Paleoecology is the study of the environmental relationships of organisms in the geological past.

A lot of assumptions must be made given the paucity of data available in order for paleoecologists to generate ecosystems of the past. They must assume:

The ecological relationships we use today to describe system dynamics are those that held in the past. Trophic dynamics, energy flow transfers, competition & predation, parasitism and so on where common controlling determinants of ecosystem functioning. We have no real reason to doubt this at this time.

That animal, plants & microbes had more or less the same environmental habitats and to an extent niches as those today - fish live in water etc.

Since all that is left generally is the morphology of bones, pollen wood etc. that these morphological adaptations to environment fit the pattern existent today. A plant with heavy cell walls with lignin was a land plant and not an aquatic one. In the last decade molecular genetic techniques may allow us to go beyond morphology, using genetic structure to get a better feel for the physiology of these organisms via DNA patterns and possibly in the future enzymes expression. Still we must even here assume biochemical - environmental analogies hold.

How true are these assumptions ? I remember hearing a talk by a paleoecologist who stated that this particular prehumanoid creature ate this, looked like this and so on based on a fossil femur piece 3" in length. A bit of skepticism was in order, though I certainly applauded his creative reconstruction.

pollen grain of fossil pine impression of leaf in

II. What are some problems inherent in paleoecology reconstruction?

1. What we don't see may be as important as what we do: Not every creature was fossilized. Organisms with soft-body parts are difficult to find. At best you can get a casting or impression of what was there, but no part of it. Organisms with shells, skeletons and plants with wood or high production of pollen will be over-represented and others under represented. Portions of ecosystems which were anaerobic vs. aerobic were more likely to be preserved.

2. Fossil beds are composites of fossils - a shallow lake make be the burial ground of not only the creatures who lived there but also those washed in by rivers. Animals digging through layers of mud or soil may 'contaminate' the historical record by bringing earlier or later fossils to a strata.

3.The older the material, the more likely it was modified, or destroyed by geological events or biological intrusions.

4. At best you are sampling just a portion of what existed; what happened to be there & could be captured at the time that an volcanic explosion or great flood erupted allowing fossilization.

In spite of this pictures of earlier systems have been constructed and in some cases, population dynamics have even been construed.

II. Before we start in on the specifics on what happened in the past you should review plate tectonics . An excellent place is: from which the following diagram is taken, and reproduced just in case you can't get there right now.

