A GRYPOSAURUS BONE BED FROM THE OLDMAN FORMATION (CAMPANIAN) OF SOUTH-EASTERN ALBERTA WITH IMPLICATIONS FOR DINOSAUR SOCIALITY

The Late Cretaceous Belly River Group of southern Alberta consists of three formations; in ascending order, these are the Foremost, Oldman, and Dinosaur Park formations. The lower Belly River Group (Foremost and Oldman formations) is recognized in Montana as the Judith River Formation. Historically, the lower Belly River Group has not enjoyed the rich collecting history of the overlying Dinosaur Park Formation due, in part, to the lack of broad regions of dissected badlands. Since 2005, the Southern Alberta Dinosaur Project has worked to describe the fauna of the lower Belly River Group in order to better understand regional patterns of dinosaur diversity and evolution in the Late Cretaceous.

We report here a preliminary description of the first Gryposaurus bone bed ("Wendy's" Bone Bed; WBB) from the Oldman Formation, located on the southern Pinhorn grazing reserve of south-eastern Alberta in the Milk River valley. The monodominant bone bed is in a mudstone lithosome which probably represents an overbank deposit. It preserves disarticulated, and sometimes associated, elements from all parts of the body, but includes a significant proportion of limb and pelvic bones. A small amount of non-hadrosaurid material (<1%) is present. Based on cranial material, the hadrosaur present is referable to either Gryposaurus or a closely related Gryposaurus-like saurolophine. Taphonomic indicators suggest a short pre-burial interval. The preserved material is dominated by juvenile and subadult-sized elements that range from less than one-third to approximately two-thirds of published adult-sizes for gryposaurs.

Juvenile sociality has previously been suggested for a variety of different dinosaurs, including ornithopod taxa. It has been proposed that the combination of oviparity and small hatchling-size in some dinosaur taxa would have required a significant time and energy commitment on the part of adults for the rearing of hatchlings, leaving juveniles to congregate together away from the nesting site. Preliminary examination of the WBB material supports the suggestion of juvenile sociality in Campanian hadrosaurs.