Richards Spur

Richards Spur is a Permian fossil locality located at the Dolese Brothers Limestone Quarry north of Lawton, Oklahoma. The locality preserves clay and mudstone fissure fills of a karst system eroded out of Ordovician limestone and dolostone. Fossils of terrestrial animals are abundant and well-preserved, representing one of the most diverse Paleozoic tetrapod communities known.[1][2] A common historical name for the site is Fort Sill, in reference to the nearby military base.[3] 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[4][5] and microsaurs such as Cardiocephalus and Euryodus.[3] Later notable discoveries include Doleserpeton (one of the most lissamphibian-like Paleozoic tetrapods),[6] the most diverse assortment of parareptiles in the Early Permian,[7] and the rare early diapsid Orovenator.[8]

Two specimens of Captorhinus aguti found at Richards Spur

Geology

The caves of Richards Spur formed in the Ordovician-age Arbuckle Limestone, which was uplifted, exposed, and tilted into a vertical orientation within the Pennsylvanian and Permian. In the early Permian, a karst system formed within the limestone, complete with caves containing speleotherms (stalagmites, stalactites, cave popcorn, etc.) made of calcite. 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.[1]

Various skulls of Delorhynchus cifellii recovered from Richards Spur, showing the excellent preservation common to the site.

Many of the fossils of Richards Spur were found in soft calcareous claystone 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, 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 calcite, 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, indicating the presence of anoxic fluids or diagenesis in the systems at some point. Most (but not all) fossils are stained a dark color by seepage of hydrocarbons into the deposits. These assorted biochemical conditions are the likely cause of unusually variable Carbon isotope values found within different preserved speleotherms.[1]

Paleoenvironment

Isotope analysis of preserved speleotherms shows several regular fluctuations in δ18O 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. Some trace elements agree with this data, as Barium and Phosphorus concentrations increase with higher δ18O (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.[9][1]

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. 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 of Germany.[10][11][2]

Age

The unique preservational environment of Richards Spur precludes geological stratigraphy. Based on the faunal composition (particularly the abundance of Captorhinus aguti, Cardiocephalus, and Euryodus), Richards Spur has been considered roughly equivalent in age to the Arroyo Formation (Lower Clear Fork) of Texas.[3][10][12] In Oklahoma, the equivalent may be the upper Garber Formation or lower Hennessey Formation.[13] 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.[2] 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 age,[9] 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.[1]

Fauna

Amphibians
Acheloma dunni, a trematopid temnospondyl[14]
Aspidosaurus sp., a dissorophid temnospondyl[15]
Cacops morrisi, a dissorophid temnospondyl[16]
Cacops woehri, a dissorophid temnospondyl[17]
Cardiocephalus peabodyi, a gymnarthrid microsaur[3]
Dissorophus multicinctus, a dissorophid temnospondyl[15]
Doleserpeton annectens, an amphibamid temnospondyl[6]
Euryodus primus, a gymnarthrid microsaur[3]
Llistrofus pricei, a hapsidopareiid microsaur[18]
Nannaroter mckinziei, an ostodolepid microsaur[19]
Pasawioops mayi, a micropholid temnospondyl[20]
Seymouria sp., a seymouriamorph[10]
Sillerpeton permianum, an aistopod[21]
Tersomius dolesensis, a micropholid temnospondyl[22]

Synapsids
Arisierpeton simplex, a caseid[23]
Dimetrodon sp., a sphenacodontid[24]
Mesenosaurus efremovi, a varanopid[25]
Mycterosaurus longiceps, a varanopid[12]
Oromycter dolesorum, a caseid[26]
Varanops brevirostris, a varanopid[12]

Parareptiles
Abyssomedon williamsi, a nyctiphruretid[27]
Bolosaurus grandis, a bolosaurid[28]
Colobomycter pholeter, a lanthanosuchoid[7]
Colobomycter vaughni, a lanthanosuchoid[29]
Delorhynchus cifellii, a lanthanosuchoid[30]
Delorhynchus priscus, a lanthanosuchoid[30]
Feeserpeton oklahomensis, a lanthanosuchoid[31]
Microleter mckinzieorum, a basal parareptile[32]

