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A NEW PALAEONISCID FISH FROM THE WITTEBERG SERIES

(LOWER CARBONIFEROUS)

OF SOUTH AFRICA

R. A. Juss

Albany Museum, Grahamstown.

(With 1 plate and 2 figures in the text)

CONTENTS

PAGE

Introductionweaa yuo i207)

Genus Mentzichthys nov. . . 270

Mentzichthys walshi sp. nov. . 270

Discussionyeme en a 72

Acknowledgments . . . 272

SUMMA Tammi ra wen 272

References BS ray ery OO

INTRODUCTION

In May 1963 Mr. G. Walsh, an official of the Sundays River Irrigation

Board, discovered a deposit of fossil fishes in the mountains just south of Lake

Mentz and close to the entrance of Karroo Poort. Mr. J. J. G. Blignaut, a

retired geologist, visited the site immediately and confirmed the importance

of its discovery. Since the beds are well exposed, from the upper portion of

the Witteberg quartzites through the complete sequence of Upper Witteberg

Shales to the Dwyka Tillite, it was possible for Mr. J. A. Marais of the Geologi-

cal Survey Department to determine the geological horizon on which the

fossil fish occur. The fossiliferous bed, which is nearly vertical and from three

to six inches thick, occurs 740 feet above the topmost white quartzite of the

Witteberg and in the upper shales which were formerly known as the Lower

Dwyka Shales. These shales are regarded as of lacustrine origin.

Lithologically, according to Haughton (1963), the Series, as now defined,

consists of fine-grained thinly bedded whitish quartzites intercalated with

dark green or blue (buff when weathered) micaceous shales and flagstones.

Locally lenses of grey sandy limestone or calcareous quartzite, sometimes

carrying plant fragments, are present, as well as bands of coarse grit. The

uppermost member (formerly Lower Dwyka Shales) consists mainly of greenish

and bluish shales and flagstones with some hard sandstone bands.

The most characteristic fossil in the quartzites of the series is the spiral

267

Ann. S. Afr. Mus. 48 (15), 1965: 267-272, 1 pl., 2 figs.

268 ANNALS OF THE SOUTH AFRICAN MUSEUM

impression known as Spirophyton which is characteristic of the Middle Devonian

of America. Other fossils previously discovered, although scanty, include

Bothrodendron, Cyclostigma (characteristic of the Carboniferous of Queensland

and New South Wales), Didymophyllum, Halonia, Knorria, Lepidodendron, Lepido-

strobus, Singularia, Selaginites and Stigmaria. Fragments of the body segments of

a eurypterid named Hastimima have also been discovered, as well as some fish

scales. A recent discovery by Mr. J. A. Marais is a species of Pszlophyton. In

age Du Toit (1954) considers these non-marine beds, about 4,000 feet in

thickness, to embrace the whole time interval from about the Middle Devonian

to the Lower Carboniferous, and it is to this latter period that the Lake Mentz

fish fossil bed appears to belong.

An outstanding feature of the exposed section of the fossil bed is the

concentration of fish impressions it contains. This concentration spoils what

could have been, in many cases, perfect impressions. As stated above, the

maximum thickness containing fishes varies from three to six inches but the

extent of the bed is unknown as it dips and disappears. Under normal circum-

stances sediments of this thickness would represent an appreciable interval

of time, but, from the great number of fishes overlapping one another, and

the disposition of some, it is evident that a mass mortality involving a large

concentration of Palaeozoic fishes occurred. Such a mass mortality, followed

by perfect preservation, could only have taken place if the primeval pool of

lake they were inhabiting was completely frozen over in the first place. Total

freezing would have resulted first in the concentration of fish in the bottom

layers, then asphyxiation followed by preservation in the bottom muds under

freezing conditions before being finally entombed by some major earth or

glacial movement. The open mouths of many of the fishes suggest asphyxiation

due either to deoxygenation of the water by the fishes themselves, or to their

being forced down into a deoxygenated hypolimnion.

Although the Witteberg Series is associated with lacustrine conditions,

certainly non-marine, it would be misleading to regard the Lake Mentz fossils

as being those of entirely freshwater species. Of the Palaeozoic and Mesozoic

fishes described from southern Africa many belong to widely distributed

genera and families which are associated with both marine and non-marine

formations. Rayner (1958) quoting Gunter points out that, as a general rule,

marine fishes are more tolerant of fresh waters than vice versa. There is ample

evidence of this today where marine species such as Carcharinus leucas, Pristis

microdon, Megalops cyprinoides and Glossogobius giuris are all found up to 300 miles

by river from the sea in many of the rivers of the east coast of Africa.

The Lake Mentz fossil fishes represent two distinct species and possibly a

third. Of the two more complete species one is a platysomid-like fish with very

large dorsal ridge scales, and the other a slender stream-lined palaeoniscid

which is described below as representing a new genus and species. The generic

name refers to the type locality and the specific name is in honour of the

discoverer of the fossil bed.

269

PALAEONISCID FISH FROM WITTEBERG SERIES

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270 ANNALS OF THE SOUTH AFRICAN MUSEUM

Family Palaeoniscidae

Genus MENTZICHTHYS nov.

