Pyrite disks or spindles are sometimes mistaken for fossils of
sand dollars or other forms (see
marcasite). Cracks, bumps,
gas bubbles, and such can be difficult to distinguish from true fossils. Specimens that cannot be attributed with certainty to either fossils or pseudofossils are treated as
dubiofossils. Debates on whether specific forms are pseudo or true fossils can be lengthy and difficult. For example,
Eozoön is a complex laminated form of interlayered
calcite and
serpentine originally found in
Precambrian metamorphosed
limestones (marbles). It was at first thought to be the remains of a giant fossil protozoan (Dawson, 1865), then by far the oldest fossil known. Similar structures were subsequently found in metamorphosed
limestone blocks ejected during an eruption of
Mount Vesuvius. It was clear that high-temperature physical and chemical processes were responsible for the formation of
Eozoön in the carbonate rock (O'Brien, 1970). The debate over the interpretation of
Eozoon was a significant episode in the history of paleontology (Adelman, 2007).
Chemical gardens can produce branching microtubuli of 2-10 μm in diameter and can resemble very closely the shapes of
fossilized primitive
fungi or
microorganisms. It has been proposed that ancient,
Precambrian, structures that have been identified as the evidence for the first fungi or even the first life, are more probably products of ancient natural chemical gardens. Image:Dendrites01.jpg|Manganese
dendrite (crystal) on a limestone bedding plane from
Solnhofen, Germany. Scale in mm. Image:Concretion01.jpg|
Concretion with calcite-filled septarian cracks. Scale in mm. Image:Eozoon01.jpg|
Eozoön canadense from the
Precambrian of Canada, a metamorphic rock made of interlayered calcite and serpentine. A well-known pseudofossil (Adelman, 2007). Scale in mm. Image:ShatterCones.jpg|Cone-in-cone structures produced by compression of limestone. Sometimes mistaken for fossils, thus becoming examples of pseudofossils. Image:Markasit hg.jpg|A
marcasite crystal form resembling a sand dollar. Image:Pseudocoprolite.jpg|A
Miocene pseudocoprolite from Washington state. This is one of the most common pseudofossils because it so closely resembles a
coprolite. Scale in mm. See Spencer (1993). Image:ConcretionPseudofossil.jpg|Cross-section of a concretion showing layers that resemble tree rings. ==References==