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Tuatara: Volume 18, Issue 1, July 1970

The Identity of the Pliocene Seal from Cape Kidnappers, New Zealand, Previously Known as Arctocephalus caninus

page 13

The Identity of the Pliocene Seal from Cape Kidnappers, New Zealand, Previously Known as Arctocephalus caninus

Pinniped skull remains from Cape Kidnappers, New Zealand were described by Berry (1928) as a new species of fossil Arctocephalus - A. caninus. In later years Berry himself appreciated the generic differences of Arctocephalus, Neophoca and Phocarctos and thought that as his specimen is considered to be the oldest fossil seal known from New Zealand it merited reassessment in the light of modern knowledge. This he did in a series of uncompleted papers and manuscripts that were still unpublished at his death in 1962. The second author has seen and examined the type specimen of A. caninus in the Dominion Museum, Wellington, (DM 532) and subsequently through the courtesy of the New Zealand Geological Survey, had access to Dr. Berry's manuscripts, and feels that our independently reached conclusions should be amalgamated.

The remains consist, (Plate 1) as Berry has already detailed them, of an incomplete left mandible with post canines 3, 4, and 5 still in position, but with the anterior part of the horizontal ramus broken in front of the level of pc 3, and the coronoid process and condyle abraded; the anterior portion of the left maxilla with the canine and post canines 1 and 2 in position; and nine separate teeth, one of which is the lower canine, and the others can almost certainly be given their correct positions in the jaws.

The bones were found about 1922 by the late Mr W. D. Southcott of Hastings. ‘Dr. Berry later went to great trouble to localise the point of collection and decided it was from the Opoitian sandstones immediately below the Black Reef Limestone, between Clifton and Cape Kidnappers, Hawke's Bay. It remains the geologically oldest fossil seal known from New Zealand’ (Fleming 1968). The Opoitian sandstones are considered to be Pliocene (Fleming 1962).

Berry (1928) refers to his specimen as Arctocephalus caninus, but it is quite obvious from his comparison with a specimen of ‘Arctocephalus hookeri’ that the modern generic name should in both instances be Phocarctos. He says that ‘the fragments obviously belonged to a young, and possibly a female animal’ and compared it with the skull of a female Phocarctos. The differences between the page 14
Map showing New Zealand and associated islands to show the distribution of Phocarctos.

Map showing New Zealand and associated islands to show the distribution of Phocarctos.

two that chiefly impressed him were in the size and shape of the lower canine of the fossil which was much shorter in relation to its width, with a less curved crown and the base of the root extending further back. Presumably it was because of these differences that he named the specimen A. caninus. Examination of large numbers of Phocarctos skulls shows well marked differences in the size of the canines and it is not difficult to determine the sex of the skulls from this character. The size of the fossil canine indicates without doubt that the animal was a young male (Plate 2), and this would explain why, when compared with a female, the fossil showed such obvious differences. Berry himself also referred to the specimen as a male in one of his manuscripts.
Berry's original estimated condylobasal length for the skull was about 140 mm, but it is considered that this is rather too small as a page 15
Plate 1 Left maxillary fragment (lateral view), right and left lower canines and left ramus lower jaw (medial view) of Cape Kidnappers specimen.

Plate 1 Left maxillary fragment (lateral view), right and left lower canines and left ramus lower jaw (medial view) of Cape Kidnappers specimen.

Phocarctos skull of this length would be from a newborn pup with the milk canines still in position. A young male skull with canines about the size of those of the fossil would be about 200-220 mm condylobasal length.

Much of the manuscripts are taken up with very detailed descriptions of the teeth, but it is considered that these were adequately noted in the original paper. Berry does however compare his fossil with the skull of a young female Phocarctos found in Maori middens in the sandy dunes at Ocean Beach, a few miles south of Cape Kidnappers. The Ocean Beach skull although from a female is of the same degree of maturity as the fossil, and is in all respects very similar. It is in fact only in the details of the cusping of the post canines that Berry considers that the fossil differs enough from the Ocean Beach specimen and other available specimens of Phocarctos to be recognised as a new species. The characters he used are:

1.

Upper pc 1 and 2 lack prominent accessory cusps — whereas in Phocarctos these are always present.

2.

Upper pc 5 has a more prominent and sharper anterior accessory cusp than in Phocarctos, but is otherwise similar.

3.

Lower pc 1 and 2 have smaller anterior accessory cusps than in Phocarctos.

4.