Once you

Age of snails, bivalve molluscs, brachipods, primitive corals, sponges and other sea creatures.Over 150 families evolved. first land plants evolved also. A colliding microcontinent pushed up the east coast Taconic Orogney). erosion of these mts lead to a layer of sediment along the continents edge. Large extinction at the end of the period. Sea levels remained high. First jawed fish, large reef communities, movement of aquatic organisms into fresh water. First land animals millponds, mites insects. FIrst vascular land plants. Large reefs in center restricted water flow: Water evaporated forming thick deposits of slat and gypsum. Sea level dropped as continents clustered. Baltica rammed Laurentia and the collision initiated the pulse of Appalachian region mt building.
Fish developed quickly: primitive sharks, bony fish, lung fish, primitive amphibians, Large barrier reefs to the west formed. Seedless vascular plants evolved and land plants covered most of the continent. NEar the end forests spread : early insects spiders, snails. Global cooling at the end of this period. Reefs hit hard. Greats mt building period in the east created the Appalachian region. lots of erosion lead to the build of sediments to the west of the Appalachians. Ramming out west lead to Franklin & Antler mts. The continents were closely clustered now. Sea levels rose and a shallow carbonate sea spread. Shallow but widespread reefs with faster moving sharks and dish. Debris from all these animals left a layer of limestone rock. On land, new spore bearing plant arose ( ferns and larger pre-angiosperm types). Amphibians as large as 20 ft. long. At end seas dropped, many species with them. Lots of erosion of mts both east and west.
Pennsylvanian: Sea levels rose and fell with glaciation of Gondwanaland. Gymnosperms appeared. Earlier plants in swampy areas died to form massive coal deposits. First reptiles appeared. When the 2 continents came together, the Alleghian Orogeny resulted, which extended the Appalachians further south, built up the Ouachita Mt belt and formed the ancestral rocky mts. Permian Siberia join with e Europe, almost completing Pangea which drifted northward.Seas restricted to the west covered less of the continent. Gymnosperms dominated. Reptiles took over the amphibians with eggs, speed. jaws. Mammal like reptiles therapsids. The climate dried.Dune built up. Basins dried up leaving salt behind . A microcontinent hit the west edge and crumpled it. THe climate cooled down and 80% of the species disappeared.
Triassic: Pangea was complete. Large reptiles joined fish as top predators in the reefs. Large crocodiles emerged. The land mass was so large, that most of the land was far from the sea, and become arid. Gymnosperms & ferns dominated the land. Thecodonts differentiated into dinosaurs. Mammals arose from reptile but were small.. Late in the period first flying vertebrates, frog & turtles appeared. by the end 20% of specie were eliminated. W. NA hit a subduction zone resulting in mts. In the e. erosion almost eliminated the Appalachians. NA moved apart from Pangea, Applachians block and faulted. Jurassic: FIsh became modernized. On land forest of cycads, gymnosperms, ginkgo common. Dinosaurs diversified. First birds crossed skies. Pangea continued to fall apart. Gulf of Mexico formed a rift zone which lead to seawater filling basins with alternating evaporations = Louann Salt deposits.As sea levels rose several times, interior flooding lead to the Sundance Sea.At the end of the period the sea was expelled.

Cretaceous: Seas were high mostly. Temperature arose early on. ( GW due to volcanoes and CO2 increase from the Pangea split). In water teleost fish, on land first angiosperms.Insects developed relationship with flowering plants. Dinosaurs still dominated though. Formation of widening Atlantic Ocean forced Greenland and Eurasia to move apart from NA. Along W. Canada a microcontinent tagged along causing a major seaway formation in interior. Laramide Orogeny out west . Major extermination after massive extraterrestrial body struck earth .Dinosaurs died out.

Cenozoic (not pictured) with loss of dinosaurs, mammals filled niches. Mt building out west formed the Rockies. Glaciers sculpted northern sections. Humans appeared.

Palogene (above): Carnivorous mammals took to the sea to form whales.Also evolved penguins, walruses seals etc. First grasses evolved. New mammal species. ungulates, elephants, rodents, rabbits, bats dogs, cats primates.. Earths poles cooled down and new ice caps caused seas to drop worldwide. Cold dense seawater sunk to bottom and flowed N. CLimates cooled and dried. forests declined and grasslands spread.TO the west a bridge of land connecting Alaska to Siberia was above sea level and erosion cut down the mt out west.

Neogene ( 23 M to present) Climates grew cooler, drier, and more seasonal. Herbs beat out trees. Animals that ate such prospered including elephants & ungulates.WIth the west mts eroded, the continent rebounded raising the modern Rockies and Colorado Plateau. Sierra Nevada range rose. Lava poured across Columbia river.> The climate fluctuated creating periods of glaciation, which formed the Great Lakes.

Modern Ice Age: 3-2.5 MYA: Major period of glaciations, sometimes covering as much as 1/3 of the continent. Why these periods and general cooling?

  • Drop in Greenhouse gases
  • Uplifting of mountains changed climate. Existing alpine glaciers reflected back light cooling trend expand glaciers.
  • Isthmus of Panama strengthened the Gulf Stream which increased snowfall in the Arctic which enlarged the ice cap.
  • Cycles may be due by changes in earths axis tilt.

Once you understand how the geological system works you can get a better understanding why the flora and fauna fossils that exist are where they are located:

Since we can't really get a grip on all the eras why don't we just concentrate on the Pleistocene and the post glacial time period.

