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

Lara Sciscio,Emese M Bordy,Miengah Abrahams,Mhairi Reid

doi:10.7717/peerj.2285

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.

Highlights

The fluvio-lacustrine and aeolian rocks of the Upper Triassic - Lower Jurassic Elliot and Clarens formations (Karoo Supergroup) preserve a range of vertebrate body fossils, and a plethora of vertebrate invertebrate and plant ichnofossils thatHow to cite this article Sciscio et al (2016), Sedimentology and ichnology of the Mafube dinosaur track site (Lower Jurassic, eastern Free State, South Africa): a report on footprint preservation and palaeoenvironment
Our detailed study of the theropod tracks and associated sedimentary structures at Mafube Mountain Retreat aims to determine the conditions under which the tridactyl dinosaur tracks were preserved, and to provide additional data concerning the dynamics of the ancient ecosystem in the Early Jurassic
Digit numbering is a function of the three toes which make up the tridactyl foot of a theropod dinosaur with the middle digit being the longest, and digits II and IV being subequal in length (Figs. 2A and 2B; Lockley, 2010)

Summary

Introduction

The fluvio-lacustrine and aeolian rocks of the Upper Triassic - Lower Jurassic Elliot and Clarens formations (Karoo Supergroup) preserve a range of vertebrate body fossils, and a plethora of vertebrate invertebrate and plant ichnofossils thatHow to cite this article Sciscio et al (2016), Sedimentology and ichnology of the Mafube dinosaur track site (Lower Jurassic, eastern Free State, South Africa): a report on footprint preservation and palaeoenvironment. These fossiliferous rocks were deposited before and after the third largest of five major biological crises which occurred during the Phanerozoic. The vertebrate footprints in the Upper Triassic to Lower Jurassic Elliot Formation have been assigned to multiple tetrapod genera some 45 years ago largely by Ellenberger (1970), Ellenberger (1972) and Ellenberger (1974), revised some 30 years later by Olsen & Galton (1984), and more recently reviewed again by D’Orazi Porchetti & Nicosia (2007) These studies focused on morphological descriptions, and did not take into account the sedimentological or taphonomic contexts of the footprint sites with the exception of the Wilson, Marsicano & Smith (2009) study at one location in Lesotho. Our detailed study of the theropod tracks and associated sedimentary structures at Mafube Mountain Retreat (eastern Free State, South Africa; Fig. 1) aims to determine the conditions under which the tridactyl dinosaur tracks were preserved, and to provide additional data concerning the dynamics of the ancient ecosystem in the Early Jurassic

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