Invertebrate Life

PALEOZOIC MARINE INVERTEBRATES

• MARINE INVERTEBRATES WITH HARD PARTS (MOSTLY CALCIUM CARBONATE SHELLS) DOMINATE THE RECORD OF PALEOZOIC LIFE
• EDIACARIAN-EARLY CAMBRIAN ADAPTIVE RADIATION
  • Late Proterozoic
    • LOW-DIVERSITY ASSEMBLAGE OF SOFT-BODIED INVERTEBRATES (EDIACARAN FAUNA) & ASSOCIATED TUBE-SHAPED FOSSILS & SIMPLE TRACE FOSSILS
    • LOW-DIVERSITY ASSEMBLAGE OF SMALL, SHELLY FAUNA & ASSOCIATED COMPLEX TRACE FOSSILS
  • Early Cambrian
    • MODERATE-DIVERSITY ASSEMBLAGE OF SMALL, SHELLY FAUNA (TOMMOTIAN FAUNA) WITH INARTICULATE BRACHIOPODS & ARCHAEOCYATHIDS
    • HIGH-DIVERSITY ASSEMBLAGE OF TRILOBITES, INARTICULATE BRACHIOPODS & ARCHAEOCYATHIDS
  • all major animal PHYLA (EXCEPT bryozoans), & several now extinct, evolved during the Cambrian
  • Ediacarian-Cambrian adaptive radiation represents an initial "experimental" diversification
  • "Classical" Cambrian fossil assemblage = trilobites (75%), inarticulate brachiopods (15-20%), & archaeocyathids (~5%)
    • ALSO SEVERAL MINOR CLASSES OF ECHINODERMS (Eocrinoidea), MOLLUSKS (Monoplacophora), & ARTHROPODS, plus HYOLITHIDS ARE IMPORTANT
  • There were lots of non-shelled animals around that generally were not preserved
    • EXCEPTION: BURGESS SHALE (MIDDLE CAMBRIAN) OF BRITISH COLUMBIA - PRESERVES MANY REPRESENTATIVES OF PHYLA WITH TRULY WEIRD BODY FORMS THAT BECAME EXTINCT IN THE CAMBRIAN
      • primitive chordates also occur in the Burgess Shale
  • Ediacarian-Cambrian adaptive radiation terminated by mass extinction
    • 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
• 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 10-21, p. 253)
    • TRILOBITES ARE NOT AS IMPORTANT & ARCHAEOCYATHIDS ARE GONE
    • ARTICULATE BRACHIOPODS REPLACE INARTICULATE BRACHIOPODS
    • BRYOZOANS EVOLVE & BECOME IMPORTANT REEF BUILDERS
    • TABULATE & RUGOSE CORALS ARE ALSO IMPORTANT REEF BUILDERS
    • MOLLUSKS, ESPECIALLY NAUTILOID CEPHALOPODS & GASTROPODS ARE ABUNDANT
    • ECHINODERMS, ESPECIALLY CRINOIDS & STELLEROIDS (starfish) ARE ABUNDANT
  • 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

MASS EXTINCTION OF MARINE INVERTEBRATES AT THE END OF THE PALEOZOIC

• EXTINCTION OF 50% OF INVERTEBRATE 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
• SEVERAL CAUSES
  • Climate became more severe (colder & drier)
  • More dry continents (rain shadows) & less continental shelf because of lower sea level & formation of Pangea

MESOZOIC MARINE INVERTEBRATES

• PROTISTA (PROTOZOA) - CLASS SARCODINA BECAME IMPORTANT
  • Radiolarians - shells of silica
  • Foraminifera - shells of calcium carbonate
  • Planktonic families became important in the Cretaceous
• COELENTERATA - SCLERACTINIAN CORALS EVOLVED & FORMED LARGE REEFS
  • live in extremely shallow warm water - contain symbiotic algae
  • scleratinian coral reefs became important marine habitat
• ARTHROPODA - CRUSTACEANS (LOBSTERS/CRABS/SHRIMP/BARNACLES) BECAME NUMEROUS
• MOLLUSCA
  • Pelecypods evolved the siphon & replace brachiopods as the dominant bivalve
    • OYSTERS ARE VERY SUCCESSFUL
    • RUDISTS EVOLVED & BECAME IMPORTANT REEF BUILDERS DURING THE CRETACEOUS
  • Cephalopods (particularly Orders Belemnoidea & Ammonoidea) flourished during the Mesozoic & ammonoids are particularly useful in Mesozoic biostratigraphy
    • BELEMNITE SHELLS - ENTIRELY WITHIN ANIMAL
    • AMMONITES = DOMINANT AMMONOIDS, PARTICULARLY DURING JURASSIC & CRETACEOUS
  • Gastropods continued to flourish
• ECHINODERMATA - ECHINOIDS BECAME THE DOMINANT ECHINODERM

