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Volume 82, 1954-55
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Note on the Type Specimen of the Maori Rat.

[Read by title and abstract before Otago Branch on April 13, 1954, received by Editor. April 26, 1954.]

Abstract

The native rat of New Zealand is a member of the exulans group of Pacific rats, and was described by Hutton as Mus maorium It was thought to be extinct but specimens hive recently been collected in various localities. The type skull in the Otago Museum has accordingly been remeasured for purposes of comparison.

During the early stages of colonisation of New Zealand there were many reports of a native rat smaller than either Rattus rattus or Rattus norvegicus. Buller (1870) described a black rat as Mus Novae Zealandiae, but there seems no doubt that this was really R. rattus. The first description of the native rat was that of Hutton (1876) based on skulls from Maori cooking places at Shag Point, Otago. In this paper he merely referred to it as the Maori Rat, but later (1878) gave it the name Mus maorium. However, this has generally been accepted as a synonym for Rattus exulans (Peale) 1848. The exulans group of rats is found all over Polynesia. The differences between the populations from various parts of the range have been used by some authorities to form a series of species, while others merely divide the species R. exulans into a number of subspecies or racial groups.

The native rat of New Zealand appears to have been very common at one stage, for there are reports of “plagues” of rats, some of which were identified as Mus maorium. Soon however, the native rat became considerably reduced in numbers and was thought to be extinct at least on the main islands. In recent year specimens have been collected from various islands off the North Island, and from Doubtful Sound and Notornis Valley in the South Island. Because of the increased interest in the native rat, and the meagreness of the published data, it was thought worth while to redescribe the type skull giving measurements which may be used in comparison with those of forms from other parts of the Pacific.

The type skull is in the collections of the Otago Museum, and I am indebted to Dr. H. D. Skinner for permission to examine the specimens held. The box labelled as the type skull contains two skulls, one in poorer condition than the other, and two jaws. Both skulls have very similar measurements. The skull having the measurements nearest to those given by Hutton, which to judge from his paper may be averages, and which is the better specimen, is designated as the type Otago Museum Number A.54.6. The jaws resemble the type skull in appearance but cannot be certainly associated with it and so are not included in the table. The measurements are as follows: Length of jaw 20.8 mm; length of tooth row 5.4 mm. For comparison the measurements of two other skulls are included in the table. One was collected in a cave on Otago Peninsula associated

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with the bones of Strigops; the other is the skull of an immature male from Doubtful Sound, collected in 1950. The table also shows Hutton's original measurements of the type and of another specimen from Picton (1887).

A comparison with the figures published by Tate (1935) shows the New Zealand native rat to be a large form of R. exulans with rather differing proportions, but one cannot go further without a long series. Some differences would be expected since New Zealand is so geographically isolated and offers an entirely different environment and climate from the tropical Pacific islands.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Type Shag Point otago Mus. No. A 54.6 Other skull from Shag Point. Otago Mus. No A.54.7 Doubtful Sound. Otage Mus. No. A 50.11 Otago Peninsula Otago Mus No. A54.13 Hutton's measurements of type. Hutton's measurements 1887.
mm. mm. mm.
Total length 35.3 35 5 31.9 1.37 ins. (35.0 mm.) 1 35 ins. (34.3 mm)
Condylo-basal length 33 7 33 8 29.6 34.8
Zygomatic breadth (16 8) (15 9) (15.0) (17.6) 0 65 ms. (16.5 mm) 0.6 ins (15.2 mm.)
Interorbital breadth 5.4 5.5 5.4 5.7
Length of nasal bone 13.9 13.4 11.6
Length of diastema 10.4 10.0 8.0 10.6
Breadth of rostrum 5.5 (6.1) 5.2 (6.2)
Breadth of braincase 14.1 14.7 13.6 14.5
Depth of braincase 9.9 10.7 10.0 10.9
Maxillary toothrow 5.9 6.1 59 5.8
Width apart of bullae 2.5
Width between outer edges of meati 13.4
Width between inner edges of meati 10.9
Length of bulla 6.1
Foramen magnum, height 4.5 4.2 4.3 4 4 0.17 ins. (4.3 mm.) 0 17 ins (4.3 mm)
Foramen magnum, breadth 5.0 5 1 5 0 5 5 0 23 ins. (5.8 mm) 0.22 ms. (5.6 mm.)

References

Buller, W., 1870. On the New Zealand Rat. Trans. N.Z. Inst., Vol 3, pp. 1–4.

Hutton, F. W., 1876. Note on the Maori Rat. Trans. N. Z. Inst. Vol. 9, p. 348.

— 1878. Note appended to a paper by T. White entitled “Note accompany nig specimens of the Black Rat Mus rattus.” Trans. N.Z. Inst. Vol. 11, p. 344.

— 1887. Note on the rat that invaded Picton in March 1884. Trans. N.Z. Inst. Vol 20. p. 43.

Peale, T. R., 1848. U.S. Exploring Expedition. VIII.

Tate, Tate. G. H., 1935. Rattus and Mus from the Pacific Islands Bull. Amer. Mus. Nat Hist. Vol. 68, pp. 145–178.