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

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.

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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