“Interpretation of the Grallator trackway in the lower Clarens Formation at the Storm Shelter ichnosite. (a) Palaeoenvironmental reconstruction (modified from original artwork by Akhil Rampersadh and Emese M. Bordy). Dinosaur outlines are adapted from Paul47 (foreground) and Rampersadh et al.36 (background). Inset shows the interpretative outline of track #3. (b) Skeletal reconstructions of the left foot and hallux of Megapnosaurus rhodesiensis are adopted from Raath43 (his figure 20). Inset shows the relative position of the hallux trace in this left footprint of the Grallator trackmaker (false-colour depth map of track #3).” courtesy of Dr. Emese Bordy from her 2020 paper in South African Journal of Science.
At some point in the Early Jurassic, a tiny dinosaur raced across a muddy environment in South Africa. We don’t know whether this bipedal carnivore was avoiding being eaten, chasing its own meal, or darting across the landscape for another reason, but we do know—based on the tracks themselves—that it was running very fast.
Only five of its footprints survived millions of years later. That short trackway and the sediment in which it was preserved give us an exciting snapshot: a window into the animal that made those prints and the environment in which it ran.
Dr. Emese M. Bordy, Associate Professor of Sedimentology at the University of Cape Town and sole author of the 2020 paper describing these footprints, suggests that the track maker might have been Megapnosaurus rhodesiensis, a type of coelophysoid dinosaur known from fossils in the area. But, she emphasized in an email, “I made the very tentative attribution to M. rhodesiensis because: 1) the tracks’ morphology suggest a theropod trackmaker (rather than, say, a heterodontosaurid one) and 2) the most common Early Jurassic theropods in the bone fossil record of southern Africa are the remains of coelophysoids. I.e., the tracks could have been made by other theropods whose bones were: 1) not preserved OR 2a) were preserved, but weathered out before being discovered; 2b) were preserved, but have not yet been discovered to-date…”
When we think of theropods, our minds might immediately turn to T. rex or other terrifyingly toothy bipedal dinosaurs. In truth, however, theropods range in size from the enormous to the very small. The dinosaur that made these footprints, for example, may have mirrored the size of today’s rooster or wild turkey, according to Dr. Bordy. It was, as she mentioned in the paper, both predator and prey in its environment.
And when it dashed across the landscape, it appears to have been running through stagnant water. Wrinkles in the rock around each fossil footprint provide evidence of microbial mats—a common feature in trace fossils throughout southern Africa and something that might have helped preserve them through time. Dr. Bordy writes of the microbial mats in the paper that “Likely, these sediment-binding biofilms developed as localized algal blooms flourished in shallow, stagnant pools of water that were generated in ephemeral downpours and that evaporated over time.”
The footprints are deep, enabling us to see not only three claws, but traces of a rare fourth.
“We know from bone fossils globally that theropods did have digit 1,” she wrote in response to my question regarding that fourth claw, “but because that digit was not used in walking/running, theropod footprints rarely preserve the impression of digit 1. Moreover, usually when it gets preserved, the digit impression points backwards (like in birds), but that is not the true anatomical representation of the digit’s position relative to the rest of the dino digits.”
This is why, throughout the paper, these footprints are referred to as “functionally tridactyl” (three-toed). The dinosaur put weight on three of its toes whenever mobile, but that doesn’t mean it only had three toes. In this case, it had at least four.
Dr. Bordy noted that the “primary aim of ichnology is NOT to figure out the tracemaker (the ‘WHO’), but the full circumstances of trackmaking (the ‘HOW’s, the ‘WHY’s, the ‘WHEN’, the ‘SO WHAT’s). It is like a good detective story: solving the crime is more than just matching the footprint to the culprit, it is also finding out the motives and other nuances of the event.”
In terms of fossil track sites, this may not be the largest or the most obviously exciting of those of which Dr. Bordy has studied, but it had its own unique rewards.
“I enjoyed most the fact that, for the first time ever, my field assistants were my 10-year-old, special-needs daughter, Lilla and our personal rock: Lilla’s dad, Rob,” she explained by email. “I also rejoiced in the commitment/focus that I could dedicate to this paper: the entire project cycle, from imitation to acceptance of the paper, was completed under various lockdown conditions in South Africa within 2020.”
There is, she added, “still >4000 km3 of fossiliferous Clarens rock in the southern African subsurface that we have not yet prospected.”
Her colleague, Professor Jonah Choiniere, is studying the bone fossils in the Stormberg Group (“the fossiliferous Upper Triassic to Lower Jurassic continual rock record”), but, she wrote, “As far as I know, these days, only my group (= my students and I) is working on the ichnology of the Stormberg Group.”
“We do so slowly but surely with several manuscripts and projects in the pipeline, so stay tuned.”
“Geological context of the Storm Shelter ichnosite. (a) Simplified geological map of the upper part of the Karoo Supergroup in the Republic of South Africa and Lesotho, showing the position of the study locality northwest of Maclear (Eastern Cape). Inset log shows the local thickness of the Clarens Formation and the relative position of the ichnosite within it. (b–d) Stratigraphic details of the ichnosite within the upper Karoo Supergroup. Map derived by combining data from Johnson and Wolmarans12 and own mapping.” from the 2020 paper in the South African Journal of Science, images courtesy of Dr. Emese Bordy.
I am always profoundly grateful and excited to connect with people for this blog. It is always an honor and a great pleasure! Connecting with you, Dr. Bordy, was particularly fun and rewarding! Thank you so much for your time, your help, and the amazing images you shared with me! I look forward to reading your future research!!
References:
- Bordy EM. Darting towards Storm Shelter: A minute dinosaur trackway from southern Africa. S Afr J Sci. 2021;117(5/6), Art. #9145. https:// doi.org/10.17159/sajs.2021/9145
Further Reading:
(I have highlighted but a few. For more, please see Dr. Bordy’s page here at the University of Cape Town: http://www.geology.uct.ac.za/emese/bordy)
- Miengah Abrahams, Emese M Bordy & Fabien Knoll (2021) 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), Historical Biology, 33:10, 2504-2519, DOI: 10.1080/08912963.2020.1810681
- Miengah Abrahams, Emese M. Bordy, Lara Sciscio & Fabien Knoll (2017) Scampering, trotting, walking tridactyl bipedal dinosaurs in southern Africa: ichnological account of a Lower Jurassic palaeosurface (upper Elliot Formation, Roma Valley) in Lesotho, Historical Biology, 29:7, 958-975, DOI: 10.1080/08912963.2016.1267164
- Sciscio L, Bordy EM, Reid M, Abrahams M. 2016. Sedimentology and ichnology of the Mafube dinosaur track site (Lower Jurassic, eastern Free State, South Africa): a report on footprint preservation and palaeoenvironment. PeerJ 4:e2285 https://doi.org/10.7717/peerj.2285
Mostly Mammoths 