Lower pc 3 has a posterior accessory cusp which is missing in Phocarctos.

5.

Lower pc 3, 4 and 5 — the anterior accessory cusp is larger than in Phocarctos and is directed more horizontally forwards.

page 16
Plate 2 Comparison of the Cape Kidnappers canines with those of male and female Phocarctos. Top row—lower canines, lower row—upper canines. From left to right: Cape Kidnappers DM 532, DM 1359 male, DM 1043 male, DM 1360 female, DM 1361 female.

Plate 2 Comparison of the Cape Kidnappers canines with those of male and female Phocarctos. Top row—lower canines, lower row—upper canines. From left to right: Cape Kidnappers DM 532, DM 1359 male, DM 1043 male, DM 1360 female, DM 1361 female.

The accessory cusps on otariid post canines show a high degree of variability in detail and from inspection of a reasonable number of Phocarctos post canines it is felt that characters 2, 3 and 5 above come within the range of variability and are not useful as characters on which to recognise a new species. Similarly (character 1) the degree of prominence of anterior accessory cusps varies considerably and their complete absence occurs not infrequently. From the photograph (Plate 3) it can be seen that the posterior accessory cusp on lower pc 3 of the fossil is extremely small. Phocarctos usually has the posterior surface of this tooth, and also that of pc 4, without any accessory cusps, but occasionally such a small cusp does occur. A similar very small one is present on pc 4 of a single skull (1843.11.25.2) in the British Museum (Natural History) collection, so though it may occur only seldom, such a cusp may presumably also occur on pc 3. Plate 3 also illustrates the close similarity in shape between a recent Phocarctos jaw (DM 1359) and the Cape Kidnappers jaw.

It is thus felt that such a very variable character as the cusping detail is not sufficient to distinguish this fossil from modern specimens of Phocarctos hookeri and it is therefore suggested that Berry's name of Arctocephalus caninus be put in the synonymy of Phocarctos hookeri.

page 17
Plate 3 Lower—medial view left ramus of Cape Kidnappers lower jaw DM 532, and top—same view of lower jaw P. hookeri DM 1359 young male, condylobasal length skull 205 mm.

Plate 3 Lower—medial view left ramus of Cape Kidnappers lower jaw DM 532, and top—same view of lower jaw P. hookeri DM 1359 young male, condylobasal length skull 205 mm.

The present distribution of Phocarctos is on the Auckland Islands, Campbell Island and on the Snares, where the animals are to be found all the year round. As stragglers they reach Macquarie Island, Stewart Island and have been recorded as far north as Kaikoura, north of Christchurch (Mr. L. D. Bowring, Kaikoura, pers. comm.). But apparently as recently as 1863 these sealions used to breed on the west coast of the South Island, though during the next thirty years they became much rarer on the New Zealand mainland, and even on Stewart Island in 1874 had not been seen for some time, though their tracks through the bush were visible. (Thomson 1921).

Both the Ocean Beach and Cape Kidnappers specimens are from young animals, so either Phocarctos bred at least as far north as Hawke Bay, or close enough so that the young animals could swim there. The apparently very recent withdrawal of resident Phocarctos from the New Zealand mainland to the more distant islands, and the presence of both the Ocean Beach specimens and the Pliocene fossil from the same area suggest that the general distribution of Phocarctos was once considerably wider than it is now.

Summary

Arctocephalus caninus from Pliocene sandstone, Cape Kidnappers, Hawke Bay. New Zealand was described by Berry in 1928. The page 18 result of Dr. Berry's unpublished manuscripts are here combined with the independent conclusions of the second author. Comparison of the Pliocene fossil with a skull of Phocarctos hookeri from a Maori midden and also with recent specimens of P. hookeri indicate that this is the correct identification of the Cape Kidnappers fossil, thus extending the known range of Phocarctos.

References

Berry, J. A., 1928. A new species of fossil Arctocephalus from Cape Kidnappers. Trans. N.Z. Inst. 59: 208-211.

Fleming, C. A., 1962. New Zealand Biogeography. A paleontologist's approach. Tuatara 10(2): 53-108.

——, 1968. New Zealand fossil seals, in: Notes from the N.Z. Geol. Survey 5. N.Z. J. Geol. Geophys. 11: 1184-1187.

Thomson, G. M., 1921. Wildlife in New Zealand. Part 1. Mammalia. N.Z. Board of Science and Art. Manual No. 2.

* Deceased

** Department of Zoology, University of New South Wales.