SYSTEMATIC DESCRIPTION

Name: Stenopterygious acutirostris (Owen, 1840).

Stratigraphy: Alum Shale Formation; Upper Liassic; Lower Toarcian; Early Jurassic.

Locality: Saltwick Alum Pit, near Whitby, Yorkshire, England.

Type specimen: BM (NH) 14553 skull plus entire right anterior paddle and imperfect left anterior paddle.

This specimen was first ascribed to I. acutirostris by Richard Owen in 1840 in his Report on British Fossil Reptiles (1839). He reports that the specimen gives a profile of the entire head and one of the anterior paddles. Also that the upper and lower jaws converge to the end of the snout which is sharp and spear-shaped. He also states that the length of the head is 11 inches and 10 lines.

In 1851 Mantell in Petrifactions and their Teachings refers to this specimen then labelled I. longipennis. In particular he refers to the long tapering fin suggesting that it may have been wider in proportion to its length and that many ossicles may have been lost. He also comments that he was unaware of any published description of this species. (see panel on Historical Review)

In 1881 Owen described I. acutirostris in the Mon. Pal. Soc., Liassic Reptiles but figured only the skull in plate 28, figure 2. However the description confirms that the skull belongs to BM(NH) 14553 because it describes the 'right entire fin' and mentions the 'preserved basal portion of the left fin' as belonging to the same specimen. The description of the 'entire' fin includes the emargination of the radius, radio-carpal and succeeding ossicle.

Owen describes the three primary digits plus a small part of the fourth but unlike Mantell believes that because of its juxtaposition that fin bones have not been lost. He also suggests that the paddle was bifurcated. However the skull length anterior to the orbit is noted as 18 inches and 7 lines.

Lydekker 1889 refers to the specimen as the type of I. acutirostris in his Catalogue of Fossil Reptiles volume 2 on page 73.

Ichthyosaurus acutirostris was referred by McGowan 1974 to Stenopterygiidae von Huene 1948 as Stenopterygius acutirostris (Owen) when he recorded that the type specimen, BM(NH) 14553, may have been lost. McGowan figured the skull after Owen 1881 in figure 11 D. Suggesting that the decurved appearance of the snout may have been a little exaggerated in this figure since the feature is not apparent in all the S. acutirostris skulls. The fin was not described in this paper beyond observing that it belonged to the longipinnate ichthyosaurs i.e. anterior paddles with three distal carpels and hence three primary digits.

Further investigation

Further investigation will compare the dimensions of the anterior right paddle and the skull with those compiled by McGowan (1974) for the other referred specimens of Stenopterygius acutirostris for example BM(NH) 1500a.