Wednesday, August 30, 2017

[Paleontology • 2017] On the Largest Ichthyosaurus: A New Specimen of Ichthyosaurus somersetensis Containing An Embryo


Ichthyosaurus somersetensis Lomax and Massare, 2017
 (NLMH 106234) 
from the Lower Jurassic (lower Hettangian) of Doniford Bay, Watchet, Somerset, UK


A formerly undescribed Ichthyosaurus specimen from the collection of the Niedersächsisches Landesmuseum (Lower Saxony State Museum) in Hannover, Germany, provides valuable new information. The skeleton was collected from the Lower Jurassic strata (lower Hettangian, Blue Lias Formation) of Doniford Bay, Somerset, UK. However, the specimen is a composite as almost the entire tail has been added and other parts are reconstructed. Regardless of the incomplete preservation, the estimated total length of this individual, based on the skull and precaudal length, is between 300 and 330 cm and it is thus the largest unequivocal example of the genus Ichthyosaurus. Cranial and postcranial characters, specifically from the maxilla, lacrimal, jugal, the humerus, and the ilium justify a referral to I. somersetensis. A fork-like shape of the proximal end of the ilium is unusual and has not been reported for any species of Ichthyosaurus. Likewise the presence of four elements in the third row of the hindfin, indicated by the presence of a bifurcation is novel for the species and has wider implications for the taxonomic utility of hindfins within the genus. The specimen also bears an embryo, which is only the third embryo known for Ichthyosaurus and the first to be positively identified to species level.

Key words: Ichthyosauria, Ichthyosaurus somersetensis, embryo, Jurassic, Hettangian, UK, Somerset.


Artist impression of pregnant Ichthyosaurus.
ILLUSTRATION: Joschua Knüppe

Fig. 2.  Skeleton of Ichthyosaurus somersetensis Lomax and Massare, 2017 (NLMH 106234) from the Lower Jurassic (lower Hettangian) of Doniford Bay, Watchet, Somerset, UK. 


Systematic palaeontology

Order Ichthyosauria de Blainville, 1835
Family Ichthyosauridae Bonaparte, 1841
Genus Ichthyosaurus De la Beche and Conybeare, 1821
Type species: Ichthyosaurus communis De la Beche and Conybeare, 1821; upper Hettangian–lower Sinemurian, Lower Jurassic of England, UK.

Ichthyosaurus somersetensis Lomax and Massare, 2017

 .....


Dean R. Lomax and Sven Sachs. 2017.  On the Largest Ichthyosaurus: A New Specimen of Ichthyosaurus somersetensis Containing An Embryo. Acta Palaeontologica Polonica. in press.  DOI: 10.4202/app.00376.2017

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