Hsanda Gol Formation Explained

Hsanda Gol Formation
Type:Geological formation
Age:Hsandagolian
~
Period:Rupelian
Region:Asia
Extent:Tsagan Nor Basin

The Hsanda Gol Formation is a geological formation located in the Tsagan Nor Basin of central Mongolia that dates to the Rupelian age of the Oligocene epoch. It formed in continental desert-like conditions and is notable for its fossil mammals, first excavated by Roy Chapman Andrews and the American Museum of Natural History in the 1920s. Hsanda Gol is included in the Hsandagolian Asian Land Mammal Age, to which it gives its name.[1]

Geology

The 2600 feet thick Hsanda Gol formation is covered in various places by Miocene-age variegated clays, sands, and gravels. It rests on top of the Early Cretaceous Hühteeg Svita formation. The lower portions of the formation are composed of yellow conglomerate, with the higher areas being dominated by red clays, silts and sands, as well as lava and basalt flows.

Hsanda Gol was traditionally assigned to the Middle Oligocene,[2] [3] but after the reassignation of the preceding Ergilian age to the Late Eocene it has now been rendered early Oligocene. It is followed after a faunal hiatus by the overlaying Loh Formation which extends from the Late Oligocene into the Miocene and also contains fossil mammals. Paleomagnetism in underlying and overlaying lava flows establish the beginning of the formation at the end of the magnetic Chron C13n 33.4 million years ago, and its end at the Chron C12n, 31 million years ago.[1]

The Hsanda Gol levels rest directly over, and are continuous with the earlier Houldjin Gravels which are sometimes counted as part of the formation, but were rather deposited during the latest Eocene under wetter and more energetic conditions. In general, the Houldjin Gravels and the Hsanda Gol formation show a transition from more humid, forested conditions to an arid climate with presence of dunes and ephemeral rivers. Some taxa lived through this change including hyaenodonts and indricotheres, but others, such as brontotheres, amynodonts, rhinocerotids and entelodonts went extinct and are as a result absent from Hsanda Gol proper. The following Loh Formation, on the other hand, represents a return to more benign conditions as indicated by the reappearance of rhinocerotids and the entry of the first chalicotheres.[1]

Paleobiota

Hsanda Gol's paleobiota resembles current desert mammal faunas, including the one found in the same area today. It is composed largely of rodents and lagomorphs with high-crowned teeth adapted to chew hard vegetation; several of these species are fossorial and none arboreal, indicating that there were no areas with high tree density. The only large browsing ungulate, Paraceratherium, was probably transient and there were no medium-large herbivores. Predators were diverse but generally small, with the largest (Hyaenodon) being wolf-sized, and were adapted to hunt by ambush. Landscape would appear as a sparse plain with few tall trees near rivers or where groundwater could be found otherwise. Pallinology studies in contemporary sites of China and Mongolia are consistent with an arid-adapted woody scrubland dominated by Mormon tea and salt-tolerant nitre bush. The few trees were broad-leaved and deciduous, related to modern elm, birch, and oak.[3] [1]

Mammals

Didymoconids

Didymoconids of the Hsanda Gol Formation
GenusSpeciesLocationStratigraphic PositionAbundanceNotes
DidymoconusD. berkeyiWest Tatal Gol
Loh
Tatal Gol
Field 538
D. berkeyi is the only species present west of Tatal Gol, and D. colgatei is the only present at Field 538. They appear together in the others. Though not believed to have modern descendants or ecological equivalents, they present an enlargement of the mastoid region convergent with kangaroo rats and sengis found in semi-arid areas.
D. colgatei

Erinaceids

Erinaceids of the Hsanda Gol Formation
GenusSpeciesLocationStratigraphic PositionAbundanceNotes
AmphechinusA. rectusLohEcologically similar to the modern long-eared hedgehog.
ExallerixE. hsandagolensisTatal Gol(?)Without modern ecological equivalent.
PalaeoscaptorP. acridensNortheast Kholobolchi Nor
Loh
Field 538
Also similar to the long-eared hedgehog.
TupaiodonT. morrisi
?T. minutus
Loh (both)Similar to the bicolored shrew.

Rodents

Rodents of the Hsanda Gol Formation
GenusSpeciesLocationStratigraphic PositionAbundanceNotes
CricetopsC. dormitor dormitor
C. d. elephantus
SW Loh
East Loh
NE Kholobolchi Nor
Loh
Tatal Gol
Field 538
Most common mammal, accounting for around one third of all jaws and teeth in the formation.A cricetid similar to a gerbil or vole. Both subspecies appear together except northeast from Kholobolchi Nor, where only C. d. dormitor is present.
CyclomylusC. lohensisLoh
Tatal Gol
Field 538
A fossorial cylindrodontid anatomically similar to a mole-rat, but ecologically closer to the Tarbagan marmot. Synonymous with Pseudotsaganomys.
EumysE. asiaticusEast Loh
Loh
Tatal Gol
Field 538
A cricetid ecologically similar to a wild house mouse.
KarakoromysK. decessusSW Loh
Loh
Tatal Gol
A gundi ecologically similar to Kozlov's pygmy jerboa.
?LeptotataromysIndeterminateLoh
Tatal Gol
A gundi possibly synonymous with Karakoromys.
?Plesispermophilus?P. lohiculusTatal GolA sciuromorph related to Paramys.
cf. ProsciurusIndeterminateTatal GolA relative of Plesispermophilus.
PseudocylindrodonIndeterminateTatal GolA cylindrodontid.
SelenomysS. mimicusSW Loh
East Loh
Loh
Tatal Gol
A fossorial relative of the mountain beaver. Possibly ecologically equivalent to the jerboas of the genus Allactaga.
TataromysT. deflexus
T. plicidens
T. sigmodon
West Tatal Gold
NE Kholobolchi Nor
Loh
Tatal Gol
Field 538
Gundis. T. sigmodon appears only at Loh, and T. deflexus only at and west of Tatal Gol.
TachyoryctoidesT. obrutschewi
T. pachygnathus
West Tatal Gol (both)Synonym of Aralomys. A fossorial relative of bamboo rats.
TsaganomysT. altaicusWest Tatal Gol
East Loh
NE Kholobolchi Nor
Loh
Tatal Gol
Field 538
Most abundant genus after Cricetops.A fossorial cylindrodontid similar to a mole-rat and possibly indicative of sandy areas.

