Phosphatization, or phosphatic fossilization, refers to the process of fossilization where organic matter is replaced by abundant calcium-phosphate minerals. It has occurred in unusual circumstances to preserve some extremely high-resolution microfossils in which careful preparation can even reveal preserved cellular structures. Such microscopic fossils are only visible under the scanning electron microscope.
Large quantities of phosphate are required, either from seawater or from the tissues of the decaying organism. In some cases microbes control the phosphatization, and the remains of the microbes that feed on the preserved tissue form the fossil. In other, the tissue itself is the source of phosphate and its phosphatized remains form the fossil. In the intermediate case the phosphatized tissue retains the impressions of the phosphatizing microbes. [1]
Soft-tissue fossils, such as those found in the Burgess Shale, are rare. In some cases their internal organs are replicated in phosphate. The phosphate mainly comes from the tissue itself, and may later be replaced by calcium carbonate. [2] A low pH makes CaCO3 less likely to precipitate, clearing the way for phosphate to be laid down. [2] This is facilitated by the absence of oxygen in the decaying tissue. Accordingly, (secondary) phosphate is generally only preserved in enclosed spaces, such as a tightly-closed bivalve shell. [3]
Higher concentrations of phosphate in the sea water do not enhance phosphatization, as may seem natural; rather, it increases the rate at which the organism breaks up, perhaps because the mineral "fertilizes" the decay micro-organisms. [2]
Phosphatization can happen quickly: The chitinous structures that support bivalve gills can be replaced by calcium phosphate, [4] with a little help from co-occurring bacteria, in just two to six days. [5] The gill axes and musculature of bivalves can also be preserved in phosphate. [4] [6] The structures that are most famously preserved in phosphate in the Burgess Shale are the midgut glands of Leanchoilia , [7] perhaps on account of their central position and plausibly a low pH.
Phosphatization can be microbially mediated, especially in decay-resistant groups such as arthropods; or substrate-dominated, where phosphate-rich tissue leads the mineralization process (as in fish). Cephalopods fall somewhere between these two extremes. [1] [4] [6]
In phosphatic fossils, the preservation is so fine that even some cellular structure has been preserved. The phosphatic microfossils of the Doushantuo Formation, a fossil-rich lagerstätte of the Ediacaran period, about 590–565 Ma (megaannua; million years ago), display some of the most spectacular cellular-level preservation known from the geologic record. The fossils include what may be metazoan blastulas, possibly animal embryos at an early stage in cell division.
The Doushantuo Formation presents a classic example of phosphatic fossilization:[ excessive quote ]
A refinement to viewing the internal structure of fossilized embryos uses specialized microscopic three-dimensional X-ray computed tomography, a kind of micro CAT scan. [9] [10]
A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the fossil record. Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give a good understanding of the pattern of diversification of life on Earth. In addition, the record can predict and fill gaps such as the discovery of Tiktaalik in the arctic of Canada.
An exoskeleton is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton which is enclosed underneath other soft tissues. Some large, hard and non-flexible protective exoskeletons are known as shell or armour.
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term taphonomy was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms from the biosphere to the lithosphere.
A concretion is a hard, compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word concretion is borrowed from Latin concretio'(act of) compacting, condensing, congealing, uniting', itself derived from concrescere'to thicken, condense, congeal', from con-'together' and crescere'to grow'.
The Doushantuo Formation is a geological formation in western Hubei, eastern Guizhou, southern Shaanxi, central Jiangxi, and other localities in China. It is known for the fossil Lagerstätten in Zigui in Hubei, Xiuning in Anhui, and Weng'an in Guizhou, as one of the oldest beds to contain minutely preserved microfossils, phosphatic fossils that are so characteristic they have given their name to "Doushantuo type preservation". The formation, whose deposits date back to the Early and Middle Ediacaran, is of particular interest because it covers the poorly understood interval of time between the end of the Cryogenian geological period and the more familiar fauna of the Late Ediacaran Avalon explosion, as well as due to its microfossils' potential utility as biostratigraphical markers. Taken as a whole, the Doushantuo Formation ranges from about 635 Ma at its base to about 551 Ma at its top, with the most fossiliferous layer predating by perhaps five Ma the earliest of the 'classical' Ediacaran faunas from Mistaken Point on the Avalon Peninsula of Newfoundland, and recording conditions up to a good forty to fifty million years before the Cambrian explosion at the beginning of the Phanerozoic.
