Richards Spur is a

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

fossil locality located at the Dolese Brothers Limestone Quarry north of

Lawton, Oklahoma Lawton is a city in and the county seat of Comanche County, in the U.S. state of Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Ce ...

. The locality preserves clay and mudstone fissure fills of a

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

system eroded out of Ordovician

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

and

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

, with the infilling dating to the

Artinskian In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of the ...

stage of the early Permian (

Cisuralian The Cisuralian is the first Series (stratigraphy), series/Epoch (geology), epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian (geology), Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the w ...

), around 289 to 286 million years ago. Fossils of terrestrial animals are abundant and well-preserved, representing one of the most diverse

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...

communities known. A common historical name for the site is Fort Sill, in reference to the nearby military base. Fossils were first reported at the quarry by workers in 1932, spurring a wave of collecting by local and international geologists. Early taxa of interest included the abundant reptile ''

Captorhinus ''Captorhinus'' (from el, καπτō , 'to gulp down' and el, ῥῑνός , 'nose') is an extinct genus of captorhinid reptiles that lived during the Permian period. Its remains are known from Oklahoma, Texas, Europe, India, the Pedra de Fog ...

'' and microsaurs such as ''

Cardiocephalus ''Cardiocephalus'' is an extinct genus of lepospondyl amphibian from the Permian period. It was a member of the family Gymnarthridae Gymnarthridae is an extinct family of tuditanomorph microsaurs. Gymnarthrids are known from Europe and Nor ...

'' and ''

Euryodus ''Euryodus'' is an extinct genus of microsaur within the family Gymnarthridae. References See also * Prehistoric amphibian * List of prehistoric amphibians This list of prehistoric amphibians is an attempt to create a comprehensive listing ...

''. Later notable discoveries include ''

Doleserpeton ''Doleserpeton'' is an extinct, monospecific genus of dissorophoidean temnospondyl within the family Amphibamidae that lived during the Upper Permian, 285 million years ago. ''Doleserpeton'' is represented by a single species, ''Doleserpeton ann ...

'' (one of the most lissamphibian-like Paleozoic tetrapods), the most diverse assortment of

parareptiles Parareptilia ("at the side of reptiles") is a subclass or clade of basal sauropsids ( reptiles), typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near t ...

in the Early Permian, and the rare early

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years a ...

Orovenator ''Orovenator'' is an extinct genus of diapsid from Lower Permian (Artinskian stage) deposits of Oklahoma, United States. It is known from two partial skulls from the Richards Spur locality in Oklahoma. The holotype OMNH 74606 consists of ...

''.

Geology

The caves of Richards Spur formed in the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

-age Arbuckle Limestone, which was uplifted, exposed, and tilted into a vertical orientation within the Pennsylvanian and

. In the early Permian, a

system formed within the limestone, complete with caves containing speleotherms (

stalagmite A stalagmite (, ; from the Greek , from , "dropping, trickling") is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typically ...

stalactite A stalactite (, ; from the Greek 'stalaktos' ('dripping') via ''stalassein'' ('to drip') is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble an ...

cave popcorn Cave popcorn, or coralloids, are small nodes of calcite, aragonite or gypsum that form on surfaces in caves, especially limestone caves. They are a common type of speleothem. Appearance The individual nodules of cave popcorn range in size from ...

, etc.) made of

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

. Most of the karsts are narrow, 40–60 cm (16-24 inches) in width, and vertically oriented. Due to active mining at the site constantly destroying and exposing new layers, the layout of the system has not been recorded. Most of the Permian infill is discarded in the quarry's waste dumps without sedimentological and stratigraphic data, hampering studies into those aspects of the locality. However, it is known that the lower sections of the system (25 meters or 82 feet below the surface) lacks fossil material. Delorhynchus cifellii skulls

Many of the fossils of Richards Spur were found in soft

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

or conglomerate. They likely ended up in the caves as a result of water runoff from the surface, as indicated by the presence of surface minerals such as

