Rugosodon

Rugosodon Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Fossil and interpretive drawing
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	†Multituberculata
Genus:	†Rugosodon Yuan et al., 2013
Species:	†R. eurasiaticus
Binomial name
†Rugosodon eurasiaticus Yuan et al., 2013

Rugosodon is an extinct

In 2009, a local fossil hunter unearthed an unusual fossil in the Tiaojishan Formation of China's Liaoning province, dating to 160 million years ago. He turned the fossil over to the Chinese Academy of Geological Sciences, where it was eventually identified as a nearly complete skeleton and given the name Rugosodon eurasiaticus.^[5] The fossil was discovered on what was the shore of an ancient lake.^[6] It was preserved in two shale slabs and measures about 17 cm (6.5 inches) long from head to rump. The site of the discovery consists of lake sediments with embedded volcanic layers, which also contained fossils of feathered dinosaur Anchiornis and the pterosaur Darwinopterus.^[4][3] The dental features of Rugosodon most resemble those of multituberculates of the Late Jurassic of Western Europe, suggesting that Europe and Asia had extensive mammal faunal interchanges (hence the specific name, eurasia) during the Jurassic.^[4][3][7]

Prior to the discovery of Rugosodon, scientists knew that multituberculates living 66 million years ago had highly flexible ankles.^[6] However, older species were mostly known from small fragments, and it was not proven that the trait was ancestral. Additionally, it was unknown what sort of diet was primitive in the lineage.^[5] The presence of the characteristic flexible ankles in Rugosodon demonstrates that the trait is ancestral and provides a strong clue that the trait was a major factor in the lineage's evolutionary success.^[6] The animal's diet provides a bridge between very early mammals, which were mostly insectivores, and later multituberculates, which were mostly herbivores.^[5]

In the initial description, Rugosodon was attributed to Paulchoffatiidae, a group of multituberculates otherwise known from Western Europe. However, later studies suggested that it lacked key morphological features of the family, and was instead placed as a member of the more inclusive Paulchoffatiid-line outside of any defined family,^[8] or possibly even more basally than that.^[9]

References