(Fossils that really aren't!)
Looks like wood Looks like bone Looks like an eye
A fossil occurs primarily in sedimentary rocks and deposits (such as Ice Age sediments). Perhaps the only thing misidentified more frequently than a real fossil is a pseudofossil or false fossil. It is a rock with an unusual shape or pattern that occurs naturally and resembles something that once lived. Pseudofossils may be formed or exposed by erosion (physical abrasion of the rock) or weathering (a chemical process that can alter a rock's appearance). Some minerals mimic the appearance of life forms.
The key to understanding whether something is a fossil or pseudofossil is to learn about the age of the rock where it was found. It is usually much easier to show the specimen (or a sharply focused photo) to a geologist or paleontologist in your area (through your state geological survey, natural history / science museum or college geology department). However, if you are really interested in fossils and rocks, learning some basic geology is necessary. Reading geological maps of the area can provide information about the age of the rocks on the surface of the landscape. For example, if the bedrock is Devonian age, then fossil dinosaur teeth, bird skulls, eggs or mice will not occur. Those creatures existed in more recent times.
As strange as this may seem, by itself, the shape of the rock is one of the least valuable methods to identify a fossil! A combination of observations – including the pattern within the rock and knowledge of the age of rocks where it was found is most important. While one may look at a puffy cumulus cloud in the sky and say, “It looks like a mouse!” you know it is a cloud, not a mouse. With a mouse-shaped rock, the shape isn’t as intuitive.
What parts of an animal are typically preserved? Most commonly, it is the hardest parts like shell and bone. Soft tissue (skin, muscle, cartilage and internal organs) is rarely preserved. Eggs are very rare because the shells are thin, soft or leathery. Bird eggs are extremely rare as fossils because they are so fragile.
Below are links to our pages with images and information about some pseudofossils (mostly from Indiana and Kentucky). Having a geologist or paleontologist hold the specimen is the best way to get something accurately identified.
“Not-Quite Ready for Primetime Fossils”
Bone-Like Egg-Like Scale, Skin & Turtle-Patterns
Wood-Like Faces & Oddities Fossils that are not what they appear
Another good site for information:
Arkansas Geological Commission's Pseudofossil Page
Created February 22, 2010, Updated August 3, 2011