MESOZOIC MASS EXTINCTIONS OF MARINE INVERTEBRATES

• END OF TRIASSIC
  • Extinction of:
    • ALL BUT 1 FAMILY OF AMMONOID CEPHALOPODS
    • CONODONTS
• END OF CRETACEOUS
  • Extinction of:
    • MANY FAMILIES OF CALCAREOUS COCCOLITHS, PLANKTONIC FORAMINIFERA, BRYOZOANS & ECHINOIDS
    • RUDISTS, AMMONOIDS & BELEMNITES
• EXTRATERRESTRIAL CAUSES
  • Meteorite or asteroid impacts
    • HIGH CONCENTRATIONS OF IRIDIUM (RARE IN CRUST, RELATIVELY ABUNDANT IN METEORITES), SHOCKED QUARTZ & SOOT (FROM IMMENSE FIRES)
    • DEPOSITION FROM TSUNAMIS
    • RESULTED IN ACID RAIN, GLOBAL DARKNESS & GREENHOUSE EFFECT
    • ALSO ASSOCIATED WITH LATE DEVONIAN MASS EXTINCITION
  • Planet X & The Companion Star Nemesis
    • PERIODICITY IN EXTINCTION RATE OF 26-30 MY MAY INDICATE DISTURBANCE OF THE OORT CLOUD OF COMETS
    • CONSISTENT WITH MULTIPLE PEAKS IN IRIDIUM
• TERRESTRIAL CAUSES
  • Volcanism - abundant during the Cretaceous (Deccan Traps & Pacific)
    • POSSIBLE SOURCE OF IRIDIUM FROM DEEP IN EARTH
  • Climate Change - mostly getting colder (warmer climates are more stable & less stressful)
  • Sea Level Change - sea level drops due to a decrease in seafloor spreading rates

CENOZOIC MARINE INVERTEBRATES

• PROTOZOANS
  • Foramifera & radiolarians recovered from terminal Cretaceous mass extinction
    • MAXIMA & MINIMA IN DIVERSITY SIMILAR TO PHYTOPLANKTON
    • EVOLUTION OF LARGE (UP TO 2 CM) BENTHONIC FORAMINIFERA (USED TO BUILD PYRAMIDS)
• COELENTERATES - Corals remain major reef builders
• BRYOZOANS - Very successful, particulary in the Eocene
• MOLLUSKS
  • Shell-less cephalopods (octopi, squid, cuttlefish) are abundant
  • Pelecypods & gastropods diversify
• ECHINODERMS - Sand-dollars evolved during the Tertiary

CENOZOIC MASS EXTINCTIONS OF MARINE INVERTEBRATES

• TWO CENOZOIC MASS EXTINCTIONS
• EOCENE
  • Marked by a decrease in diversity of marine plankton
• CAUSES
  • Climate change
    • FIRST GLACIAL ICE IN ANTARCTICA
    • SEALEVEL LOW
    • DRIER & COLDER CONDITIONS
  • Extraterrestrial - Planet X & the Companion Star Nemesis

PALEOZOIC & MESOZOIC TERRESTRIAL INVERTEBRATES

• FIRST ANIMALS TO ADAPT TO LIFE ON LAND
• ARTHROPODS
  • 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
  • Expansion during the Mesozoic
    • INSECTS - IMPORTANT POLLINATORS FOR CYCADS, GINKOES & ANGIOSPERMS
• MOLLUSKS
  • land snails evolved in Devonian

Study Questions

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

2. Summarize the details of the Burgess Shale & its significance.

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

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

5. What were the times of mass extinction during the Paleozoic?

6. What were the important groups that became extinct?

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

8. What invertebrate groups became extinct?

9. Briefly summarize the differences between Paleozoic & Mesozoic marine invertebrates.

10. Summarize the details of the terminal Triassic & Cretaceous mass extinctions.

11. What goups that became extinct?

12. What were the probable causes?

13. Briefly summarize changes in the marine invertebrate community.

14. Briefly summarize the Cenozoic mass extinction.

15. Summarize the details of Paleozoic land invertebrate evolution.

16. Briefly summarize the role of insects in land plant evolution.

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