Dinosaur trackways from the Upper Cretaceous Oldman and Dinosaur Park formations (Belly River Group) of southern Alberta, Canada, reveal novel ichnofossil preservation style

Abstract

Dinosaur tracksites recently discovered in exposures of the Belly River Group in the Milk River Natural Area (MRNA) and Dinosaur Provincial Park (DPP) of southern Alberta represent a novel type of ichnofossils. The tracks, all referable to hadrosaurs, occur as sideritic or calcareous concretions protruding above fine-grained deposits and are here termed concretionary tracks. Detailed sedimentological, petrographic, and geochemical analyses reveal that, although the MRNA and DPP tracks are of different mineralogical compositions (calcium carbonate versus siderite, respectively), they display similar internal structures (microscopic convoluted laminations) and occur in depositional settings indicative of wet paleoenvironments, where the ground was soft and water saturated. These characteristics suggest that concretionary tracks are footprint casts that formed as groundwater rich in dissolved carbonates flooded depressions left in the soft substrate. As the ponded water evaporated, minerals began to precipitate and mix with clastic material transported into the depressions, settling as finely laminated mud within the tracks and filling them either completely or partially. The geochemical composition of the precipitate would depend on the prevalent groundwater conditions (e.g., pH, dissolved carbonate and sulphate concrentrations). Cementation of the tracks occurred relatively soon after burial (<100 years), possibly in response to microbial activity and saturation by mineral-rich groundwater, and modern erosion exposed the concretionary tracks by removing the softer host unit. Recognition of this novel type of ichnofossils suggests dinosaur tracks may be more common than previously thought. Unfortunately, concretionary tracks tend to break apart rapidly when the encasing and underlying substrate erodes away, altering their diagnostic shape and rendering them indistinguishable from nonichnogenic concretions. As such, concretionary tracks may be transient ichnofossils in the badlands, explaining why they are rarely recognized. Résumé :Des sites préservant des empreintes de pas de dinosaures récemment découverts dans des affleurements du Groupe de Belly River dans la Milk River Natural Area (MRNA) et dans le Dinosaur Provincial Park (DPP) du sud de l'Alberta représentent un nouveau type d'ichnofossiles. Les empreintes, qui ont toutes été produites par des hadrosaures, sont préservées sous forme de concrétions sidéritiques ou calcaires émergeant de dépôts fins et sont ici nommées « empreintes concrétionnaires ». Des analyses sédimen-tologiques, pétrographiques et géochimiques détaillées révèlent que, bien que les empreintes de la MRNA et du DPP soient de compositions minéralogiques différentes (carbonate de calcium et sidérite, respectivement), elles possèdent des structures internes semblables (lamination convolutée microscopique) et se trouvent dans des milieux de dépôt qui reflètent des paléoenvironnements humides où le sol était mou et saturé en eau. Ces caractéristiques suggèrent ou indiquent que les tra...

Geometric morphometric analysis of intratrackway variability: a case study on theropod and ornithopod dinosaur trackways from Münchehagen (Lower Cretaceous, Germany)

“…Threshold values were selected for each bivariate ratio, allowing for the classification of unknown material. Although the majority of the analyzed material stems from the Lower Cretaceous of La Rioja, Spain, this approach has recently been applied to classify footprints from different epochs of different parts of the world ( Mateus & Milán, 2008 ; Romilio & Salisbury, 2011 ; Schulp & Al-Wosabi, 2012 ; Therrien et al, 2015 ). Thulborn (2013) recently questioned the use of this approach to classify contentious material, noting that (1) the threshold values are defined subjectively to provide the best separation between point clouds in the bivariate plots, (2) the analysis is essentially a set of bivariate plots and thus not a real multivariate analysis, (3) most of the employed ratios reflect the length-width ratio of the footprint, resulting in a high degree of redundancy, and that (4) all digital axes are required to originate from a single point on the heel outline and thus cannot appropriately describe the footprint shape in many examples.…”

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

“…Alaskan ichnoassemblages within the Chignik and lower Cantwell formations are most often dominated by Hadrosauropodus , although the latter unit is probably early Maastrichtian in age [ 29 , 31 , 32 ]. Similarly, late Campanian track horizons within the Oldman, Dinosaur Park, Horseshoe Canyon, and St. Mary River formations of southern Alberta, as well as the ‘Mesaverde Group’ of Utah, Wyoming, Colorado, and the Fruitland Formation of New Mexico, are all hadrosaurid-dominated [ 3 , 43 , 60 , 75 , 87 , 145 – 153 and references therein] ( Fig 16 ). In Mexico, ichnofaunas of the Cerro del Pueblo Formation are hadrosaurid-dominated in terms of footprint abundance, although theropod tracks occur at a larger number of tracksites [ 139 , 154 – 156 ].…”

Introduction to the Special Issue commemorating the 30th anniversary of the Royal Tyrrell Museum of Palaeontology, with a summary of the museum’s early history and its research contributions

“…Within Alberta, examples include (i) Lower Cretaceous footprints and trackways of dinosaurs, crocodylians, and birds in the Grande Cache region (e.g., Currie 1989a;McCrea and Currie 1998;McCrea et al 2014); (ii) Upper Cretaceous dinosaur and Palaeocene mammal footprints and trackways in the southern part of the province (e.g., Currie et al 1991;McCrea et al 2004McCrea et al , 2005Therrien et al 2014Therrien et al , 2015; (iii) Upper Cretaceous dinosaur, crocodilian, and turtle eggs and eggshells from various localities in the southern part of the province, particularly at Devil's Coulee and in the DPP and Onefour areas (e.g., Zelenistsky et al 1996Zelenistsky et al , 2002Zelenistsky et al , 2008; and (iv) a putative tyrannosaurid coprolite from southern Alberta (Chin et al 2003). Also notable is the discovery of an ironstone-hosted plant locality in the late 1980s by then-RTMP technician Kevin Aulenback, just east of the museum and within the upper Campanian portion of the Horseshoe Canyon Formation.…”