Descriptions of Fossil Fish from New Zealand
[Read before the Otago Institute, 14th November, 1933; received by the Editor, 30th November, 1933; issued separately, September, 1934.]
For the opportunity of describing these exceptionally interesting specimens I am indebted to Professor W. N. Benson, D.Sc., Otago University, Dunedin.
The new species of Portheus shows a very high geological range for that genus, which, so far, has been limited to the Neocomian up to the Senonian, whereas in New Zealand it is found in beds which may extend into basal Eocene.
The occurrence of Eothyrsites in the Burnside marls, especially in its relationship to Thyrsitocephalus, helps to confirm the horizon as Oligocene. This is further supported by the foraminiferal fauna found in the same stratum.
All type specimens have been placed in the collections of the Geology Department, Otago University.
Descriptions of the Fossils.
Genus Portheus Cope
Portheus Dunedinensis, sp. nov.
Plate 12, fig. 1.
Description.—Type specimen representing the larger part of the cranium with supra-occipital and lower jaws, the anterior vomerine portion wanting.
The cranium measures about 18 cm. in height; 17 cm. in length; and about 12 cm. in width.
The cranial region, on the left side, shows the bones of the frontal region much crushed, with the pre-frontal and ethmoid truncated by fracture.
The ossified sclerotic plates are well preserved; the bony ring has a diameter of 43 mm., with the plates measuring 15 mm. in depth.
Maxilla, in widest part, measuring 32 mm. Total length of maxilla as preserved, 13.5 cm. Dentary series with backwardly curved and conical teeth, varying from 5 to 9 mm. in length, and plicate near the base. Sixteen of these teeth are preserved, but the entire series for the ramus probably numbered about 36. Premaxilla wanting. Mandibular ramus strong and deep, at the widest part 4.3 cm.
Right side of the cranium shows the frontal bones much crushed, the sclerotic plates present, but obliquely displaced. Maxillary with only six teeth preserved. Mandibular ramus 4.7 cm. deep.
Matrix of Specimen.—The rock in which the cranium of the fish was embedded is a hard, marly greensand, of a greenish grey colour. Washings of the rock yield a residue which is almost purely glauconitic. Amongst the glauconite casts of foraminifera were recognised, infillings of Globigerina, ? Rotalia and a plane-convex rotaline form which may be Globotruncana (a Cretaceous genus).
Observations.—The present species, Portheus dunedinensis, was, when complete, rather more than half the length of Portheus molossus Cope (1875, pp. 184, 194, fig. 8 woodcut, pls. xxxix-xli; pl. xliv, figs. 5, 10, 11; pl. xlv, figs. 9–11). In the latter the cranium is higher and the teeth of the maxilla are not curved at the apex as in P. dunedinensis.
In its general dimensions P. dunedinensis compares very closely with Portheus australis (A. S. Woodward, 1894, pp. 44, pl. ix, figs. 1, 1a) from Clutha Station, near Hughenden, Queensland. These Cretaceous beds, with an accompanying fauna of reptilian remains, are now referred to the Tambo Series, equivalent to the Upper Albian of Europe. The teeth in the New Zealand species, however, are stouter and broader at the base, and are less regularly spaced on the maxilla, as compared with the Queensland P. australis, in which they are fairly evenly arranged.
E. T. Newton (1877, p. 511, pl. xxii, fig. 13) has described Portheus daviesii, from the Lower Chalk (Turonian) near Maidstone, Kent, but here the teeth of the maxilla are in a shorter series, and are more slenderly conical than in P. dunedinensis.
The same author also described another species of the genus as Portheus gaultinus (Newton, 1877, p. 512, pl. xxii, figs. 1–12 and woodcut), from the Albian (Gault) of Folkestone, Kent. This form differs from the New Zealand species in the much smaller size and lighter build of the maxillary, and in the generally longer and slenderer teeth.
Portheus lewesiensis (Agassiz), which was described by that author under the genus Hypsodon (1843, p. 99, pls. xxv a, xxv b), has a very heavy type of mandible, and the teeth are correspondingly strong, short, conical, and broad at the base.
