Browsing by Author "Joubarne, Tristan"

Now showing 1 - 1 of 1
  • Thumbnail Image
    ItemOpen Access
    Taphonomic comparison of Hypacrosaurus stebingeri (Hadrosauridae: Lambeosaurinae) bonebeds from the upper Campanian Oldman and Two Medicine formations of Alberta and Montana
    (2024-06-19) Joubarne, Tristan; Zelenitsky, Darla; Sullivan, Corwin; Dolphin, Glenn
    Hadrosaurid social structure is still poorly understood. Evidence from bonebeds suggests that juvenile individuals lived apart from herds composed of older individuals, a phenomenon called age segregation. However, the timing at which juvenile individuals became segregated and later rejoined a multigenerational herd is still unknown. Three monodominant bonebeds that preserve the remains of multiple individuals of the lambeosaurine hadrosaurid Hypacrosaurus stebingeri at different ontogenetic stages offer an opportunity to better understand the timing of the age structuring in this species’ social structure. One of the three bonebeds, known as the Devil’s Coulee juvenile hadrosaur bonebed (JBB) from the Oldman Formation of Alberta (Canada), studied here for the first time, preserves a minimum of four similar-sized late juvenile individuals. The two other bonebeds, Blacktail Creek North (BCN) and Lambeosite (LS) from the Two Medicine Formation of Montana (U.S.A.), preserve a minimum of 23 nestling individuals, and four similar-sized late juvenile individuals with one adult, respectively. These bonebeds show uniform taphonomic signatures throughout the assemblage, characterized by little to no weathering and abrasion, uniform style of fracturing, and rare tooth marks in the assemblages. All three bonebeds are interpreted as mass-mortality assemblages. Histological data indicates that the late juvenile individuals from the JBB were three years old at the time of death, similar to the slightly larger late juvenile individuals from the LS, whereas the individuals from the BCN were less than one year old. A taphonomic comparison with osteological considerations of the three bonebeds reveal that Hypacrosaurus stebingeri individuals became segregated when they were less than one year old, and rejoined a multigenerational herd when they were three years old, as evidenced by the presence of an adult with four three-year-old individuals in the LS. Furthermore, the smaller number of individuals associated with later ontogenetic stages reveals that group size appears to decrease as Hypacrosaurus stebingeri individuals grew older.