By Paul F Wilson

Today’s museums are home to an overwhelming number of objects from the depths of history, ranging from relics of cultures and societies long past to the remains of ancient leviathans that defy modern understanding. Among these myriad objects are a smaller proportion with great cultural or scientific significance. Their importance to human understanding of the past means they remain sequestered away in museum collections, safely kept in the knowledge that their significance has already been fully explored.

The right dentary of Megalosaurus bucklandii, part of the lectotype of the specimen (one part of a collection of specimens that is the quintessential example of a species), is one such example at the Oxford University Museum of Natural History (OUMNH). This jawbone represents the first scientifically described dinosaur, the first fossil specimen to be recognised as belonging to a then as-yet unknown group of animals. Described by the Reverend Williams Buckland in 1824, and then included among the first description of the ‘Dinosauria’ by Richard Owen in 1842, Megalosaurus and its cousins Iguanodon and Hylaeosaurus went on to kickstart the first dinosaur craze in Victorian England, a legacy that arguably persists to this day.

In spite of this, surprisingly little is known about the specimen itself. Museum records for the specimen are scant. It is known that it was purchased in 1797 but little information appears to have been recorded on what actually happened in the interim between then, its description and today. Images of the specimen that exist take the form of idealised or inaccurate lithographs, the trail running cold in the mid-19th century. This is especially concerning as the specimen shows considerable evidence of restoration in plaster, as noted by Benson et al. (2008). When this damage and replacement took place is uncertain, although records seem to suggest that something may have happened when the specimen first went on display in the early 20th century.

What restoration was done to the object is not clear however. The process of conservation, the treatment and stabilisation of damage and the degradation of a museum object mandates knowledge on what has previously been done to the object. An absence of this information makes future conservation efforts challenging and risky, making the venerable specimen a conservation concern in its own right.

In order to overcome this, we attempted to reverse engineer the conservation history of the specimen, utilising cutting-edge imaging techniques. Previous research (Wilson et al. 2017) explored the specimen using the X-Ray Computed Tomography (XCT) facilities at the Centre for Imaging, Metrology and Additive Technologies (CiMAT) at the University of Warwick. This method uses the transmission of x-rays through an object to reconstruct the internal and external structure of an object based on its relative density. This process revealed the presence of two separate plasters used to repair the specimen. This yielded some useful information including the location of all restored material, being characterised in 3D, and the recognition of strange, super-dense particles within one of the plasters.

This was insufficient to properly determine the nature of the plasters however. To better characterise them, two elemental mapping methods were used in a convergent approach, Energy-Dispersive X-ray Spectroscopy (EDS) and X-Ray Fluorescence (XRF) being employed. Both of these methods rely on the principle of bombarding a material with high-energy x-rays and detecting the emission of characteristic secondary x-rays, which determine the elemental makeup of the sample.

Analysis of the two plasters revealed that the more abundant plaster, P1, was an impure gypsum plaster (plaster of paris) filled with sand grains, grains of the original specimen and small particles of the mineral minium (a reddish lead oxide). The plaster was also coated in shellac. The second plaster, P2, was also a gypsum plaster, lacking the minium and sand grains but instead being coated in barium hydroxide, a moisture sealant, rather than shellac. The identification of these plasters has helped to better elucidate previous conservational efforts and how to treat the specimen in the future in line with modern conservation standards.

This overall represents an extremely conservative approach to treatment by the conservator. The integration of reddish, dense minium particles represents a conscious effort to tint the plaster to better match the weight and colour of the original specimen and to prioritise the verisimilitude of the plaster restoration.

The restoration was also extremely conservative in the geometry of the specimen as well, with small fragments of the original damaged specimen being suspended in the plaster.

Also revealed from the analysis are a number of new findings. Hidden teeth, in the process of growing and being replaced, were elucidated by the XCT analysis, shedding some insight on the tooth replacement of Megalosaurus. Additionally, a complex series of dentary canals within the jawbone were revealed, structures that are poorly explored but that recent research has begun to show could be of evolutionary significance. Thus, even one of the museum’s most austere objects still has some new insights to show.

This project has also provided some benefit to the Museum’s public engagement. Through the medium of 3D printing, replicas of the legendary jawbone have been made that allow visitors to get hands-on with the specimen for the first time. This possibility reflects a new avenue in replica fabrication and museum display methods that could revolutionise the ways in which museums present their content to audiences.

Overall then, Megalosaurus presents a powerful case study for conservation professionals on how cutting edge technologies can reverse-engineer the chequered history of objects that are poorly understood. These state-of-the-art analytical techniques can also present opportunities to get new life out of old objects, proving that even revered objects can still surprise.

Special thanks and credit to the WMG and the University of Warwick and the Oxford University Museum of Natural History.

This paper originally appeared as a blog post here: http://blogs.biomedcentral.com/on-physicalsciences/2019/03/08/reverse-en...

The article is also published through the journal Heritage Science and its publisher, SpringerOpen. The article can be found here: https://heritagesciencejournal.springeropen.com/articles/10.1186/s40494-...

(For the full article, see the December 2019 "News in Conservation" Issue 75)

AUTHOR BYLINE

Paul F Wilson is an early career fellow at WMG, the University of Warwick. He specialises in the use of 3D printed replicas in public engagement within museums. He focuses on their creation and fabrication using cutting-edge digitisation methods including micro-CT, photogrammetry, laser scanning and the workflows by which they are created.