A GRYPOSAURUS SP. BONEBED FROM THE OLDMAN FORMATION (CAMPANIAN) OF ALBERTA WITH IMPLICATIONS FOR JUVENILE SOCIAL STRUCTURES

Histological evidence derived from tibiae from a monodominant Gryposaurus sp. bonebed in the Oldman Formation (Campanian) indicates that the individuals represent two growth stages, early and late juveniles. Bone microstructure data indicates that the gryposaurs experienced rapid growth and achieved approximately 70% of adult size before the end of their second year. Evidence of hydraulic winnowing and limited transport of the elements is present, however, the condition and random orientation of the bones suggest that the bonebed represents a reliable picture of the living group. The parautochthonous nature of the bonebed, and the lack of small neotate and large adult material, suggests that the bonebed represents an isolated group of juveniles. This group of gryposaurs may have separated itself from a larger social grouping, possibly as an evolutionary strategy to allow greater allocation of resources to altricial hatchlings. The discrete zonation of bone tissues observed in the tibiae closely resembles that of previously described “polar” hadrosaurines from the North Slope of Alaska suggesting that the environmental controls proposed for dinosaurs living at high latitudes may not have been all that different than those acting on similar animals living in more temperate coastal environments.