The Ermaying Formation is a geological formation of Anisian (Middle Triassic) age in north-central China. It is found across much of the Ordos Basin, at outcrops within the provinces of Shaanxi, Shanxi, and Inner Mongolia. It is composed of up to 600 m thick sequence of mudstone and sandstone, overlying the Heshanggou Formation and underlying the Tongchuan Formation. In the southern part of the Ordos Basin, the Zhifang Formation is equivalent to the Ermaying Formation.
The Ermaying Formation is divided into two members, each with a distinctive assemblage of tetrapod fossils. A 2013 study used SHRIMP U-Pb radiometric dating to assign an imprecise age of 245.9 ± 3.2 Ma for the upper member. A 2018 study assigned a more precise age of around 243.53 Ma based on three ash samples near the base of the upper member. This would indicate that the Upper Ermaying Formation is no older than the late Anisian stage.
A few studies apply the name "Ermaying Formation" to a sedimentary unit in the Yanshan belt, a fold-thrust belt northeast of Beijing. In the Yanshan belt, reported exposures of the formation are dated to the Late Triassic, lying below the Early Jurassic Xingshikou Formation. The Yanshan belt exposures are also known as the Huzhangzi Formation, an alternative name proposed to reflect their chronological and geographic divergence from exposures in the Ordos Basin.
Paleobiota The Ermaying Formation is notable for its diversity of well-preserved tetrapods.
The upper member occupies most of a biozone historically known as the Sinokannemeyeria fauna. This fossil assemblage has more recently been termed the Sinokannemeyeria-Shansisuchus Assemblage Zone, including approximately coeval sediments of the Kelamayi Formation in Xinjiang. The biozone also extends up to the early part of the Tongchuan Formation.
Tetrapod burrows are known from the formation, occupying both large and small size classes. The larger burrow is reniform (kidney-shaped) in cross section, about in height and in width. It shallowly slopes down when seen from the side and smoothly undulates when seen from above. Scatches and grooves are readily visible on the inside. The burrow-maker was medium-sized animal, likely a juvenile dicynodont. The smaller burrows are low tapered chambers with incomplete or collapsed entry ramps. They may have been dug out by procolophonids or juvenile cynodonts. Synapsids Apart from the taxa listed here, fossils of an unnamed genus of kannemeyeriiform dicynodont have been found in the Upper Ermaying Formation at the Sanjiao site in Shanxi Province. Not counting Shansiodon, this unnamed form is the third "kannemeyeriid" genus known from the Upper Member, as it is distinct from both Parakannemeyeria and Sinokannemeyeria. Cynodonts Cynodonts of the Ermaying FormationTaxaSpeciesMaterialMemberNotesImagesSinognathusS. gracilisA skullUpperA sinognathine trirachodontid cynodont. Dicynodonts Dicynodonts of the Ermaying FormationTaxaSpeciesMaterialMemberNotesImagesParakannemeyeriaP. dolicocephalaA skull and partial skeleton.UpperA "kannemeyeriid" dicynodont, the type species of Parakannemeyeria. P. ningwuensisSkulls and partial skeletons.UpperA "kannemeyeriid" dicynodont.P. shenmuensisA skullUpperA "kannemeyeriid" dicynodont.P. xingxianensisA skull and postcrania.LowerA "kannemeyeriid" dicynodont. Sometimes considered a junior synonym of P. ningwuensis.P. youngiMultiple partial skeletons.Lower?, UpperA "kannemeyeriid" dicynodont.ShaanbeikannemeyeriaS. buerdongiaA skull and postcrania.LowerA "kannemeyeriid" dicynodont. Sometimes considered a species of Kannemeyeria or Rechnisaurus, and more recently as a junior synonym of S. xilougouensis.S. xilougouensisMultiple partial skeletons.LowerA "kannemeyeriid" dicynodont, the type species of Shaanbeikannemeyeria. Sometimes considered a species of Kannemeyeria or Rechnisaurus, though its validity was strongly supported by a 2022 redescription.ShansiodonS. shaabeiensisA skullUpperA shansiodontid dicynodont. S. wangiA nearly complete skeleton with skull.UpperA shansiodontid dicynodont, the type species of Shansiodon.S. wuhsiangensisSkulls and postcrania.UpperA shansiodontid dicynodont.S. wupuensisA skullUpperA shansiodontid dicynodont.SinokannemeyeriaS. pearsoniMultiple partial skeletons.UpperA "kannemeyeriid" dicynodont, the type species of Sinokannemeyeria. S. sanchuanheensisA skullUpperA "kannemeyeriid" dicynodont, sometimes considered a species of Kannemeyeria.S. yingchiaoensisSkulls and partial skeletons.UpperA "kannemeyeriid" dicynodont.
Therocephalians Therocephalians of the Ermaying FormationTaxaSpeciesMaterialMemberNotesImagesNothogomphodonN. sanjiaoensisA partial jaw.UpperA baurioid therocephalian.OrdosiaO. youngiA partial skull and postcrania.LowerA baurioid therocephalian, sometimes considered a species of Ordosiodon.OrdosiodonO. lincheyuensisA partial jaw.LowerA baurioid therocephalian, initially misidentified as a diademodontid cynodont.TraversodontoidesT. wangwuensisA skull and postcrania.UpperA traversodontid cynodont or baurioid therocephalian.YikezhaogiaY. megafenestralaA skull and postcrania.LowerA therocephalian of uncertain affinities, potentially a "scaloposaur".
Reptiles Reptiles of the Ermaying FormationGenus / TaxonSpeciesMaterialMemberNotesImages"Chasmatosuchus""C. ultimus"A partial skull preserving the snout, jaw, and palate.UpperA dubious (crown)-archosaur previously misidentified as the proterosuchid Chasmatosuchus.EumetabolodonE. bathycephalusAn incomplete skull.LowerA procolophonid which is much more common in the Heshanggou Formation.FenhosuchusF. cristatusFragmentary skeletons.UpperA dubious archosauriform, possibly a chimera of fossils from Shansisuchus and paracrocodylomorph archosaurs.GuchengosuchusG. shiguaiensisA partial skeleton consisting of an incomplete skull, vertebrae, ribs, and (now missing) forelimb material.LowerA basal erythrosuchid archosauriform.HalazhaisuchusH. qiaoensisA partial skeleton consisting of forelimb and shoulder material, vertebrae, ribs, and osteoderms.LowerA euparkeriid archosauriform.NeoprocolophonN. asiaticusA skull.UpperA procolophonid.PaoteodonP. huanghoensisA maxilla fragment.LowerA dubious procolophonid.ShansisuchusS. heiyuekouensisFragmentary skeletons.UpperAn erythrosuchid archosauriform of uncertain validity. S. kuyeheensisA partial skeleton consisting of an incomplete skull, vertebrae, humerus, and shoulder materialUpperAn erythrosuchid archosauriform of uncertain validity.S. shansisuchusMultiple partial skeletons.UpperA large erythrosuchid archosauriform, the type species of Shansisuchus.TaihangosuchusT. wuxiangensisTwo partial skeletons, one including a skullUpperA gracilisuchid pseudosuchian"Turfanosuchus""T. shageduensis"A partial skeleton consisting of limb and shoulder material, vertebrae, and a mandible.LowerA dubious archosauriform, presumably a euparkeriid unrelated to Turfanosuchus dabanensis."Wangisuchus""W. tzeyii"Maxillae.UpperA dubious archosauriform.
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