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

, kaolinite, and sulfides among the fossils. Individual organisms may have been already disarticulated by scavenging or decomposition on the surface, decomposed within the caves after the fresh corpse had been washed in, or even died within the caves after becoming trapped. Organisms which became disarticulated on the surface experienced more wear and erosion on their fossils, induced by exposure to the elements and transportation by water within and/or outside the karst system. On the other hand, recently deceased or living organism would have been more articulated due to their decomposition occurring in the more stable cave environment, with their tendons keeping their individual bones in place prior to fossilization. The most complete fossils were encased in a residue which was almost completely

, indicating that the cave structures precipitated around their skeletons. The caves likely had to have been submerged in water (or at least persistently humid) for active speleotherm formation, and therefore this mode of spectacular preservation, to have been possible. Some fossils are encrusted by

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...

, indicating the presence of

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

fluids or

diagenesis Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...

in the systems at some point. Most (but not all) fossils are stained a dark color by seepage of

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

s into the deposits. These assorted biochemical conditions are the likely cause of unusually variable

Carbon isotope Carbon (6C) has 15 known isotopes, from to , of which and are stable. The longest-lived radioisotope is , with a half-life of years. This is also the only carbon radioisotope found in nature—trace quantities are formed cosmogenically by t ...

values found within different preserved speleotherms.

Paleoenvironment

Isotope analysis of preserved speleotherms shows several regular fluctuations in ''δ''¹⁸O levels within a time span of 1-20 thousand years. Similar fluctuations in modern low-latitude environments are considered to be indicative of strong variation in precipitation between wet and arid periods on the scales of

centuries A century is a period of 100 years. Centuries are numbered ordinally in English and many other languages. The word ''century'' comes from the Latin ''centum'', meaning ''one hundred''. ''Century'' is sometimes abbreviated as c. A centennial or ...

millennia A millennium (plural millennia or millenniums) is a period of one thousand years, sometimes called a kiloannum (ka), or kiloyear (ky). Normally, the word is used specifically for periods of a thousand years that begin at the starting point (ini ...

. Some

trace element __NOTOC__ A trace element, also called minor element, is a chemical element whose concentration (or other measure of amount) is very low (a "trace amount"). They are classified into two groups: essential and non-essential. Essential trace elements ...

s agree with this data, as Barium and

Phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

concentrations increase with higher ''δ''¹⁸O (drier periods); this is explained by increased incorporation of dust and seafoam in drier, windier periods, as demonstrated by climatological analyses in a modern cave system in

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

. Other than exceedingly rare fragments of xenacanthids and eryopoids, aquatic animals are practically absent from Richards Spur. Although amphibians are common at the site, most of them are terrestrially-adapted taxa such as

dissorophoids Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...

, microsaurs, and

seymouriamorphs Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are s ...

. This is in strong contrast to contemporary floodplain environments in Oklahoma and Texas, which have abundant fossils of aquatic animals like ''

Eryops ''Eryops'' (; from Greek , , 'drawn-out' + , , 'face', because most of its skull was in front of its eyes) is a genus of extinct, amphibious temnospondyls. It contains the single species , the fossils of which are found mainly in early Permian (a ...

'' and ''

Diplocaulus ''Diplocaulus'' (meaning "double caul") is an extinct genus of lepospondyl amphibians which lived from the Late Carboniferous to the Late Permian of North America and Africa. ''Diplocaulus'' is by far the largest and best-known of the lepospond ...

'', along with large lowland amniotes like ''

Edaphosaurus ''Edaphosaurus'' (, meaning "pavement lizard" for dense clusters of teeth) is a genus of extinct edaphosaurid synapsids that lived in what is now North America and Europe around 303.4 to 272.5 million years ago, during the Late Carboniferous to ...