Eureptiles
Baeotherates fortsillensis, a captorhinid[33]
Captorhinus aguti, a captorhinid[5]
Captorhinus magnus, a captorhinid[34]
Labidosauriscus richardi, a captorhinid[33]
Opisthodontosaurus carrolli, a captorhinid[35]
Orovenator mayorum, a basal neodiapsid[8]

References
  1. MacDougall, Mark J.; Tabor, Neil J.; Woodhead, Jon; Daoust, Andrew R.; Reisz, Robert R. (2017-06-01). "The unique preservational environment of the Early Permian (Cisuralian) fossiliferous cave deposits of the Richards Spur locality, Oklahoma". Palaeogeography, Palaeoclimatology, Palaeoecology. 475: 1–11. doi:10.1016/j.palaeo.2017.02.019. ISSN 0031-0182.
  2. Sullivan, Corwin; Reisz, Robert R.; May, William J. (2000-09-25). "Large dissorophoid skeletal elements from the Lower Permian Richards Spur Fissures, Oklahoma, and their paleoecological implications". Journal of Vertebrate Paleontology. 20 (3): 456–461. doi:10.1671/0272-4634(2000)020[0456:LDSEFT]2.0.CO;2. ISSN 0272-4634.
  3. Gregory, J.T.; Peabody, Frank E.; Price, Llewellyn I. (1956). "Revision of the Gymnarthridae: American Permian microsaurs". Yale Peabody Museum Bulletin. 10: 1–77.
  4. Price, L.I. (1935). "Notes on the brain case of Captorhinus". Proceedings of the Boston Society of Natural History. 40 (7): 377–386.
  5. Olson, Everett Claire (29 July 1954). "Fauna of the Vale and Choza; 9. Captorhinomorpha". Fieldiana Geology. 10 (19): 211–218.
  6. Bolt, J. R. (14 November 1969). "Lissamphibian origins: possible protolissamphibian from the lower permian of oklahoma". Science. 166 (3907): 888–891. doi:10.1126/science.166.3907.888. ISSN 0036-8075. PMID 17815754.
  7. Macdougall, Mark J.; Scott, Diane; Modesto, Sean P.; Williams, Scott A.; Reisz, Robert R. (2017-07-01). "New material of the reptile Colobomycter pholeter (Parareptilia: Lanthanosuchoidea) and the diversity of reptiles during the Early Permian (Cisuralian)". Zoological Journal of the Linnean Society. 180 (3): 661–671. doi:10.1093/zoolinnean/zlw012. ISSN 0024-4082.
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  9. Woodhead, Jon; Reisz, Robert; Fox, David; Drysdale, Russell; Hellstrom, John; Maas, Roland; Cheng, Hai; Edwards, R. Lawrence (May 2010). "Speleothem climate records from deep time? Exploring the potential with an example from the Permian". Geology. 38 (5): 455–458. doi:10.1130/G30354.1. hdl:1959.13/931960. ISSN 0091-7613.
  10. Sullivan, Corwin; Reisz, Robert R (1999-08-21). "First record of Seymouria (Vertebrata: Seymouriamorpha) from Early Permian fissure fills at Richards Spur, Oklahoma". Canadian Journal of Earth Sciences. 36 (8): 1257–1266. doi:10.1139/e99-035. ISSN 0008-4077.
  11. Olson, Everett C. (1991-03-28). "An eryopid (Amphibia: Labyrinthodontia) from the Fort Sill fissures, Lower Permian, Oklahoma". Journal of Vertebrate Paleontology. 11 (1): 130–132. doi:10.1080/02724634.1991.10011379. ISSN 0272-4634.
  12. Maddin, Hillary C.; Evans, David C.; Reisz, Robert R. (2006-12-11). "An Early Permian varanodontine varanopid (Synapsida: Eupelycosauria) from the Richards Spur locality, Oklahoma". Journal of Vertebrate Paleontology. 26 (4): 957–966. doi:10.1671/0272-4634(2006)26[957:AEPVVS]2.0.CO;2. ISSN 0272-4634.
