertebrates Tabulata (Tabulate Corals) favosites favosites1 Favosites EARLY PALEOZOIC LIFE Metazoan Invertebrates Tabulata (Tabulate Corals) Halysites halysites Echinodermata EARLY PALEOZOIC LIFE Metazoan Invertebrates Echinodermata Crinoidea Crinoids Middle Cambrian to Recent Crinoid crinoid1 crinoid Crinoid with diver in background (#27A) Scypho Scyphocrinites File:Scyphocrinites elegans (Maroc) .jpg 157-scyphocrinites-schema-leg Echinoidea Echinodermata - Asterozoa •Devonaster eucharie (Hall •Middle Devonian, Ulster Co., New York •External Mold in shale • Devonaster starfishjudy2smallx Graptolites range from the middle Cambrian to the Carboniferous. Dendroidea are found across this entire span while Graptoloida are found from the Ordovician until the earlyDevonian. Graptolites are most commonly found in deep water, dysoxic facies (black shales), but do extend into shallow facies. Because they did not biomineralize an easily preservable skeleton they are nearly always carbonized. The process of carbonization combined with the highly compressible nature of shales made most graptolite fossils extremely flat and therefore difficult to study. Graptolites caplangrap27 caplangrap21 Graptolites Graptoloidea Historical Geology The Paleozoic Fauna Graptolites •Phylum: Hemichordata •Class: Graptolithina •Order: Graptoloidea Mongraptus sp. Characteristics marine planktonic all depths all temperatures colonial multiple cups on central rod each holding tiny animal Download now Graptolite shales – typical Silurian rock 3420410350_ace0e4f1f1 •Silurian graptolite shales graptolite climgrapx Climacograptus caplangrap7 Didymograptus from Victoria, Australia (Lower Ordovician) Graptolites range from the middle Cambrian to the Carboniferous. Dendroidea are found across this entire span while Graptoloida are found from the Ordovician until the early Silurian. Graptolites are most commonly found in deep water, dysoxic facies (black shales), but do extend into shallow facies. Because they did not biomineralize an easily preservable skeleton they are nearly always carbonized. KINGDOM: ANIMALIA PHYLUM: CHORDATA SUB-PHYLA: UROCHORDATA (sea squirts) HEMICHORDATA (pterobranchs, graptolites*) CAMB. CEPHALOCHORDATA (lancets) CAMB. CRANIATA (vertebrates) CAMB. CLASSES: CONODONTA* CAMB. AGNATHA (jawless fish) CAMB. Gnathostomata ACANTHODI (spiny sharks)* SIL. PLACODERMI (armored fish)* SIL. CHONDRICHTHYES (cartilaginous sharks) DEV OSTEICHTHYES (bony fish) SIL. AMPHIBIA (amphibians) DEV. REPTILIA (reptiles) CARB. AVES (birds) JURASSIC MAMMALIA (mammals) TRIASSIC platypus_j01 Subphylum Vertebrata •Subphylum Vertebrata has several divisions you need to be familiar with: –Superclass Agnatha – Jawless Fish; Lampry Eel; Ostracoderm (fossil) –Superclass Gnathostomata •Class Placodermi – First Jawed Fish (Fossils) •Class Chondricthyes – Cartilagenous Fish; Sharks; Rays •Class Osteichthyes –Subclass Actinopterygii – Ray-finned Fish; Goldfish; Sea Horse –Subclass Sarcopterygii – Lobe-finned Fish; Coelocanth • • • urochordata 081 1a18 bluebird chipmunk anmwi056_2 kangaroo11 velociraptor cvarag giantt1 Greatwt0 lampreymouth black_headed_gouldian hagfish orca11 rabbit4 python01 Proboscidea amphioxus.jpg (57059 bytes) f24-2_cladogram_of_the_ Geologic Ranges of Major Fish Groups 2561_1305 EARLY PALEOZOIC LIFE Vertebrates Fish p-placoderm EARLY PALEOZOIC LIFE Vertebrates Conodonts Chordate Resemble teeth Proterozoic to Triassic Calcium phosphate conodont conanimals palmatolepis_devonien Conodonta CONODONTA img007 img008 EARLY PALEOZOIC LIFE Vertebrates Conodonts conodonts1bd Pre-1964 examples Ordovician-29-39 Silurian-25-27 Devonian-16,17,21-24,28 Mississippian-4,8-15,18-20 Pennsylvanian-1-3,5-7 EARLY PALEOZOIC LIFE Vertebrates Fish Agnatha (Agnathids) Jawless fish Agnatha_186 agnatha agnathids_homepagecephstage1 Cambrian to Recent EARLY PALEOZOIC LIFE Vertebrates Fish Agnatha (Agnathids) Jawless fish astrapis Astrapis title illustration Astraspis Devonian Jawless Fish ~20 cm f24-2_cladogram_of_the_ jawevol_2 jawevol_1 EARLY PALEOZOIC LIFE Vertebrates Fish Placodermi (Placoderms) Plate-skinned fishes Late Silurian to Permian placoderm Bothryolepis Placoderm_radiation placodermi dunkleosteus DEVONIAN ORDOVICIAN CAMBRIAN SILURIAN DEVONIAN CARBONIFEROUS