Richards Spur is a

Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...

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, Oklahoma, Comanche County, in the U.S. state of Oklahoma. Located in western Oklahoma, approximately southwest of Oklahoma City, it is the principal city of the Lawton metropolitan ar ...

. The locality preserves clay and mudstone fissure fills of a

karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

system eroded out of Ordovician

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and dolomite, with the infilling dating to the Artinskian stage of the early Permian (

Cisuralian The Cisuralian, also known as the Early Permian, is the first series/epoch of the Permian. The Cisuralian was preceded by the Pennsylvanian and followed by the Guadalupian. The Cisuralian Epoch is named after the western slopes of the Ural Mou ...

), 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 first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

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'' and microsaurs such as '' Cardiocephalus'' and '' Euryodus''. Later notable discoveries include ''

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

'' (one of the most

lissamphibia The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia ( ...

n-like Paleozoic tetrapods), the most diverse assortment of parareptiles in the Early Permian, and the rare early diapsid ''

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 o ...

''.

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, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

-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 (, ; ; ) 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 composed of calcium carbonate, but may consist ...

stalactite A stalactite (, ; , ) 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 and that can be deposited as a colloid, or is in suspension (chemistry ...

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 (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

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

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 Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

kaolinite Kaolinite ( ; also called kaolin) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina () ...

, and

sulfides Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families of ...

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 Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue ...

, indicating the presence of

anoxic 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 dissolved ox ...

fluids or

diagenesis Diagenesis () is the process of 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 role as sedi ...

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 Hydrophobe, hydrophobic; their odor is usually fain ...

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

Carbon isotope Carbon (6C) has 14 known isotopes, from to as well as , of which only and are stable. The longest-lived radioisotope is , with a half-life of years. This is also the only carbon radioisotope found in nature, as trace quantities are formed ...

values found within different preserved speleotherms.

Paleoenvironment

Isotope analysis Isotope analysis is the identification of isotopic signature, abundance of certain stable isotopes of chemical elements within organic and inorganic compounds. Isotopic analysis can be used to understand the flow of energy through a food we ...

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 or

millennia A millennium () is a period of one thousand years, one hundred decades, or ten centuries, 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 p ...

. Some

trace element __NOTOC__ A trace element is a chemical element of a minute quantity, a trace amount, especially used in referring to a micronutrient, but is also used to refer to minor elements in the composition of a rock, or other chemical substance. In nutr ...

s agree with this data, as

Barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

and

Phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

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, officially the State of Israel, is a country in West Asia. It Borders of Israel, shares borders with Lebanon to the north, Syria to the north-east, Jordan to the east, Egypt to the south-west, and the Mediterranean Sea to the west. Isr ...

. 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, microsaurs, and seymouriamorphs. This is in strong contrast to contemporary floodplain environments in Oklahoma and Texas, which have abundant fossils of aquatic animals like '' Eryops'' and '' Diplocaulus'', along with large lowland amniotes like ''

Edaphosaurus ''Edaphosaurus'' (, meaning "pavement lizard" for dense clusters of its 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 ...

''. 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 Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain t ...

. The only other productive Early Permian geological locale commonly considered to preserve an upland community is the Tambach Formation of

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

Age

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

Captorhinus aguti ''Captorhinus'' (from , 'to gulp down' and , 'nose') is an extinct genus of Captorhinidae, captorhinid reptiles that lived during the Permian period. Its remains are known from North America (Oklahoma, Texas) and possibly South America. Descr ...

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

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

. In Oklahoma, the equivalent may be the upper Garber Formation or lower Hennessey Formation. 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 period. 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 fo ...

in age, but after a later refinement to the ICS timescale, it was specified as belonging to the early Artinskian. 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') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

: '' Aspidosaurus sp.'', a dissorophid

: '' Cacops morrisi'', a dissorophid

: '' Cacops woehri'', a dissorophid

: '' Cardiocephalus peabodyi'', a gymnarthrid microsaur : '' Dissorophus multicinctus'', a dissorophid

: '' Doleserpeton annectens'', an

amphibamid The Amphibamidae are an ancient family of dissorophoid temnospondyls known from Late Carboniferous-Early Permian strata in the United States. Classification Amphibamidae has traditionally included small-bodied, terrestrial dissorophoids. The n ...

: '' Euryodus primus'', a gymnarthrid microsaur : '' Llistrofus pricei'', a hapsidopareiid microsaur : '' Nannaroter mckinziei'', an ostodolepid microsaur : '' Pasawioops mayi'', a micropholid

: ''

Seymouria ''Seymouria'' is an extinct genus of 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 reptilian features—so ma ...

sp.'', a seymouriamorph : '' Sillerpeton permianum'', an aistopod : '' Tersomius dolesensis'', a micropholid

Synapsids

: '' Arisierpeton simplex'', a caseid : ''

Dimetrodon ''Dimetrodon'' ( or ; ) is an extinct genus of sphenacodontid synapsid that lived during the Cisuralian (Early Permian) Epoch (geology), epoch of the Permian period, around 295–272 million years ago. With most species measuring long and ...

sp.'', a

sphenacodontid Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family of sphenacodontoid synapsids. Small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian "pelycosaurs". The most recent one, ''Dimetrodon angelensis'', is ...

: '' Mesenosaurus efremovi'', a varanopid : '' Mycterosaurus longiceps'', a varanopid : '' Oromycter dolesorum'', a caseid : '' Varanops brevirostris'', a varanopid

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 '' N ...

: '' Bolosaurus grandis'', a bolosaurid : '' Colobomycter pholeter'', a lanthanosuchoid : '' Colobomycter vaughni'', a lanthanosuchoid : '' Delorhynchus cifellii'', a lanthanosuchoid : '' Delorhynchus multidentatus'', a lanthanosuchoid : '' Delorhynchus priscus'', a lanthanosuchoid : '' Feeserpeton oklahomensis'', a lanthanosuchoid : '' Microleter mckinzieorum'', a basal parareptile

Eureptiles

: '' Baeotherates fortsillensis'', a

captorhinid Captorhinidae is an extinct family of tetrapods, traditionally considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea. Description Captorhinids are a clade of ...

: ''

'', a

: ''

Captorhinus kierani ''Captorhinus'' (from , 'to gulp down' and , 'nose') is an extinct genus of captorhinid reptiles that lived during the Permian period. Its remains are known from North America (Oklahoma, Texas) and possibly South America. Description While ...

'', a

: '' Captorhinus magnus'', a

: '' Labidosauriscus richardi'', a

: '' Maiothisavros dianeae'', a basal neodiapsid : '' Opisthodontosaurus carrolli'', a

: '' Orovenator mayorum'', a basal neodiapsid

Invertebrates

: '' Dolesea subtila'', an indeterminate

millipede Millipedes (originating from the Latin , "thousand", and , "foot") are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derive ...

: '' Karstiulus fortsillensis,'' a xyloiuloid

: '' Oklahomasoma richardsspurense'', a

juliform Juliformia is a taxonomic Order (biology), superorder of millipedes containing three living orders: Julida, Spirobolida, and Spirostreptida, and the extinct group Xyloiuloidea known only from fossils. Morphology The species possess long cylind ...

References

{{reflist Permian paleontological sites Paleontology in Oklahoma