  13. Holmes, Robert (1977). "The osteology and musculature of the pectoral limb of small captorhinids". Journal of Morphology. 152 (1): 101–140. doi:10.1002/jmor.1051520107. ISSN 1097-4687. PMID 30253636.
  14. Polley, Brendan P.; Reisz, Robert R. (2011-04-01). "A new Lower Permian trematopid (Temnospondyli: Dissorophoidea) from Richards Spur, Oklahoma". Zoological Journal of the Linnean Society. 161 (4): 789–815. doi:10.1111/j.1096-3642.2010.00668.x. ISSN 0024-4082.
  15. Gee, Bryan M.; Bevitt, Joseph J.; Reisz, Robert R. (2019-07-30). "Dissorophid diversity at the early Permian cave system near Richards Spur, Oklahoma, USA". Palaeontologia Electronica. 22 (2): 1–32. doi:10.26879/976. ISSN 1094-8074.
  16. Gee, Bryan M.; Reisz, Robert R. (2018-03-04). "Cranial and postcranial anatomy of Cacops morrisi, a eucacopine dissorophid from the early Permian of Oklahoma". Journal of Vertebrate Paleontology. 38 (2): e1433186. doi:10.1080/02724634.2018.1433186. ISSN 0272-4634.
  17. Fröbisch, Nadia B.; Reisz, Robert R. (2012-01-01). "A new species of dissorophid (Cacops woehri) from the Lower Permian Dolese Quarry, near Richards Spur, Oklahoma". Journal of Vertebrate Paleontology. 32 (1): 35–44. doi:10.1080/02724634.2012.633586. ISSN 0272-4634.
  18. Gee, Bryan M.; Bevitt, Joseph J.; Garbe, Ulf; Reisz, Robert R. (2019-01-25). "New material of the 'microsaur' Llistrofus from the cave deposits of Richards Spur, Oklahoma and the paleoecology of the Hapsidopareiidae". PeerJ. 7: e6327. doi:10.7717/peerj.6327. ISSN 2167-8359. PMC 6348957. PMID 30701139.
  19. Anderson, Jason S.; Scott, Diane; Reisz, Robert R. (2009-06-12). "Nannaroter mckinziei, a new ostodolepid 'microsaur' (Tetrapoda, Lepospondyli, Recumbirostra) from the Early Permian of Richards Spur (Ft. Sill), Oklahoma". Journal of Vertebrate Paleontology. 29 (2): 379–388. doi:10.1671/039.029.0222. ISSN 0272-4634.
  20. Fröbisch, Nadia B.; Reisz, Robert R. (2008-12-12). "A new Lower Permian amphibamid (Dissorophoidea, Temnospondyli) from the fissure fill deposits near Richards Spur, Oklahoma". Journal of Vertebrate Paleontology. 28 (4): 1015–1030. doi:10.1671/0272-4634-28.4.1015. ISSN 0272-4634.
  21. Anderson, Jason S. (November 2002). "Revision of the aïstopod genus Phlegethontia (Tetrapoda: Lepospondyli)". Journal of Paleontology. 76 (6): 1029–1046. doi:10.1017/S0022336000057851. ISSN 0022-3360.
  22. Anderson, Jason S.; Bolt†, John R. (2013-05-01). "New information on amphibamids (Tetrapoda, Temnospondyli) from Richards Spur (Fort Sill), Oklahoma". Journal of Vertebrate Paleontology. 33 (3): 553–567. doi:10.1080/02724634.2013.726676. ISSN 0272-4634.
  23. Reisz, Robert R. (2019-04-11). "A small caseid synapsid, Arisierpeton simplex gen. et sp. nov., from the early Permian of Oklahoma, with a discussion of synapsid diversity at the classic Richards Spur locality". PeerJ. 7: e6615. doi:10.7717/peerj.6615. ISSN 2167-8359. PMID 30997285.
  24. Brink, Kirstin S.; MacDougall, Mark J.; Reisz, Robert R. (2019-01-04). "Dimetrodon (Synapsida: Sphenacodontidae) from the cave system at Richards Spur, OK, USA, and a comparison of Early Permian–aged vertebrate paleoassemblages". The Science of Nature. 106 (1): 2. doi:10.1007/s00114-018-1598-1. ISSN 1432-1904. PMID 30610457.
