Paleozoic Life

PALEOZOIC LIFE - OVERVIEW

1. GREAT DIVERSIFICATION OF LIFE DURING THE EARLY PALEOZOIC
   • Evolution of many new phylla from the few Vendian/Ediacarian phylla
   • Evolution of vertebrates
     • fish evolved in the Cambrian (diversified in the Devonian); amphibians & then reptiles evolved in the Late Paleozoic
   • Evolution of land-dwelling organisms
     • land plants evolved in the Ordovician (diversified in the Silurian)
   • Mass extinctions closedthe Paleozoic - great reduction in diversity

MARINE INVERTEBRATES

1. PALEOZOIC FOSSIL RECORD = MARINE INVERTEBRATES WITH HARD PARTS DOMINANT
2. VENDIAN/EDIACARIAN-EARLY CAMBRIAN ADAPTIVE RADIATION
   • Late Proterozoic (VENDIAN/EDIACARIAN)
     • Low-diversity assemblage of soft-bodied invertebrates (Ediacaran Fauna) & associated tube-shaped fossils & simple trace fossils
   • Early Cambrian
     • Low-diversity assemblage of small, shelly fauna & associated complex trace fossils (Nemakit-Daldynian)
     • Moderate-diversity assemblage of small, shelly fauna (Tommotian Fauna) with inarticulate brachiopods & Archaeocyathids
     • High-diversity assemblage of Trilobites, inarticulate brachiopods & Archaeocyathids
   • Probably resulted from:
     1. Increasing Oxygen & Carbon dioxide levels,
     2. Continental fragmentation,
     3. End of glaciation
     4. Flooding of continents,
     5. Evolution of herbivores to feed on cyanobacterial mats
     6. Evolution of predators
   • all major animal PHYLA (EXCEPT bryozoans), + several now extinct, evolved during Vendian/Ediacarian-Early Cambrian adaptive radiation, which represents an initial "experimental" diversification
   • "Classical" Cambrian fossil assemblage = trilobites (75%), inarticulate brachiopods (15-20%), & archaeocyathids (~5%) + SEVERAL MINOR CLASSES
   • lots of non-shelled animals around that generally were not preserved
     • exception: Middle Cambrian Burgess Shale (British Columbia ) - many phyla with truly weird body forms that became extinct in the Cambrian
       • primitive chordates (Pikaia) also occur in the Burgess Shale
   • Ediacarian-Cambrian adaptive radiation terminated by mass extinction of:

     many "experimental" phyla, including all archaeocyathids; many families of trilobites; many classes of early echinoderms

     "The history of metazoan life is a tale of winnowing and culling and stabilization of a few surviving anatomies" - Stephen Jay Gould

3. ORDOVICIAN ADAPTIVE RADIATION
   • secondary adaptive radiation - most modern marine invertebrates CLASSES evolved
   • very different from Cambrian fauna = PALEOZOIC FAUNA
     • trilobites are not as important & archaeocyathids are gone
     • Articulate Brachiopods replace Inarticulate Brachiopods
     • bryozoans evolve - important reef builders, with stromatoporoids and corals
     • mollusks, especially nautiloid cephalopods & gastropods are abundant
     • echinoderms, especially crinoids & starfish are abundant
   • Ordovician terminated by mass extinction
4. SILURIAN & DEVONIAN ADAPTIVE RADIATION
   • recovery & rediversification of decimated taxa
     • tabulate & rugose corals & stromatoporoids - major reef-builders
     • Ammonoids evolved during Devonian & diversified
   • near end of Devonian - another mass extinction
5. CARBONIFEROUS & PERMIAN ADAPTIVE RADIATION
   • recovery & rediversification
     • Fusilinid foraminifera - abundant & diversified during Pennsylvanian & Permian
     • Bryozoans - characterized by lacy, delicated fan-shaped colonies
     • Productid (spined) brachiopods became important
     • Ammonoid cephalopods recovered & rediversified
     • Echinoderms abundant, especially crinoids [Mississippian = "Age of Crinoids"]
   • end of Permian - TREMENDOUS mass extinction [see below]

TERRESTRIAL INVERTEBRATES

1. FIRST ANIMALS TO ADAPT TO LIFE ON LAND
2. ARTHROPODS
   • wingless insects in Early Devonian; cockroaches & dragonflies in Carboniferous
   • scorpions & spiders in Early Devonian
   • possible millipede trace fossils in nonmarine Late Ordovician; centipedes in Pennsylvanian
   • exoskeleton (evolved for protection against predators) keeps arthropods from drying out
3. MOLLUSKS - land snails evolved in Devonian

