Wooster’s Fossils of the Week: Mystery fossil solution — an oyster from the Middle Jurassic of southern England
Mark Wilson August 30th, 2016
Last week I gave my students in Wooster’s Invertebrate Paleontology course a fossil to identify (shown above), using any techniques they want. This was their first task in the course, so it was difficult for most of them. I hope it was a good introduction to practical paleontology and the mysteries of taxonomy. One student, Josh Charlton, nailed it all the way to the species. Several other students got close.
These are Middle Jurassic oysters properly identified as Praeexogyra hebridica (Forbes, 1851). I collected them many years ago from the Frome Clay (Bathonian) at Langton Herring along the coast of Dorset, southern England. They are extremely common fossils there, crunching underfoot as they erode out into the surf. These oysters lived in estuaries, where there was a mix of fresh and marine waters. In 1976, John Hudson and our friend Tim Palmer sorted out the systematics and evolution of this oyster species, moving it from Ostrea and Liostrea to the genus Praeexogyra.
This oyster species was originally described in 1851 as Ostrea hebridica by Edward Forbes (1815-1854) from Jurassic sediments on the Scottish Isle of Skye in the Inner Hebrides (hence the name). As was typical of many nineteenth century fossil descriptions, the illustrations (above) and diagnoses are not particularly helpful. Forbes (1851) wrote, “Being very familiar with the oysters of the Wealden and Purbeck I cannot admit this identification, nor can I refer the Loch Staffin shell to any known fossil, although, as usual in this variable genus, it is difficult to express in words its marked distinctions.” We wouldn’t get away with such a conclusion for a new species today, but to be fair, oysters are notoriously difficult to describe. Forbes knew that this species “inhabited brackish water” in the Jurassic.
Edward Forbes FRS, FGS (above) was born on the Isle of Man in 1815, the year of Waterloo. He was, as they said then, a sickly child unable to attend a regular school for long. He traveled to London when he was 16, though, to study art. That didn’t work out, so he became a medical student at the University of Edinburgh. Forbes was intrigued more with natural history than medicine (a common story!), so he dropped his medical plans and set out to become a naturalist skilled in paleontology, mineralogy, zoology, anatomy and botany. His younger brother David became a well-known mineralogist. Edward Forbes caught on quickly. In 1838 he published a summary of the mollusks found on the Isle of Man. He was 23 years old. Forbes traveled widely, accumulating more observations, experiences and colleagues. He had many publications and advocated numerous hypotheses about the distribution of life forms. Some had lasting value (like the distribution of flora before and after glaciation intervals) and others were a bit naive (such as his idea that there is no marine life below 300 fathoms). He was a president of the Geological Society of London (1853), and in 1854 became the Professor of Natural History at Edinburgh, his driving ambition. Unfortunately his health problems caught up with him and he died that year at age 39.
Edward Forbes played a critical role in the history of science by being a mentor of Thomas Henry Huxley. Forbes advised Huxley as a young man and helped him publish his earliest works. Forbes introduced Huxley to his circle of colleagues, which eventually led to the latter’s election to the Royal Society while only 26 years old. Huxley wrote a touching obituary for his young friend Edward Forbes.
Anderson, F.W. and Cox, L.R. 1948. The “Loch Staffin Beds” of Skye; with notes on the molluscan fauna of the Great Estuarine Series. Proceedings of the Royal Physical Society of Edinburgh 23: 103-122.
Forbes, E. 1851. On the Estuary Beds and the Oxford Clay at Loch Staffin, in Skye. Quarterly Journal of the Geological Society 7(1-2): 104-113; plate 5, figs. 4a-4c.
Hudson, J.D. and Palmer, T.J. 1976. A euryhaline oyster from the Middle Jurassic and the origin of the true oysters. Palaeontology 19: 79-93.