Cretaceous Fossils from the Chatham Islands
[Communicated by C. A. Fleming and read before the Wellington Branch on November 13, 1957; received by the Editor, November 18, 1957.]
Rotularia chathamensis n. sp., a coiled, shelled annelid, Inoceramus sp. indet., Exogyra cf. conica (Sowerby), Struthioptera (?) sp. indet., described from calcareous tuff at Pitt Island, Chatham Islands, indicate a Lower or Middle Cretaceous age (Neocomian to Cenomanian). They are the first evidence of marine Mesozoic rocks at the Chatham Islands.
In the autumn of 1957 Dr. W. A. Watters and Messrs. A. R. Mutch and R. F. Hay, New Zealand Geological Survey, discovered a few marine Cretaceous fossils in calcareous tuffs on Pitt Island, Chatham Islands. The fossils include a well-preserved Exogyra, three specimens of a coiled Serpulid worm (Rotularia), and a poorly preserved gastropod (possibly Struthioptera). The Exogyra and Rotularia are of general interest because they are New Zealand representatives of groups that were distributed sporadically throughout the world in Cretaceous times, Exogyra being here recorded for the first time in the New Zealand area.
Fossiliferous Cretaceous sediments occur in both North and South Islands of New Zealand, ranging in age from Lower to Upper Cretaceous (Maestrichtian), but an assemblage exactly comparable to that of Pitt Island has not previously been recorded, perhaps due to accidents of preservation or possibly because the Pitt Island Cretaceous calcareous tuffs may represent a shallower near-shore-shelf facies than the geosynclinal deposits of the North and South Islands of New Zealand (cf. Well-man, 1956, p. 28, Fig. 3).
In addition to the Cretaceous fauna here recorded, a flora of spores and pollen grains has recently been extracted by Dr. R. A. Couper, New Zealand Geological Survey, from dark blue-grey carbonaceous shales on Pitt Island, indicating an age not younger than middle Senonian. The lower age limit is uncertain, but the flora is probably not older than Neocomian (Dr. R. A. Couper, pers. comm.). The Chatham Islands have previously yielded large Cenozoic faunas, ranging from Lower Eocene (Mangaorapan) to Lower Pleistocene (Nukumaruan) (Marwick, 1928). The Cretaceous fauna and flora is the first indication of Mesozoic marine sediments in the Chatham Islands area.
The fossils (GS 6968) were collected from coarse-grained calcareous tuff exposed as low sea cliffs, three-quarters of a mile south of Kahuitara Point on the east side of Pitt Island (Text-fig. 1). The spore- and pollen-bearing shales are exposed chiefly in Waihere Bay, on the west coast. The structural relation between the shales and tuffs is unknown.
Genus Inoceramus W. Smith, 1816
Strata ident. org. Foss.: 10; f. 1.
Type (by subsequent designation, Cox, 1930: 291): I. cuvieri Smith non J. Sowerby = I. involutus J. de C. Sowerby. Upper Cretaceous, England.
Inoceramus sp. indet.
Attached to the under surface of the Exogyra specimen described below, is a piece of Inoceramus shell too fragmentary to be identified specifically. The shell is 2 mm thick, and a section of a single low concentric rib is preserved.
Genus Exogyra T. Say, 1820
Am. Jour. Sci., vol. 2: 43.
Type (by original designation): E. costata Say. Upper Cretaceous, North America.
Exogyra of. conica (J. Sowerby, 1813). Pl. 11, Figs. 1—3.
1813. Chama conica Sowerby, Min. Conch., vol. 1: 69; Pl. 26. f. 3.
1829. Exogyra conica (Sowerby); J. de C. Sowerby, Min. Conch., vol. 6: 219; Pl. 605, f. 1, 2, 3.
1913. Exogyra conica (Sowerby); Woods, Cret. Laniell. England, vol. 2, pt. 9: 407; Text-fig. 215—242.
Material. One complete, well-preserved shell (TM 2004).
