What does a working cement quarry in the Beaujolais region have to do with fossils collected in Somerset 150 years ago? The JESBI Project goes international in a new collaboration with Paleorhodania; BRLSI Collections Manager Matt Williams tells all.
I have recently returned from fieldwork with an association called Paleorhodania, who organise an annual two week long dig in the Lower Jurassic strata of Rhône (Beaujolais) in the East of France. The quarry in which they excavate is owned and run by Lafarge, who generously allow access and assist with the occasional use of heavy machinery. This year there were 20 people working together during the first week, and I was fortunate enough to be invited to be part of that team.
Excavation
My particular role was to investigate the presence of nodules (hard limestone concretions within a bed of clay-rich shales) in one of the lowest horizons of the Toarcian strata which we believe is exactly the same age as our collections of fossils from Strawberry Bank in Ilminster, Somerset. As you can find out by visiting the JESBI project pages, our own collection of these beautifully preserved fossils was made over 160 years ago, and the quarry from which they came was in filled by 1860, so I went with high hopes of discovering a new site of this extraordinary preservation.
The team split into three groups, with my group focussing on the equivalent strata to Strawberry Bank. Isolated bones of ichthyosaurs, crocodiles, and fish, alongside a rich invertebrate fauna, and occasional terrestrial plant remains (such as the flowering cones of conifers) were found across the quarry throughout the week, but by the evening of day five we had still not found the beautiful uncompressed and articulated animals I had hoped for, despite the backbreaking labour of breaking many nodules (hard limestone concretions within a bed of clay-rich shales).
Discovery
Despite my despondency, we continued to look for nodules, turning our attention from the trench in which we had been excavating, to the spoil heap turned up by the gigantic bulldozer that had helped us reach the right depth. I returned from taking our smaller finds to a safe location for cataloguing to find that in my absence two of our Estonian colleagues had found articulated bones in a huge nodule. From these I could immediately see that this was part of an articulated ichthyosaur skeleton (a fast swimming predatory marine reptile), and with what appeared to be soft tissue preservation, just like Strawberry Bank.
That evening we made plans for how to proceed, and the next day we carefully excavated around turned over the nodule. In the mud underneath a slight skin of bone was left, which corresponded to bone exposed on the opposite side to the vertebrae and ribs. After gently cleaning the surface Dr. Jeremy Martin (President of Paleorhodania and Marie Curie postdoctoral fellow at the School of Earth Sciences, University of Bristol) and I were delighted to find the top of an ichthyosaur snout, broken along the tip in a diagonal plane, but leaving most of the apparently uncompressed skull in the rock. Since I have returned I have spoken to Dr. Martin, and further cleaning of the specimen has revealed that one of the forelimbs of the animal is also partially exposed. We expect that once the skeleton is prepared out of the rock, that it will be mostly complete all the way back to the base of the ribcage where the nodule ends.
To the left of this image you can see the cros sections of ribs, the pinkish discolouration below and to the right of the ribs is probable soft tissue preservation, and three of the vertebrae can be seen is cross section at the bottom-right of the nodule (the scale bar is 50mm).
To the left is the rostrum (snout) of the ichthyosaur before being carefully cleaned of mud.
Below is the rostrum of the ichthyosaur following cleaning, this is also seen in section, we are looking down at the dorsal surface of the rostrum, with the anterior of the nasal on the right, followed to the left by the premaxilla (both upper jaw bones) and dipping ventrally through a diagonal plane to the dentary (lower jaw). The teeth can also be seen, in cross section, towards the left side.
This is exciting news for both the BRLSI and Paleorhodania: there now exists site where we can excavate for more extraordinary fossils of an age and type that previously could only be found form the BRLSI’s historic collection. The two projects hope to find ways of continuing and expanding this international collaboration, and plans are already in place for further excavations in 2013.
The Science
The quarry contains a complete sequence of Lower Jurassic rocks, abundant in fossils, from a stage known as the Toarcian (183.0 to 175.6 million years old) as well as the lower part of the younger Aalenean (175.6 to 171.6 million years old).
The objective of this French led international team of palaeontologists, sedimentologists, and other geologists is to make a systematic study of these strata, to prospect and collect the fossilised remains of extinct marine vertebrates within a well-constrained paleoenvironmental context in order to reconstruct the evolution of these faunas during this key period of the Mesozoic. Alongside ammonites, belemnites, and fish it is possible to find the remains of prehistoric sea monsters: ichthyosaurs, plesiosaurs, and marine crocodiles. The JESBI projects new role in the Paleorhodania team, who have already been working on the site for four years,is principally to investigate the presence of nodules in one of the lowest horizons of the Toarcian, which we believe is exactly the same age as our collection of fossils from Strawberry Bank in Ilminster Somerset (see the JESBI project). This layer is called the falciferum Zone, AKA the Harpoceras falciferum Zone. The falciferum Zone is between 183 and 182 million years old and is named after a species of ammonite from the genus Harpoceras, a genus only present in rocks of this age, and divided into Harpoceras falciferum and Harpoceras serpentinum Subzones.
The discovery of a large, articulated, and un-compacted marine vertebrate in a nodule from this horizon in Rhône is an indication that a very similar, if not identical, depositional environment occurred at this time on at least two and possibly many sites across Europe, opening up previously impossible avenues of research.
