Article by: Adam Manning
Edited by: Harry T. Jones and J. D. Dixon
Most people are familiar with body fossils: fossils of bones, teeth and claws. However, these hard parts aren’t the only remains that can fossilise. Also preserved in the fossil record are the remains of the activity of life, called ichnotaxa, or trace fossils. These fossils show behaviour rather than morphology, and can take many forms. For example, Thalassinoides are fossil burrow structures, produced by animals such as crustaceans. Perhaps the most disgusting of these trace fossils are the rocks known as coprolites: the fossilised remains of animal excrement. Palaeontologists have found them invaluable in studying prehistoric animals, but why are fossilised faeces so important?
Coprolites were first described in scientific literature in 1829 by William Buckland, but they had already been identified as fossilised faeces by Mary Anning by 1824, at least. Anning identified the coprolites residing behind the ribs and pelvis of several fossil ichthyosaurs, suggesting that it was faecal matter that had fossilised inside the animals as they didn’t have the chance to excrete it before they died. Since then, coprolites from a huge variety of extinct organisms have been discovered all over the world. The earliest vertebrate coprolites date all the way back to the Ordovician Period, while some coprolites are even attributed to invertebrates in the Cambrian Period.
Coprolites are extremely useful to palaeontologists because they can suggest a lot of information about an animal’s diet, and therefore the ecosystem in which the animal was living. However, it can often be hard to identify coprolites as being made by one species of animal because different species co-existed with one another and the fossils themselves are ambiguous.
Therefore, it can be quite exciting when a taxonomically distinct coprolite is discovered. For example, a coprolite from a theropod dinosaur was discovered in the Maastrichtian Frenchman Formation, Montana that was 44 cm long, 13 cm high, 16 cm wide, and weighed over 7.1 kg in total. This is still smaller than what it would have been prior to fossilisation, due to processes such as compaction. This huge coprolite has been attributed to the famous Tyrannosaurus rex, the only theropod dinosaur known from the Maastrichtian Frenchman Formation large enough to produce it. What was interesting to the palaeontologists studying this specimen was the presence of aligned, rounded bone fragments in the coprolite, possibly from a juvenile ornithischian dinosaur. These fragments represent large bone shards that have degraded, disproving the idea that large theropods digested most consumed bone like modern crocodiles. Therefore, this discovery implies that Tyrannosaurus rex crushed, consumed and incompletely digested vast quantities of bone when feeding.
Coprolites have also been used to determine the evolution of plants, specifically grass. Coprolites from the Late Cretaceous of India, thought to be produced by titanosaurs, have preserved silicified plant tissues. This suggests that modern grass (Poaceae) had evolved, diversified and spread before India became geographically isolated in the Late Cretaceous after splitting from Gondwana. Not only does this give new evidence to the evolutionary history of grass, but it also gives evidence of the diets of Late Cretaceous animals, as it implies the titanosaurs were extremely unpicky eaters when it came to their greens, eating many different kinds of plants including grasses, cycads, conifers and dicotyledons.
So, coprolites are exceedingly useful to palaeontologists, giving unique information on the diets and behaviours of ancient animals and even the evolutionary history of organisms. Not bad for such a gross type of fossil.
Image References
[1] A) Vertebrate coprolites of various shapes, dating back to the Late Triassic. Image from Hansen, et al., 2015. B) Thalassinoides burrows dating back to the Middle Jurassic from Makhtesh Qatan, southern Israel. Image by Mark A. Wilson.
[2] A giant coprolite, attributed to Tyrannosaurus rex, from Montana, USA. Scale bar = 10cm. Image taken from Chin, et al., 1998.
Information References and Further Sources
[1] Andrews, P., and Fernandez-Jalvo, Y. (1998). ‘101 uses for fossilized faeces’, Nature, 393 (6686), pp 629-630. Accessed 16th July 2020. Click Here.
[2] Buckland, W. (1829). ‘XII.—On the Discovery of Coprolites, or Fossil Fæces, in the Lias at Lyme Regis, and in other Formations.’, Transactions of the Geological Society of London, 2 (3), pp. 223-236. Accessed 16th July 2020. Click Here.
[3] Hansen, B. B., Milàn, J., Clemmensen, L. B., Adolfssen, J. S., Estrup, E. J., Klein, N., Mateus, O., and Wings, O. (2015). ‘Coprolites from the Late Triassic Kap Stewart Formation, Jameson Land, East Greenland: Morphology, classification and prey inclusions’, Geological Society London Special Publications, 434 (1), pp. 49-69. Accessed 16th July 2020. Click Here.
[4] Hunt, A. P., Lucas, S. G., Milàn, J., and Spielmann, J. A. (2012). ‘Vertebrate coprolite studies: summary and prospectus’, New Mexico Museum of Natural History and Science, Bulletin 57. Accessed 16th July 2020. Click Here.
[5] Chin, K., Tokaryk, T. T., Erickson, G. M., and Calk, L. C. (1998). ‘A king-sized theropod coprolite’, Nature, 393 (6686), pp. 680-682. Accessed 16th July 2020. Click Here.
[6] Prasad, V., Strömberg, C. A. E., Alimohammadian, H., and Sahni, A. (2005). ‘Dinosaur Coprolites and the Early Evolution of Grasses and Grazers’, Science, 310, 5751, pp. 1177-1180. Accessed 16th July 2020. Click Here.
[7] Torrens, H. (1995). ‘Mary Anning (1799–1847) of Lyme; ‘the greatest fossilist the world ever knew’’, The British Journal for the History of Science, 28 (3), pp. 257-284. Accessed 16th July 2020. Click Here.
[8] Torsvik, T. H., Tucker, R. D., Ashwal, L. D., Carter, L. M., Jamtveit, B., Vidyadharan, K. T., Venkataramana, P. (2000). ‘Late Cretaceous India–Madagascar fit and timing of break‐up related magmatism’, Terra Nova, 12 (5), pp. 220-224. Accessed 16th July 2020. Click Here.