Shedding light on an isolated skull: a newly described elasmosaur skeleton from the Late Cretaceous of Morocco

Fig. 2. Life restoration of Z. oceanis by Nobumichi Tamura (www.palaeocritti.com/ and http://spinops.blogspot.co.uk/).

The bodiless plesiosaur

In 2011, a plesiosaur specimen, consisting of an isolated and crushed skull, was described. The collected skull sadly lacked any postcranial remains, but was identified as an elasmosaurid plesiosaur and considered to be something new. Therefore, it was given the name Zarafasaura oceanis. The skull was collected in the Sidi Daoui area, near the city of Oued Zem, situated within the Khouribga Province of the northeast Oulad Abdoun Basin in Morocco. There, the phosphates date to the Maastrichtian Stage of the Cretaceous, the last stage of the Mesozoic Era, famous for many fossils, such as Tyrannosaurus rex from the USA. The study suggested that Zarafasaura shared close connections with other elasmosaurids from the Late Cretaceous of North America and Japan. The elasmosaurs had the longest necks of any plesiosaurs and flourished during the Maastrichtian. It was hoped that future discoveries of more complete remains would shed light on the general appearance and understanding of Zarafasaura.

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Fig. 1. Mounted skeleton of Zarafasaura oceanis (WDC CMC-01) at the Wyoming Dinosaur Center. Photograph by Dean Lomax.

‘The body that fits the head’

In April 2004, seven years before the description of Z. oceanis, an almost complete plesiosaur skeleton was discovered in the Sidi Daoui area in Morocco, at the same location as the skull discussed previously. The specimen (museum number WDC CMC-01) was excavated by a small team and covered by five large plaster jackets (to protect the fragile bones). It was largely articulated, consisting of a relatively complete but crushed skull, much of the vertebral column including a nearly complete neck, portions of the pectoral and pelvic girdle, fore and hind fins, along with numerous ribs. Together, the material represents perhaps 70% of the animal.

After excavation, the specimen was prepared in a laboratory and completely freed of matrix (surrounding rock). To ensure no information was lost, every element was individually marked. Portions of the skeleton were partially constructed with plaster. In fact, the original skull, although excellently prepared and each bone numbered, was completely removed from its surrounding matrix and reconstructed three dimensionally, giving the specimen more of an aesthetic appeal. Also, only few of the original teeth were associated with the skull, most of which were broken, and so were replaced with isolated teeth found in the same area. For a palaeontologist, it is incredibly difficult to describe and interpret a skull or any bones that have been largely reconstructed, which is a shame, as the original shape, morphology and structure is lost forever. However, before and during preparation, detailed photographs were taken of the skull and skeleton. After preparation, the entire skeleton was mounted for display and public sale. In spite of this, the specific identification of the animal remained undetermined and was simply recorded as an indeterminate plesiosaur.

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Fig. 2. Life restoration of Z. oceanis by Nobumichi Tamura (www.palaeocritti.com/ and http://spinops.blogspot.co.uk/).

Having been mounted and listed for sale, the specimen went on display in 2006 at the famous Tuscon Fossil Show. Dr Burkhard Pohl, director of the Wyoming Dinosaur Center (WDC), was attending the show and this specimen captured his eye. The specimen was subsequently purchased and accessioned into the WDC’s collection. It is extremely lucky that individuals such as Dr Pohl acquire such specimens, essentially ‘saving them’ for science and education; otherwise it is possible that this, and many similar fossils, may quite easily disappear into private collections, never to be seen again.

In 2009, I spent three and a half months conducting field work, exhibition development and research at the WDC. Before my visit, the elasmosaur had been mounted and placed on display, for the first time. Seeing the specimen and having some knowledge of Moroccan fossils, I thought this may potentially be something quite significant. Bill Wahl, a fantastic palaeontologist and preparation laboratory manager at the WDC, works with a variety of fossils, but has primarily researched plesiosaurs. I discussed the specimen and its background with him, taking a few notes. However, it was not until 2011, after the new elasmosaur was described (the crushed skull discussed previously), that Bill and I wondered whether the large specimen on display may actually belong to the newly described Zarafasaura oceanis. In 2011, we set out to research the beasty and began collaborating on a project. In 2012, I spent three weeks with Bill at the WDC, examining parts of the skeleton, especially the skull. Sadly, as a result of how the skeleton was mounted and reconstructed, thorough interpretation of the bones was difficult. Having examined the skull as rigorously as possible and compared hundreds of photographs of the skull (before preparation), we determined that WDC CMC-01 belongs to the same animal as that described in 2011 – Z. oceanis. Therefore, we had a body associated with a skull, enabling us, for the first time, to look at the postcranial skeleton of an animal that was previously known only from an isolated skull. Many aspects of palaeontology are often seen as piecing together a giant jigsaw puzzle, but, in this case, we were privileged enough to be able to fit several pieces at the same. We now have a much greater understanding of this animal. Our study was published in 2013.