''. As a result, the site is considered to represent animals living in a drier environment upland from the humid floodplains which preserve most of the Permian red beds. The only other productive Early Permian geological locale commonly considered to preserve an upland community is the

Tambach Formation The Tambach Formation is an Early Permian-age geologic formation in central Germany. It consists of red to brown-colored sedimentary rocks (red beds) such as conglomerate, sandstone, and mudstone, and is the oldest portion of the Upper Rotliegend ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

Age

The unique preservational environment of Richards Spur precludes geological stratigraphy. Based on the faunal composition (particularly the abundance of ''

Captorhinus aguti ''Captorhinus'' (from el, καπτō , 'to gulp down' and el, ῥῑνός , 'nose') is an extinct genus of captorhinid reptiles that lived during the Permian period. Its remains are known from Oklahoma, Texas, Europe, India, the Pedra de F ...

'', ''

'', and ''

''), Richards Spur has been considered roughly equivalent in age to the Arroyo Formation (Lower Clear Fork) of

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

. In Oklahoma, the equivalent may be the upper

Garber Formation The Garber Formation is a geologic formation in Oklahoma. It preserves fossils dating back to the Permian period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainme ...

or lower

Hennessey Formation The Hennessey Formation is a geologic formation in Oklahoma. It preserves fossils dating back to the Permian period. See also * List of fossiliferous stratigraphic units in Oklahoma * Paleontology in Oklahoma Paleontology in Oklahoma refers ...

. The South Grandfield site of the Hennessey Formation is an example of a more typical Oklahoman fossil locale which has similar captorhinid and microsaur taxa to Richards Spur. To determine the absolute age of the Richards Spur deposits, the speleotherm studied for the Oxygen isotope and trace element analyses was also sampled for Uranium-Lead dating. It was determined that the speleotherm was formed between 289.68 and 288.32 million years ago. This time period was originally stated to be

Sakmarian In the geologic timescale, the Sakmarian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Sakmarian lasted between 293.52 and million years ago (Ma). It was preceded by the Asselian and followed by t ...

in age, but after a later refinement to the ICS timescale, it was specified as belonging to the early

. Two more speleotherms studied later gave date ranges of 283.8 to 289.6 Ma, and 286.0 to 286.4 Ma, indicating that the locality was deposited over several million years.

Fauna

Amphibians

: '' Acheloma dunni'', a trematopid

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...

: ''

Aspidosaurus ''Aspidosaurus'' is an extinct genus of dissorophoid temnospondyl within the family Dissorophidae. Description Like other dissorophids, ''Aspidosaurus'' species had a single row of plates formed by expansions of the neural spines.

sp.'', a dissorophid

: ''

Cacops morrisi ''Cacops'' ("ugly look" for its strange appearance), is a genus of dissorophid temnospondyls from the Kungurian stage of the early Permian of the United States. ''Cacops'' is one of the few olsoniforms (dissorophids and the larger trematopids ...

'', a dissorophid

: '' Cacops woehri'', a dissorophid

: '' Cardiocephalus peabodyi'', a gymnarthrid

microsaur Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been consider ...

: '' Dissorophus multicinctus'', a dissorophid

: '' Doleserpeton annectens'', an amphibamid

: '' Euryodus primus'', a gymnarthrid

: '' Llistrofus pricei'', a hapsidopareiid

: '' Nannaroter mckinziei'', an ostodolepid

: '' Pasawioops mayi'', a micropholid

: ''

Seymouria ''Seymouria'' is an extinct genus of seymouriamorpha, seymouriamorph from the Early Permian of North America and Europe. Although they were amphibians (in a biological sense), ''Seymouria'' were well-adapted to life on land, with many reptile, re ...

sp.'', a

seymouriamorph Seymouriamorpha were a small but widespread group of limbed vertebrates (tetrapods). They have long been considered reptiliomorphs, and most paleontologists may still accept this point of view, but some analyses suggest that seymouriamorphs are s ...