Lagomorphs

Lagomorphs of the Hsanda Gol Formation
GenusSpeciesLocationStratigraphic PositionAbundanceNotes
DesmatolagusD. gobiensisSW Loh
East Loh
NE Kholobolchi Nor
Loh
Tatal Gol
Field 538
Pikas. "D." robustus may belong to a different genus.
SW Loh only contains D. gobiensis; NE Kholobolchi Nor only "D." robustus.
D. gobiensis may be ecologically similar to Pallas's pika and "D." robustus to the desert hare.
"D." robustus
?Gobiolagus?G. teilhardiTatal GolA leporid.
OchotonolagusO. argyropuloiTatal GolA pika similar to the Daurian pika.
ProcaprolagusP. maximusTatal Gol (all)Leporids.
P. mongolicus
P. orlovi
P. vetustus
P. youngi
SinolagomysS. tatalgolicusTatal GolA pika.

Carnivorans

Carnivorans of the Hsanda Gol Formation
GenusSpeciesLocationStratigraphic PositionAbundanceNotesImages
AmphicticepsA. shackelfordiSW Loh
Loh
An amphicynodontid.
AmphicynodonA. teilhardiLohA small primitive bear similar to a mustelid.
?Cynodictis?C. elegans
?C. constans
LohA small bear dog comparable to a red fox.
NimravusIndeterminateTatal GolA small nimravid or "false sabertooth". There are at least two different species represented, both unnamed: a smaller one similar to a wildcat and a larger one resembling a Eurasian lynx.
PalaeogaleP. ulyesses
P. parvula
East Loh
Loh
Tatal Gol
Field 538
Mustelids comparable to the marbled polecat and the least weasel.
PalaeoprionodonP. gracilisSW LohA feliform.
Cf. PlesictisIndeterminateTatal GolA larger mustelid comparable to a wolverine.
ProailurusIndeterminateTatal GolOne lower jaw fragment.An early felid better known from Europe and North America. Some authors have instead assigned this material to the nimravid Eofelis or the more advanced felid Pseudaelurus, based on dental features.[4]

Artiodactyls

Artiodactyls of the Hsanda Gol Formation
GenusSpeciesLocationStratigraphic PositionAbundanceNotesImage
EumeryxE. culminisSW Loh
East Loh
Loh
Tatal Gol
Field 538
A gelocid pecoran related to the chevrotain, but ecologically comparable to the goitered gazelle.
Cf. MiomeryxIndeterminateA gelocid.
PalaeohypsodontusP. asiaticusTatal GolA hypsodont bovid possibly indicative of the presence of grass.
PseudomeryxP. gobiensisTatal GolA gelocid.

Creodonts

Creodonts of the Hsanda Gol Formation
GenusSpeciesLocationStratigraphic PositionAbundanceNotesImages
HyaenodonH. ambiguusWest Tatal Gol
SW Loh
NE Kholobolchi Nor
Loh
Tatal Gol
Field 538
The largest carnivore in the formation, a predatory creodont similar to a grey wolf that lived in many different Holarctic environments. H. pervagus is the only species found outside of Tatal Gol.
H. aymardi
H. compressus
H. gigas
H. pervagus

References

[9] ^ Fossilworks: Gateway to the Paleobiology Database

Notes and References

  1. Book: Prothero . Donald R. . Rhinoceros Giants: The Paleobiology of Indricotheres . 2013 . Indiana University Press . 978-0-253-00819-0 . j.ctt16gz58f .
  2. Mellett . James Silvan . 1966 . Fossil mammals from the Oligocene Hsanda Gol formation, Mongolia. Part I: Insectivora, Rodentia and Deltatheridia, with notes on the paleobiology of Cricetops dormitor . 40155505 .
  3. Mellett . James S . The Oligocene Hsanda Gol Formation, Mongolia: a revised faunal list . American Museum Novitates . 28 March 1968 . 2318 . 2246/2528 .
  4. Rothwell . Tom . New Felid Material from the Ulaan Tologoi Locality, Loh Formation (Early Miocene) of Mongolia . Bulletin of the American Museum of Natural History . June 2004 . 285 . 157–165 . 10.1206/0003-0090(2004)285<0157:C>2.0.CO;2 . 85951519 . free .