Rock Hyrax Butt-Drag Fossils Reveal Pleistocene Traces

Rock hyraxes, more commonly called "dassies" in southern Africa, are furry, stocky animals with short legs and no obvious tails. They pass a great deal of time basking on rocky outcrops.

They also occasionally drag their bottoms across the ground.

For dog owners, this behaviour may signal a parasitic infection. The cause in hyraxes is apparently less certain, although the movement produces recognisable marks in sandy terrain.

Fossilised rock hyrax traces on the Cape south coast

At the African Centre for Coastal Palaeoscience, our Cape south coast ichnology project investigates traces and tracks, including ancient examples preserved as fossils.

During the past few decades, we have recorded almost 400 vertebrate tracksites along this coastline. Some are as old as 400,000 years and occur in Pleistocene aeolianites: cemented dunes dating from an epoch that extended from roughly 2.58 million years ago until about 11,700 years ago.

Our work is gradually revealing what the environment was like in that era, as well as how its animals and plants lived.

Two of our most recent discoveries seem to be fossil traces left by rock hyraxes in the distant past. One is a tracksite; the other is a butt-drag impression that may contain a fossilised dropping.

An enthusiastic tracker, Mike Fabricius, alerted us to the likely tracksite, which lies near Walker Bay on the Cape south coast. It is approximately 76,000 years old. We identified the probable butt-drag impression east of Still Bay, on the same coast, and it is most likely about 126,000 years old.

The butt-drag impression is the first fossil of this type to be described anywhere in the world. These also appear to be the only possible fossilised hyrax tracks ever identified. Such unusual evidence matters in palaeontology, and we are privileged to interpret it.

Decoding the butt-drag impression

We have dated our sites using optically stimulated luminescence, a method that establishes when substances such as sand were last exposed to light.

The butt-drag impression measures 95 cm in length and 13 cm in width, and has five parallel striations.

Its outer edges are slightly elevated. Inside it sits a raised feature measuring 10 cm by 9 cm and standing 2 cm high. Something clearly crossed the surface while it was still loose sand.

We assessed explanations other than a hyrax's buttocks, including a leopard or ancestral human pulling prey, or possibly an elephant dragging its trunk.

Yet these possibilities should, first, have produced tracks. Second, they offer no explanation for the raised feature.

A hyrax interpretation, however, is logical: the buttock trace would have followed the tracks, erasing them. The raised feature may also be a coprolite, a fused fossilised mass of hyrax droppings.

Rock hyrax dung, urine and hyraceum

Rock hyraxes produce far more than tracks and butt-drag marks. Since they favour rocky habitats, their tracks are seldom preserved, but they can polish rock surfaces until they shine.

This resembles the behaviour of buffalo on the North American prairie, which create "buffalo rubbing stones".

Hyraxes additionally deposit urine and dung. Their urine contains concentrated urea and electrolytes, while they excrete substantial quantities of calcium carbonate. This material cements together, creating broad whitish deposits across rock surfaces.

Because they live communally, hyraxes frequently urinate in the same favoured spots over many generations.

Their urine and dung commonly combine into hyraceum, a rock-like substance that can build up into large, dark, tar-like deposits. Hyraceum has traditionally been used medicinally for a range of conditions, including epilepsy, as well as for gynaecological purposes.

Hyraceum can be tens of thousands of years old and may be considered a threatened, non-renewable resource. Sensitive to environmental change, these middens contain fossil pollen and other signs of ancient life, making them valuable natural records for reconstructing former climates, vegetation and ecology.

Viewing hyraceum as a trace fossil - which apparently has not previously been done - could support protection of this undervalued resource.

Fossilised urine is rare worldwide, but it has a name: "urolite", distinguishing it from "coprolite" (fossilised poo). Hyraxes seem to account for the lion's share of the world's urolite.

At palaeontology conferences, students sometimes wear T-shirts boldly declaring: "coprolite happens". In southern Africa, "urolite happens" may be the more fitting expression.

By recognising the significance of butt-drag impressions, urolites, coprolites and hyraceum, and by understanding the Pleistocene environments of rock hyraxes and other animals, we may never see these appealing creatures in quite the same way again.

Mathilde Stuart contributed to this research.

Charles Helm, Research Associate, African Centre for Coastal Palaeoscience, Nelson Mandela University and Lynne Quick, Senior Research Fellow, Nelson Mandela University

This article is republished from The Conversation under a Creative Commons licence. Read the original article.