Coelosimilia
Encyclopedia
Coelosimilia is a genus
of extinct scleractinia
n coral from the Late Cretaceous
period. The specimens were found in rocks around 70 million years old dating from the Late Cretaceous of the Mesozoic Era. Coelosimilia is similar to modern-day scleractinians, except for the composition of its calcitic
, non-aragonitic
skeleton. It is the only known scleractinian so far to have an entirely calcitic skeleton.
Coelosimilia is known from several specimens collected from carbonate
Maastrichtian
deposits located in the modern-day country of Poland
. Together, these areas would have been the continental shelves of the Late Cretaceous European continent. Polish locations known to have produced specimens of the taxon include chalk-pits and quarries in Nasiłów, Lubycza Królewska
and Mielnik
. The specimens collected from these locations, identified as the ZPAL H.II series (6,7,8) are in the collections of the Paleobiological Institute of the Polish Academy of Sciences
.
The discovery and analysis of Coelosimilia has changed the previous understanding of the evolution of the Scleractinia
. Modern-day scleractinian corals have skeletons composed of aragonite
, a calcitic mineral. Analysis of the skeleton of Coelosimilia does not seem to support development from aragonitic compounds. Instead, the skeleton is primarily calcitic — a type rarely if not ever seen in extant scleractinia. It is the first recorded instance of a scleractinian coral producing a non-aragonitic skeleton. Production of non-aragonitic skeletons by marine organisms, or the evolution of organisms capable thereof has been explained as a response to the ratio of the elements Magnesium
(Mg) and Calcium
(Ca) dissolved in seawater. Magnesium is a component of aragonite, and an abundance of the element is necessary for the development of aragonitic structure-building organisms. The presence of Coelosimilia during the Late Cretaceous has been suggested as an indicator of a low ratio (less than 2) of Mg to Ca in Cretaceous seas. In contrast, modern-day ratios of the two elements would be more than twice the suggested Cretaceous value, at a ratio of around 5.2. This has been used as an indicator of the shifts in the ratios of the two minerals in the oceans over the geologic time scale.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of extinct scleractinia
Scleractinia
Scleractinia, also called stony corals, are exclusively marine animals; they are very similar to sea anemones but generate a hard skeleton. They first appeared in the Middle Triassic and replaced tabulate and rugose corals that went extinct at the end of the Permian...
n coral from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
period. The specimens were found in rocks around 70 million years old dating from the Late Cretaceous of the Mesozoic Era. Coelosimilia is similar to modern-day scleractinians, except for the composition of its calcitic
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, non-aragonitic
Aragonite
Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...
skeleton. It is the only known scleractinian so far to have an entirely calcitic skeleton.
Coelosimilia is known from several specimens collected from carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
deposits located in the modern-day country of Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
. Together, these areas would have been the continental shelves of the Late Cretaceous European continent. Polish locations known to have produced specimens of the taxon include chalk-pits and quarries in Nasiłów, Lubycza Królewska
Lubycza Królewska
Lubycza Królewska is a village in Tomaszów Lubelski County, Lublin Voivodeship, in eastern Poland, close to the border with Ukraine. It is the seat of the gmina called Gmina Lubycza Królewska. It lies approximately south-east of Tomaszów Lubelski and south-east of the regional capital...
and Mielnik
Mielnik
Mielnik is a village in Siemiatycze County, Podlaskie Voivodeship, in north-eastern Poland, close to the border with Belarus. It is the seat of the gmina called Gmina Mielnik...
. The specimens collected from these locations, identified as the ZPAL H.II series (6,7,8) are in the collections of the Paleobiological Institute of the Polish Academy of Sciences
Polish Academy of Sciences
The Polish Academy of Sciences, headquartered in Warsaw, is one of two Polish institutions having the nature of an academy of sciences.-History:...
.
The discovery and analysis of Coelosimilia has changed the previous understanding of the evolution of the Scleractinia
Scleractinia
Scleractinia, also called stony corals, are exclusively marine animals; they are very similar to sea anemones but generate a hard skeleton. They first appeared in the Middle Triassic and replaced tabulate and rugose corals that went extinct at the end of the Permian...
. Modern-day scleractinian corals have skeletons composed of aragonite
Aragonite
Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...
, a calcitic mineral. Analysis of the skeleton of Coelosimilia does not seem to support development from aragonitic compounds. Instead, the skeleton is primarily calcitic — a type rarely if not ever seen in extant scleractinia. It is the first recorded instance of a scleractinian coral producing a non-aragonitic skeleton. Production of non-aragonitic skeletons by marine organisms, or the evolution of organisms capable thereof has been explained as a response to the ratio of the elements Magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(Mg) and Calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
(Ca) dissolved in seawater. Magnesium is a component of aragonite, and an abundance of the element is necessary for the development of aragonitic structure-building organisms. The presence of Coelosimilia during the Late Cretaceous has been suggested as an indicator of a low ratio (less than 2) of Mg to Ca in Cretaceous seas. In contrast, modern-day ratios of the two elements would be more than twice the suggested Cretaceous value, at a ratio of around 5.2. This has been used as an indicator of the shifts in the ratios of the two minerals in the oceans over the geologic time scale.