CENOZOIC PALEONTOLOGY

I. Decline of the Paleozoic Fauna

    A. What was the Paleozoic fauna

• the second major fauna of the Paleozoic
• replaced the earlier Cambrian fauna dominated by trilobites (77%), inarticulate brachiopods and worms
• initially expanded during the Ordovician to over 300 families
• consisted of filter feeders (80%): crinoids, articulate brachiopods, bryozoans, and corals and stalking predators such as the cephalopods
• highest diversity during Ordovician -Devonian (>300 families) declining to some 300 families during Carboniferous- Permian
• serious declines during Late Ordovician, Late Devonian, and Permian extinctions
• seldom more than 100 families after Paleozoic

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II. Rise of the Modern Fauna

    A. What is the "Modern Fauna"

• abundant molluscs
• more infaunal than Paleozoic fauna
• more predators than Paleozoic fauna
• dominated (>83%) by:
• swimming predators (fish and cephalopods)
• burrowing organisms (crustaceans, bivalves, and echinoids)
• opportunists (gastropods, cabs, lobsters, etc..)

    B. The Rise: When did it occur?

• the first modern families of invertebrates occurred in the Cambrian but constituted only as few families
• by the end of the Devonian the number of modern families had risen to ~100
• by the Permian the number of modern families reached some 175 and were little influenced by the great Permian extinction (as compared to Paleozoic faunas
• a step increase in modern families began during the Triassic, numbering some 300 by the end of the Jurassic and 500 by late Cretaceous
• after a C/T decline to some 400 families, the modern fauna has risen to ~650 families.

    C.  What caused the Rise of the Modern Fauna?

1. Predation

a. Middle Cretaceous- new predators
Modern gastropods
1. drilling radulae
2. acid sections and poisons
 Shell-crushing crustaceans became abundant
Fish
b. Response of modern invertebrates in soft sediment environments
1. successful filter feeders are mobile
2. burrowing bivalves and echinoids diversified, pumped water to filter feed in their burrows.
 
2. Commotion on the ocean floor or can't anyone have some privacy
• the modern fauna has a great diversity and abundance of active burrowers (bivalves, worms, echinoids, and crustaceans)
• active burrowing makes attachment and growth of fixed filter feeder larvae difficult (most of the Paleozoic filter feeders were fixed forms)
• increase in turbidity
• sometimes called the "bulldozer hypothesis"
 
 

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III. Some Noteworthy Cenozoic Evolutionary Events

    A. Paleogene (Paleocene, Eocene, Oligocene)

1. Marine Life
• extinction of the rudists at the ended of the Cretaceous ended their previously Cretaceous dominance over corals. Scleractinian corals slow to recover but were widespread by the Eocene.
• new niche expansion into shifting, shallow sandy environments
• e.g. sand dollars evolved from their biscuit-shaped sea urchin ancestors
• e.g. new groups of molluscs capable of quick reburial
• penquins evolve during Eocene
• pinnipeds (Walruses, seals, and sea lions) probably evolved during Eocene
• whales evolved from land mammals during the Eocene
• whales and giant sharks replaced the giant marine reptiles of the Mesozoic (e.g. Mosasaurs) as top predators
• ancestors were bear like hoofed mammals (mesonychids)
• teleost fish took over the mid-level predator status vacated by the extinct ammonites.
• large foraminifera during the Eocene (e.g. Nummulites)
  
  
2. Terrestrial Life
• major radiation of placental mammals during the Paleocene to earliest Eocene
  
  
3. Plant Life
• Paleocene evolution of grasses. Initially restricted to wooded and swampy areas. Expanded into open regions during the Late Oligocene and Miocene.
 

    B. Neogene (Miocene, Pliocene, Pleistocene)

1. Marine Life
• algal ridges became important to reefs in high energy regions
• only modest changes in invertebrates during this brief 23 m.y.
• expansion of diatoms in freshwater environments
• diversification of whales

2. Terrestrial Animal Life
• grazing mammals evolved with expansion of Miocene grasses
• clove-hoofed ungulates expanded (deer, antelopes, sheep, and goats)
• carnivorous animals gain modern character
• bear and hyena families (Miocene) added to Paleogene dog and cat families

2. Plant Life
• diversification of herbaceous plants (one family alone has 13,000 species)
• expansion of grasses (now some 10,000 species)