Chapter 8: Paleoenvironments

Learning Objectives

The goals of this chapter are to:

  • Categorize fossil assemblages to determine their habitats
  • Develop connections between modern and ancient paleoenvironments
  • Evaluate paleoenvironments through time and space

8.1 Introduction

Some use fossils to determine stratigraphy and correlate stratigraphic sequences. Others prefer to study the paleoecology to determine ancient habitats where both plants and animals co-existed. This avenue leads to discoveries about past climate, predator-prey relationships and even depth of the ocean. Using this information, artists like to create reconstructed paleoenvironments (Figure 8.1) to display these ancient habitats.

Figure 7
Figure 8.1 – Using only fossil pollen, here is a series of reconstructed paleoenvironments for Cretaceous through Paleogene time in Patagonia. Before the major Cretaceous-Paleogene extinction, there was diverse plant flora (left side), then after the meteorite impact near Chicxulub, Mexico most of the species died (middle) and then as plants started to rebound there was a change in fauna (right side). Image credit: Barreda et al. (2012) CC BY.

Remember fossils are not just interesting curiosities but were once living organisms that reproduced, had sex, ate each other, and interacted with their environment just like we do. The fossil’s paleoecology depends on many factors of their paleoenvironment such as physical conditions (temperature, light,  water depth,  and energy such as calm or turbulent) and chemical conditions (salinity, pH, oxygen, and toxic chemicals). Some animals will thrive if these variables change and others will die off. Have you ever been to the beach and seen large piles of seaweed? Well, these happen when the ocean currents changed and the wind and waves brought this seaweed from floating in the middle of the sea onto the beach. Some organisms can survive environmental change such as oysters that can live in both salty and fresh water. Many of these factors you cannot determine directly from ancient settings but have to infer from studying the fossil record. This ability to reconstruct a fossil paleoenvironment is one of the most valuable tools that a paleontologist has to offer to broader fields of geology.

Understanding every detail of how a fossil lived is not necessary to help you use fossils to interpret an ancient environment in the rock record. For example, if you know that a phylum is exclusively marine or exclusively terrestrial, this can easily change your interpretation of an otherwise dull sedimentary layer. This is just the beginning of you being able to use fossils to determine paleoenviroment; if you know how it lived, then you can determine where it lived.

For any taxonomic group (species to phylum), ask yourself some basic questions such as what was the type of the skeleton, what was its body plan (symmetry), what was its habitat, and finally how did it feed and behave. You might find these are hard to determine with fossils but give it a try. Below is a list of characteristics that you can use for determining its paleoenvironment:

Where is skeleton relative to tissue as this can be internal, external, or none. Also, look at the number of parts in the skeleton and its construction as this can be either single element or multiple elements including bivalves (two part), multivalve (range of 3 to ~15 parts), plates, ossicles or bones (many parts from 10’s to 100’s) or spicules (very many small parts numbering up to 1,000’s).

Symmetry similar to what you described in the last chapter but now consider how it relates to how the organism lived. Bilateral symmetry means that both locomotory and sensory organs can be placed efficiently. In contrast, organisms with radial symmetry tend to be slow or immobile (sessile). They also respond to stimuli from all directions. Organisms with spherical symmetry will live in open water. Finally, those with no symmetry are typically immobile (sessile).

Table 8.1 – Comparison of skeleton types and symmetry between marine fossils
Skeleton Type Number of Parts in Skeleton Symmetry
Organism Internal External Single Element Multi Element Plates or bones Bilateral Radial
Ammonite X X X
Belemnite X X X
Bivalve X X X
Blastoid X X X
Brachiopod X X X
Bryozoa X X X
Crinoid X X X
Echinoid X X X
Gastropod X X X
Graptolite X X X
Rugosa X X X*
Scleractinia X X X*
Tabulata X X X*
Trilobite X X X

*In colonial forms, symmetry is difficult to identify because of how close together the organisms grow.

8.2 Marine Paleoenvironments

Most of the fossils you have studied are marine but remember that there are a host of other environments including terrestrial (land including lakes, streams, and wet lands), transitional (estuaries, lagoons, and salt marshes) and marine (continental shelf, slope, and abyssal basin). Within these environments, organisms can have different modes of life including not moving (sessile), attached by cement to the bottom or unattached and able to move (motile). Some also categorize organisms as benthic, those who live on the bottom or just beneath the surface compared to pelagic that live by either floating or swimming.

