Sedimentology and ichnology of the Mafube dinosaur track site (Lower Jurassic, eastern Free State, South Africa): a report on footprint preservation and palaeoenvironment

Abstract

Footprint morphology (e.g., outline shape, depth of impression) is one of the key diagnostic features used in the interpretation of ancient vertebrate tracks. Over 80 tridactyl tracks, confined to the same bedding surface in the Lower Jurassic Elliot Formation at Mafube (eastern Free State, South Africa), show large shape variability over the length of the study site. These morphological differences are considered here to be mainly due to variations in the substrate rheology as opposed to differences in the trackmaker’s foot anatomy, foot kinematics or recent weathering of the bedding surface. The sedimentary structures (e.g., desiccation cracks, ripple marks) preserved in association with and within some of the Mafube tracks suggest that the imprints were produced essentially contemporaneous and are true dinosaur tracks rather than undertracks or erosional remnants. They are therefore valuable not only for the interpretation of the ancient environment (i.e., seasonally dry river channels) but also for taxonomic assessments as some of them closely resemble the original anatomy of the trackmaker’s foot. The tracks are grouped, based on size, into two morphotypes that can be identified as Eubrontes-like and Grallator-like ichnogenera. The Mafube morphotypes are tentatively attributable to large and small tridactyl theropod trackmakers, possibly to Dracovenator and Coelophysis based on the following criteria: (a) lack of manus impressions indicative of obligate bipeds; (b) long, slender-digits that are asymmetrical and taper; (c) often end in a claw impression or point; and (d) the tracks that are longer than broad. To enable high-resolution preservation, curation and subsequent remote studying of the morphological variations of and the secondary features in the tracks, low viscosity silicone rubber was used to generate casts of the Mafube tracks.

Tracking the Pliensbachian–Toarcian Karoo firewalkers: Trackways of quadruped and biped dinosaurs and mammaliaforms

“…The trace fossil assemblage at the Highlands ichnosite (geographical coordinates: 282 4'53.50"S 28˚15'11.14"E) was studied both in the field and laboratory after obtaining their photogrammetric models and silicon rubber replicas, by: describing their architectural and surficial morphologies, obtaining their physical and digital morphometric measures for indepth descriptions and for ichnotaxonomic treatment. Standard ichnological methods as outlined in MacEachern et al [60,61]; Falkingham [62]; Lallensack et al [63]; Sciscio et al [64] and Falkingham et al [65] were followed. In addition, vertical and regional changes in the host sedimentary facies architecture were described in the field by applying principles of facies analysis (e.g., measurement of grain size, thickness, palaeocurrents, sedimentary structures) following standard sedimentological methods as outlined in Miall [66][67][68][69].…”

The first megatheropod tracks from the Lower Jurassic upper Elliot Formation, Karoo Basin, Lesotho

“…Track length (TL) is considered, here, as the length from the tip (but not including claw mark where preserved) of digit III to the base of the heel margin. Track measurements were taken as described in [ 13 ].…”

“…Stratigraphically, the megatheropod trackway site is found within the Lower Jurassic upper Elliot Formation ( Fig 1B and 1C ), which is well-documented because of its diverse and abundant vertebrate track assemblages (e.g., [ 13 , 20 , 21 , 24 – 28 ]). Detailed palaeontological, stratigraphic and sedimentological accounts of the Upper Triassic-Lower Jurassic fluvio-lacustrine Elliot and Clarens formations of southern Africa are presented, among others, in [ 29 – 40 ].…”

“…In general, Upper Triassic strata are dominated by an abundance of theropod ichnites between 20 cm to 25 cm in length (grallatorid-sized) [ 8 ]. However, there does appear to be a preponderance for an increase in their size in the Early Jurassic based on the increased number of larger theropod ichnites, with the oldest known example of Eubrontes (35 cm) in North America (in a unit that is 10 ky younger than TJB-defined by palynomorphs [ 5 ]) and 34 cm in South Africa [ 13 ]. Despite the abundance of these Lower Jurassic theropod tracks and trackways, they are currently of relatively low generic diversity due to similarities in track morphology.…”

Late Permian-Early Jurassic vertebrate tracks from patagonia: Biochronological inferences and relationships with southern african realms

“…In Patagonia, there are few outcrops within this temporal range, but the relationships with the record from southern Africa are also analysed (e.g., Pol and Powell, 2007;Pol et al, 2011). Indeed, the similarities between the ichnological record from both places have also been studied (e.g., Díaz-Martínez et al, 2017;Citton et al, 2018;Lagnaoui et al, 2018), which coincides with the improved knowledge of this record in recent years (Sciscio et al, 2016;Abraham et al, 2017;Bordy et al, 2017;Rampersadh et al, 2018). In order to better understand this type of correlations during the latest Permian-Early Jurassic, the similarities and differences regarding the geology, environment and ichnological fossil record between Patagonia and southern Africa are described.…”