PERMIAN EARLY PALEOZOIC LIFE Vertebrates Fish Placodermi (Placoderms) Dunkleosteus2 Dunkleosteous1t dunkleosteus Dunkleosteus p-shark ACANTHODI EARLY PALEOZOIC LIFE Vertebrates Fish Acanthodii (Acanthodians) Early jawed fish Late Silurian to Permian acanthodian acanthodian1 Acanthodii WICHG31307 Devonian Seafloor ostracoderm (Hemicyclaspis) placoderm (Bothriolepis) acanthodian (Parexus) ray-finned fish (Cheirolepis) de_shark R-ctenacanthus Ctenacanthus sp, a Late Devonian and Carboniferous shark The very earliest signs of sharks are minute fossil scales and teeth which are found in rocks from the late Silurian to early Devonian period {around 400 million years ago). It becomes more and more difficult, however, to identify shark scales in older rocks because they closely resemble those from jawless fishes called the lodonts, which lived at the same time. Only microscopic differences separate shark and the lodont scales, and the two kinds seem to become more and more alike the further one goes back. Chondrichtyes -Paryby R-sharks Cladoselache (top left, Middle Devonian), Ischyodus (top right, Upper Jurassic) and Hybodus (bottom, Lower Jurassic) © •Bony fish (Osteichtyes) •There are two groups of bony fish 1.Ray-finned fish (Actinopterygii) began their evolution in Devonian lakes and streams (freshwater) and then spread to the sea. They are the dominant fishes of the modern world. 2.Lobe-finned fish Sarcopterygii 3.Lobe-finned fish have muscular fins with articulating bones. There are two groups of lobe finned fish. a.The lungfish (Dipnoi)Lungfish live today in freshwater. b.The crossopterygians Crossopterygii. This is an important group of lobe-finned fish because it gave rise to the amphibians during the Devonian. Actinopterygii Chondrostei - chrupavčití •Arrangement of fin bones for • • (a) a ray-finned fish • (b) a lobe-finned fish –muscles extend into the fin allowing greater flexibility Ray-Finned and Lobe-Finned Fish WICHG31310 Eusthenopteron(p) Eusthenopteron Le Prince de Miguasha -- a 30 cm long specimen of Eusthenopteron Crossopterygii 1. coelacanth Latimeria chalumnae p-shark Dipnoi Neoceratodus Neoceratudos forsteri Lungfish_distribution Protopterus Protopterus ssp Lepidosiren Lepidosiren paradoxa comparison Tiktaalik roseae lived approximately 375 million years ago. Paleontologists suggest that it is representative of the transition between non-tetrapod vertebrates (fish) and early tetrapods such as Acanthostega and Ichthyostega, known from fossils about 365 million years old. Its mixture of primitive fish and derived tetrapod characteristics led one of its discoverers. Tiktaalik roseae, has a skull, a neck, ribs and parts of the limbs that are similar to four-legged animals known as tetrapods File:Tiktaalik BW.jpg Amphibia Crawling out of the Water Ichthyostega Eustheonopteron Rhynochodipterus Devonian Timeline MAJOR PLANT GROUPS •Four major periods of plant evolution –New structures evolved, adaptive radiations followed •Origin of plants from aquatic ancestors •Diversification of vascular plants •Origin of seeds •Emergence of flowering plants 29-03-Plant Evoluton PLANT ANCESTRY •Plants represent a monophyletic group –Evolved from a common ancestor –Who was this common ancestor? •Multiple lines of evidence indicate that plants evolved from a group of green algae termed Charophytes –What is this evidence? 29-04-Charophytes VASCULAR PLANTS •Adaptations of vascular plants •Differentiated bodies –Subterranean root systems (water & minerals) –Aerial stems and leaves (photosynthesis) •Vascular tissue –Xylem (water & minerals) –Phloem (organic nutrients) •Lignin –Cell wall component providing mechanical support F14_16B F15_12 F14_17 Plant evolution E. Devonian plantscape E. Devonian tree (Archaeopteris, 30m) 5. Late Devonian i. Seeds a. Advantages ii. Adaptive radiation F15_12 Plant evolution F15_00 Psilopsida & Rhyniopsida •Earliest land plants •Does not possess leaves or true roots •Stems photosynthesize •Simple, dicotomous branching •Apical reproductive structures, • spores in sporangia •Rhynia is earliest fossil •Reconstruction of Early Devonian landscape. WICHG31321 Dawsonites / Protolepidodendron\ - Bucheria –showing some of the earliest land plants DevonianLabel SEEDLESS VASCULAR PLANTS •Dominated forest landscapes of Devonian and Carboniferous period •Three living divisions –Lycophyta –Horsetails (Shenophyta) –Ferns (Pterophyta) 29-25-CarboniferousForest LYCOPHYTES •Division Lycophata •Evolved in Devonian period –Prevalent in Carboniferous period –Woody tree lineage •Became extinct near end of Carboniferous period –Herbaceous lineage •Represented today by ~1,000 species cyathea lepidodendron lyan1 LYCOPHYTES 29-21a-ClubMoss 29-21x1-Lycophyte Club Moss Ground Pine Plavuň vidlačka Sphenophyta •Division horsetail •Ancient lineage of seedless vascular plants –Dates back to Devonian Prevalent during Carboniferous •Modern survivors include ~15 species in the genus Equisetum –Most common in Northern hemisphere –Generally found in damp locations, streambanks 29-21c-Horsetail FERNS •Division Pterophyta •Ancient ancestry –Origins in Devonian period –Prevalent in Carboniferous period •Currently most prevalent seedless vascular plant –>12,000 species exist today –Most diverse in tropics 29-21d-PolypodiumFern •The evolution of the seed during the Late Devonian –liberated land plants from their dependence on moist conditions –and allowed them to spread over all parts of the land • •In the seed method of reproduction –the spores are not released to the environment –but are retained on the spore-bearing plant –where they grow into the male and female forms • Evolution of Seeds Gymnosperms – nahosemenné rostliny Vyšší rostliny – nahosemenné Vyvinuly se v mladších prvohorách, blízké příbuzné kapradin (jejich výtrusnice vznikají na přeměněných listech), vytvářejí zvláštní rozmnožovací útvary – semena, která ještě nejsou chráněna v plodech (jsou „nahá“). Pteridosperms •Seed ferns •Have similar phenotypic characters as the true ferns, but with seeds & cones instead of spores • What is a mass extinction? * A mass extinction occurs when a large fraction of all living species becomes rapidly extinct. * The fossil record shows that at least five major mass extinctions have occurred in the past 500 million years. * Impacts of asteroids on Earth are suspected as a primary cause of mass extinction. * Three of the five major mass extinctions occurred during the Paleozoic era: • –At the end of the Ordovician period, –during the late Devonian period, and –at the end of the Permian period. – – j0332189 exttinct * The graph shows when the five extinctions occurred. As you can see, the Permian extinction was the most severe. Mass Extinctions EARLY PALEOZOIC LIFE Ordovician Mass Extinction Caused by glaciation and associated lowering of sea level sepkoski Next, in terms of severity, was probably the Ashgillian (latest Ordovician) event when perhaps 50% of marine species went extinct. The Ordovician extinction occurred at the end of the Ordovician period, about 440-450 million years ago. This extinction, cited as the second most devastating extinction to marine communities in earth history, caused the disappearance of one third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, and graptolites. Much of the reef-building fauna was also decimated. In total, more than one hundred families of marine invertebrates perished in this extinction. Echinoderms, trilobites, nautiloids and many other groups suffered significant losses,. * This extinction occurred at end of the period, about 440-450 mya. * * It is thought to be caused by a global cooling, which caused the continent Gondwana to glaciate. Geologists have found glacial deposits in the Saharan desert, which provided the evidence for this theory. • KW6 * Since more water was in ice form, the sea level lowered all over the world, causing a reduction of space for life on continental shelves. * The most affected animal group was the marine invertebrates, in which more than 100 families were wiped out. 3py_2vff[1] The Ordovician Extinction •This event is theorized to be caused by an episode of global cooling similar to that of the Ordovician extinction. •This time, the glacial deposits have been found in northern Brazil. •However, meteorite impacts have also been thought a possible cause of this mass extinction, although the evidence remains inconclusive. •This extinction had little effect on land animals, mostly affecting (again) the marine life, in particular, the