A new fossil find from the Tiaojishan Formation of China represents the most well-preserved skeleton belonging to the ancient group known as multituberculates found to this date.
Scientists from the Institute of Geology at the Chinese Academy of Geological Sciences reported on the 160-million-year-old species August 16 in the journal Science.
Paleontologist Chong-Xi Yuan led the study that analyzed the new fossil skeleton for clues into the evolution of the multituberculates. The most profuse and diverse group of mammals during the Mesozoic, the multituberculates were small rodent-like mammals that lived from the middle Jurassic to the Paleogene. Members of this group had both omnivorous and herbivorous diets – though scientists have never been sure which came first or how exactly these creatures were able to sustain varying forms of nutrition.
Rugoson eurasaiticus, the new rat-like, terrestrial multituberculate, dispels some of this mystery. Its dentition – which sports unusual ridges and grooves – tells scientists it was an omnivore. Blade-like teeth were used for tearing into worms and other small arthropods; teeth of a different shape and size could chew on greenery. Later multituberculates were exclusively herbivorous – their diets evolved from omnivores such as Rugosodon in the Jurassic, to vegetarians in the Paleogene.
Rugosodon represents the only complete skeleton belonging to the oldest family of multituberculates: Paulchoffatiidae. Previous members of this group have been found in areas confined to Europe – but Rugosodon‘s Asian home means the Paulchoffatiidae were more spread out than previously thought.
The fossil shows the intricate morphological adaptations members of Paulchoffatiidae acquired in order to live in a variety of habitats and attain a variety of feeding habits. Scientists hope that analyzing common characteristics among all multituberculates and comparing them to Rugosodon will inform us of the features of the oldest common ancestor of all multituberculates.
Rugosodon‘s teeth weren’t its only curious feature – its ankle joint displayed a high degree of flexibility, an ability that would have been useful for crawling quickly across uneven land surfaces. This characteristic showed up much later in multituberculate ancestry- indicating that the mobile ankle evolved early in multituberculate evolution.
The research on Rugoson eurasaiticus was published August 16, 2013 in the journal Science.
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