Description. Left (attached) valve very convex, with an approximately oval outline. Anterior margin rounded, posterior margin irregular. Umbo not preserved. A large area of attachment on the posterior half of the valve bounded by a sharp ridge curving from the umbonal region to the posterior ventral margin. The anterior, free surface of the valve high, convex and almost smooth except for growth lines, the posterior part concave, conforming to the shape of the attacheInoceramus valve. The slope of the attached area makes an acute angle with the free half of the valve.
Right valve almost flat with a small spiral umbo curving backwards, reminiscent of a Haliotis in appearance. Anterior margin smoothly curved, posterior and ventral margin more irregular. Surface smooth except for marked growth lines.
Dimensions. Dorso-ventral maximum length: 36 mm; anterior-posterior maximum breadth: 25 mm.
Remarks. The Chatham Island specimen appears to be morphologically comparable to Exogyra conica described by J. Sowerby from the Upper Greensand of England. Woods (1913, p. 407), has given a full description with figures of this species, which varies greatly in size and height of shell and relative area of the attachment surface, and includes several forms previously described as distinct species (E. recurvata, plicat, and haliotoidea, J. Sowerby; E. undata Goldfuss; E. rauliniana d'Orbigny; etc.). Sowerby figured small specimens with a small area of attachment as his Chama conica (1813, p. 69; Pl. 26, f. 3) and a small shell with a relatively large area of attachment as his Chama haliotoidea (ibid, p. 67; Pl. 25, f. 1—5), between which two forms a series of intermediates are found (vide Woods, 1913, p. 410). Dimensions of the Chatham Island specimen are comparable to those of small forms of E. conica. Sowerby gives for his type of E. conica: “about 1 inch long and three-fourths wide” (i.e., approximately 25 mm × 18 mm) and for his type of E. haliotoidea: “about an inch and a-half long and an inch broad” (i.e., approximately 38 mm × 25 mm). On the Chatham Island specimen the area of the attachment surface, relative to the size of the whole valve, is intermediate between forms such as E. conica and E. haliotoidea.
No records of Exogyra have previously been published from the New Zealand area, but two small specimens from Cretaceous rocks are in the N.Z. Geological Survey collections: a right valve from GS 6171, Conway River, Marlborough (Piri-pauan), and a complete though worn specimen from GS1401, Koranga, East Cape Peninsula (Raukumara Series). The latter is a much smaller shell with a relatively larger area of attachment than the Chatham Island specimen, but is possibly also Exogyra cf. conica (Sowerby).
Woods (1913, p. 413) records E. conica (Sowerby) from several localities in England ranging in age from Aptian to Cenomanian. Similar forms have been recorded from France (d'Orbigny, 1847, p. 726 ff.), from localities in Germany, Poland, Bohemia, Sweden, South India (Stoliczka, 1871, p. 456, 458) and possibly
Brazil (White, 1888, p. 33) and it appears to be a characteristic fossil of middle Cretaceous rocks. No records of Exogyra in Cretaceous rocks of Australia or Antarctica have been seen, and so it is not possible to make comparisons with areas closer to New Zealand.
Genus Struthioptera Finaly & Marwick, 1937
N. Z. Geol. Surv. Pal. Bull. 15: 61.
Struthioptera (?) sp.
One partially decorticated, incomplete specimen was collected. It is too poorly preserved for certain generic or specific location, but is not unlike some slim specimens of Struthioptera novo-seclandica (Wilckens, 1922, p. 13) from Amuri Bluff (Piripauan) or the Struthioptera sp. described by Wilckens (1922, p. 34) from older rocks of Bluff River, Clarence Valley, New Zealand.
The spire is narrow, conical; columella straight; outer lip not preserved. Whorls angled, faint signs of a single ridge of oblique tubercles on penultimate whorl, continuing to body whorl, which develops a second non-tuberculate basal keel. Some finer regular spiral sculpture preserved on body whorl and base. Growth lines faint, on body whorl recurving from suture, curving forward to lower keel, thence recurving.