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  26. Reisz, Robert R. (2005-12-30). "Oromycter, a new caseid from the Lower Permian of Oklahoma". Journal of Vertebrate Paleontology. 25 (4): 905–910. doi:10.1671/0272-4634(2005)025[0905:OANCFT]2.0.CO;2. ISSN 0272-4634.
  27. Mark J. MacDougall and Robert R. Reisz (2014). "The first record of a nyctiphruretid parareptile from the Early Permian of North America, with a discussion of parareptilian temporal fenestration". Zoological Journal of the Linnean Society. 172 (3): 616–630. doi:10.1111/zoj.12180.
  28. Reisz, Robert R.; Barkas, Vaia; Scott, Diane (2002-03-14). "A new early Permian bolosaurid reptile from the Richards Spur Dolese Brothers Quarry, near Fort Sill, Oklahoma". Journal of Vertebrate Paleontology. 22 (1): 23–28. doi:10.1671/0272-4634(2002)022[0023:ANEPBR]2.0.CO;2. ISSN 0272-4634.
  29. MacDougall, Mark J.; Modesto, Sean P.; Reisz, Robert R. (2016-09-02). "A new reptile from the Richards Spur locality, Oklahoma, U.S.A., and patterns of Early Permian parareptile diversification". Journal of Vertebrate Paleontology. 36 (5): e1179641. doi:10.1080/02724634.2016.1179641. ISSN 0272-4634.
  30. Reisz, Robert R.; Macdougall, Mark J.; Modesto, Sean P. (2014-07-29). "A new species of the parareptile genus Delorhynchus, based on articulated skeletal remains from Richards Spur, Lower Permian of Oklahoma". Journal of Vertebrate Paleontology. 34 (5): 1033–1043. doi:10.1080/02724634.2013.829844. ISSN 0272-4634.
  31. Macdougall, Mark J.; Reisz, Robert (2012-09-01). "A new parareptile (Parareptilia, Lanthanosuchoidea) from the Early Permian of Oklahoma". Journal of Vertebrate Paleontology. 32 (5): 1018–1026. doi:10.1080/02724634.2012.679757. ISSN 0272-4634.
  32. Linda A. Tsuji; Johannes Muller; Robert R. Reisz (2010). "Microleter mckinzieorum gen. et sp. nov. from the Lower Permian of Oklahoma: the basalmost parareptile from Laurasia". Journal of Systematic Palaeontology. 8 (2): 245–255. doi:10.1080/14772010903461099.CS1 maint: uses authors parameter (link)
  33. Modesto, Sean P.; Scott, Diane; Reisz, Robert R. (2018). "A new small captorhinid reptile from the lower Permian of Oklahoma and resource partitioning among small captorhinids in the Richards Spur fauna". Papers in Palaeontology. 4 (2): 293–307. doi:10.1002/spp2.1109. ISSN 2056-2802.
  34. Kissel, Richard A.; Dilkes, David W.; Reisz, Robert R. (2002-09-01). "Captorhinus magnus, a new captorhinid (Amniota: Eureptilia) from the Lower Permian of Oklahoma, with new evidence on the homology of the astragalus". Canadian Journal of Earth Sciences. 39 (9): 1363–1372. doi:10.1139/e02-040. ISSN 0008-4077.
  35. Reisz, R. R.; LeBlanc, Aaron R. H.; Sidor, Christian A.; Scott, Diane; May, William (2015-08-20). "A new captorhinid reptile from the Lower Permian of Oklahoma showing remarkable dental and mandibular convergence with microsaurian tetrapods". The Science of Nature. 102 (9): 50. doi:10.1007/s00114-015-1299-y. ISSN 1432-1904. PMID 26289932.
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