Fig. 3.—Eothyrsites holosquamatus. gen. et sp. nov. Side of cranium with part of mandible and teeth. Mail-pit. Burnside. Green Island, near Dunedin, N.Z. Upper Oligocene Syntype. Two-thirds nat. size.
Fig. 4.—Eothyrsites holosquamatus, gen. et sp. nov. Pectoral fin. Marl-pit. Burnside, Green Island, near Duuedin. N Z Syntype Two-thirds nat. size.
Fig. 5.—Eothyrsites holosquamatus, gen. et sp. nov Same as Fig. 2. showing strong character of squamation, with veitebiae. Enlaiged one and a-half times.
Locality and Horizon.—The above-described fossil was found in the glauconitic mudstone at Abbotsford, near Dunedin. It occurs about 500 feet above the horizon which contains a Wangaloan fauna, referred to by New Zealand stratigraphists as either Palae-eocene or Danian.
From the previous records of the genus Portheus it is a distinctly Cretaceous genus. The Abbotsford bed, therefore, can hardly be regarded as younger than Danian.
Genus Eothyrsites, gen. nov. Chapman, 1933.
Generic Characters.—Body moderately elongated; form probably near that of the recent Thyrsites atun, but somewhat deeper. Abdominal vertebrae with diameter of centrum more than half the length, instead of less, as in Thyrsites. Surface of body almost covered with moderately large cycloid scales. In Thyrsites, a degenerate genus, these scales are confined to the lateral line. Pectoral fins long and narrow, as in Thyrsites.
Eothyrsites Holosquamatus sp. nov.
Plate 13, fig. 2; plate 14, figs. 3–5.
Description of Genotype and Holotype.—An imperfect fish, consisting of three portions.
1. A slab, 24 × 12 cm., showing 6 vertebral bones, rays of the dorsal fin, ventral fin, and squamation of the median part of the body.
2. A crushed slab, 14 × 9 cm., showing crushed facial bones (? quadrate and pterygoid), part of mandible with teeth, and on the opposite face of slab, the preopercular.
3. Fish remains, 13 × 5 cm. on slab of mudstone, with a complete left pectoral fin.
Vertebrae.—The series of abdominal vertebrae shown here are of much the same contour as those in the recent Barracouta (Thyrsites atun), but on the whole much stouter and heavier. One of these centra has a length of 27 mm. and a maximum diameter of 19 mm.; in the middle of the centrum it narrows down to 12 mm. The rounded border of the adjacent centra indicates the former existence of a distinct cartilage pad, as in Thyrsites.
Pectoral Fin.—Narrow, slender, and only slightly curved; the proximal end shows a distinct articulating surface for attachment to the brachial. The rays are bony, narrow, and closely fasciculated. The length of the fin is 70 mm., and the greatest width 21 mm.
Teeth.—These number 5 and are arranged along part of the maxilla in an even series in a line measuring 16 mm. They are slender towards the tip, which is inwardly curved; they widen rapidly to the base, and in the alveolar socket are broad and cylindrical, as seen where a tooth has fallen out.
Length of teeth, 4 mm.; total length, with alveolar base, 6 mm.; width near base, 1 mm.
Squamation.—One of the highly important and interesting structures in Eothyrsites is the more or less complete scaly armour of the body. So distinct is this feature that, on first acquaintance with the specimens, it appeared as if the relationship to Thyrsites might be questioned. Upon examining the skin of a living Barracouta, it was seen that cycloid scales, precisely of the same character, and often of the exact dimension, of those in the fossil form Eothyrsites, were present along the lateral line of the fish, forming a close protective armature. It therefore seems entirely reasonable to suppose that in Eothyrsites we have an Oligocene form ancestral to the living Thyrsites and other related and almost scale-less fishes, as Lepidopus. In the case of Thyrsites a degeneration of the skin armature has taken place, the skin still being marked, however, by scale-like areolae, in which a vestige of the earlier scaly character has been retained for the protection of the slime canals. The average diameter of the scales in Eothyrsites is 4 mm., although in some cases they measure as much as 7 mm.; in Thyrsites the scales measure from 1.5 to 3 mm. The scales in Eothyrsites appear to be strengthened by ganoine and more or less calcified, whereas in Thyrsites they are thin and flexible.
