Cymatoceras nichollsi, a new Late Cretaceous nautiloid from the Northland Allochthon, New Zealand

Abstract

Cymatoceras is a genus of nautiloid (Superfamily Nautiloidea), of worldwide distribution in Cretaceous strata, but has not previously been reported from New Zealand. A new species, C. nichollsi, is described from a stream boulder collected near Kaeo, Northland, New Zealand. Lithology and regional association indicate that the boulder probably came from the Whangai Formation of the Northland Allochthon, of Late Cretaceous (Haumurian) age.

Keywords:

• Cenomanian
• Cymatoceras nichollsi
• Haumurian
• Late Cretaceous
• Maastrichtian
• new species
• New Zealand
• Northland Allochthon
• Whangai Formation

Introduction

In the later part of the 1980s, the late EJ Searle passed to me for identification a fossiliferous nodule given to him by the late George Nicholls of Arkles Bay, Whangaparaoa. It had been found by his son, Murray, now of Taupo, as float in a stream on the northern edge of Omahuta State Forest, between Otangaroa and Mangapa, near Kaeo, Bay of Islands. The nodule had formed around a single moderately large cephalopod and consisted of a very fine-grained, light cream-coloured indurated rock, very light yellowish-grey on weathered surfaces and rusty brown where the conch has been replaced by a limonitic film. The lithology is either chert or silicified mudstone.

Identification of the fossil was not immediately possible, although RA Henderson, James Cook University of Queensland, Australia, and the late CA Fleming of the then New Zealand Geological Survey, Lower Hutt, now GNS Science, agreed it was likely to be a nautiloid. Henderson (in lit. 18 April 1980) suggested it had similarities with Cymatoceras, although he reported that he could not find any species as strongly sculpted or compressed.

Work on the fossil then languished because I had more urgent tasks and priorities, but retirement has provided the opportunity to return to the specimen. In trying to contact George Nicholls I learned he was by then deceased but was survived by a son. His son Murray then contacted me and told me he had been the finder of the specimen; he provided me with a map of its location and agreed to lodge it in the collections of the School of Environment, University of Auckland.

Geological setting

The lithology of the sample, siliceous siltstone, is characteristic of the Whangai Formation (previously Ngatuturi Siltstone – Isaac et al. 1994), a unit within the Mangakahia Complex, part of the Northland Allochthon, which is up to 500 m thick in a zone from Whangaroa Harbour southwest to Hokianga Harbour. The nautiloid is likely to have come from nappe iii of this unit which is dated as Piripauan–Haumurian (Late Cretaceous; Santonian–Maastrichtian; Brook & Hayward 1989) or Haumurian (Campanian–Maastrichtian; Isaac et al. 1994), and a geological map of the area is included in Brook & Hayward (1989). Fossil biota from the Whangai Formation from sites adjacent to the nautiloid locality include O04/f195 with microfauna and microflora that give a Piripauan–Haumurian age.

Systematics

Class: Cephalopoda Cuvier, 1797.

Subclass: Nautiloidea Agassiz, 1847.

Order: Nautilida Agassiz, 1847.

Superfamily: Nautiloidea de Blainville, 1825.

Family: Cymatoceratidae Spath, 1927.

Genus: Cymatoceras Hyatt, 1884.

Type species: Nautilus pseudoelegans d'Orbigny, 1840, Cretaceous, France.

Cymatoceras nichollsi Grant-Mackie, n. sp

Material

Unique holotype, specimen C2135, registered in the Cephalopod types catalogue of the School of Environment, University of Auckland, an oval siliceous boulder as float in Herenga Stream, immediately downstream from the junction of two tributaries, one from the south and the other from the southeast, 1.7 km SSW of Otangaroa township, near Kaeo, Northland; fossil locality O04/f261 in the New Zealand Fossil Record File, grid reference approximately O04/682757 (1984 ed. NZMS260); collection-lot AU21272 in the University of Auckland's School of Environment's Palaeontology Catalogue; collected by Murray Nicholls now of Taupo, December1976.

