Tumbler Ridge has become known as a BC hotspot for dinosaurs, based on the string of trackway and skeletal discoveries that have been reported over the past two decades. Amidst all this welcome publicity, it can be easy to forget that dinosaurs were just one group of trackmakers that inhabited the region’s Cretaceous marshes and swamps. Crocodylians form another such group, but have received less attention, even though a report of one discovery, entitled ‘Crocs in the Peace’, was briefly featured in Issue 63 of the BCPA Newsletter (Helm, 2017). That deficiency has now been comprehensively addressed through a recently published article in Cretaceous Research (Lockley et al., 2021).

The site reported on was identified in 2015 by local geologist Kevin Sharman, within the Quintette Mine operated by Teck Resources, and within the boundary of the Tumbler Ridge UNESCO Global Geopark (TRUGG). Four slabs containing exquisitely preserved swim traces (and a few tail-drags) of Cretaceous crocodylians were described – arguably these are among the finest of their kind ever identified (Figures 1–3).

Equally impressive, perhaps, is the story of how these specimens came to be part of the Tumbler Ridge Museum collections. Once Teck Resources was made aware of the scientific importance of the discovery, the company took the unprecedented step of specially constructing a rough 200 metre-long road to provide access to the site, after which heavy equipment was used to retrieve the specimens and bring them safely to the museum with the help of LaPrairie Crane. A forklift was then used to position them in a shed which had been constructed to house such massive, heavy specimens. This remarkable story of collaboration between industry and science will form part of the revamped exhibits that are planned for the Dinosaur Discovery Gallery, where a replica of the surface of the largest slab is currently on exhibit (Figure 4).

Martin Lockley of the University of Colorado was the lead author of the publication, which inter alia compared these swim traces with similar traces in the western USA. Guy Plint of the University of Western Ontario was the second author. Co-authors from the Tumbler Ridge Museum were Charles Helm and Kevin Sharman. Ongoing research of this nature is one of the necessary criteria for the TRUGG revalidation in 2022.

The swim traces are from the Cretaceous Period, and are approximately 112 million years old. The crocodiles were swimming in a tidal channel on a low-lying coastal plain, and scratching the muddy bottom with their claws. It is possible to estimate the length of the crocodiles from the distance between the toes in the swim traces, and it appears that they were about a metre in length.

Dinosaurs are extinct (other than their avian descendants). Crocodiles are not: they have ‘survivor status’, and are still with us today with a recognizably similar body plan. Those of us involved in this research feel that there is something extra-special about crocodiles.

Moreover, awareness of the morphology of such swim traces led to a serendipitous bonus. Most of my research work is in Pleistocene sediments on the Cape south coast of South Africa. Because of the Tumbler Ridge discoveries, I had ‘my eye in’ for crocodylian swim traces on that coast. When fossil crocodile tracks were unexpectedly identified there in 2018, I was able to spot the tell-tale signs of probable swim traces, the first of their kind ever reported from Africa. Description of these sites was published in the South African Journal of Science (Helm et al., 2020; Helm and Lockley, 2021). African scientists can be forgiven for their reticence in documenting such traces through neoichnology – the Nile crocodile typically inhabits muddy, turbid streams in which bottom-traces are invisible. And the notion of donning goggles and snorkel to have a closer look in croc-infested waters has its drawbacks.

Subsequent exploration in the Tumbler Ridge area has led to the identification of a number of further crocodylian trace fossil sites from a variety of ages. This is an active area of research, and future scientific publications describing these findings can be anticipated.

One example, found in 2017, has come to be known as ‘Croc Rock’ (Figure 5). Here tracks and swim traces occur as natural casts on a loose slab just above the level of the Wolverine River, a short distance downstream from a surface containing dinosaur tracks and skin impressions that has become a popular attraction for visitors through museum-led lantern tours. Consideration was given to flying the specimen to the museum with helicopter support using a long-line. However, Croc Rock is situated directly under a bridge, making this option unfeasible. The Wolverine River is 80 km long – the chances of the precious fossil specimen occurring directly below such a four-metre-wide bridge are less than 1:20,000!

We recognized that flood events might damage or destroy these tracks and traces. In order to preserve them for future work, museum staff and volunteers, led by Tammy Pigeon, made a replica of the surface using silicone. This was followed by photogrammetry. The slab was then moved as afar as possible up the slope using pry-bars, which will reduce (but not eliminate) the risk of damage from flood events. Protective rocks were placed around it, to help prevent anyone treading on the traces. Once these measures were in place, a spur trail was constructed, and the Wolverine River lantern tour now includes a side-trip to Croc Rock.

There is clearly a spectrum of swim traces. In very shallow aqueous environments they may be virtually indistinguishable from tracks and traces made on dryland substrates. As water depth progressively deepens, we can expect tracks to become less and less evident, and swim traces to dominate. At a certain depth only the trace of the longest digit will touch and scrape the bottom, and if the water is deeper still, well, there will be no trace at all of the crocodile’s passage.  A special issue of the New Mexico Museum of Natural History and Science Bulletin (Milàn et al., 2010) examined many aspects of crocodile tracks and traces. It is rightly regarded as the ‘gold standard’, and is a useful reference work on this topic.

‍

Article first published in the BC Paleontological Alliance Newsletter, Issue 70, October 2021

BCPA Educational Blog Initiative

References:

Helm, C. 2017. Crocs in the Peace –100-million-year-old tracks uncovered at BC coal mine and preserved in TumblerRidge Museum. British ColumbiaPaleontological Alliance Newsletter 63, 14–16.

Helm, C.W., Lockley, M.G. 2021.Pleistocene reptile swim traces confirmed from South Africa’s Cape south coast.South African Journal of Science117(3/4), Art.#8830. https://doi.org/10.17159/sajs.2021/8830

Helm, C.W., Cawthra, H.C., Combrink,X., Helm, C.J.Z., Rust, R., Stear, W., Van Den Heever, A., 2020. Pleistocenelarge reptile tracks and probable swim traces on South Africa’s Cape southcoast. South African Journal of Science116 (3/4), Art. #6542. https://doi.org/10.17159/sajs.2020/6542

Lockley, M.G., Plint, A.G., Helm,C.W., Sharman, K.J., Vannelli, K.M. 2021. Crocodylian swim tracks from theGates Formation (Albian), British Columbia, Canada: comparisons with Cretaceouscrocodylian ichnology in western USA. CretaceousResearch 128, 104967. https://doi.org/10.1016/j.cretres.2021.104967

Milàn J., Lucas, S.G., Lockley, M.G.,Spielmann, J.A. (editors). 2010. Crocodyletracks and traces. New Mexico Museum of Natural History and ScienceBulletin 51. 244 pp. https://play.google.com/books/reader?id=RLjECQAAQBAJ&printsec=frontcover&pg=GBS.PP1

‍