® ©
® ©
B ©
Fig. 75. Excalibosaurus costini (BRSMG Cc881). A) skull. B) forefin, depicted as the left, in dorsal view. Scales each equal 100 mm.
ably tripartite, with no fusion between ischium and pubis.
Long bodied, preflexural vertebrae >90, and probably exceeds
95; presacral vertebrae >44. Fore- and hindfins not
markedly long and slender; number of elements in longest
digit of forefin <16; forefin less than half as long as skull;
hindfin markedly smaller than forefin. Forefin with four
digits, the post-axial one being much the smallest; radius
probably notched. Medium to large sized, with total length
exceeding 6 m. Rare.
Remarks: Maisch & Matzke (2000B: 86) synonymized
Excalibosaurus with Eurhinosaurus on the grounds that
“apart from the differences in the extent of the overbite,
there are no fundamental distinguishing features . . . ”. It
should be pointed out that the differences in the extent of
the overbite between the two taxa are fundamentally different.
In Eurhinosaurus the mandible averages only 52
percent of the skull length (observed range 45-59, n=12,)
whereas it is 76 percent in the holotype of Excalibosaurus
costini.
A recently discovered complete skeleton, referred to
the present species (McGowan, in press), provides additional
data for distinguishing between Excalibosaurus and
Eurhinosaurus. The vertebral count to the tailbend is 98,
compared with an observed range of 91-95 for Eurhinosaurus
(N=8). Given that vertebral counts are relatively stable
in ichthyosaurs, this is considered an important distinguishing
feature. Although the hindfins are incomplete in
the new material, they are obviously markedly smaller
than the forefins. This contrasts with the condition in
Eurhinosaurus, where the hindfins are almost as long as the
forefins. Furthermore, the forefin is not as long and slender
in Excalibosaurus, and it is less than half the length of the
skull. Excalibosaurus appears to be relatively longer bodied
than Eurhinosaurus, the tailbend being set well back, probably
further back than level 95. Eurhinosaurus is geologically
younger than Excalibosaurus, postdating it by about 16
million years.
Excalibosaurus costini McGowan, 1986B
Fig. 75; PI. 3
Excalibosaurus costini McGowan, 1986B: 454
Holotype: BRSMG Cc881, a complete skull, with associated
forefin, pectoral girdle, vertebrae and ribs. The holotype
is about half the size of the referred specimen (ROM
47697).
Diagnosis: As for genus.
Occurrence: Lilstock, Somerset, England.
Stratigraphic range: Lower Lias; Lower Jurassic (Sinemu-
-rian). ..
Plate 3
Excalibosaurus costini, holotype, BRSMG Cc881. Scale measures 500 mm.
Genus Eurhinosaurus Abel, 1909
Eurhinosaurus,A bel, 1909: 245
Type species: Eurhinosaurus longirostris (Mantell, 1851).
Diagnosis: Mandible considerably shorter than skull, <60
percent of skull length; snout, premaxillary, and prenarial
ratios each >1.0; orbital ratio >0.20. Basioccipital with extensive
extracondylar area, lying largely ventral to condyle,
from which it is clearly set off, basioccipital peg
present. Pelvic girdle tripartite, without fusion between
pubis and ischium. Long-bodied, preflexural vertebrae
>85, but probably not >95; presacral vertebrae probably
>44. Fore- and hindfins both long and slender; number of
elements in longest digit of forefin >17; forefin at least half
as long as skull; hindfin well developed, approaching
length of forefin. Forefin with 4 or 5 digits; notching either
absent, or occurring in few elements (perhaps <4) of leading
edge. Notching usually occurs in hindfin, may be restricted
to <8 elements. Large ichthyosaurs, reaching total
lengths just in excess of 7 m.
Remarks: As shown elsewhere by McGowan (1974A: 25;
1989A: 412; 1994B: 747) Ichthyosaurus longirostris was first
described by Mantell (1851: 385) based on a partial skeleton
from the Upper Lias of Whitby, Yorkshire (BMNH
14566). As the specimen was dorsoventrally compressed,
and exposed from the dorsal aspect, Mantell had no way
of knowing that the mandible was greatly attenuated. Subsequent
preparation of the specimen confirms that this is
the case (McGowan, 1994B), and the material is unquestionably
referable to the monotypic genus Eurhinosaurus.
Eurhinosaurus longirostris (Mantell, 1851)
Fig. 76; PI. 3
Ichthyosaurus longirostris Mantell, 1851: 385
Ichthyosaurus longirostris [non Owen and Jäger]; Jäger,
1856: 948
Ichthyosaurus longirostris [non Owen]; Owen 1 8 8 1 :1 1 8 [partim]
Ichthyosaurus latifrons; L ydekker 1889A: 89, 91 [partim]
Ichthyosaurus longirostris [non Jäger]; F raas, 1891: 63
Eurhinosaurus longirostris Abel, 1909: 245
Ichthyosaurus longirostris; H uene, 1922: 32
Eurhinosaurus sp. H uene, 1928: pi. 37
Eurhinosaurus huenei Swinton, 1930: 275
Eurhinosaurus longirostris; Huene, 1951A: 277
Eurhinosaurus huenei; McGowan, 1979B: 116
Eurhinosaurus longirostris; McGowan, 1994B: 751
Holotype: BMNH 14566, a dorsoventrally compressed
skull with most of the vertebral column and a partial
forefin.
Diagnosis: As for genus.
Occurrence: The holotype is from Whitby, Yorkshire, England,
but most of the other material comes from Holz-
maden, southern Germany.