Genus Rotularia Defrance, 1827
Dict. Sci. Nat. 46: 331.
Type (fide Wrigley, 1951, p. 184): Serpula spirulaea Lamarck, 1818.
1827. Spirulaea Bronn, Zeit. f. Mineral, Frankfurt, 2.
1861. Burtinella Morch (= Moerchia Mayer, 1860, non A. Adams), Proc. zool. Soc. Lond.: 147.
1867. Tubulostium Stoliczka, “Cret. Fauna of S. India,' Pal. Indica, vol. 2: 236.
1951. Wrigley, Proc. geol. Assoc., vol. 62: 183.
Wrigley (1951, p. 183) has summarised reasons for using the generic name Rotularia Defrance, based upon Serpula spirulaea Lamarck, for the large extinct group of spirally-coiled, shelly serpulid worms previously described under the generic names Serpula, Vermicularia, Rotularia, Spirulaea, Burtinella, and Tubulostium. The group was distributed in Northern and Southern Hemisphere seas during late Jurassic, and (mainly) Cretaceous and early Tertiary times.
Material. Two specimens (TM 2002, 2003) and a fragmentary cross section in the Geological Survey Collection. The larger, better-preserved shell is the holo-type (TM 2002.)
Locality. GS 6968, coast south of Kahuitara Point, Pitt Island, Chatham Islands, in calcareous tuffs.
Description. Shells fairly large for the group, discoidal, tubes planospirally coiled. An outer layer of callus developed round the tubes, fusing between adjacent walls. Diameter of the tubes increasing rapidly and callus of outer volutions almost enveloping those preceding.
Shells attached to foreign objects by callus on under surface of disc; on the smaller specimen a small pebble is still affixed (Fig. 6), and on the larger, the bulging sutural margin on the lower surface of the outer-whorl callus indicates the previous position of a foreign object. The callus on the fragmentary cross section also bulges at the sutural margin.
Following Wrigley (1951, p 180) the specimens are orientated for description with the attachment surface downwards, as in the position of life, and the direction of coiling is viewed on the upper or umbilical face. Coiling of specimens dextral.
Cross-section of tubes internally circular and externally roughly circular. Whorls smooth. periphery convex, without ridges or keels, surface unsculptured except for undulating growth lines.
S. N. Beatus, Photos. Figs. 1, 2, 3.—Exogyra of. conica (Sowerby). Left (attached) valve, right valve, dorsal view of left valve. × 1.
In neither of the specimens does the apertural end of the tube show signs of becoming uncoiled and free from the preceding whorl, but this may be due to immaturity or breakage.
The small shell has been bored by a sponge.
Dimensions. Holotype: maximum diameter of coiled disc, 24 mm; maximum internal diameter of tube at aperture, 5 mm.
Paratype (incomplete shell): maximum diameter of coiled disc, 17 mm.
Paratype (fragmentary cross section): maximum diameter across disc, approx. 32 mm; maximum internal diameter of tube, approx. 6 mm.
Text-fig. 2—.Rotularia chathamensis n. sp., fragmentary cross section of whorls at right angles to plane of coiling. × 2 approx.
Remarks. The significant characters of the Chatham Island specimens are the unridged and uncarinated whorls with roughly circular exterior cross-section, and the planospiral coiling. Several similar forms of Rotularia have been recorded, including:
R. concava (J. Sowerby) (1813, p. 125, f. 1—5). English Gault and Upper Greensand, Albanian-Cenomanian.
R. lituola (Leymeric) (1846, Pl. 6, f. 5), Neocomian of France.
R. damesi (Noetling) (1885, p. 206; Pl. 1, f. 7—10), Cenomanian of the Baltic.
R. gregaria (Etheridge) (1907, p. 318, Pl. 57; Pl. 60, f. 1—3), Lower Cretaceous “Rolling Downs Formation” of Queensland.
