Post-Cambrian Paleozoic Life
Chapters 11 (pp. 250-259; 277), 12 (pp. 282-293; 298-305; 323-324), & 13 (pp. 362-380)

POST-CAMBRIAN PALEOZOIC LIFE - OVERVIEW

• GREAT DIVERSIFICATION OF LIFE FOLLOWING THE CAMBRIAN MASS EXTINCTIONS
  • Evolution of land-dwelling organisms
    • LAND PLANTS EVOLVED IN THE ORDOVICIAN (DIVERSIFIED IN THE SILURIAN)
  • Mass extinctions closed the Paleozoic - great reduction in diversity

MARINE INVERTEBRATES

• MARINE INVERTEBRATES WITH HARD PARTS (MOSTLY CALCIUM CARBONATE SHELLS) DOMINATE THE RECORD OF PALEOZOIC LIFE
• ORDOVICIAN ADAPTIVE RADIATION
  • secondary adaptive radiation, during which most of the CLASSES of modern marine invertebrates evolved
  • very different from Cambrian fauna = PALEOZOIC FAUNA (see figure 11.10)
    • TRILOBITES ARE NOT AS IMPORTANT & ARCHAEOCYATHIDS ARE GONE
    • ARTICULATE BRACHIOPODS REPLACE INARTICULATE BRACHIOPODS
    • BRYOZOANS EVOLVE & BECOME IMPORTANT REEF BUILDERS (see figure 12.21)
    • TABULATE & RUGOSE CORALS ARE ALSO IMPORTANT REEF BUILDERS
    • MOLLUSKS, ESPECIALLY NAUTILOID CEPHALOPODS & GASTROPODS ARE ABUNDANT
    • ECHINODERMS, ESPECIALLY CRINOIDS & STELLEROIDS (starfish) ARE ABUNDANT
  • ecological relationships are more complex & tiering develops (see figures 11.4 & 11.5)
  • Ordovician diversification terminated by mass extinction of many marine invertebrate families
• SILURIAN-DEVONIAN ADAPTIVE RADIATION
  • recovery & rediversification of decimated taxa
    • TABULATE & RUGOSE CORALS - MAJOR REEF-BUILDERS [REEFS LARGER THAN THOSE OF THE ORDOVICIAN]
    • AMMONOIDS EVOLVED FROM NAUTILOIDS DURING DEVONIAN & DIVERSIFIED
    • EURYPTERIDS & OSTRACODES ABUNDANT
  • near end of Devonian - another mass extinction, mostly affecting reef community organisms & ammonoids
• CARBONIFEROUS & PERMIAN ADAPTIVE RADIATION
  • again 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 BECAME ABUNDANT, ESPECIALLY CRINOIDS [MISSISSIPPIAN CALLED "AGE OF CRINOIDS"]
      • extinct blastoids also abundant during Mississippian
  • end of Permian - TREMENDOUS mass extinction [see below]

TERRESTRIAL INVERTEBRATES

• FIRST ANIMALS TO ADAPT TO LIFE ON LAND
• ARTHROPODS (see figure 12.12)
  • oldest insects - wingless forms in Early Devonian and cockroaches & dragonflies in Carboniferous rocks
  • oldest arachnids - scorpions & spiders in Early Devonian and centipedes in Pennsylvanian rocks
  • possible millipede trace fossils in Late Ordovician nonmarine beds
  • exoskeleton (evolved for protection against predators) keeps arthropods from drying out
• MOLLUSKS
  • land snails evolved in Devonian
    

