Fig. 80. Ichthyosaurus communis. A) complete skeleton (based upon BMNH R1073). B) skull (BMNH 39492). C) forefin from Lyme Regis
(BMNH R1162). D) forefin from Street, Somerset (BMNH 14565). Both fins depicted as left, in dorsal view. Notice that the Somerset
forefin has fewer digits. Scales equal 100 mm (A-B) and 50 mm (C-D).
tures that distinguish it from Ichthyosaurus communis.
These features, shared with a recently rediscovered specimen
(SMNS 13111; Maisch, 1997: fig. 5), are a shortened
quadratojugal and a high maxillary tooth count (in excess
of 20). Furthermore, SMNS 13111 has “waisted” teeth,
where the crown is narrow and the root inflated, as figured
by Conybeare (1822: pi. 15, fig. 8) as characteristic of
I. intermedius. Regarding the quadratojugal, in both skulls
(SMNS 13111; Conybeare 1822: pi. 17), the quadrate has
been displaced such that its proximal end lies both poste-
Plate 8
Ichthyosaurus communis, skull of neotype, BMNH R1162. Scale on photo measures 100 mm.
rior and ventral to its normal position, and is no longer in
articulation with the supratemporal. This may help explain
why the quadratojugal does not appear to extend
very far down towards the distal end of the quadrate. It
should also be noted that it is usually not possible to
determine the true extent of the quadratojugal in the typically
flattened specimens, so this is not a very useful
diagnostic feature. Although it is true that the maxillary
tooth count is higher in both skulls than has been reported
for Ichthyosaurus communis (McGowan, 1974B), CM discontinued
using this feature because of its variability. For
example, in Stenopterygius macrophasma, 35 maxillary teeth
have been recorded, which is remarkably high, but which
may relate to maturity (McGowan, 1979B: 113). Tooth
shape is also variable and thus an unreliable diagnostic
feature in ichthyosaurian taxonomy. For example, the
trenchant tooth form Conybeare (1822: 108 and pi. 15,
fig. 7) described and figured for Temnodontosaurus platyo-
don can be seen, alongside thé typically conical teeth, within
the dentition o f a single in d ivid u a l (McGowan, 1994A).
H awkins (1834), disregarding the priority of the species
that had already been described, erected names of his own,
based on features of fin structure, which he thought were
more appropriate. All of his names are subjective junior
synonyms. Six years later, H awkins (1840) removed the
prefix “chiro” and modified the spelling of some of his
species names, elevating them to generic rank. These included
Polyostinus and Paramecostinus, both being subjective
junior synonyms for Ichthyosaurus communis. Jaekel
(1911) gave a variety name (Ichthyosaurus communis var.
hyperdactyla) to a specimen from Lyme Regis in which there
were upward of eight digits. Such a high digital count is
within the range of variation for the species. His name,
treated here as a subspecies (according to the ICZN), is
accordingly synonymized with I. communis. See M cGowan
(1974B) for further discussions regarding the synonymies
of the species referred to the genus Ichthyosaurus.