R. cf. concava (J. Sowerby), Lower Cretaceous Uitenhage Series of South Africa, recorded by Kitchin (1908, p. 63; Pl. 2, f. 1, a.), later named R. kitchini by Bonarelli and Nagera (1921, p. 20).
R. cf. kitchini (Bonarelli and Nagera), Aptian beds in the Lake San Martin area, Patagonia, recorded by Bonarelli and Nagera (1921, p. 20; Pl. 2, f. 3).
Rotularia australis Cox (1953, p. 12; Pl. 2, f. 13, 14), Aptian, Alexander I Land, Antarctica.
In minor features, the Chatham Islands specimens differ from each of the above-named species. They are rather larger than individuals of other species of which measurements can be found. In R. concava (Sowerby) the diameter “seldom exceeds three-fourths of an inch”; in R. kitchini Bonarelli and Nagera “the greatest diameter across the whorls is 8 mm”; R. gregaria Etheridge “ranges from 5—15 mm in diameter”; in R. australis Cox “the diameter of the spiral part is 14 mm”. In addition, the Chatham Island shells appear to be more involute than other comparable species—i. e., the callus of the outer whorls almost envelopes those preceding.
It is interesting to note that both shells show signs of being attached to foreign objects at a late stage of growth. Gardner's figures of R. leptostoma (Gabb) (1938, Pl. 6, f. 5, 14.) from the Eocene of the Gulf Province, U.S.A., shows a similar condition, but it has not been noted in any of the close relatives of R. chathamensis listed above, all of which presumably became free-living after an early period of attachment by the apical portion, cf. R. bognoriensis (Mantell) (Wrigley, 1951, p. 180).
The concave-whorled, unkeeled, planospirally (or near planospirally) coiled forms of Rotularia listed above, including R. chathamensis, seem to be a fairly compact assemblage within the genus, with a restricted time range from Neocomian to Cenomanian.
In contrast, the forms occurring in the lower Tertiary and Upper Cretaceous are distinctly keeled or corded, with an angular exterior cross-section. These forms vary, sometimes within the species, from almost discoidal to conic, with varying degrees of elevation of the spire. Well-known examples are:
R. spirulaea (Lamarck), Eocene, Biarritz to Bavaria.
R. bognoriensis (Mantell), Eocene, London Clay.
R. discoideum (Stoliczka), Cenomanian, Utatur series of South India.
R. leptostoma (Gabb) and 3 species described by Gardner (1938), Eocene, Gulf Province, U.S.A.
R. ornatum (Wilckens), Upper Senonian, Amuri Bluff, New Zealand.
R. fallax (Wilckens), Senonian, Snow Hill, Antarctica.
Age of the Fauna
The Chatham Islands Cretaceous fauna cannot be directly compared with others of more definite age in New Zealand, where Exogyra is rare and poorly known and the genus Rotularia is represented by different species—namely, R. ornatum (Wilckens) and undescribed forms. The Struthioptera (?) specimen is too poorly preserved to compare in detail with species described from the Upper Cretaceous of New Zealand.
The nearest record of a similar species of Rotularia is R. gregaria Etheridge from the Lower Cretaceous “Rolling Downs Formation” of Queensland. Comparable forms of Rotularia also occur in the Neocomian to Cenomanian in South Africa, South America and Antarctica and in the Northern Hemisphere.
Records of Exogyra conica (Sowerby) in the Southern Hemisphere are few, but in the Northern Hemisphere they range from Aptian to Cenomanian.
In all, analogies with overseas faunas seem to point to a Lower or mid-Cretaceous age for the Chatham Island fossils, probably not younger than Cenomanian.
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Mrs. G. H. Scott,
N.Z. Geological Survey, P.O. Box 368, Lower Hutt, N.Z.