Table 8.2 – Comparison of habitat between marine organisms
Habitat
Organism Terrestrial Transitional Marine Attached
Ammonite X
Belemnite X
Bivalve X X
Blastoid X X
Brachiopod X
Bryozoa X X
Crinoid X X
Echinoid X
Gastropod X X X
Graptolite X
Rugosa X X
Scleractinia X X
Tabulata X X
Trilobite X

How an organism feeds itself is important to determine its role in both paleoenvironment and paleoecology. Does it eat by suspension feeding as collects small particles from water column? Or perhaps it eats by deposit feeding and ingesting sediment to get nutrients. Is it an herbivore that only eats plant material, carnivore that captures and kills its prey, omnivore that eats both plants and animals, or scavenger that only eats dead material? One fascinating debate among paleontologists is whether Tyrannsaurus rex was a carnivore or scavenger. Ask yourself: if it was a carnivore, how could it catch its prey with such tiny forearms? Whereas if it was a scavenger, having small arms might be an advantage for just using its large teeth to tear apart the dead meat.

The final question is to determine if the organism lived a solitary life or in a colony with others of its own kind. If you can answer some or all of these questions from your observations, you’ll be able address more fascinating aspects of ancient life.

Table 8.3 – Comparison of mobility and feeding characteristics between marine organisms
Mobility Feeding
Organism Attached Mobile Suspension Deposit Herbivore Carnivore Scavenger
Ammonite X
Belemnite X X
Bivalve X X
Blastoid X X
Brachiopod X
Bryozoa X X
Crinoid X X
Echinoid X X X
Gastropod X X X X X
Graptolite X X
Rugosa X X
Scleractinia X X
Tabulata X X
Trilobite X X

Exercise 8.1 – Marine Paleoenvironments

First, review these summaries of the characteristics of Bryozoans and Echinoidea that can be used to determine their paleoenvironments:

Bryozoans: External skeleton. Individuals (zooids) are bilaterally symmetric, but colonies are typically asymmetric. Marine immobile (sessile), typically attached to the substrate, benthic, suspension feeders, and lives in colonies.

Echinoidea: Internal skeleton. Radial (5-fold or pentamerous) symmetry. Marine benthic scavenger or deposit feeder, mobile, and solitary life-style.

Using these descriptions as a guide along with your observations, Table 8.1, and material from Chapter 7, characterize a coral (Rugosa) and brachiopod.

  1. Summarize the characteristics that will be useful to determine paleoenvironment of a Rugosa coral.
  2. Summarize the characteristics that will be useful to determine paleoenvironment of a brachiopod.
  3. Next, speculate on the paleoenvironment for all four (bryozoans, echinoidea, rugosa, and brachiopod) of these organisms. Would all of these four organisms (bryozoans, echinoidea, rugosa, and brachiopod) live in the same paleoenvironment?
  4. Both bryozoans and echinoidea lived throughout the fossil record and thus are not good index fossils. In contrast, rugosa and brachiopods are both more limited in their age range. Using the diversity plots in Chapter 7, what age could a paleoenvironment be if it had both of these fossils?

Exercise 8.2 – Devonian Reef

Head to the PaleoDB Navigator. A large map of the world should open with a number of colored circles. The circles represent locations where fossils have been discovered and the color of the circle corresponds to the geologic timescale at the bottom of the page. You can click through the different time periods to see where fossils of that age have been discovered. On the right side there is a list of the most abundant fossil groups based on the time period you have selected on your map view. For example, you could zoom in on fossils found in South America from the Ordovician Period. The menu on the right will update with what fossils are found on your map for that period. Depending on your zoom level, you may see that the Trilobita Class is the most abundant, or you may see it broken down into several orders of Trilobita and the Asaphida Order as the most abundant. If there is a lower diversity of fossils in your map view and time period, you will see the classification broken down to lower levels. You may find you need to Google some of the names to figure out what phylum, class, or order they belong to. You can clear whatever filters you select on the lower left side of the page.