Derivation of name

Named to commemorate the Nicholls family who found the fossil, arranged for it to be studied and donated it to the School of Environment.

Description

Conch nautiliconic, evolute, somewhat compressed, rounded, pentangular to oval in whorl section, higher than wide, with narrowly rounded venter, gently rounded flanks and indistinct umbilical shoulder and wall. Greatest whorl inflation at about mid-whorl. Umbilicus moderately narrow. Ornament of sigmoidally curved ribs, asymmetrically rounded in section, steeper on apertural flank; interspaces rounded and asymmetrical, mimicking ribs in form and orientation. Ribs totalling c. 34 in last preserved whorl emerge from umbilicus with radial disposition, curving gently aperturally, crossing flank in broad sweep, curving abapically to venter and meeting ribs of opposite flank in rounded adapically directed chevrons; 7–10 secondary ribs of equal strength to primaries inserted at irregular intervals 10–20 mm ventral to umbilicus; flanks of chevrons diverge at c. 70 degrees.

Aperture not preserved, suture and siphuncle unknown.

Dimensions (mm)

All dimensions are approximate due to crushing of one flank and the partial erosion of the venter. Maximum diameter: 190; maximum whorl height: 115; maximum conch width: 80; maximum umbilical diameter: 30.

Remarks

The specimen is only partly preserved. One flank seems well preserved and undistorted/uncompressed and therefore permits depiction of the whorl profile (Fig. 1C), while the other flank is apparently crushed and is enclosed within the nodule. The venter is partially exposed and eroded but enough is preserved to clearly show the ventral sinus of the ornament. Ribbing seems undistorted on the exposed flank. From the absence of any suture-line the exposed fossil appears to be the body chamber, and the sediment-plugged umbilicus precludes any sign of earlier sutures.

Figure 1 Cymatoceras nichollsi, holotype, C2135, from O04/f261, float in Herenga Stream, near Kaeo. A, lateral view; dark patch on conch flank is that part of conch which was unexposed when found, where shell material has been limonitised; B, ventral view; C, approximate whorl profile, derived from partially preserved conch; V, venter; X–X, portion of profile not exposed, assumed. Centimetre scale applies only to A and B.

Discussion

The genus Cymatoceras includes more than 60 species (v. Kummel 1956). They dominate nautiloid fauna of the Cretaceous period and are especially diverse in the Early Cretaceous; only one species each is known from the Late Jurassic (C. perstriatum (Steuer, 1921); Late Jurassic–Early Cretaceous of Argentina) and Palaeogene (C. tsukushiense (Kobayashi, 1954); Oligocene of Japan) according to Kummel (1956).

Location in the genus Cymatoceras is indicated by the combination of prominent sigmoidally curving ribs on flanks and venter, narrow umbilicus and rounded whorl profile. The present specimen differs from the type species, C. pseudoelegans (d'Orbigny, 1840), from the Early Cretaceous of Europe, Morocco and Turkmenistan, which is more inflated and possesses about twice as many ribs (which are, nevertheless, generally very similar in form and orientation to nichollsi), has a shallower ventral sinus and a narrower umbilicus (v. e.g. Kummel 1956, pl. 16). Most other species are also more inflated than nichollsi and can therefore be rejected as likely conspecifics. Kummel also provided a series of conch profiles (1964, fig. 23) which indicates that C. neocomiense (d'Orbigny, 1840) from the Swiss Valanginian–Hauterivan (Jaccard 1869), reported also from the Albian–Cenomanian of Papua New Guinea (McTavish 1960), has a comparable umbilical size and a cross-sectional form very like that of the Kaeo specimen. Although the ribs have the same orientation as in the new species they do not have its asymmetric cross-section.

