Exciting discovery of a new genus and species of neornithischian dinosaur named Enigmacursor Mollyborthwickae. This dinosaur is recognized from its three-dimensionally preserved postcranial skeleton unearthed in the Morrison Formation in Colorado, USA.

Enigmacursor Mollyborthwickae inhabited our planet during the late Jurassic period, approximately 150-145 million years ago.

This dinosaur was a bipedal herbivore standing about 0.5 m (1.6 feet) tall and measuring over 1 m (3.3 feet) in length.

It would have navigated the floodplains of the western United States alongside giants like diplodocus and Stegosaurus.

“There are indications that these dinosaurs are not fully mature. The upper vertebrae (neuronal arch) are formed separately and fused at the lower section, suggesting incomplete fusion,” noted Paul Barrett, a paleontologist at the Museum of Natural History in London, alongside Susannah Maidment.

The partial but well-preserved skeletons, along with several associated teeth, were excavated in 2021 and 2022 from a commercial quarry in Moffat County, Colorado, within the Morrison Formation.

Initially, this specimen was classified as Nanosaurus, a lesser-known herbivorous dinosaur first named in the 1870s.

However, upon thorough examination, paleontologists determined that the original Nanosaurus specimen was too poorly preserved to serve as a reliable reference for identification.

As a result, they set aside the name until higher quality fossils of Nanosaurus could ensure taxonomic stability.

The differences between the original and newly found specimens confirmed the classification as a new genus and species.

“The discovery of Enigmacursor Mollyborthwickae enhances our understanding of the diversity of ornithischian dinosaurs from the Morrison Formation and provides new insights into their anatomy,” researchers explained.

“Moreover, it highlights a previously unrecognized diversity among the small Morrisonian dinosaurs, suggesting they represent a more diverse component of these late Jurassic ecosystems than previously acknowledged.”

A paper detailing Enigmacursor Mollyborthwickae was published this week in the journal Royal Society Open Science.

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Susanna CR Maid & Paul M. Barrett. 2025. Enigmacursor Mollyborthwickae, a neornithischian dinosaur from the Jurassic Morrison Formation in the western United States. R. Soc. Open Sci. 12(6): 242195; doi: 10.1098/rsos.242195