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What Kinds of Fossils Are Found in Fluvial Rocks?

When you hear the word "fossil," you may think of the outline of an ancient arthropod embedded in a hunk of limestone. But "fossil" encompasses a variety of prehistoric organisms and evidence of past life, from actual animal remains to plant matter to animal tracks. Fluvial fossil environments are streambed or riverbed environments, and fossils found here tend to be of a specific variety. For example, since fluvial environments involve shallow water depths, it is unusual to find well-preserved animal fossils here, since scavengers would have destroyed or scattered the remains eons ago.

Animal Body Fossils
- Since fluvial environments were easily accessed by scavengers, the most common types of animal body fossils you'll find in these areas are those that are most resilient, like vertebrate teeth or bones. Mineralized dinosaur bones can be found in fluvial deposits, as well as bones of early mammals. Dinosaur and early mammal teeth are also commonly found in fluvial environments.
  
  Occasionally, a more complete fossilized prehistoric animal will be found, usually because sediment covered the animal very soon after it died. This is a much more rare occurrence, however.
Fossilized Flora
- In direct contrast to the rarity of complete animal fossils in fluvial environments, prehistoric plant life fossils are much more common. However, similarly to animal fossils, the most resilient varieties are the most common -- fossilized pollen and seeds are the most abundantly found botanical fossils in fluvial areas.
  
  Occasionally, a past flood event will make a wide variety of whole plant fossils available. Entire tree stumps can be preserved in overbank (fine-grained sediment in large amounts, as with a flood) deposits when a flood partially buried the tree, for example. You may encounter pieces of branches, entire branches and leaves in both channel (coarser-grained material from longer-running water) and overbank deposits.
Trace Fossils or Icnofossils
- Trace fossils include all indirect evidence of life in the past that have been preserved in rock. Dinosaur tracks are an example of a trace fossil, as are tail-drag tracks, insect nests and burrows, coprolites (fossilized feces) and gastroliths (dinosaur stomach stones). Coprolites and gastroliths provide a wealth of information about prehistoric animal diets, while tracks offer valuable clues about animal locomotion.
  
  Trace fossils are commonly found in fluvial environments because of the very nature of streambeds and floodplains. Tracks were likely to be made in soft sand or soil, and if it dried hard and was later covered with sediment, the tracks would be well-preserved and eventually become fossils.
Value of Fossils Found in Fluvial Rock
- Fluvial environments have proved to be a rich source of fossil evidence. Because of the sediment that helped to preserve them, animal body parts such as bones can offer information on the structure and behavior of dinosaurs and prehistoric mammals. Botanic fossils provide even more evidence of prehistoric biodiversity and can help fill in knowledge gaps about topics like climate and the chemical composition of prehistoric soil.
  
  While it may seem that trace fossils would not be as valuable as body or plant fossils in establishing general information about a time or an organism, this is not the case. Ant and termite nest fossils provide information about the water table that can lead to conclusions about paleoclimate, for example. Dinosaur tracks are studied exclusively by a large number of paleontologists because they offer insight into how dinosaurs walked that cannot be found by studying skeletal remains alone.

Animals & Science