An unexpected survivor of the end-Cretaceous mass extinction

Deltatheroida was a clade of metatherians, a group of mammals that exists today in the form of one of their most intriguing evolutionary lineages – the marsupials. Studies suggest that deltatheroidans represented one of the earliest-branching metatherian groups, originating relatively shortly after metatherians (marsupials and their relatives) and eutherians (placentals and kin) separated from their last common ancestor.

Some anatomical features of deltatheroidans, such as the morphology of their teeth, resembled those of placentals. This even led the first researchers studying these early mammals to consider them as belonging to Placentalia.

To date, deltatheroidans were known exclusively from the Cretaceous strata. However, a new study by a team of researchers led by Xijun Ni from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences shows that these small early mammals were more successful than previously thought.

The new paper by Ni and colleagues descibes a tiny new deltatheroidan from the Xinjiang Province in China (South Gobi) named Gurbanodelta kara. The discovery wouldn’t be surprising if the animal weren’t originating from Cenozoic strata.

Gurbanodelta kara lived during the Paleocene. It was some 10 million years younger than its closest relatives, and represented the only known deltatheroidan survivor of the end-Cretaceous mass extinction.

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