The Nocona Formation is a geological formation in Texas, dating back to the Wolfcampian series (Early Permian). As part of the Texas red beds, it is one of several formations renowned for dense bonebeds of terrestrial vertebrate fossils.
Geology The Nocona Formation was named as a distinct geological unit in 1987; its fossil deposits were previously assigned to the Admiral Formation, a time-equivalent marine deposit located further southwest in Texas. The Nocona Formation is considered equivalent to most of the Admiral Formation (apart from the highest few layers), as well as the Coleman Junction Formation. The Nocona Formation overlies the Archer City Formation and underlies the Petrolia Formation. A few sources consider the Nocona Formation to be part of the Archer City Formation, but most regard it as a distinct unit.
Reddish-brown mudstone is the most common rock type in the formation, though grey mudstone and other laminated fine sediments are predominant in bonebeds. 11 distinct layers of dark brown sandstone are thick and extensive enough to be mapped out on a regional scale. The formation is most well-exposed in Archer and Clay counties, extending as far northeast as the Red River which defines the Texas-Oklahoma border. It reaches its thickest extent of around 350 feet in Clay County, where individual sandstone beds can reach a thickness of 40 feet. The most southern extent of the Nocona Formation is the southwestern portion of Archer County.
Bonebeds One particularly notable bonebed is the Geraldine Bonebed in Archer County, discovered by Alfred Sherwood Romer in 1932. Numerous partial and complete skeletons have been recovered from this site, including some of the best fossils of Edaphosaurus boanerges, Archeria crassidisca, Eryops megacephalus, and (to a lesser extent) Dimetrodon natalis. The skeletons are generally preserved in straight, relaxed poses, with the skull aligned towards the east, southwest, or north. Both conditions are similar to modern abrupt mortality events where the animals' corpses end up in permanent bodies of water. Plant debris and charcoal are common in the bonebed as well. It is conceivable that most of the animals killed by a single catastrophe, perhaps a forest fire which polluted the air and water to kill both terrestrial and aquatic animals in the confines of a small lake or pond.
Other productive Nocona Formation bonebeds in Archer County include the Briar Creek Bonebed, Coprolite Bonebed (named for its concentration of shark coprolites), Loftin Bonebed, and Rattlesnake Canyon 2 Bonebed. Their fossil content is more diverse than the Geraldine Bonebed, but also less well-preserved. Unlike the catastrophic scenario implied for Geraldine, these other bonebeds are assumed to be a product of gradual processes of death and decay experienced in calm pond environments.
The Briar Creek, Rattlesnake Canyon, and Rattlesnake Canyon 2 localities are regarded as being deposited in the Upper Nocona Formation.
Paleobiota
Synapsids An egg-like object was discovered by Llewellyn Price in the vicinity of Rattlesnake Canyon, and subsequently described by Romer and Price in 1939. It had a shell-like texture which was not easily comparable to nodules from the Permian of Texas, and the authors considered it to have potentially been laid by a "pelycosaur". If this identification is correct, it is the oldest amniotic egg in the fossil record. Later investigations concluded that a distinct calcareous shell layer was not present, though the high concentration of phosphorus in the object suggests that it may still be an egg, albeit one with a softer outer membrane. Synapsids of the Nocona FormationGenusSpeciesLocalitiesStratigraphic levelNotesImagesDimetrodonD. booneorumBriar CreekUpperA medium-sized sphenacodontid of uncertain validity.D. limbatusBriar Creek, Coprolite, Loftin, Rattlesnake Canyon 2UpperA large sphenacodontid with a tall neural spine sail.D. natalisGeraldine, Briar Creek, Rattlesnake Canyon 2UpperA small sphenacodontid with a tall neural spine sail. Represented by three partial skeletons. Sometimes regarded as a juvenile of D. limbatus, but confirmed to be a unique species with small adults, according to histological analyses.EdaphosaurusE. boanergesGeraldine, Briar Creek, Coprolite, Loftin, Rattlesnake Canyon 2?UpperA medium-sized herbivorous edaphosaurid. One of the most common and characteristic fossils of the Geraldine bonebed, with multiple articulated skeletons displayed in museums around the world.LupeosaurusL. kayiBriar Creek, Coprolite?UpperA large edaphosaurid known from rare fragments.OphiacodonO. retroversusRattlesnake CanyonUpperAn ophiacodontid.O. uniformis?(vicinity of) Geraldine, Briar CreekUpperAn ophiacodontid. Histology indicates it might be the juvenile of a larger species.SecodontosaurusS. obtusidensBriar Creek Rattlesnake CanyonUpperA medium-sized sphenacodontid.
Reptiles Reptiles of the Nocona FormationGenusSpeciesLocalitiesStratigraphic levelNotesImagesAraeoscelisA. caseiGodwin CreekAn araeoscelidian initially named as a new genus, Ophiodeirus.BolosaurusB. striatusGeraldine, Briar Creek, Godwin CreekUpperA bolosaurid parareptile.Captorhinidae indet.LoftinRare captorhinid vertebrae.ProtocaptorhinusP. priceiRattlesnake CanyonUpper A captorhinid reptile.
