Calitzdorp’s fossil termite nests over 300 000 years old

When local artist Tim Robson dug up several pipe-shaped structures near Calitzdorp in the early 2000s, he thought he had found ovens used by early humans. Researchers have since identified them as fossilised underground termite nests and named the distinctive structures after the Klein Karoo town.

Preserved for more than 300 000 years, the nests still hold evidence of the intricate chambers and connecting passages built by their tiny inhabitants.

Palaeontologist Dr John Almond recorded the site in a 2005 heritage study and suggested the structures might be termite nests. Years later, University of Cape Town (UCT) geologist Prof Emese Bordy drew Dr Miengah Abrahams’s attention to the report, and the team began investigating in 2021.

Abrahams, a senior lecturer in UCT’s Department of Geological Sciences, led the study with colleagues from South Africa, Argentina and Australia. Their findings were published in the Journal of Quaternary Science in June.

The team examined eight nests preserved where they were built, in old river deposits along the Gamka River. The researchers named the newly described type of trace fossil Columnanidus calitzdorpensis, recognising the town near which it was found.

Trace fossils preserve evidence of an animal’s activities, such as a nest, burrow or footprint. Studying them allows scientists to piece together how ancient animals behaved and interacted with their surroundings.

The Calitzdorp nests reach about a metre in height and roughly 65 cm across. Their hollow centres are surrounded by thick walls containing networks of tunnels and chambers.

CT scans of sections of the walls allowed researchers to examine the internal structures in greater detail. Flat chambers were stacked like shelves around the hollow centre, while more irregular tunnels ran through the outer part of the wall. Ramps connected different levels.

The combination of the nests’ cylindrical shape and the distinct arrangements of chambers and tunnels helped researchers recognise them as a new type of trace fossil.

The termites may also have helped preserve their own handiwork. Researchers believe the insects changed the soil around their nests in ways that encouraged carbonate minerals, including calcium carbonate, to accumulate.

Over time, those minerals hardened the sand through a process known as calcretisation. This preserved the structures long after the insects themselves had disappeared.

Using uranium-series dating, the team identified two phases of mineral build-up dating to about 401 000 and 323 000 years ago.

The study puts the minimum age of the nests at roughly 323 000 years, as the dated minerals formed after the nests were built.

The deposits also point to long periods of dry conditions in the Calitzdorp area during the Middle Pleistocene. Together, the nests and surrounding sediments help researchers understand the landscape in which these insects lived.

The team plans to investigate similar fossilised termite and ant nests in the Northern Cape and near Ceres and Worcester.

One of the Calitzdorp specimens is housed at the town’s museum. In October, Abrahams and UCT student Chandré Janse van Rensburg visited the museum to present a poster explaining the discovery.

Abrahams said sharing the findings with the museum and its volunteers was an opportunity to connect residents with the fossil heritage on their doorstep.

“We hope visitors to the museum, especially children, will gain a deeper appreciation for the natural world around them,” she said. (MALISSA SPIES)

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