Few events in prehistory have attracted as much popular interest as the extinction of the dinosaurs. The disappearance of these iconic beasts has been debated and speculated over pretty much since the first discovery and identification of their bones. Today most researchers agree that the extinction was the result of some global ecological catastrophe, be it an asteroid impact or a massive volcanic eruption but over the years there have been some other, less conventional suggestions. One of these was published in 2008 by researchers from China and it identified an unusual suspect: fungi.
The research focused on a selection of fragmented dinosaur egg shells recovered from the Hugang Formation in Central China. They date to the Late Cretaceous and belonged to three different species; Elongatoolithus andrewsi, Elongatoolithius elongaggatus and Macroolithus. By using an ESEM (environmental scanning electron microscope) the researchers examined the microstructure of the egg shells and they discovered something that shouldn’t have been there. In the original paper they describe it as a filamentous fungi; “needle-like”, “ribbon-like” and “silk-like” found within the biomineralised layer of the egg. They were wider at the bottom, tapered to their tips and were unbranched. At only a few nanometres long they were tiny but they seemed to be living throughout the entirety of the shell. A chemical analysis seemed to confirm that the fossilised fungi had indeed been a living thing and not some depositional quirk, whilst the fact that the fungi showed the same fracturing and main chemical composition as the rest of the fossil suggested it was fossilised alongside the egg rather then having entered afterwards. The paper concluded that this fungi was a parasite which had infiltrated the egg either during development or shortly after it was laid, and that such parasitism would have severely hampered the normal development of the embryo inside the egg. If such infections were wide-spread enough amongst dinosaur eggs then it could have contributed to the eventual downfall of the dinosaurs.
Of course therein lies the problem. There is no evidence that such infection really was widespread amongst dinosaur eggs. So far I know of no other reports of such fungi having been found inside fossil eggs (if you have please send me the paper reference!) despite the fact that dinosaur egg shells have been well studied over the years using a variety of microscopic techniques. Although this could be because of some particularly special type of preservation present at Hugang at the moment there is no reason to think that if egg shells are themselves preserved then the fungi inside them wouldn’t have been too, not least because of the protection offered by the shells. At the very least this could suggest that such infections were comparatively rare. Then there is also the overwhelming geological evidence of some massive climatic upheaval at the time of the extinction and the rather inconvenient fact that it wasn’t only the dinosaurs that suffered during this event. Many marine reptiles, all Pterosaurs, and dozens of other animal groups also went extinct or saw massive declines at this time proving it was a worldwide event not something which effected only the dinosaurs.
Nevertheless this discovery is extremely interesting even if it didn’t polish off the dinosaurs. Fungi are poorly represented in the fossil record because of their small size and comparative fragility so any fossil fungi is vitally important to our record of these organisms. To discover a parasitic one is particularly fascinating especially as its habit of living within an eggshell marks this type of fungi out as something called an endolith. Today most commonly studied endlothic fungi live inside the shells of marine life, and although most are harmless some are parasitic. Some species can also lives inside limestone and other rocks. They are fascinating organisms which have adopted a very specialist mode of life in order to survive and thrive and evidence of them in the fossil record pushes back their evolution by millions of years. It is also entirely possible that such infection did afflict dinosaur eggs and perhaps caused the loss of whole clutches but then this isn’t itself unusual. Many disease affect modern birds and lizards and they do play an important part in the ecosystems these animals inhabit. There is no reason to think dinosaurs were somehow immune to disease, and in fact we have other evidence of parasitic infections in that most iconic of all dinosaurs; T-rex, albeit not a fungal one.
I think this discovery is fascinating in its own right – potentially parasitic fungi in the fossil record are very, very rare – without the need to invoke their involvement in that most famous of all mass extinctions. Although dinosaurs often grab the headlines insights into the ecosystems around them are equally important and research likes this sheds increasing light on the dynamics of disease millions of years ago.
Gong, Y, et al. 2008. Endolithic fungi: A possible killer for the mass extinction of Cretaceous dinosaurs. Science in China Series D: Earth Sciences. 51(6). pp.801-807. DOI: 10.1007/s11430-008-0052-1