Smallest dinosaur in North America uncovered

22 October 2009

A new species of dinosaur is the smallest ever found in North America scientists report in the Proceedings of the Royal Society of London B today.

The pigeon-sized Fruitadens haagarorum lived 150 million years ago in the Late Jurassic period. It was an agile fast runner, handy as it lived at the same time as other giant dinosaurs such as the long-necked Brachiosaurus and the meat-eating Allosaurus.

Tiny jaw fossil of the Fruitadens dinosaur showing 5 teeth

Tiny jaw fossil of the Fruitadens dinosaur showing 5 teeth © The Dinosaur Institute, Los Angeles Museum of Natural History

An international team led by Dr Richard Butler of the Bavarian State Collection for Palaeontology, Germany, and the Natural History Museum, London, made the discovery by re-examining fossils uncovered in the 1970s.

'This discovery demonstrates just how remarkably diverse and successful the dinosaurs were,' says Dr Butler. 'We have this diminutive dinosaur living alongside titans such as Brachiosaurus that probably weighed 40,000 times as much.'

Examining the fossils

The team studied fossils from 4 Fruitadens individuals that were uncovered from the Morrison Formation in Colorado and kept at the Natural History Museum, Los Angeles County. Tiny details inside the leg bones revealed Fruitadens grew to about 70cm in length and weighed less than 1kg.

Fruitadens had a combination of different shaped teeth including canine-like teeth at the front of the lower jaw and leaf-shaped teeth in the cheek area. This, combined with its small size, means Fruitadens was probably an omnivore, eating both plants and small animals.

Group of early dinosaurs

Fruitadens belonged to the heterodontosaurids, an important group of early dinosaurs previously unknown from North America, and is one of the latest surviving members of this group.

Heterodontosaurids, also had the unusual combination of canine-like and leaf-shaped teeth. Earlier members of this group were larger than Fruitadens and adapted to have a diet of tough vegetation. The more recent Fruitadens evolved to be smaller and have a more generalised varied diet.

More discoveries to come?

Fossil experts have been studying the Morrison Formation rocks where Fruitadens was uncovered for 130 years. 

Dozens of dinosaur species have been discovered there and there could be many more to come. 

Dr Butler says of the site, 'It is still possible to discover completely unique and remarkable species. If dinosaur ecosystems were that diverse, who knows what astonishing beasts are waiting for us to discover?'

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