Gluteus minimus (fossil)
Encyclopedia
Gluteus minimus is a fossil
from the Upper Devonian of Iowa
. It was first collected in 1902, but only described in 1975. Each animal appears as a bi-lobed lens up to 11 millimetre, and almost all specimens share the same slight asymmetry. The species is of uncertain affinities
, having been thought of as either a fish tooth or a brachiopod
.
, Washington County, Iowa
. The Upper Devonian Maple Mill Shale appears as a series of shale
lenses
which are rich in fossils, including conodont
s, fish
remains, possible sporocarp
s, gastropods
, brachiopod
s, bivalves
and scolecodonts.
At a similar time to Weller's collections, Charles Rochester Eastman collected specimens from the Kinderhook Beds at Burlington
, Des Moines County, Iowa
. C. H. Belanski collected specimens thirty years later from the Lime Creek Formation in Floyd County, Iowa
. Thousands of specimens have since been collected from the Maple Mill Shale and nearby sites, and two have been found in a well at Columbus City
, Louisa County, Iowa
.
in a paper in the journal Science
in 1975 by Richard Arnold Davis and Holmes A. Semken, Jr. of the University of Cincinnati
and the University of Iowa
, respsectively. They studied more than 3,200 specimens, many of which were deposited at the University of Iowa's Department of Geology and the University of Cincinnati Geology Museum. They referred to the fossils as "horse collar
s", a name which had been used colloquially among university staff.
Gluteus minimus appears as lenticular (lens-shaped), bi-lobed fossils, with a size of up to 11 by 8 mm (0.433070866141732 by 0.31496062992126 ). In a sample of 400 specimens, the median
diameter was 7.4 mm (0.291338582677165 in), with a range of 4.5 millimetre. Each fossil has two dissimilar surfaces – one smooth with one or rarely two furrows, and one with conspicuous "growth lines", parallel with the outer edge of the fossil. The overall shape is broadly symmetrical, but the furrow is almost always on the same side of the "reentrant" (the cleft between the two halves). Opposite the reentrant is a "salient", which separates two indentations in the margin.
The specimens of G. minimus are made of apatite
, comprising 56% calcium oxide
, 39% phosphate
, 3.5% fluoride
and 1.5% organic carbon. Davis and Semken could not rule out the possibility that the apatite was introduced after deposition, since the shell of an animal similar to Bellerophon in the same sediments had been replaced with apatite. No amino acid
s could be recovered.
tooth
or a brachiopod
, it cannot be confidently placed in any phylum
.
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
from the Upper Devonian of Iowa
Iowa
Iowa is a state located in the Midwestern United States, an area often referred to as the "American Heartland". It derives its name from the Ioway people, one of the many American Indian tribes that occupied the state at the time of European exploration. Iowa was a part of the French colony of New...
. It was first collected in 1902, but only described in 1975. Each animal appears as a bi-lobed lens up to 11 millimetre, and almost all specimens share the same slight asymmetry. The species is of uncertain affinities
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
, having been thought of as either a fish tooth or a brachiopod
Brachiopod
Brachiopods are a phylum of marine animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection...
.
Collection history
Specimens of G. minimus were first collected by Stuart Weller in 1902, from the Maple Mill Shale near Maple Mill on the English RiverEnglish River (Iowa)
The English River is a tributary of the Iowa River in southeastern Iowa in the United States. The main stem of the river is long. Including its longest headwaters tributary, the North English River, the total length increases to . Via the Iowa River, it is part of the Mississippi River...
, Washington County, Iowa
Iowa
Iowa is a state located in the Midwestern United States, an area often referred to as the "American Heartland". It derives its name from the Ioway people, one of the many American Indian tribes that occupied the state at the time of European exploration. Iowa was a part of the French colony of New...
. The Upper Devonian Maple Mill Shale appears as a series of shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
lenses
Lens (geology)
In geology a lens is a body of ore or rock or a deposit that is thick in the middle and thin at the edges, resembling a convex lens in cross-section. Adjective: "lenticular"....
which are rich in fossils, including conodont
Conodont
Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...
s, fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
remains, possible sporocarp
Sporocarp
Sporocarp can refer to any of several structures whose primary function is the production and release of spores.* Sporocarp , a multicellular structure on which spore-producing structures are borne....
s, gastropods
Gastropoda
The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large...
