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THE FOSSIL FISHES OF THE CHALK.
(BEING A PRESIDENTIAL ADDRESS DELIVERED TO
THE CLUB ON 27TH FEBRUARY, 1926.)
BY SIR ARTHUR SMITH WOODWARD, LL.D., F.R.S.
(With One Plate and Seven Text Figures.)
THE imperfection of the geological record is especially
well illustrated by the fossil fishes of the English Chalk.
Apart from a few scattered fragments, they occur in satisfactory
numbers only in certain layers of restricted extent, which seem
to record accidental death and rapid burial. In Essex they
are found occasionally in the Upper Chalk of Grays and Purfleet,
and in the Lower Chalk of the Cambridgeshire border, but
they are indeed few and imperfect. Fishes must have swarmed
in the seas in which these limy sediments were deposited, but
the commonest species are rarely represented by more than
small pieces, while many are known only by two or three speci-
mens. Our knowledge of most of them depends on more
satisfactory examples preserved nearly whole in soft laminated
limestones of the same age in Kansas (U.S.A.), and the Lebanon.
A few other complete specimens occur in an Upper Cretaceous
greensand in Westphalia.1
The Cretaceous fishes are especially interesting because
they represent the dawn of modern fish life. Among them the
old types of sharks with firmly fixed teeth no longer predominate,
and the ganoid fishes are very few, while some are apparently
rare. Most of the sharks have comparatively loose teeth, with
forked roots, like the majority of later times; while nearly
all the more active higher fishes are true teleosteans like those
of the present day. Some of the genera, indeed, appear to
survive in existing seas, and all are closely related to modern
forms. They have merely sometimes changed in habit, for
while all the Cretaceous fishes lived near the surface of the sea
(as shown by the hardness of their skeletons), many of their
existing relations or descendants have retreated to ocean
depths. Very few of the Cretaceous fishes began to show
adaptations for the latter mode of life.
The ordinary sharks' teeth of the family Lamnidae found
in the Chalk resemble those of the existing Lamna, Oxyrhina,
1 See A. S. Woodward, The Fossil Fishes of the English Chalk (Palaeontographical Society,
1902-1912), and Catalogue of the Fossil Fishes in the British Museum, 4 vols., 1889-1901.
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