Coelurus

Coelurus was a small, lightly built coelurosaurian theropod that lived during the Late Jurassic period in North America. Its fossils have been unearthed from several sites in the famous Morrison Formation, particularly in Wyoming. Reaching a length of around two metres and weighing perhaps twenty kilograms, it had a long and slender frame with remarkably hollow, air-chambered vertebrae, a feature that inspired its name. This agile bipedal predator likely hunted small vertebrates including lizards, early mammals, and juvenile dinosaurs through prehistoric floodplains. For over a century after its naming by Othniel Charles Marsh, the classification of Coelurus was deeply confused, often being conflated with other contemporary small theropods such as Ornitholestes. Today it is recognised as a distinctive basal member of Coelurosauria, offering rare insight into the early diversity of the vast lineage that eventually gave rise to tyrannosaurs, dromaeosaurs, and modern birds.

Its vertebrae were filled with extensive internal air pockets to save weight.

Where and when

Coelurus lived in the Late Jurassic, from 155 to 148 million years ago (Kimmeridgian-Tithonian age). Its remains come from United States, in the Morrison Formation.

The numbers

Length 2.2 m (estimates run from 2 to 2.4 m). Mass about 19 kg. Hip height about 0.7 m. That is 1.3 human-lengths, or 0.2 of a double-decker bus. These are estimates from partial skeleton; fields marked estimated by the site are length, mass, hip height.

Compare Coelurus with a bus Place on the timeline