, brachiopod
Brachiopod
Brachiopods are a phylum of marine animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection...
s, bivalves
Bivalvia
Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...
and scolecodonts.
At a similar time to Weller's collections, Charles Rochester Eastman collected specimens from the Kinderhook Beds at Burlington
Burlington, Iowa
Burlington is a city in, and the county seat of Des Moines County, Iowa, United States. The population was 25,663 in the 2010 census, a decline from the 26,839 population in the 2000 census. Burlington is the center of a micropolitan area including West Burlington, Iowa and Middletown, Iowa and...
, Des Moines County, Iowa
Des Moines County, Iowa
-2010 census:The 2010 census recorded a population of 40,325 in the county, with a population density of . There were 18,535 housing units, of which 17,003 were occupied.-2000 census:...
. C. H. Belanski collected specimens thirty years later from the Lime Creek Formation in Floyd County, Iowa
Floyd County, Iowa
-2010 census:The 2010 census recorded a population of 16,303 in the county, with a population density of . There were 7,526 housing units, of which 6,886 were occupied.-2000 census:...
. Thousands of specimens have since been collected from the Maple Mill Shale and nearby sites, and two have been found in a well at Columbus City
Columbus City, Iowa
Columbus City is a city in Louisa County, Iowa, United States. The population was 376 at the 2000 census. It is part of the Muscatine Micropolitan Statistical Area.-Geography:Columbus City is located at ....
, Louisa County, Iowa
Louisa County, Iowa
-2010 census:The 2010 census recorded a population of 11,387 in the county, with a population density of . There were 5,002 housing units, of which 4,346 were occupied.-2000 census:...
.
Description
Gluteus minimus was formally describedAlpha taxonomy
Alpha taxonomy is the discipline concerned with finding, describing and naming species of living or fossil organisms. This field is supported by institutions holding collections of these organisms, with relevant data, carefully curated: such institutes include natural history museums, herbaria and...
in a paper in the journal Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
in 1975 by Richard Arnold Davis and Holmes A. Semken, Jr. of the University of Cincinnati
University of Cincinnati
The University of Cincinnati is a comprehensive public research university in Cincinnati, Ohio, and a part of the University System of Ohio....
and the University of Iowa
University of Iowa
The University of Iowa is a public state-supported research university located in Iowa City, Iowa, United States. It is the oldest public university in the state. The university is organized into eleven colleges granting undergraduate, graduate, and professional degrees...
, respsectively. They studied more than 3,200 specimens, many of which were deposited at the University of Iowa's Department of Geology and the University of Cincinnati Geology Museum. They referred to the fossils as "horse collar
Horse collar
A horse collar is a part of a horse harness device used to distribute load around a horse's neck and shoulders when pulling a wagon or plow. The collar often supports and pads a pair of curved metal or wood pieces, called hames, to which the traces of the harness are attached...
s", a name which had been used colloquially among university staff.
Gluteus minimus appears as lenticular (lens-shaped), bi-lobed fossils, with a size of up to 11 by 8 mm (0.433070866141732 by 0.31496062992126 ). In a sample of 400 specimens, the median
Median
In probability theory and statistics, a median is described as the numerical value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to...
diameter was 7.4 mm (0.291338582677165 in), with a range of 4.5 millimetre. Each fossil has two dissimilar surfaces – one smooth with one or rarely two furrows, and one with conspicuous "growth lines", parallel with the outer edge of the fossil. The overall shape is broadly symmetrical, but the furrow is almost always on the same side of the "reentrant" (the cleft between the two halves). Opposite the reentrant is a "salient", which separates two indentations in the margin.
The specimens of G. minimus are made of apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
, comprising 56% calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
, 39% phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
, 3.5% fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
and 1.5% organic carbon. Davis and Semken could not rule out the possibility that the apatite was introduced after deposition, since the shell of an animal similar to Bellerophon in the same sediments had been replaced with apatite. No amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s could be recovered.
Classification
The identity of Gluteus minimus has been enigmatic since its original discovery. Weller's specimens collected in 1902 are labelled "Fish remains?" in his sister's handwriting, Burlington's specimens are labelled "Cone scales?", and Belanski described them as "apparently dermal ossifications of some fish". While Gluteus minimus has been interpreted as either a fishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
tooth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
or a brachiopod
Brachiopod
Brachiopods are a phylum of marine animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection...
, it cannot be confidently placed in any phylum
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
.