The Shara Murun Formation is a geologic formation in Inner Mongolia, northern China. The deposits of the Shara Murun Formation date to the Middle Eocene, and preserve fossils of a diverse, perissodactyl-dominated mammal fauna. The fossil fauna of the Shara Murun Formation is the type fauna of the Sharamurunian, one of the Asian land mammal ages (ALMAs).

Research history

The deposits of the Shara Murun Formation are situated in the Erlian Basin, a structural basin located in central Inner Mongolia in northern China, close to the border between China and Mongolia. The first study on the Erlian Basin was published by the Russian geologist Vladimir Obruchev in 1892. The basin was later extensively studied by the Central Asiatic Expeditions of the American Museum of Natural History, over the course of five field seasons in the 1920s. The researchers of the Central Asiatic Expeditions were responsible for naming most of the formations in the basin, including the Shara Murun Formation. Later studies and field expeditions in the Erlian Basin were conducted by the Sino-Soviet Paleontological Expedition in 1959–1960, the Regional Geological Survey of the Nei Mongol Autonomous Region in the 1960s and 1970s, and the Institute of Vertebrate Paleontology and Paleoanthropology, American Museum of Natural History, and Carnegie Museum of Natural History since the 1980s.

The Erlian Basin preserves near-continuous sedimentary layers from the late Paleocene to the early Oligocene. The Shara Murun Formation preserves strata of Middle Eocene age. It overlies the Tukhum Formation and underlies the Ulan Gochu Formation.

Because the Eocene sediments in the Erlian Basin are near-continuous, there has been much debate historically over where certain stratigraphic units end and others begin. The Asian land mammal ages (ALMA) of the Eocene are mainly based on the different fossil faunas found in the Erlian Basin; the fauna of the Shara Murun Formation is the type fauna of the Sharamurunian ALMA. Debate on the stratigraphy have complicated reconstructions of the Asian Eocene, since definitions and interpretations of the stratigraphic units impact the definitions of the land mammal ages. In some cases, different researchers have used entirely different frameworks and stratigraphic unit names. Much work has been done in the 21st century to establish a functional framework, though some stratigraphic issues still remain.

Depositional environment The Erlian Basin experienced a subtropical and humid climate during the Eocene. The vegetation was highly diverse and dominated by deciduous trees and shrubs.

Fossil fauna

Mammals

Artiodactyla +Genus/familySpeciesLocalityNotes/affinitiesImagesArchaeomeryxA. optatusUla UsuA ruminant.BrachyhyopsB. neimonngoliensisTwin OboesAn entelodont.LophiomeryxL. angaraeTwin OboesA ruminant.TapiruloidesT. usuensisUla UsuA tapirulid.UlausuodonU. parvusAn anthracothere.

Hyaenodontia Genus/familySpeciesLocalityNotes/affinitiesImagesPropterodonP. cf. morrisi"Pterodon""P". hyaenoidesSpring Camp

Lagomorpha Genus/familySpeciesLocalityNotes/affinitiesImagesDesmatolagusD. vetustusTwin OboesD. sp.GobiolagusG. andrewsiTwin OboesG. tolmachovi

Mesonychia Genus/familySpeciesLocalityNotes/affinitiesImagesMongolestesM. hadrodensTwin OboesA mesonychid.

Perissodactyla +Genus/familySpeciesLocalityNotes/affinitiesImagesAmynodontidaeAmynodontidae indet.Spring CampIndeterminate amynodont fossils.CadurcodonC. ardynensisEast of Spring CampAn amynodont.CaenolophusC. obliquusUla UsuAn amynodont.C. promissusUla UsuDeperetellaD. cristataUla UsuA deperetellid.D. cf. cristataTwin OboesAbout 25% larger than the D. cristata fossils from Ula Usu.EomoropusE. majorTwin OboesAn eomoropid.GigantamynodonG. promisusUla UsuAn amynodont. Regarded as a nomen dubium.JuxiaJ. sharamurenensisUla UsuTwin OboesEast of Spring CampA paracerathere.LushiamynodonL. sharamurenensisUla UsuAn amynodont. Lushiamynodon may be a synonym of Sharamynodon. L. sharamurenensis is based on fragmentary fossils.MetamynodontiniMetamynodontini indet.Twin OboesAmynodonts. Some fossils have historically been referred to the genus Metamynodon, otherwise treated as a solely North American genus.PachytitanP. ajaxNorth of Baron Sog LamaseryA brontothere.PappacerasP. minutaEast of Spring CampA rhinocerotoid.ParabrontopsP. cf. gobiensisSpring CampA brontothere.RhinotitanR. andrewsiUla UsuA brontothere.R. kaiseniUla UsuRhodopagus?R.? minimusUla UsuA rhinocerotoid (hyracodont?). R. minimus was originally described as a species of Caenolophus.SharamynodonS. mongoliensisUla UsuSpring CampNorth of Baron Sog LamaseryAn amynodont."Sianodon"S. ulausensisUla UsuAn amynodont. The genus Sianodon is a synonym of Cadurcodon, but S. ulausensis likely belongs to a new genus.TitanodectesT. minorSpring CampA brontothere. The species T. ingens was previously also considered to be from the Shara Murun; following reassessments, only T. minor is represented in the Shara Murun.TriplopusT.? progressusUla UsuA rhinocerotoid. T. progressus was originally described as a species of Caenolophus.T. turgaiensisTwin Oboes

Olseniidae Genus/familySpeciesLocalityNotes/affinitiesImagesOlseniaO. miraEnigmatic ungulate-like mammal; previously treated as a mesonychid.

Pholidota Genus/familySpeciesLocalityNotes/affinitiesImagesCryptomanis?C. gobiensisTwin OboesAlternatively classified as a creodont. It is unclear if these fossils are from the Shara Murun or Ulan Gochu formation.

Rodentia Genus/familySpeciesLocalityNotes/affinitiesImagesYoumysY. cavioides

Reptiles Genus/familySpeciesLocalityNotes/affinitiesImagesArretosaurusA. ornatusTwin OboesAn arretosaurid lizard.

References