Another taxon, C. loricatum (Schlüter, 1876), Cenomanian of Germany, is also more compressed than in most species and possesses other features that ally it to the New Zealand form. The ribs, 50–60/whorl, are regularly asymmetrical like the new species, although their adapical sides are steeper and shorter and the abapical flanks are broader and flatter, show a similar pattern of curvature and form a ventral sinus comparable to that in nichollsi. These similarities, however, are not close enough to suggest the two are conspecific.

The German Cenomanian C. tourtiae (Schlüter, 1876) also possesses ribs of a generally similar form to ours, but there are more of them (c. 100) and the venter is flattened, with a shallower sinus. C. kayeanum (Blaneford, 1861), from the Campanian of Madagascar, is somewhat compressed but has nearly twice the number of finer ribs and is slightly more evolute.

Cymatoceras hendersoni (Etheridge Jr, 1892), from Cretaceous strata of Queensland, Australia and from the Albian and Cenomanian of Papua New Guinea (Glaessner 1958), possesses ‘fine wavy ridges … unequal in strength and spacing’ (Glaessner 1958, p. 211) only on the outer surface of the thick shell material, unlike nichollsi.

All other species of which I am aware are more inflated, most have more ribs and others have a narrower umbilicus; all can be ignored in terms of a close relationship with the New Zealand form which appears to be morphologically unique and therefore a valid new taxon.

There are nine genera included in the family Cymatoceratidae, but only two possess the features seen in the New Zealand specimen (narrowly evolute, with rounded whorls and conspicuous sigmoidal ribs over venter and whorl flanks): Cymatoceras and Paracymatoceras Spath, 1927, the latter a Northern Hemisphere group covering a small number of species in the Cretaceous of Japan, USA, Mexico and Greenland. Location of the new species in Paracymatoceras cannot unequivocally be ruled out of contention but, tentatively at least, allocation to the more geographically widespread and species-rich genus Cymatoceras is favoured because of its presence in other Southern Hemisphere fauna.

Age: Cymatoceras species are found throughout the Cretaceous. Among those most similar to the New Zealand species, C. neocomiense occurs in the Valanginian–Cenomanian interval while C. loricatum and C. tourtiae are restricted to the Cenomanian. Ages for fossils found around Whangaroa Harbour have been cited as Piripauan and Haumurian (Santonian–Maastrichtian based on inoceramids, ammonites and other molluscs, and on microfaunas and microfloras; Isaac et al. 1994), and the Whangai Formation in the region is Haumurian–Teurian (Campanian–Paleocene). If the nautiloid was derived from the Whangai Formation then this latter age would be correct for it, but such an allocation must be tentative at best. Nearby in situ records include O04/f195, also from the Whangai Formation, with a microbiota of Piripauan–Haumurian age. The age range for this formation has been refined more recently (Isaac et al. 1994) to Haumurian, and this age is accepted as the most likely for Cymatoceras nichollsi. Even without a more certain age indication, this find is an important one as being the first record of the genus in New Zealand.

Acknowledgements

Deep appreciation must firstly go to the finder of this nautiloid, Murray Nicholls, now of Taupo, who also agreed to donate it to the School of Environment, University of Auckland, and to his father, George Nicholls late of Arkles Bay, Whangaparaoa, who passed it to us for study. That this study has taken so long to be completed is a matter of great regret. Initial helpful comments on identity were provided by RA Henderson, James Cook University, Queensland and the late Charles Fleming, then of Wellington. With gratitude I acknowledge the always excellent work of Louise Cotterall, School of Environment, in providing the illustrations. Literature searches were aided by Neville Hudson, School of Environment, who also provided valuable criticism of the final version, Donald MacFarlan, New Plymouth, and Hamish Campbell, GNS Science, Lower Hutt. Appreciation is due to an unnamed referee.

Associate Editor: Professor Kathy Campbell.

Disclosure statement

No potential conflict of interest was reported by the author.