Enigmacursor mollyborthwickae

Enigmacursor mollyborthwickae is a small, bipedal neornithischian from the Morrison Formation. Historic names for similar Morrison dinosaurs are based on incomplete or poorly diagnostic fossils, creating more than a century of taxonomic confusion. The three-dimensionally preserved Enigmacursor holotype supplies a modern anatomical reference built from much more of the body, although most of the skull is still absent. Phylogenetic analysis places it outside Cerapoda and identifies the Chinese Yandusaurus as its closest sampled relative.

Its fossils occur between approximately 152 and 145 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

NHMUK PV R 39000 includes three teeth, 21 vertebrae from the neck through tail, ribs and chevrons, both shoulder blades, much of both forelimbs, parts of the pelvis and both hind limbs and feet. The femur is 169 millimetres long and the tibia 209 millimetres, producing the long lower-leg proportions behind its runner name. Diagnostic details include the alignment of articular facets on the front dorsal vertebrae and a hooked inner condyle on the upper tibia. The skull is otherwise unknown.

• Long tibiae and elongated feet associated with agile bipedal movement
• Three-dimensionally preserved partial skeleton
• Four functional toes retained on each foot
• Distinctive offset articular facets on the front dorsal vertebrae
• Hook-like inner condyle at the upper end of the tibia

Dinosaurs of America LLC excavated the specimen in 2021–2022 at Skull Creek Estates in Moffat County, Colorado. It entered the Natural History Museum, London collection in 2024 after Molly and David Lowell Borthwick funded its acquisition. Susannah Maidment and Paul Barrett named it in June 2025. Enigma refers to the confused taxonomy of small Morrison ornithischians, cursor is Latin for runner, and mollyborthwickae honours Molly Borthwick.

Discovery credit: Dinosaurs of America LLC field team.

Naming authors: Susannah C. R. Maidment, Paul M. Barrett.

Northern Colorado's Morrison Formation preserves river channels and seasonally wet floodplains with ferns, cycads, conifers and other low vegetation. Enigmacursor lived alongside much larger dinosaurs including Allosaurus, Stegosaurus and Diplodocus, but occupied a small-bodied terrestrial herbivore niche that is comparatively poorly sampled.

Long lower legs and feet support an agile running interpretation, probably useful when escaping predators. Small denticulate teeth are consistent with herbivory, but the missing skull prevents a detailed reconstruction of bite mechanics or food selectivity. Sociality, burrowing, nesting and parental care are unknown.

• Its name literally highlights both a taxonomic puzzle and its runner-like legs.
• It lived in the same formation as Allosaurus, Stegosaurus and Diplodocus.
• The only known specimen is now permanently displayed in London.
• Its closest sampled relative in the describing analysis lived in Late Jurassic China.

A research repository is not necessarily a public exhibit. Loan and display status can change, so check with the institution before visiting.

1. 01
   Enigmacursor mollyborthwickae, a neornithischian dinosaur from the Upper Jurassic Morrison Formation of the western USA

   Susannah C. R. Maidment, Paul M. Barrett · Royal Society Open Science 12(6) · 2025

   Open source
2. 02
   Enigmacursor: Dino Directory

   Natural History Museum, London · 2025

   Open source