Structure of Devonian reef
Figure 8.2 – Distribution of organisms in a typical Devonian reef. The thickness of the organism curves represents the relative abundance of the organisms. Image credit:
  1. In the PaleobioDB Navigator, set your time period to Devonian and zoom in on New York State. What is the most common group of Devonian fossils found in New York? Remember, you may need to search more technical taxonomic names to determine which fossils you’re looking at (I’m talking about you, Rhynchonellata and Strophomenata).
  2. What are some other organisms that are present?
  3. What type of environments are most of these organisms found in?
  4. Compare the locations of gastropods and cephalopods. You can do this by clicking on the classes on the right-hand menu. Look at the two locations of these fossils compared to each other. You may find it easier to have two browser windows open for this. Based on the locations from the navigator and the typical locations of fossils around a Devonian reef, what direction was the coastline located?
  5. Remove any organism filter and now look at the distribution of all fossils throughout the Devonian in New York. Click on “E”, “M”, and “L” under Devonian to look at the distribution from early to middle to late Devonian. Was sea level rising or falling in this region during the Devonian (you already know which way the coastline was based on your previous answer)?

Exercise 8.3 – Himalayan Mountains

Figure 8.3 – Mount Everest showing geological relationships with the unmetamorphosed Qomolangma Formation overlying the Everest Series metamorphic rocks and the Rongbuk Granite. Image credit: photo of Everest by Pavel Novak CC SA with geology superimposed.
  1. Figure 8.3 shows the tallest peak on Earth, Mount Everest at 8,848 m (29,029 ft) (Tibetan name Qomolangma) has a layer of unaltered limestone from the Ordovician at its summit. What does this tell you about the environment of Mt. Everest during that time?
  2. Using the PaleoDB navigator, look at the distribution of fossils for the Himalaya Mountains, particularly near the Nepal/China border. During which two geologic time periods were fossils most abundant?
  3. What were the most abundant organisms for each of those periods? The pane on the right side tells you the percentage of each organism found in your current map view. You may need to search the technical taxonomic name.
  4. Based on the changes in fossils over the time periods, determine whether sea level was rising, falling, or constant. Be sure to explain your answer.
  5. Does your sea level interpretation match the global sea level record from Figure 5.21?

8.3 Continental Paleoenvironments

Depending on the continental paleoenvironment, these can be as fossiliferous as marine environments. For example, swamps and lagoons can have a wide variety of fish, plant, and insect fossils. In continental paleoenvironments, you commonly do not find index fossils as these are not as widespread. Think how quickly the environment can change during a drive through the countryside. Instead these paleoenvironments can record biodiversity and can be used for paleobehavioral analysis. Often these are the fossils more commonly known to the general public as they catch our imagination. What child doesn’t know the name of common dinosaurs or ice age mammals?

Exercise 8.4 – Jurassic Park

Using the PaleobioDB Navigator, look up “Dinosauria” (an unranked clade). A clade is a group of organisms that share a common ancestor and cladistics is a way to classify organisms based on common characteristics. You’ll notice that one of the groups in the Dinosauria clad is Aves, which is the class comprising birds. Yes, according to cladistics and taxonomic rankings, dinosaurs and birds are related.

Figure 8.4 – Jurassic Park sign at Universal Studios Hollywood. Image credit: HarshLight CC SA.
  1. During which geologic time periods were Dinosauria most abundant (excluding Aves)?
  2. Which one of those time periods were Dinosaurs (not Aves) most abundant?
  3. The movie franchise Jurassic Park showcases a number of different dinosaurs. The table below contains the seven dinosaur genera that were shown in the original film from 1993. Complete the table below with what geologic time periods these dinosaurs actually lived.
    Table 8.4 – Worksheet for exercise 8.4.
    Genera Geologic Time Period
    Tyrannosaurus
    Brachiosaurus
    Triceratops
    Velociraptor
    Dilophosaurus
    Gallimimus
    Parasaurolophus
  4. Does Jurassic Park seem like a fitting name based on when these dinosaurs lived? Why or why not?

 

Exercise Contributions

Daniel Hauptvogel and Virginia Sisson

Exercise 8.1 was inspired by an exercise on Life Mode Characteristics by Steven J. Hageman  at Appalachian State University available

References

Barreda V.D., Cúneo N.R., Wilf P., Currano E.D., Scasso R.A., Brinkhuis H., 2012, Cretaceous/Paleogene Floral Turnover in Patagonia: Drop in Diversity, Low Extinction, and a Classopollis Spike. PLoS ONE 7(12): e52455. https://doi.org/10.1371/journal.pone.0052455

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The Story of Earth: An Observational Guide by Daniel Hauptvogel & Virginia Sisson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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