52
HISTORIC NARWHAL
TUSKS.
HISTORIC NARWHAL TUSKS. BY DUDLEY W .
COLLINGS, M . B . ,
M.R.C.S.
THE family Delphinidae, comprising the aquatic mammals known as Dolphins and Porpoises, includes one species of considerable interest : the Narwhal (Monodon monocerus, Linn.). This animal, which attains a length of just about fifteen feet, is now essentially arctic in its distribution but, on rare occasions, still strays to our shores. There are only three British records one in 1648 in the Firth of FÜrth, one near Boston in Lines in 1800, and one somewhere in Scotland in 1808. However, formerly it was doubtless more abundant with us, for in 1846 Owen figured in " British Fossil Mammals," p. 521, a fragmentarv tusk from the Essex coast, probably in London Clay of the early Eocene epoch ; and since then remains of the Narwhal have been found in the so-called Forest Bed of Norfolk, which was formed in early Pleistocene times. T h e female of the species, except for a few rudimentary teeth, is edentulous ; but the male is characterised by the presence in the left side of the upper jaw of a single, spirally twisted, elongate horn, actually the incisor-tooth entirely analogous with Elephants' tusks. Very occasionally the right tusk also is developed, but this is never known to be present alone. The Narwhal horn is the sole spiral tooth in the world, and its twist is always left-handed, whether the tusk be right or left. Males may fight with such weapons, as stags in the rutting season, and they have been seen crossed ; or, it has been thought, the tusk is a possible ice-breaker. T h e details of a typical tusk are :—Total length 55 f inches, having had a short portion of extreme base sawn off; greatest girth 5f in. ; pulp cavity conical and 12 in. in length ; the apical three in. are straight and ungrooved ; a cross-section shows 12 convex ridges and there are 4 | complete turns in the remaining 52 in., i.e. one turn in each I I I in. ; the tooth is composed entirely of ivory, and has no coating of enamel. Always the whole skull is curiously asymmetrical, and has the nostril-bones twisted well to the left. Considering the Narwhal's present rarity, even in arctic seas, a comparatively large number of tusks have come to light in Suffolk during the current year. Two speeimens, over the entrance-door of Ipswich Museum, are respectively fifty-four and seventy-five and a half inches in length: unfortunately their history is unknown. Another, broken and now about forty-two inches long, is preserved in Bury Museum and was exhibited to our Society in May last: no data are available.