VERTEBRATES

1. SUBGROUP OF PHYLUM CHORDATA
   • Chordates have a stiff, elongate support structure [= notochord in primitive chordates; vertebrae in vertebrates] & a hollow, central nervous system at some stage of their life
   • Chordates & echinoderms probably evolved from common ancestor
   • Oldest Chordates (Pikaia) in Burgess Shale
2. FIRST VERTEBRATES - FISH
   • oldest fossil fish remains - small jawless fish plates in Upper Cambrian of Wyoming
   • Devonian = "Age of Fish" - great abundance & diversity of fish
3. FIVE (5) CLASSES OF FISH
   • Agnatha (jawless fish) - Paleozoic forms called Ostracoderms because of bony armor
     • Ostracaderms became extinct during Devonian mass extinction
     • only modern jawless fish - lampreys & hagfish
4. Acanthodii &
5. Placodermi (archaic jawed fish) [jaw evolved from gill arch]
   • BOTH evolved in Silurian & became extinct during Permian mass extinction
6. Chondrichthyes (cartilaginous fish - sharks, rays, skates) &
7. Osteoichthyes (bony fish)
   • both evolved during Devonian
   • Ray fin Bony Fish - arose in Devonian lakes = Most modern fish
8. Lobe fin Bony Fish - adapted to drought prone areas by having sturdy lobe fins (for overland movement?), nostrils & lungs; one group evolved into Amphibians
   • 3 groups evolved from Devonian lobe fin Osteoichtyans: modern lung fish, modern Coelacanths, & extinct Rhipidistians (evolved into amphibians)
9. AMPHIBIANS
   • still tied to a moist environment; must lay eggs in water & amphibian larva breath via gills like fish
   • ichthyostegids (transitional form between fish & amphibians) evolved during Late Devonian
     • Had more than 5 digits
     • Tetrapod limbs evolved to hold on underwater, not for walking on Land
   • first amphibians (labyrinthodonts [from elaborate pattern of teeth]) evolved from ichthyostegids during Carboniferous
   • modern amphibians & reptiles evolved from labyrinthodonts
10. REPTILES
    • not dependent on moist environment; "amniotic" egg (shelled or skinned) protects developing embryo from drying out
    • primitive reptiles evolved in Early Pennsylvanian & gave rise to all other reptiles
    • advanced mammal-like reptiles evolved in Permian
      • Pelycosaurs (early mammal-like reptiles), including sail-backed forms like Dimetrodon - dominant in Early Permian, became extinct during the Permian
      • Therapsids (advanced mammal-like reptiles) - dominant in Late Permian; survived into Jurassic; most (80%) reptile families - extinct during Permian mass extinction
        • Therapsids had fewer bones in skull, a better joint between skull & neck, enlarged lower jaws, differentiated teeth, limbs were beneath the body, & they probably had fur
        • Therapsids gave rise to mammals in the Mesozoic

PLANTS

1. PRECAMBRIAN THROUGH CAMBRIAN
   • bacteria (Monerans), algae (Protistans or Thallophytes) & fungi only
     • mostly marine, + some freshwater varieties, particularly green algae (thought to be ancestal to land plants)
2. LAND PLANTS
   • mostly vascular (have tubes to carry water & nutrients)
   • Oldest remains - spores in Middle-Upper Ordovician African rocks
   • Psilophytes - Oldest body remains from the Middle Silurian
     • horizontal stalks underground & vertical stems bearing branches & spore sacs
     • very primitive - no true leaves or roots, & seedless (reproduced with spores)
     • diversified in the Late Silurian & went extinct during the Devonian
   • Scale trees (leaves grew directly from the trunk) [LYCOPSIDS], Rushes & horsetails [SPHENOPSIDS] and True ferns [PTEROPSIDS] evolved from Psilophytes during the Early & Middle Devonian
     • all had well-developed leaves, but only ferns have true roots
     • all were still seedless
     • some species of all were tree-sized (10's of meters tall)
   • Seed ferns evolved from true ferns during the Late Devonian
     • seed ferns had typical fern leaves - reproduced using seeds rather than spores
     • however, they had no flowers & were the first gymnosperms
     • The Glossopteris flora typifying Gondwana was a seed fern
   • Carboniferous coal forests were dominated by these 4 plant groups that evolved during the Devonian
     • all 4 groups declined in importance at the end of the Paleozoic
     • seed ferns became extinct during Jurassic; the other 3 groups have living descendants
   • The other 3 gymnosperm groups evolved from seed ferns during the Late Paleozoic -> Conifers and Cycads evolved during the Mississippian (although your book indicates that cycads evolved during the Triassic), and Ginkos evolved during the Permian
     • Conifers were important away from Carboniferous coal swamps
   • Note: Flowering, seed-bearing plants [ANGIOSPERMS] evolved from conifers during the Late Jurassic or Early Cretaceous

MASS EXTINCTION AT THE END OF THE PALEOZOIC

1. EXTINCTION OF 50% OF INVERTEBRATE, 75% OF AMPHIBIAN, & 80% OF REPTILE FAMILIES, & 90% OF INVERTEBRATE SPECIES
   • Extinction of:
     • Fusilinids [superfamily]
     • Rugose & tabulate corals [orders]
     • Bryozoans [2 orders]
     • Productid [order] & several other orders of articulate brachiopods
     • Trilobites [class] & Eurypterids [order]
     • Blastoids [subphylum] & several other subclasses of attached echinoderms, mostly crinoids
     • Acanthodians & Placoderms [classes]
     • Pelycosaurs [order]
2. SEVERAL CAUSES
   • Climate became more severe (colder & drier)
   • More dry continents (rain shadows) & less continental shelf because of lower sea level & formation of Pangea
   • Extensive volcanic activity (Siberian flood basalts)

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