: '' Sillerpeton permianum'', an aistopod : '' Tersomius dolesensis'', a micropholid

Synapsids

: '' Arisierpeton simplex'', a

caseid Caseidae are an extinct family of basal synapsids that lived from the Late Carboniferous to Middle Permian between about 300 and 265 million years ago. Fossils of these animals come from the south-central part of the United States (Texas, Oklaho ...

: '' Dimetrodon sp.'', a

sphenacodontid Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family (biology), family of small to large, advanced, carnivore, carnivorous, Late Pennsylvanian to Guadalupian, middle Permian pelycosaurs. The most recent one, ''Dimetrodon ang ...

: '' Mesenosaurus efremovi'', a

varanopid Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an '' Archaeothyris''-like synapsid in the Late Carbonifer ...

: '' Mycterosaurus longiceps'', a

: '' Oromycter dolesorum'', a

: ''

Varanops brevirostris ''Varanops'' is an extinct genus of Early Permian varanopid synapsids known from Texas and Oklahoma of the United States. It was first named by Samuel Wendell Williston in 1911 as a second species of '' Varanosaurus'', ''Varanosaurus brevirost ...

'', a

Parareptiles

: '' Abyssomedon williamsi'', a

nyctiphruretid Nyctiphruretidae is an extinct family of hallucicranian parareptiles known from the late Early to the late Middle Permian of European Russia and south-central United States. Nyctiphruretidae was named by Efremov in 1938. The type genus is ''Nyct ...

: ''

Bolosaurus grandis ''Bolosaurus'' (from Ancient Greek ''bolos'', "lump" + ''sauros'': lizard]) is an extinct genus of bolosaurid ankyramorph parareptile from the Cisuralian epoch (middle Sakmarian to early Kungurian stages) of North Asia and North America (Red ...

'', a

bolosaurid Bolosauridae is an extinct family of ankyramorph parareptiles known from the latest Carboniferous (Gzhelian) or earliest Permian (Asselian) to the early Guadalupian epoch (latest Roadian stage) of North America, China, Germany, Russia and France. ...

: '' Colobomycter pholeter'', a lanthanosuchoid : '' Colobomycter vaughni'', a lanthanosuchoid : ''

Delorhynchus cifellii ''Delorhynchus'' is an extinct genus of lanthanosuchoid parareptile known from the late Early Permian (Artinskian age) Garber Formation of Comanche County, Oklahoma. It contains three species: the type species ''D. priscus'' is based on a series ...

'', a lanthanosuchoid : ''

Delorhynchus priscus ''Delorhynchus'' is an extinct genus of lanthanosuchoid parareptile known from the late Early Permian (Artinskian age) Garber Formation of Comanche County, Oklahoma. It contains three species: the type species ''D. priscus'' is based on a series ...

'', a lanthanosuchoid : ''

Feeserpeton oklahomensis ''Feeserpeton'' is an extinct genus of parareptile from the Early Permian of Richard's Spur, Oklahoma. It is known from a single species, ''Feeserpeton oklahomensis'', which was named in 2012 on the basis of a nearly complete skull. ''Feeserpet ...

'', a lanthanosuchoid : ''

Microleter mckinzieorum ''Microleter'' is an extinct genus of basal procolophonomorph parareptiles which lived in Oklahoma during the Early Permian period. The type and only known species is ''Microleter mckinzieorum''. ''Microleter'' is one of several parareptile ...

'', a basal parareptile

Eureptiles

: '' Baeotherates fortsillensis'', a captorhinid : ''

'', a captorhinid : '' Captorhinus magnus'', a captorhinid : '' Labidosauriscus richardi'', a captorhinid : '' Opisthodontosaurus carrolli'', a captorhinid : '' Orovenator mayorum'', a basal

neodiapsid Neodiapsida is a clade, or major branch, of the reptilian family tree, typically defined as including all diapsids apart from some early primitive types known as the araeoscelidians. Modern reptiles and birds belong to the neodiapsid subclade ...

References

{{reflist Permian paleontological sites Paleontology in Oklahoma