London, June 1 (Reuters): The discovery of a short-necked dinosaur from the Late Jurassic period has turned on its head the accepted theory that the long-necks ruled the roost, scientists said today.

The skeleton of the pocket-sized dinosaur ? which was less than 10 metres long ? discovered in Patagonia goes against the grain of increased body size and neck length that typified sauropod dinosaurs.

“The long neck is a particular hallmark of sauropod dinosaurs and is usually regarded as a key feeding adaptation,” scientists from the Bavarian State Collection for Palaeontology and Geology in Munich wrote in the journal Nature.

They said the discovery of the short-necked specimen from a group of dinosaurs known as dicraeosaurids demonstrated a clear counter trend and “indicates that the ecology of dicraeosaurids might have differed considerably from that of other sauropods”.

And in case of any confusion, the scientists led by Oliver Rauhut stress that the specimen is that of an adult not an infant or adolescent.

The researchers said they believed the short-necked dinosaurs of southern Latin America ? whose closest known relatives are to be found in Africa ? may have evolved to deal with specific feeding requirements. “The tendency towards neck shortening in dicraeosaurids indicated that these...were progressively adapting for low browsing and might have been specialised on specific food sources.”

They said it seemed the pocket dinosaur was adapted to feeding on plants one to two metres in height in contrast to their long-necked cousins which could feed off a far wider variety of vegetation.