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Fig. 3. Two of the original field jackets displaying portions of the articulated skeleton. Scale bars equals 20cm. Reproduced from Lomax & Wahl, 2013.

Plesiosaur fossils in Morocco

Plesiosaur fossils are rare in Africa, with very few known that are substantially complete. In fact, in Morocco, only four types of plesiosaur have been described (including Zarafasaura oceanis), with the other three having been collected from older deposits from the earliest part of the Late Cretaceous (Turonian Stage). Several fragmentary remains, some including partial skeletons, limb elements and isolated series of vertebrae, have all been discovered. The material has been identified as belonging to elasmosaurs. However, as no skull material has been found associated with the postcranial remains, it has simply been impossible to refer isolated material to the taxon Z. oceanis. But, with the discovery and description of WDC CMC-01, we may now be able to review and identify some of the isolated plesiosaur specimens that have been collected, perhaps allowing for their referral to Z. oceanis, and potentially unlocking the true taxonomic and scientific significance of fragmentary plesiosaurs collected in Morocco. Other remains from the phosphate beds consist of isolated teeth. These are often identified or sold by dealers under the name Plesiosaurs mauritanicus and many fossil collectors reading this may recognise (and potentially have a tooth with) this name. It was determined that the name P. mauritanicus is dubious (nomen dubium), in that a single tooth is not enough to establish a valid taxon. In fact, many of these isolated teeth may actually be referable to Z. oceanis.

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Fig. 4. The reconstructed skull of WDC CMC-01. Reproduced from Lomax & Wahl, 2013.

Acknowledgements

I would like to thank Bill Wahl for co-authoring the scientific publication of the specimen, and Dr Burkhard Pohl and the Wyoming Dinosaur Center for allowing access to the fossil, enabling the study. Thanks also go to Reece Davies for creating the fantastic illustrations of the skull and Nobumichi Tamura for the excellent life restoration of this animal.

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Fig. 5. Interpretative illustrations of the reconstructed skull by Reece Davies.

References/further reading

Buchy, M. C. 2005. An elasmosaur (Reptilia: Sauropterygia) from the Turonian (Upper Cretaceous) of Morocco. Carolinea, 63:5–28.

Lomax, D. R. 2011. The Wyoming Dinosaur Center. Deposits. Issue number 25. pp. 10–14.

Lomax, D. R. and Wahl, W. R. 2013. A new specimen of the elasmosaurid plesiosaur Zarafasaura oceanis from the Upper Cretaceous (Maastrichtian) of Morocco. Paludicola, 9:97–109.

Sci-news online news report: http://www.sci-news.com/paleontology/article01115-plesiosaur-zarafasaura-oceanis.html.

Vincent, P., Bardet, N., Pereda Suberbiola, X., Bouya, B., Amaghzaz, M. and Meslouh. S. 2011. Zarafasaura oceanis, a new elasmosaurid (Reptilia: Sauropterygia) from the Maastrichtian Phosphates of Morocco and the palaeobiogeography of latest Cretaceous plesiosaurs. Gondwana Research, 19:1062–1073.

Vincent, P., Bardet, N., Houssaye, A., Amaghzaz, M. and Meslouh, S. (In Press). New plesiosaur specimens from the Maastrichtian Phosphates of Morocco and their implications for the ecology of the latest Cretaceous marine apex predators, Gondwana Research. http://dx.doi.org/10.1016/j.gr.2012.11.011.

Fig. 2. Life restoration of Z. oceanis by Nobumichi Tamura (www.palaeocritti.com/ and http://spinops.blogspot.co.uk/).

Fig. 3. Two of the original field jackets displaying portions of the articulated skeleton. Scale bars equals 20cm. Reproduced from Lomax & Wahl, 2013.

Fig. 4. The reconstructed skull of WDC CMC-01. Reproduced from Lomax & Wahl, 2013.

Fig. 5. Interpretative illustrations of the reconstructed skull by Reece Davies.


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