The occurrence of the definite system of cycloid scales along the lateral line in the living Thyrsites does not appear to have been recorded by any previous writers excepting McCoy (1879), who says “greater part of the body naked” (loc. cit. p. 19).
Observations.—In its skeletal form the genus Thyrsitocephalus represented by T. alpinus vom Rath, resembles Eothyrsites. The former fossil, however, does not show the squamose characters, so that it seems safer to institute the new genus for the New Zealand specimen. Vom Rath's type of Thyrsitocephalus came from the Oligocene of Canton Glarus, Switzerland (Rath, 1859, p. 114, pl. III, fig. 4).
Locality and Horizon.—Marl Pit, Burnside, Green Island, near Dunedin, New Zealand. Upper Oligocene.
Note.—In my monograph on the Cretaceous and Tertiary Foraminifera of New Zealand (Chapman 1926, p. 16) I gave the horizon of the foraminifera of the Burnside marl as “Upper Eocene probably).” From a recent examination of the recorded fauna, together with additional foraminifera found by Miss Crespin and myself in the matrix with the fish skeleton, we find that it exactly agrees in the faunal horizon of the Goon Nure Bore, Gippsland, Victoria, below 2020 feet, which we have referred to the Upper Oligocene.
1. Agassiz, L. 1843. Recherches sur les Poissons Fossiles. Vol. V. Neuchatel.
2. Chapman, F. 1926. The Cretaceous and Tertiary Foraminifera of New Zealand., N.Z. Geol. Surv. Pal. Bull. No. 11.
3. Cope, E. D. 1875. The Vertebrata of the Cretaceous Formations of the West. Pisces Rep. of the U.S. Geol. Surv. of the Territories, Vol. II, pp. 179–244F, pls. xxxix-lv.
4. McCoy, F. 1879. Prodr. Zool. Vict., Vol. I. Dec. IV, pp. 19, 20, pl. xliv, fig. 1.
5. Newton, E. T. 1877. On the remains of Hypsodon, Portheus, and Ichthyodeotes, from British Cretaceous strata, with Descriptions of New Species. Quart. Journ. Geol. Soc. London. Vol. XXXIII, pp. 505–523, pl. xxii.
6. Rath, G vom 1859. Beitrag zur Kenntniss der fossilen Fische des Plattenberges in Canton Glarus. Zeitschr. d. deutsohen geol. Gesellsch. Vol. XI, pp. 108–132, pls. iii-v.
7. Woodward, A. S. 1894. On some Fish remains, of the genera Portheus and Cladocyclus, from the Rolling Downs Formation (Lower Cretaceous) of Queensland. Ann. and Mag. Nat. Hist., Ser. 6, Vol. XIV, pp. 444, 447, pl. x, figs. 1–7.
Explanation of Plates.
Fig. 1. Portheus dunedinensis, sp. nov. Left side of cranium. Abbotsford, near Dunedin, N.Z. Of probable Palae-eocene or Danian age. Holotype. Half nat. size.
Fig. 2. Eothyrsites holosquamatus, gen. et sp. nov. Slab of mudstone with vertebrae, rays of dorsal fin, ventral fin, and scales of the median part of body. Marl-pit, Burnside, Green Island, near Dunedin, N.Z. Upper Oligocene. Syntype. Half nat. size.
Fig. 3. Eothyrsites holosquamatus, gen. et sp. nov. Side of cranium with part of mandible and teeth. Marl-pit, Burnside, Green Island, near Dunedin, N.Z. Upper Oligocene. Syntype. Two-thirds nat. size.
Fig. 4. Eothyrsites holosquamatus, gen. et sp. nov. Pectoral fin. Marl-pit, Burnside, Green Island, near Dunedin, N.Z. Syntype. Two-thirds nat. size.
Fig. 5. Eothyrsites holosquamatus, gen. et sp. nov. Same as Fig. 2, showing strong character of squamation, with vertebrae. Enlarged one and a-half times.