Pseudofossils, or false fossils, are objects that do not have a biological origin but may be mistaken as a fossil. They have mineralized markings or objects that look like fossils but are actually just unusual formations in the rock. If mineral-bearing water enters a gap between two pieces of rock, the minerals may deposit in patterns that resemble fossilized moss or ferns. Such pseudofossils are called dendrites, from the Greek dendron, meaning “tree.”
"Fossil bird head" (Image from Natural History Museum)
It's got everything - neck, beak, even an eye. But this shape is created by the growth of a mineral upon the rock surface.
"Fossil fish" (Image from Natural History Museum)
This looks like a guppy with a long flowing tail and fin. But this is a type of rock flint known as banded flint. Banded flints form a series of roughly parallel lines such as this, which can create all sorts of misleading shapes. The cause is still not fully understood but the movement of water and silica through the flint is thought to be involved. The rock flint can mimic any kind of fossil you can think of - bones, eggs, whole heads, and bodies, you name it.
Faking Fossils
Skeptic, vol. 16, no. 4, 2011
Fossil Fakes: Part two
Skeptic, vol. 17, no. 1, 2011
UNUSUAL CAMBRIAN PSEUDOFOSSILS FROM NORTHAMPTON COUNTY, PENNSYLVANIA
Proceedings of the Pennsylvania Academy of Science, vol. 28, 1954, pp. 91–95.
Fake fossil not one but two new species
Science News, vol. 159, no. 16, 21 Apr. 2001
Bee-Nest Pseudofossils from Montana, Wyoming, and South-West Africa
Journal of Paleontology, vol. 46, no. 3, 1972, pp. 421–425.
A septarian concretion or Pseudofossil, Cut and polished septarian concretion, 15 cm wide, showing the mineral-filled cracks. Although sometimes mistaken for fossils, septarian concretions have an inorganic origin.
A septarian concretion or Pseudofossil. Photograph. Britannica ImageQuest, Encyclopædia Britannica, 25 May 2016.
quest.eb.com/search/119_1789311/1/119_1789311/cite. Accessed 3 Dec 2020.
Pseudofossil, dendrites of Manganese Dioxide.
Museums Victoria, Accessed 3 December 2020.
Dendritic form of manganese oxide (orange) in a sedimentary rock on a beach.
Manganese oxide, dendritic form. Photography. Britannica ImageQuest, Encyclopædia Britannica, 25 May 2016.
quest.eb.com/search/132_1235347/1/132_1235347/cite. Accessed 10 Feb 2022.