Hidden for one hundred years: a diverse theropod ichnoassemblage and cross-sectional tracks from the historic Early Jurassic Tsikoane ichnosite (Clarens Formation, northern Lesotho, southern Africa)

ABSTRACT

The upper Stormberg Group of Lesotho has an abundant and diverse ichnological record that dates to the Early Jurassic. Herein, we re-evaluate a known ichnosite in the lowermost Clarens Formation (Karoo Supergroup) at Tsikoane in northern Lesotho. The site was reported to preserve tridactyl tracks as natural casts in the ceiling of overhangs and true track impressions on a fallen sandstone block. At least three track-bearing palaeosurfaces, associated with horizontally laminated sandstones and desiccated green mudstones, can be traced over a distance of 250 m. Associated with one of the track-bearing palaeosurfaces, discrete, U-shaped, cross-sectional structures are interpreted as a series of natural casts, surface tracks, true tracks and undertracks. Although the Tsikoane tracks were historically assigned to a single ichnogenus, later synonymised with Grallator, our findings show a higher diversity of tridactyl ichnites, with tracks that have Kayentapus-like and Eubrontes-like features in addition to previously recognised Grallator-like features. These new findings, within their high-resolution sedimentological context, improve the understanding of theropod palaeodiversity and palaeoecology in southern Africa during a crucial period in dinosaur history marked by increases in both abundance and diversity.

KEYWORDS:

• Sinemurian – Pliensbachian
• Karoo Supergroup
• Kayentapus
• Eubrontes
• Grallator

Article Highlights

• Lower Jurassic ichnosite exposing tridactyl true tracks and natural casts assigned to Grallator, Eubrontes and Kayentapus

• Natural casts of a high anatomical fidelity are preserved in the ceilings of overhangs; true tracks are impressed into a fallen block that has been relocated for the first time since 1908

• The first documented tracks preserved in cross-section for the Clarens Formation with the true track, undertracks and natural cast infillings observable

Acknowledgments

We acknowledge Robert A. Muir for locating the fallen block during one of the many field visits to Tsikoane, curator Suzanne Jiquel for access to the Ellenberger Collection at the Université de Montpellier (France), Riyaad Mukaddam for taking photographs of the Ellenberger Collection and Akhil Rampersadh and Howard Head for field assistance. We also thank Emmanuel Fara and Matteo Belvedere for their constructive comments on an earlier version of this manuscript. We also thank reviewers Peter L Falkingham and Ignacio Díaz-Martínez as reviewers, and Gareth Dyke as chief editor for meaningfully contributing with their insightful comments to the overall quality of this study. Opinions expressed and conclusions reached are those of the authors and are not necessarily to be attributed to the CoE in Palaeosciences or NRF or anybody else.

Disclosure statement

The authors receive no financial benefit from this research.

Additional information

Funding

The research component of this project was supported from the following research grants obtained by EB as principal investigator: DST-NRF Centre of Excellence in Palaeosciences [CoE PAL 2015]; National Research Foundation (NRF) of South Africa Competitive Programme for Rated Researches (CPRR) and African Origins Programme (AOP) [93544, 113394, 98825]; FK is supported by the research project CGL2017-89123-P funded by ERDF/Spanish Ministry of Science and Innovation-State Research Agency. He is a member of the reference research group E04_20R FOCONTUR, co-founded by the Government of Aragon and the ERDFF; During the study MA was a recipient of postgraduate funding from the DST-NRF Centre of Excellence in Palaeosciences (CoE in Palaeosciences).