Trace fossils and not-quite dinosaurs
By Nick J Booth, on 27 September 2012
On Friday this week (28th September) I will be helping to clean one of the largest, and to my mind most impressive, specimens on display in UCL’s Rock Room – the 243 million year old footprint of a mammal-like reptile (but definitely NOT a dinosaur) called Chirotherium. I say definitely not a dinosaur because I’ve made this rather embarrassing geological/ zoological mistake a couple of times and been told off for it.
As the footprint is displayed in its own (heavy) glass it has taken more planning than you would have thought is required just to clean a specimen. In honour of this I have decided to write my first Geology blog on the subject.
The Chirotherium lived during the Triassic Period, 248 – 206 million years ago, when most of the land on earth formed the super continent Pangaea. Its track prints have been known about since 1834, when examples were found in the German central state of Thuringia, however they have since been found across Europe, North America and parts of Africa.
The fossil footprints fall into the broad category of what is fast becoming my favourite type of geological specimen, trace fossil. Trace fossils are preserved impressions of actions from millions of years ago which, through extraordinarily fortuitous series of events, have been preserved. For this to happen there needs to have been the correct conditions at the time, they have to have survived millions of years of geological activity and need to have been discovered in the relatively recent past when people could appreciate what they are and look after them well enough so that we can see them today.
I love the fact trace fossils preserve a moment in time from millions of years ago, whether it was a rock being dragged along a river bed, or a trilobite scurrying across an ancient seabed, or a Chirotherium thundering across a desert.
Our footprints are preserved in a large red sandstone slab, and are actually the cast of the original footprints, rather than the footprints themselves. The slab shows not only the Chirotherium’s footprint, but also cracks on the surface this mammal-like reptile walked across. This indicates that it lived in a dry environment (desert?) with a stream or wet spot, which then dried out (hence the cracks), before being covered by sand. This specimen has been at UCL for over 30 years. Sadly, however, we don’t know where exactly it came from.
When first identified, the tracks were seen as remarkable because they looked like they had a thumb, jutting to the side. This feature determined Chirotherium’s name (‘Hand beast’ in Latin). Being the early days of geology, this gave rise to some interesting theories. Understandably, based upon the knowledge of the day, there were suggestions that they were the hand prints of biblical flood victims. Other ideas were that they came from an ape, bear or large amphibian. The strange location of the fossil footprint ‘thumb’ (actually the equivalent of its little toe) led early geologists to think that/assert that the animal walked with its legs crossed (?!?).
Despite its tracks being found across 3 modern day continents, no actual remains of the Chirotherium have ever been found. Despite this, Ichnologists (scientists who specialise in studying footprints – who knew?) have been able to make some educated guesses about what it might have looked like based on specimens like ours. From clues such as the front tracks being smaller than the back, a narrow gait and the fact that there are no tail drag marks, they have been able to come up with the impression you see on this page. In fact, in the 1960’s a near complete skeleton of a similar animal was discovered. This was Ticinosuchus, an Archosaur in the region of 2-3 meters long, whose existence lends even more support to this image.
If you would like to get a closer look at this 243-million-year-old footprint, please come along to the Rock Room, UCL’s Geology Museum, on the 28th of September.
The Rock Room, UCL’s Geology museum, is now open to the public every Friday between 1 – 3pm. A member of staff is always present during this time to welcome visitors and answer any questions you can throw at them.