Taphonomy and taxonomy of a juvenile lambeosaurine (Ornithischia: Hadrosauridae) bonebed from the late Campanian Wapiti Formation of northwestern Alberta, Canada

Abstract

Hadrosaurid (duck-billed) dinosaur bonebeds are exceedingly prevalent in upper Cretaceous (Campanian–Maastrichtian) strata from the Midwest of North America (especially Alberta, Canada, and Montana, U.S.A) but are less frequently documented from more northern regions. The Wapiti Formation (Campanian–Maastrichtian) of northwestern Alberta is a largely untapped resource of terrestrial palaeontological information missing from southern Alberta due to the deposition of the marine Bearpaw Formation. In 2018, the Boreal Alberta Dinosaur Project rediscovered the Spring Creek Bonebed, which had been lost since 2002, along the northern bank of the Wapiti River, southwest of Grande Prairie. Earlier excavations and observations of the Spring Creek Bonebed suggested that the site yielded young hadrosaurines. Continued work in 2018 and 2019 recovered ~300 specimens that included a minimum of eight individuals, based on the number of right humeri. The morphology of several recovered cranial elements unequivocally supports lambeosaurine affinities, making the Spring Creek sample the first documented occurrence of lambeosaurines in the Wapiti Formation. The overall size range and histology of the bones found at the site indicate that these animals were uniformly late juveniles, suggesting that age segregation was a life history strategy among hadrosaurids. Given the considerable size attained by the Spring Creek lambeosaurines, they were probably segregated from the breeding population during nesting or caring for young, rather than due to different diet and locomotory requirements. Dynamic aspects of life history, such as age segregation, may well have contributed to the highly diverse and cosmopolitan nature of Late Cretaceous hadrosaurids.

Osteohistological and taphonomic life‐history assessment of Edmontosaurus annectens (Ornithischia: Hadrosauridae) from the Late Cretaceous (Maastrichtian) Ruth Mason dinosaur quarry, South Dakota, United States, with implication for ontogenetic segregation between juvenile and adult hadrosaurids

“…Although smaller sized individuals can be subject to hydraulic sorting (Brown, Evans, Ryan, & Russell, 2013; Brown, Evans, Campione, et al, 2013), the results of the RMDQ autopodial element size‐frequency distribution (Figure 6) indicated that autopodial elements were present in excess and did not vary in their overall degree of completeness relative to long bones from the same population. This suggests that taphonomic biases had not contributed toward the absence of nestling‐sized long bones in the RMDQ sample, which were hydraulically equivalent to late juvenile‐adult autopodial elements, providing further evidence that segregation between nestling‐juvenile and adult hadrosaurids may have been a real biological signal (e.g., Holland et al, 2021; Lauters et al, 2008; Varricchio & Horner, 1993; Wosik et al, 2020).…”

“…Hadrosaurid dinosaurs have been historically defined as being gregarious based on evidence of numerous bonebed accumulations (e.g., Christians, 1992; Colson et al, 2004; Horner et al, 2004; Lauters et al, 2008; Scherzer & Varricchio, 2010; Bell & Campione, 2014; Eberth et al, 2014; Hone et al, 2014; Evans et al, 2015, Woodward et al, 2015, Ullmann et al, 2017; Bell et al, 2018, Holland et al, 2021). However, before estimating the population dynamics of an extinct animal, the depositional origin of the sampled assemblage, including the manner of death, need to be assessed.…”

The dinosaur tracks of Tyrants Aisle: An Upper Cretaceous ichnofauna from Unit 4 of the Wapiti Formation (upper Campanian), Alberta, Canada

“…Large ornithopod tracks from Tyrants Aisle are attributed to hadrosaurids, whose skeletal remains and tracks are ubiquitous throughout the Wapiti Formation [ 8 , 10 – 12 , 15 – 17 , 55 , 105 ]. Within Unit 4, a ‘mummified’ specimen of the saurolophine Edmontosaurus regalis (UALVP 53722) was found near Red Willow Falls, ~16km upstream from Tyrants Aisle [ 15 ].…”

“…Skeletal and other evidence, including rare nesting sites (e.g., [ 116 – 118 ]) and common hadrosaurid-dominated bonebeds (e.g., [ 20 , 25 , 119 – 123 ]) further indicate widespread herding behaviour among these dinosaurs. More specifically, hadrosaurid-dominated bonebeds are also known from the Wapiti Formation [ 8 , 55 ]. In this context, it is possible that the abundant hadrosaurid trackmakers at Tyrants Aisle were also engaging in gregarious behaviours.…”

“…All tracks were identified to the lowest possible taxonomic level, using their overall morphological characters and contextual (i.e., chronostratigraphic) relevance. Based on skeletal material recovered within Late Cretaceous terrestrial strata of both the Wapiti Formation and more broadly in western Canada [ 8 , 12 , 15 , 16 , 54 , 55 ], tridactyl prints from Tyrants Aisle can be confidently regarded as belonging to either hadrosaurid, theropod or, possibly, thescelosaurid dinosaurs; tracks that possess broad, rounded digits with blunt terminations and relatively broad heels were treated as hadrosaurid tracks, while prints with relatively slender digits, sharp claw marks, and more narrow heels were regarded as theropod-like tracks [ 7 , 56 ]. The term “theropod-like” is used herein to accommodate the theoretical possibility that some of these tracks may pertain to thescelosaurids, which arguably produced similar track morphologies to those of theropods, making them difficult to distinguish.…”