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