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

PLoS One. 2020 Jan 29;15(1):e0226847. doi: 10.1371/journal.pone.0226847. eCollection 2020.

Abstract

The Karoo igneous rocks represent one of the largest continental flood basalt events (by volume) on Earth, and are not normally associated with fossils remains. However, these Pliensbachian-Toarcian lava flows contain sandstone interbeds that are particularly common in the lower part of the volcanic succession and are occasionally fossiliferous. On a sandstone interbed in the northern main Karoo Basin, we discovered twenty-five tridactyl and tetradactyl vertebrate tracks comprising five trackways. The tracks are preserved among desiccation cracks and low-amplitude, asymmetrical ripple marks, implying deposition in low energy, shallow, ephemeral water currents. Based on footprint lengths of 2-14 cm and trackway patterns, the trackmakers were both bipedal and quadrupedal animals of assorted sizes with walking and running gaits. We describe the larger tridactyl tracks as "grallatorid" and attribute them to bipedal theropod dinosaurs, like Coelophysis, a genus common in the Early Jurassic of southern Africa. The smallest tracks are tentatively interpreted as Brasilichnium-like tracks, which are linked to synapsid trackmakers, a common attribution of similar tracks from the Lower to Middle Jurassic record of southern and southwestern Gondwana. The trackway of an intermediate-sized quadruped reveals strong similarities in morphometric parameters to a post-Karoo Zimbabwean trackway from Chewore. These trackways are classified here as a new ichnogenus attributable to small ornithischian dinosaurs as yet without a body fossil record in southern Africa. These tracks not only suggest that dinosaurs and therapsids survived the onset of the Drakensberg volcanism, but also that theropods, ornithischians and synapsids were among the last vertebrates that inhabited the main Karoo Basin some 183 Ma ago. Although these vertebrates survived the first Karoo volcanic eruptions, their rapidly dwindling habitat was turned into a land of fire as it was covered by the outpouring lavas during one of the most dramatic geological episodes in southern Africa.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Africa, Southern
  • Animals
  • Body Size
  • Dinosaurs / anatomy & histology*
  • Dinosaurs / classification
  • Dinosaurs / physiology
  • Fossils
  • Gait
  • Mammals / anatomy & histology*
  • Mammals / classification
  • Mammals / physiology
  • Volcanic Eruptions

Grants and funding

This work was supported by grants to EMB from the National Research Foundation-DST Centre of Excellence in Palaeosciences [COE PAL grant number COE2019-OP04], National Research Foundation of South Africa [NRF CPRR grant number 113394; NRF AOP grant number 98825], as well as COE PAL bursaries to AR and MA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.