A late Paleocene probable metatherian (?deltatheroidan) survivor of the Cretaceous mass extinction

Abstract

Deltatheroidans are primitive metatherian mammals (relatives of marsupials), previously thought to have become extinct during the Cretaceous mass extinction. Here, we report a tiny new deltatheroidan mammal (Gurbanodelta kara gen. et sp. nov.) discovered at the South Gobi locality in China (Xinjiang Province) that is the first Cenozoic record of this clade and renders Deltatheroida a Lazarus taxon (with a new record 10 million years younger than their supposed extinction). The vertebrate fauna associated with Gurbanodelta is most similar to that from the slightly older late Paleocene Subeng locality in Inner Mongolia. The upper molars of Gurbanodelta exhibit a broad stylar shelf with one prominent cusp (stylocone), and a paracone that is sharp and significantly taller than the metacone. The lower molar tentatively assigned to Gurbanodelta has a very small talonid without an entoconid. This combination of these features is known only in deltatheroidans. Phylogenetic analysis places Gurbanodelta as the sister taxon of the North American latest Cretaceous Nanocuris. Gurbanodelta is the smallest-known deltatheroidan, and roughly the same size as the smallest living marsupial. It is likely that the Gurbanodelta lineage dispersed between Asia and North America as part of known intercontinental mammalian dispersals in the late Paleocene, or possibly earlier.

Skeleton of an unusual, cat-sized marsupial relative (Metatheria: Marsupialiformes) from the middle Eocene (Lutetian: 44-43 million years ago) of Turkey

“…Overall, our phylogenetic results are broadly similar to other recent analyses [ 37 , 75 , 80 , 103 , 148 , 174 , 175 ], although some relationships within Marsupialiformes remain to be confidently resolved. Notably, our analyses recovered relationships within Marsupialia that are congruent with recent molecular studies [ 5 , 176 – 178 ], in contrast to the phylogenetic analysis of Wilson et al [ 75 ], which failed to recover monophyly of Australidelphia.…”

Craniodental morphology and phylogeny of marsupials

“…Instead we included three well-preserved Paleocene fossil metatherians: †Pucadelphys andinus, †Mayulestes ferox and †Allqokirus australis. These three taxa consistently fall outside Marsupialia, and more distant from the crown-clade than either †Herpetotherium or †Mimoperadectes, in recent phylogenetic analyses (see Rougier et al, 1998;Luo et al, 2003;Asher et al, 2004;Rougier et al, 2004;Ladevèze and Muizon, 2007;Sánchez-Villagra et al, 2007;Beck et al, 2008a;Horovitz et al, 2008;Forasiepi, 2009;Horovitz et al, 2009;Ladevèze and Muizon, 2010;Luo et al, 2011;Beck, 2012;Williamson et al, 2012;Beck et al, 2014;Engelman and Croft, 2014;Forasiepi et al, 2014a;Williamson et al, 2014;Rougier et al, 2015;Suarez et al, 2015;Ni et al, 2016;Wilson et al, 2016;Beck, 2017a;Carneiro and Oliveira, 2017b;Carneiro and Oliveira, 2017a;Maga and Beck, 2017;Bi et al, 2018;Carneiro et al, 2018;Engelman et al, 2018;Muizon et al, 2018;Abello and Candela, 2019;Carneiro, 2019;Rangel et al, 2019;Ladevèze et al, 2020; the phylogenetic analysis of Goin et al [2006] is a notable exception). All three are represented by exceptionally complete cranial material (Muizon, 1994;Marshall and Muizon, 1995;…”

The earliest Asian bats (Mammalia: Chiroptera) address major gaps in bat evolution

“…The fossils described here were sorted from screen-washed residue collected from the early Eocene Red Rodent locality in the Gurbantunggut Desert, northeastern Junggar Basin, Xinjiang Province, China. This locality is approximately 20 km northwest of the South Gobi locality, where a diverse late Palaeocene vertebrate fauna occurs [27]. Palaeogene strata in the northeastern Junggar Basin belong to an unnamed lithological unit, consisting of reddish-brown mudstones interbedded with greyish-green fluvial sandstones.…”

“…This gypsum bed is approximately 10 m thick and can be traced laterally over tens of kilometres. The South Gobi fauna, which has been tentatively correlated with Gashatan faunas on the Mongolian Plateau and Clarkforkian faunas in North America [27], occurs below this gypsum bed. Fossils from the Red Rodent locality occur in a reddish-brown palaeosol containing abundant calcareous concretions approximately 2 m above the laterally persistent gypsum bed.…”