In geology, petrifaction or petrification is the process by which organic material becomes a fossil through the replacement of the original material and the filling of the original pore spaces with minerals. Petrified wood typifies this process, but all organisms, from bacteria to vertebrates, can become petrified. Petrification takes place through a combination of two similar processes: permineralization and replacement. These processes create replicas of the original specimen that are similar down to the microscopic level.
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
The Emu Bay Shale is a geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätte. It is one of two in the world containing Redlichiidan trilobites. The Emu Bay Shale is dated as Cambrian Series 2, Stage 4, correlated with the upper Botomian Stage of the Lower Cambrian.
The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 69 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion. Additional sites with a similar form of preservation are known from the Ediacaran and Ordovician periods.
In paleontology, Doushantuo preservation is a type of fossilization unique to the Doushantuo formation. It involves very early phosphatisation on a cellular level - with cells being replaced by phosphate before they degrade.
The preservational regime of Beecher's Trilobite Bed and other similar localities involves the replacement of soft tissues with pyrite, producing a three-dimensional fossil replicating the anatomy of the original organism. Only gross morphological information is preserved, although the fossils are compressed some relief is preserved.
Embryo fossils are the preserved remains of unhatched or unborn organisms. Many fossils of the 580 million year old Doushantuo Formation have been interpreted as embryos; embryos are also common throughout the Cambrian fossil record.
The molluscshell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.
The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.
Dinosaur eggs are the organic vessels in which a dinosaur embryo develops. When the first scientifically documented remains of non-avian dinosaurs were being described in England during the 1820s, it was presumed that dinosaurs had laid eggs because they were reptiles. In 1859, the first scientifically documented dinosaur egg fossils were discovered in France by Jean-Jacques Poech, although they were mistaken for giant bird eggs.
Ediacaran type preservation relates to the dominant preservational mode in the Ediacaran period, where Ediacaran organisms were preserved as casts on the surface of microbial mats.
Permineralization is a process of fossilization of bones and tissues in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue. Because of the nature of the casts, permineralization is particularly useful in studies of the internal structures of organisms, usually of plants.
The fossils of the Burgess Shale, like the Burgess Shale itself, are fossils that formed around 505 million years ago in the mid-Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 65,000 specimens in a series of field trips up to the alpine site from 1909 to 1924. After a period of neglect from the 1930s to the early 1960s, new excavations and re-examinations of Walcott's collection continue to reveal new species, and statistical analysis suggests that additional discoveries will continue for the foreseeable future. Stephen Jay Gould's 1989 book Wonderful Life describes the history of discovery up to the early 1980s, although his analysis of the implications for evolution has been contested.
Shallow water marine environment refers to the area between the shore and deeper water, such as a reef wall or a shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below. The water in this environment is shallow and clear, allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.
Egg taphonomy is the study of the decomposition and fossilization of eggs. The processes of egg taphonomy begin when the egg either hatches or dies. Eggshell fragments are robust and can often travel great distances before burial. More complete egg specimens gradually begin to fill with sediment, which hardens as minerals precipitate out of water percolating through pores or cracks in the shell. Throughout the fossilization process the calcium carbonate composing the eggshell generally remains unchanged, allowing scientists to study its original structure. However, egg fossils buried under sediments at great depth can be subjected to heat, pressure and chemical processes that can alter the structure of its shell through a process called diagenesis.