Saturday 16 September 2017

Ichthyosaurus somersetensis: A pregnant Ichthyosaur from the Early Jurassic of Somerset, England.

Ichthyosaurs were Marine Reptiles known from the Triassic to the Cretaceous. They were fully-aquatic with a Dolphin-like form, and known to have given birth to live young, rather than emerging from the water to lay eggs, as is the case in Turtles and Crocodiles. England is noted for having produced a large range of Early Jurassic Ichthyosaur specimens, with the majority of these have come from the Jurassic Coast area of Dorset, and the area around the village of Street in Somerset, where a number of limestone quarries have produced Ichthyosaur specimens since the middle nineteenth century.

In a paper published in the journal Acta Paleaontologica Polonica on 28 August 2017, Dean Lomax of the School of Earth and Environmental Sciences at The University of Manchester, and Sven Sachs of the Naturkundemuseum Bielefeld, describe a new pregnant Ichthyosaur specimen from Doniford Bay in Somerset, England.

The new specimen is assigned to the species Ichthyosaurus somersetensis, the largest species in the genus, reaching about 1.5 meters, though this is not the largest specimen of the species (it is, however, the first pregnant Ichthyosaurus specimen assigned to a species). The specimen was excavated in the 1990s by commercial fossil hunter Peter Langham, who prepared it by using a tail from another specimen (it lacked one) and adding several Ammonites to the slab on which it was preserved. It was then sold to Swiss fossil and mineral dealers Siber + Siber, who in turn sold it on to the Hanoverian art collector Ernst Schwitters (1940-1998). After his death the specimen, along with other items from his collection, was left to the Kurt & Ernst Schwitters Foundation, who first loaned and then sold specimen to the Niedersächsisches Landesmuseum in Hannover.

(A) Skeleton of Ichthyosaurus somersetensis from the Lower Jurassic (lower Hettangian) of Doniford Bay, Watchet, Somerset, UK. (B) Explantory photograph with the composite/reconstructed sections shown in black; the question marks indicate that the element may have been added to the specimen; arrow points to a large crack that runs across the specimen; star indicates the position of the embryo. Lomax & Sachs (2017).

The embryo in the specimen is located between the ribs, near the mid-posterior dorsal vertebrae. It is identified from a series of 23 vertebral centra, 16 of which are articulated and one of which appears damaged and possibly restored, forming a section of vertebral column 6.37 cm in length. This is associated with a number of delicate ribs and a number of other bones, including a partial fin.

Embryo of Ichthyosaurus somersetensis from the Lower Jurassic (lower Hettangian) of Doniford Bay, Watchet, Somerset, UK, showing articulated vertebral column, isolated forefin, probable scapula (white arrow), ribs, and isolated centra. Lomax & Sachs (2017).

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