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1901. Neu. Jahrb. f. Min. Geol. u. Pal., vol. 14, p. 365.
Genotype: Avicula gryphaeoides Sowerby, Albian-Cenomanian.
Figured: 1901. Pompeckj, op. cit., plate 16, figs. 6–8.
1905. Woods, Cret. Lam., vol. 2, pt. 2, pi. 10, figs. 6–13.
Pompeckj named two species, A. aptiensis d'Orb. and A. gryphaeoides Sowby. as types for his genus, and as far as the writer is aware, no one has yet, in accordance with modern procedure, designated a definite genotype. Since it seems desirable that this should be done, the older species A. gryphaeoides Sowby. is here choseen.
Aucellina sp.
Localities: G.S. 1403. Ridge at head of Elmar and Harding Streams, Motu Surv. Dist., north-west corner.
G.S. 1989. Track, Moanui Survey District, 50 chains north of Koranga River and 5 miles 10 chains at 315° from Maungatapere Trig.
G.S. 2084. Ridge leading up west from head of Harding Stream, Motu Surv. Dist., south-west corner.
Age: Taitai Series (probably Upper Aptian).
The writer (Marwick, 1929, p. 5) previously identified these fossils as the Jurassic Buchia (= Aucella) spitiensis (Holdhaus). Since then Pompeckj's paper has become available, and in the light of this and of the association with Maccoyella, the specimens seem undoubtedly to be Aucellina. Owing to poor preservation, however, the critical hinge and ear details have not yet been made out.
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The New Zealand shells have a greatly inflated, oblique left valve with high, strongly incurved beaks. The right valve is almost flat and subcircular, with a short hinge line. The right byssal ear is not fully preserved except as casts which indicate a relatively large, thick, spoon-shaped ear with ridges on the lower side. It appears to have been set obliquely, so that the byssal notch is also oblique and not wide open like typical Aucellina. However, this may be due to distortion.
Of the two European species, A. aptiensis d'Orb. and A. gryphaeoides Sowby., described in detail and beautifully figured by Pompeckj, the New Zealand specimens agree closer with gryphaeoides. They are, however, on the average, more oblique, and the beaks are considerably higher and more strongly incurved. The left valve of A. hughendenensis Etheridge, Queensland, figured by that author (1907, pl. 61, fig. 8) as a typical specimen is very like some of the New Zealand specimens, and Pompeckj considered hughendenensis “closely related to, perhaps even in part identical with” gryphaeoides. Consequently it seems probable that the New Zealand shells belong also to the gryphaeoides stock; but whether they are to be considered as specifically identical or whether they should be recognised as distinct can be decided when more material is available.
Age of the Taitai Series.
In Australia, according to Whitehouse (1929), Maccoyella is limited to the Roma Series which is Aptian, and Aucellina to the Tambo Series which is Upper Albian. In Europe, on the other hand, Aucellina occurs as early as the Upper Aptian, so that the association of Aucellina with Maccoyella in the Taitai Series is not surprising. Moreover, the presence of quaternary ribs on Maccoyella magnata agrees with the Aucellina in indicating a late Aptian horizon. Consequently the age of the Taitai Series can reasonably be regarded as Upper Aptian, that is, Gargasian.
Stratigraphic Significance.
Considerable interest attaches to the Taitai Series because of the possibility that over a wide area it has been overthrust for many miles to rest upon rocks of the Tapuwaeroa and Raukumara series. (M. Ongley, 1930, p. 376). The present writer's mistake in identifying the Aucellina as Aucella cf. spitiensis seemed to give strong palaeontologic support to the overthrust hypothesis. The present evidence does not altogether withdraw this support, but modifies it, in that the time interval between the Taitai and the Raukumara Series is greatly reduced.
No reliable age has yet been assigned to the Tapuwaeroa Series except that this seems undoubtedly younger than the Raukumara Series. The only significant fossil so far discovered in the Raukumara beds is Inoceramus (Callistoceramus) bicorrugatus Marw. which occurs also in Marlborough, rather above the middle of the Clarentian (Nidd mudstone). The associated beds were, on the evidence of the ammonites, correlated by H. Woods (1917, p. 2) with the Lower Utatur of India, equivalent to the Upper Gault and Upper Greensand.
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Fig. 1.—Maccoyella magnata n.sp. Holotype, a left valve.
Fig. 2.—Same showing hinge.
(Both slightly reduced.)
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According to this. Inoceramus bicorrugatus should be Upper Albian or Cenomanian. R. Heinz (1928. p. 123), indeed, on the occurrence of the species in Germany, favoured a higher horizon, namely upper Upper Turonian. No evidence suggests that the Raukumara Series is as old as Aptian. Therefore, if the Taitai Series is really, as the Maccoyella indicates, Upper Aptian then it seems certainly to have been overthrust to its present position.
The alternative, already suggested, is that we must extend the time range of one or both of the fossils concerned. The hypothesis of forms lingering on in one country has often been invoked to solve stratigraphic difficulties that were really the result of incorrect data. Nevertheless, it is a commonplace that some animal groups (also plants) have survived in one region long after they have died out in another. This is particularly true as applied to the larger zoological divisions; but, so far as the finer divisions, such as speeies, are concerned, the principle has a limited application in time because of the evolutionary changes that constantly went on.
From this viewpoint, the problem to be decided is whether:—
| 1. |
To take Inoceramus bicorrugatus at its face value and extend the range of Maccoyella in New Zealand to the Cenomanian or even (according to Heinz) into the Turonian. |
| 2. |
To consider Maccoyella magnata as agreeing in age with its Australian relatives and to push the range of I. bicorrugatus back to Lower Aptian. |
| 3. |
To extend the range of Maccoyella into the Upper Albian and that of I. bicorrugatus back to the Lower Albian. |
Each of these solutions has its objections, and in view of the fact that only one battered and broken specimen of Maceoyella is known from New Zealand, it is perhaps rash to express an opinion on the matter.
It can, nevertheless, be said that the palaeontological evidence so far as it goes supports the hypothesis of overthrust.