Pleistocene extended from 2,000,000 years till post glacial recent period of 10,000 years ago. It is known as the 'Ice-age", the time of the first true humans & the mixture and thinning out of the mammalian fauna. It was a period of great climatic fluctuations throughout the globe with 4 major periods of ice sheet advance and retreat in NA. Between each glaciation period there was an interglacial period during which conditions changed from cold to temperate. Thus a successional progression occurred starting with tundra plants and boreal spruce & fir, replaced by pine & birch. Eventually the soil would build up again and temperature warm enough for the more typical oak, beech and ash

During this period there was also a spatial discontinuity in climate. Along with the continued drying and cooling due to the glaciers which led to the developments of forests dominated by evergreens ( why evergreens?) in the north there was also the spread of more arid lands and grasslands in the interior. The trend in increasing dryness was a result of the uplift of the western mountains ( remember the climate class). The rain shadow caused the change from forest to savanna ( grassland with few trees) to grassland. During these millions of years animals immigrated &emigrated changing species with the climate.

The last great ice sheet, the Laurentian reached it s maximum advance about 18,000 BP during the Wisconsin glaciation period. Canada was under ice, as you will see in the diagram below. Tundraextended across the US along its border with a bit of an extension into the Appalachians. West of Kansas there was basically just desert like areas. As the glacier finally retreated, the boreal forests disappeared to be replaced by grasslands

 The following maps were taken directly from the following site:

A period summary of the global situation at 18,000, 8,000 and 5,000 years ago.

Overwhelmingly, the picture of the world 18,000 radiocarbon years ago is of a much colder and more arid place. Treeless and barren landscapes were more extensive almost everywhere, even at low latitudes. The only notable exception is in the southwestern USA, where there was a greater area of woodland than at present. The precise degree to which tropical forests retreated under the glacial-age climate remains far more speculative than for the higher latitude forests. However, it seems safe to assume that there was a net reduction in forest cover in all three main tropical forest regions, relative to the pre-agricultural Holocene.

By 8,000 years ago - in the early Holocene - dense and woody vegetation had made a dramatic comeback. Forests occupied a greater area than present in many regions, for instance extending further north in the high arctic. In some areas, such as the Sahara, climate seems to have been much moister than at present, allowing savanna and grassland to exist in areas that are now barren desert. In other areas, such as western Canada, conditions were possibly somewhat drier than now. However, the overall picture is of considerable similarity to the present-day world, as compared to a very different situation at 18,000 years ago.

By around 5,000 years ago, the broad distribution of biome types in some areas seems to have been essentially identical to that existing today, although differences can certainly be found in many regions.. The km. per year advance of forest species although slow, allowed the major transition to that what we see today.

Animals of that time :

Large animals which roamed the US included the mastodons, giant beaver, musk oxen, giant tortoises, ground sloths, horses, camels, mammoths, sabre-tooth cats, dire wolf, . They disappeared rather suddenly about 10-11 thousand years ago. A few large animals remained: bison, condor and grizzly bear. Most of the species which survived were smaller - deer, antelopes, raccoon, mallards etc.

Sites to visit to get information on the fauna of the US can be found at the following address:

To get directions information on specific animals go to:

I did an inquiry on mastodons for all time in US- here's what was found: obviously the critters were common to all US at singular points in time...

1. What differences would you find between the fauna of 16000 years ago and that of 1000 years ago?

2. What theories exist to explain the loss of the large Pleistocene mammals? What counter arguments exist? can you offer an alternative explanation given that it was primarily large mammals only that were affected??

3. Choose one of the following, research it and tell the class what this animal was about...

Ground Sloths ) * Beautiful Armadillo * * Short-faced Skunk * Dire Wolf * Short-faced Bear * American Lion * Jaguar * Saber-toothed Cats * Giant Beaver * Perissodactlya (horses, rhinos, and tapirs) * Horses * Tapirs , camels, and pigs) * Peccaries (extinct) * Stag-moose (extinct) * Bison * Musk Ox (some types extinct) *American Mastodon (extinct) * Mammoths (extinct)