Amphibians Amphibians of the Nocona FormationGenusSpeciesLocalitiesStratigraphic levelNotesImagesArcheriaA. crassidiscaGeraldine, Briar Creek, Coprolite, Loftin, Rattlesnake Canyon 2UpperA large archeriid embolomere. Multiple articulated skeletons have been found in the Geraldine bonebed, representing the most complete and well-described fossils of this species.CardiocephalusC. sp.GeraldineRare microsaur teeth.DiadectesD. sideropelicusGeraldine, Briar Creek, Coprolite, Loftin, Rattlesnake Canyon 2UpperA large diadectid diadectomorph.DiplocaulusD. sp.Loftin, Briar CreekUpperA diplocaulid nectridean.EryopsE. megacephalusGeraldine, Briar Creek, Coprolite, Loftin, Rattlesnake Canyon 2UpperAn eryopid, a type of large semiaquatic temnospondyl. Articulated skeletons and other remains are common in the Geraldine bonebed.RubeostratiliaR. texensis"east of Henrietta"An amphibamiform, a type of small terrestrial temnospondyl.ScapanopsS. neglectaHalsell HillA eucacopine dissorophid, a type of small terrestrial temnospondyl. Previously consider a specimen of Conjunctio.TrimerorhachisT. insignis(vicinity of) Geraldine, Godwin Creek, Rattlesnake Canyon, Loftin, Rattlesnake Canyon 2UpperA trimerorhachid dvinosaur, a type of small aquatic temnospondyl.ZatrachysZ. serratus(vicinity of) Geraldine, Rattlesnake Canyon 2, Briar Creek UpperA zatracheid temnospondyl, a type of medium-sized terrestrial temnospondyl.SeymouriaS. baylorensisUpperA reptiliomorph.
Fish Indeterminate palaeoniscoids are known from the Geraldine, Coprolite, Loftin, and Rattlesnake Canyon 2 bonebeds. Iniopterygian tooth whorls have been reported from the Rattlesnake Canyon area. Fish of the Nocona FormationGenusSpeciesLocalitiesStratigraphic levelNotesImagesAcanthodesA. sp.GeraldineAcanthodian fin spines and scalesBarbclaborniaB. luedersensisRattlesnake CanyonUpperRare xenacanth shark teethEctosteorhachisE. nitidusGeraldine, Coprolite, LoftinA megalichthyid tetrapodomorphHelodusH. sp.GeraldineRare holocephalan teethHybodusH. sp.CoproliteA hybodont sharkJanassa?J.? sp.GeraldineA single petalodont toothOrthacanthusO. platypternusGeraldineXenacanth shark teethO. texensisGeraldine, Briar Creek, Coprolite, Loftin, Rattlesnake Canyon 2UpperVery common xenacanth shark teeth and coprolitesPlatysomus?P.? sp.GeraldineA single palaeoniscoid toothProgyrolepisP. tricessimalarisRattlesnake CanyonA palaeoniscid known from a partial skeleton.SagenodusS. periprion(vicinity of) Geraldine, Coprolite, Rattlesnake Canyon 2UpperLungfish teethSpermatodusS. pustulosusRattlesnake Canyon 2A coelacanthXenacanthusX. sp.GeraldineXenacanth shark spine fragments
Plants Plant fossils are known from several bonebeds of the Nocona Formation, though they are subordinate to vertebrate fossils at most sites. Insect damage has been recorded on leaves from the Coprolite Bonebed. It is uncommon (only a third as frequent as in modern plants), even when compared to only slightly younger sites such as the Taint locality in the Waggoner Ranch Formation. Despite the rarity of insect damage, the Coprolite Bonebed shows the oldest occurrence of skeletonization (removal of all but the veins), as well as galls, which are rarely found in Permian plant fossils. Plants of the Nocona FormationGenusSpeciesLocalitiesNotesImagesAnnulariaA. cf. stellataGeraldine, CoproliteFoliage of a large calamitacean sphenophyte (horsetail) which formed thickets in shallow water and shorelines.AutuniaA. cf. confertaGeraldine, CoproliteFoliage of a peltasperm "seed fern", previously considered a species of Callipteris. Abundant in the Geraldine and Coprolite bonebeds.CalamitesC. undulatusGeraldine, CoproliteCommon stem impressions of a large calamitacean sphenophyte (horsetail) which formed thickets in shallow water and shorelines.CallipteridiumC. cf. pteridiumGeraldineFoliage of a medullosalean "seed fern".C. virginianumGeraldineFoliage of a medullosalean "seed fern".CordaitesC. principalisGeraldine, CoproliteFoliage of a cordaitalean gymnosperm, a small tree found in both swamps and uplands. Common in the Geraldine and Coprolite bonebeds.DadoxylonD. sp.Geraldine, Rattlesnake Canyon 2Conifer wood and charcoal.OdontopterisO. genuinaGeraldineFoliage of a medullosalean "seed fern".O. cf. lingulataCoproliteFoliage of a medullosalean "seed fern".O. cf. osmundaeformisGeraldineFoliage of a medullosalean "seed fern".PecopterisP. arborescensGeraldineFoliage of a marattialean tree fern, among the most common trees in Permian swamp environments.P. candolleanaGeraldineP. hemitelioidesGeraldine, CoproliteP. unitaGeraldinePsaroniusP. sp.Geraldine, LoftinStems and roots of a marattialean tree fern, likely the same plant which produced Pecopteris leaves.RussellitesR. taeniataGeraldine, CoproliteFoliage of a cycadophyte, previously referred to Tingia. Common in the Coprolite Bonebed.SamaropsisS. spp.GeraldineTwo species of gymnosperm seeds, possibly from the same plants as Walchia and Cordaites.SigillariaS. brardiiGeraldineBark and stems of a lycophyte.SphenophyllumS. oblongifoliumGeraldineFoliage of a fern.SphenopterisS. cf. macilentaGeraldineFoliage of a fern or "seed fern".WalchiaW. piniformisGeraldine, CoproliteFoliage of an early conifer, a small tree accustomed to dry uplands. Associated stems and charcoal show similarity to the form genus Schizodendron. Very common in the Geraldine and Coprolite bonebeds.
See also
List of fossiliferous stratigraphic units in Texas Paleontology in Texas
References