VERTEBRATES

• SUBGROUP OF PHYLUM CHORDATA
  • Chordateshave a stiff, elongate support structure [called a notochord in primitive chordates] & a hollow, central nervous system at some stage of their life
    • NOTOCHORD IS REPLACED BY VERTEBRAE IN VERTEBRATES
  • Chordates & echinoderms probably evolved from common ancestor
  • Oldest Chordates in Burgess Shale
• FIRST VERTEBRATES - FISH
  • oldest fossil fish remains - small plates of jawless fish (Ostracoderms) in Upper Cambrian rocks of Wyoming
  • Devonian = "Age of Fish" - great abundance & diversity of fish
• FIVE (5) CLASSES OF FISH (See Figure 12-7)
  • Agnatha (jawless fish) - Paleozoic forms called Ostracoderms because of bony armor
    • ONLY MODERN JAWLESS FISH - LAMPREYS & HAGFISH
  • Acanthodii & Placodermi (archaic jawed fish) - jaw evolved from modified gill arch
    • BOTH EVOLVED IN SILURIAN & BECAME EXTINCT DURING PERMIAN MASS EXTINCTION
  • Chondrichthyes (cartilaginous fish - sharks, rays & skates) & Osteoichthyes (bony fish) [most modern fish]
    • BOTH EVOLVED DURING THE DEVONIAN
  • Ray-finned Bony Fish - arose in Devonian lakes = Most modern fish
  • Lobe-finned Bony Fish - adapted to drought prone areas by having sturdy lobe fins for overland movement, nostrils & lungs; 1 group evolved into Amphibians
    • 3 GROUPS EVOLVED FROM DEVONIAN LOBE FIN OSTEOICHTYANS: MODERN LUNG FISH (DIPNOI), MODERN COELACANTHS (ONE GROUP OF CROSSOPTERYGII), & EXTINCT RHIPIDISTIANS (A SECOND GROUP OF CROSSOPTERYGIANS THAT EVOLVED INTO AMPHIBIANS)
• AMPHIBIANS (see figures 12.13 & 13.61)
  • still tied to a moist environment; must lay eggs in water & larva breath via gills like fish
  • ichthyostegids (transitional form between fish & amphibians) evolved during Late Devonian
    • HAD MORE THAN 5 DIGITS
  • labyrinthodonts [from elaborate pattern of teeth](1st amphibians) evolved during Carboniferous
  • modern amphibians & reptiles evolved from labyrinthodonts
• REPTILES
  • not dependent on moist environment; "amniotic" egg (shelled or skinned) protects developing embryo from drying out (see figure 13.62)
  • primitive reptiles (Cotylosaurs) evolved in Early Pennsylvanian & gave rise to all other reptiles
  • advanced reptiles (mammal-like reptiles) evolved in Permian
    • EARLY MAMMAL-LIKE REPTILES (PELYCOSAURS, INCLUDING SAIL-BACKED FORMS LIKE DIMETRODON) - DOMINANT IN EARLY PERMIAN; BECAME EXTINCT DURING THE PERMIAN (see figure 13.63)
    • ADVANCED MAMMAL-LIKE REPTILES (THERAPSIDS) - DOMINANT IN LATE PERMIAN & SURVIVED INTO JURASSIC, ALTHOUGH MOST (80%) REPTILE FAMILIES WENT EXTINCT DURING PERMIAN MASS EXTINCTION (see figures 13.64 & 13.65)
      • Had fewer bones in skull, better joint between skull & neck, enlarged lower jaws, differentiated teeth, limbs beneath the body, & they probably fur (probably were warm-blooded)
      • Therapsids gave rise to mammals in the Mesozoic

PLANTS

• PRECAMBRIAN THROUGH CAMBRIAN
  • bacteria (Archaebacteria & Eubacteria) , algae (Protistans or Thallophytes) & fungi only
    • MOSTLY MARINE, ALTHOUGH SOME FRESHWATER VARIETIES, PARTICULARLY GREEN ALGAE (THOUGHT TO BE ANCESTAL TO LAND PLANTS)
• LAND PLANTS (See Figures 12.9, 12.10, 13.57, &13.60; box 13.3)
  • mostly vascular (have tubes to carry water & nutrients)
  • Oldest remains - spores in Middle-Upper Ordovician African rocks
  • Psilophytes (Rhyniophytes & Zosterophyllophytes) - Oldest body remains from the Middle Silurian
    • HORIZONTAL STALKS UNDER THE GROUND
    • 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 [PTERIOPHYTES] 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 [PTERIDOSPERMOPHYES] evolved from true ferns during the Late Devonian
    • SEED FERNS HAD TYPICAL FERN LEAVES, BUT 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 and Early Mesozoic -> Conifers and Cycads evolved during the Mississippian, and Ginkos evolved during the Pennsylvanian
    • CONIFERS WERE IMPORTANT AWAY FROM CARBONIFEROUS COAL SWAMPS
  • Note: Flowering, seed-bearing plants [ANGIOSPERMS] evolved from seed ferns or conifers during the Late Jurassic or Early Cretaceous

MASS EXTINCTION AT THE END OF THE PALEOZOIC

• 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 [CLASS]
    • PELYCOSAURS [ORDER]
• SEVERAL CAUSES
  • Climate became more severe (colder & drier)
  • More dry continents (rain shadows) & less continental shelf because of lower sea level & formation of Pangea

Study Questions

1. What were the major events in Paleozoic organic evolution?

2. When & what groups of vertebrates evolved during the Paleozoic?

3. When & what groups of land plants evolved during the Paleozoic?

4. When did important adaptive radiations occur during the Paleozoic?

5. What were the important groups that evolved during these adaptive radiations?

6. What were the times of mass extinction during the Paleozoic? What were the important groups that became extinct?

7. Summarize the details of Paleozoic land invertebrate evolution.

8. Summarize the details of Paleozoic vertebrate evolution.

9. What are the details of fish evolution (the different fish classes that evolved, the classes that are extinct & the class that is reduced in importance)?

10. What was the structure modified to form fish jaws?

11. What were the changes required to adapt to land?

12. What were the characteristics of Paleozoic amphibians?

13. What is the significance of the evolution of the amniote egg?

14. Summarize the details of reptile evolution (the progression from primitive stem reptiles to advanced mammal-like reptiles).

15. Summarize the details of Paleozoic land plant evolution (the sequence of different phyla that evolved, the divisions that are extinct & the divisions that are reduced in importance).

16. Summarize the differences in reproductive strategies used by the various divisions & the significance of the evolution of the seed.

17. What were the causes of the terminal Paleozoic mass extinction?

18. What groups became extinct?