AGE:
Early Cretaceous (Aptian-Albian), 100-125 million years ago

SIZE:
Up to 5 metres long

MEANING OF NAME:
'Before the Bactrian reptile'

PRONUNCIATION:
Pro-bak-tro-SAWR-us

CLASSIFICATION:
ORNITHOPODA Iguanodontia; Iguanodontidae

In the jaw of an iguanodontid, there is a row of functional teeth and beneath them, another row of unerupted teeth which gradually replace the functional teeth. This dentition was suitable for cropping soft vegetation.

Out of the iguanodontids arose the hadrosaurids or duckbilled dinosaurs. The duckbills had as many as five rows of teeth m the jaw, one beneath the other. Adjacent teeth fitted tightly together like a set of tiles rather than being separated to the degree found in our own teeth or those of iguanodontids. At any one time, one complete row of teeth would be functioning to chew the animal's food and worn, broken teeth were quickly replaced. This enabled hardrosaurids to eat much tougher vegetation than their iguanodontid ancestors.

Probactrosaurus gobiensis is intermediate in the structure of its dentition between the iguanodontids and hadrosaurids. Clearly it was a plant eater and spent some time on all four feet, but when it was moving fast probably travelled on its hind limbs (bipedially).

Probactrosaurus had a very stiff back as tendons with bony material in them criss-crossed between each vertebra-preventing much movement between them.