Mussaurus

Mussaurus was a primitive sauropodomorph dinosaur that lived in Patagonia, Argentina, during the Early Jurassic period. When first named in 1979, it was described from tiny fossil hatchlings that were only twenty centimetres long, inspiring its name meaning mouse lizard. Decades later, discoveries of subadult and adult specimens revealed that fully grown individuals reached up to six metres in length and weighed roughly a tonne. Biomechanical studies on this growth series showed that Mussaurus underwent a dramatic postural shift: babies walked on all fours, while adults became predominantly bipedal as their center of mass moved backward. Communal nesting sites complete with fossilised eggs have also provided remarkable evidence of social organisation and colonial nesting behavior in early herbivorous dinosaurs.

It transitioned from quadrupedal hatchlings to bipedal adults during its life cycle.

Where and when

Mussaurus lived in the Early Jurassic, from 199 to 193 million years ago (Sinemurian age). Its remains come from Argentina, in the Laguna Colorada Formation.

The numbers

Length 4.5 m (estimates run from 3 to 6 m). Mass about 710 kg. Hip height about 1.5 m. That is 2.6 human-lengths, or 0.4 of a double-decker bus. These are estimates from near-complete skeleton; fields marked estimated by the site are length, mass, hip height.

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