Taphonomy of a monodominant Gryposaurus sp. bonebed from the Oldman Formation (Campanian) of Alberta, Canada

A monodominant Gryposaurus sp. bonebed in the lower unit of the Campanian Oldman Formation of southern Alberta is the oldest hadrosauroid bonebed documented in the province and the first described from the formation. The sedimentology of the locality and the taphonomy of the hadrosaurid material indicates that the bonebed represents an assemblage of juvenile-sized individuals that were probably transported only a short distance from where they died to where they were finally deposited and preserved in a fine-grained mudstone within an overbank sequence. Histological examination of six limb elements confirms that all individuals are juveniles, with two age classes (<1 and <2 years of age at the time of death) that likely died in the same event. Bone microstructure data indicate that Gryposaurus experienced rapid growth over the 2-year life spans documented, equivalent to other Late Cretaceous hadrosaurids in North America. The parautochthonous nature of the bonebed, and the lack of small neonate (newborn) material and almost complete lack of large adult material, suggests that the bonebed represents a segregated group of juveniles. This group of immature individuals may have been an autonomous unit that had separated itself from a larger social grouping, possibly in an effort to increase their survivability.

Automated summary

This study reports the oldest hadrosauroid bonebed in southern Alberta, Canada, and the first one described from the Campanian Oldman Formation. The bonebed consists of juvenile-sized individuals that were transported a short distance after death and preserved in fine-grained mudstone. Histological examination confirms that all individuals are juveniles from two age classes (<1 and <2 years old at death). Bone microstructure data indicate rapid growth similar to other Late Cretaceous hadrosaurids.