reef-builders. • • j0083187 Paper bag In Famennian strata only about 15 percent of Frasnian brachiopod genera are found. Ammonoids trilobites, and conodonts experienced a similar decline, and many types of gastropods and trilobites disappeared as well. The reef community became forever changed. After the Famennian, tabulate corals, stromatoporoids, and rugose corals are rare. These had achieved their greatest faunal diversity during Middle Devonian time and had been important reef contributors for 120 million years. The time of extinctions was also when acritarchs (the only phytoplankton with an extensive Devonian fossil record), became rare. Placoderms almost disappear at this time. Until then, during the Devonian, they had been the dominant pelagic carnivores. On the land, life appears to have been little affected, although the marine record is that world climate may have cooled significantly at this time. The evidence for this (in New York State) is that glass sponges, which today are restricted to cool waters, began to thrive where formerly successful tropical marine fauna had become extinct. Evidence supporting the Devonian mass extinction suggests that warm water marine species were the most severely affected in this extinction event. This evidence has lead many paleontologists to attribute the Devonian extinction to an episode of global cooling, similar to the event which is thought to have cause the late Ordovician mass extinction. BRYOPHYTES – first in Ordovician •The gametophyte is the dominant generation in the life cycles of bryophytes GR ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM BRYOPHYTE Acritarchs from the lower Paleozoic Upper Ordovician Upper Ordovician Upper Ordovician-SEM photo • • • Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 30.1 •For the gametophyte to exist within the sporophyte has required extreme miniaturization of the the gametophyte of seed plants. •The gametophytes of seedless vascular plants are small but visible to the unaided eye, while those of seed plants are microscopic. Alternation of generations in seedless and seed plants •The evolution of the seed during the Late Devonian –liberated land plants from their dependence on moist conditions –and allowed them to spread over all parts of the land • •In the seed method of reproduction –the spores are not released to the environment –but are retained on the spore-bearing plant –where they grow into the male and female forms • Evolution of Seeds • SEED PLANTS •Key adaptations of seed plants •Reduction of the gametophyte –Minute gametophytes retained within and protected by the sporophyte •Advent of the seed –Seeds replaced spores as a means of dispersing offspring •Evolution of pollen –Eliminated the liquid H2O fertilization requirement •Generalized life history of a seedless vascular plant •The mature sporophyte plant produces spores Seedless Vascular Plant WICHG31322a –which upon germination grow into small gametophyte plants •Major events in the evolution of land plants –The Devonian Period was a time of rapid evolution for the land plants Plant Evolution 2561_tble1302 – –the appearance of leaves –and emergence of seeds MYA--Epoch 50 Tertiary 100 150 Cretaceous 200 Jurassic 250 Triassic 286 Permian 360 Carboniferous 400 Devonian 425 450 500 Silurian 600 Cambrian--Ordovician Cooksonia Rhyniophyta Trimerophytes Progymnosperms Seed Ferns Angiosperms Cycads Ferns Conifers Zosterophyllophytes Lycophytes Ginkgos Gnetophytes Gymnosperm phylogeny is a mess. •Generalized life history of a seedless vascular plant •The mature sporophyte plant produces spores Seedless Vascular Plant WICHG31322a –which upon germination grow into small gametophyte plants SEEDLESS VASCULAR PLANTS 29-23-FernLifeCyc-L Vertebrate Phylogeny Life7e-Fig-34-08-0 Agnatha Historical Geology Ordovician Life Ecological Complexity Progymnosperms •Seedless vascular plants – but likely progenitors of seed plants •Unlike other seedless vascular plants, progymnosperms had secondary vascular tissue (both xylem and phloem) and its structure is very like that of modern conifers •While the earliest progymnosperms lacked seeds, by the end of the Devonian, some species had evolved seeds rv20is06 Reconstruction of progymnosperm Archaeopteris twogenerations2