Definition: Body fusiform and elongate; principal rays of pectoral fins not

articulated till towards their terminations; dorsal and anal fins situated pos-

teriorly, moderate in size, triangular in shape, the former originating slightly

ahead of the latter; caudal fin heterocercal, inequilobate and deeply cleft,

the axial lobe being well developed; distinct fulcra on all fins; head with

prominent rostrum and relatively large anteriorly placed orbit with large

postorbital; suspensorium very oblique, gape wide, teeth consisting of short

well-spaced cutting teeth and fine conical teeth on the maxillary, and numerous

fine conical teeth on dentary; opercular large, larger than subopercular,

branchiostegal rays fairly numerous, head bones sculptured with striae and

tubercles; scales rhombic, of moderate size, with large peg-and-socket articula-

tion, entire posteriorly, ridge-scales running from the occiput to the origin of

the dorsal and along the leading edge of the caudal fin.

Mentzichthys walshi sp. nov.

(Figures 1, 2. Plate VI A, B)

Specific diagnosis: Slender fusiform fishes whose maximum total length appears

to be about 18 cm., the length of the head being contained about four and a

half times, and the greatest depth six and a half times in the total length of

the body.

The Skull

The shape and arrangement of the bones of the skull are shown in Figure

2, which has been prepared, allowing for distortion, from three impressions of

heads which were cleaned and then polished with a nylon brush before photo-

graphing. Plasticine casts were also used for reconstructing the skull, broken

lines being used in the final drawing where sutures could not be determined

with confidence.

The ornament of the frontals, supratemporals, parietals and post-temporals

consists of striae running more or less antero-posteriorly. The postrostral is

ornamented mostly with tubercles which extend down to the nasals (see

Plate VI A). The branchiostegal rays are not ornamented but the large and

prominent postorbital bone is markedly rugose. Numerous transverse striae

ornament the maxillary and particularly the dentary. The suspensorium is

very oblique. The opercular and subopercular are also ornamented, the

former being much larger than the latter. The teeth showing on the dentary

are minute and numerous, similar teeth appear on the maxillary but there

are well spaced short cutting teeth as well which are confined to the anterior

and middle section.

NEW PALAEONISCID FISH FROM THE WITTEBERG SERIES 271

The Paired Fins

Preservation is not good enough to detect ornamentation of the supra-

cleithrum or cleithrum. The pectoral fin, situated low down ventrally, is

medium in size with a base length about one third that of the longest lepido-

trichia. The lepidotrichia, which number about 19 are unarticulated and

unbranched until their distal ends. The anterior edge of the pectoral fin is

covered with small fulcra. The pelvic fin, whose origin is about midway

between the origin of the pectoral and the origin of the anal, is relatively

small with about 13-15 lepidotrichia which are articulated and distally

branched. The anterior edge is covered with small fulcra.

The Unpaired Fins

The dorsal fin, which is situated nearer to the caudal fin than to the head,

is one and a quarter times as high as the length of the base. It is triangular in

shape with from 28-35 lepidotrichia which are articulated and branched

distally. The anal fin, whose origin is posterior to that of the dorsal, has a base

longer than its height. It is triangular in shape with 35-45 lepidotrichia which

are articulated and branched distally. Small fulcra are present along the

anterior edge. One of the outstanding features of this new species is the large

axial lobe of the caudal fin. This fin is distinctly heterocercal, deeply cleft

and inequilobate, the leading edge being covered with ridge scales.

Squamation

Not many scales are available for examination as, in most of the samples,

just the underneath pattern of the squamation appears in the impression.

The scales are medium in size and rhombic in shape with pronounced peg-

and-socket articulation. The few scales available, mostly immediately posterior

of the head, show transverse furrows with pits, the posterior edges being rough

but entire. There are from 16-18 rows of scales from the dorsal to the ventral

surface at the point of maximum girth, and 52-58 scales along a lateral series.

Moderately enlarged ridge-scales, numbering about 21, extend from the

occiput to the origin of the dorsal fin. Ridge-scales of a similar size anteriorly

extend along the caudal peduncle and up the leading edge of the caudal fin.

Material

The holotype is an impression on a slab No. A.M./64/4562 in the Albany

Museum, Grahamstown. A photograph of this is shown in Plate B. This

slab, from two to three inches thick, has numerous impressions on both faces.

Other samples of importance in constructing the illustrations in Figures 1 and

2 were A.M. 64/4563, A.M. 64/4564 and A.M. 64/4565, in the Albany Museum.

Further material, S.A.M. K1169 and S.A.M. K1170 is preserved in the

South African Museum, Cape Town.

272 ANNALS OF THE SOUTH AFRICAN MUSEUM

DiscussIon

Reasonably entire specimens of M. walshi have the following extreme

measurements :

Total length: 90 mm. Std. length: 70 mm.

Total length: 145 mm. Std. length: 110 mm.

From these measurements it has been possible to estimate the maximum

size of incomplete fossils to be about 180 mm. The type, Figure 1 and Plate

B, has a total length of 145 mm.

M. walsh belongs to the group pf palaeoniscids having a very oblique

mandibular suspensorium (Woodward, 1891). The remarkable development

of the axial caudal lobe, the smaller orbits and the large postorbital bones

distinguish this new genus from Rhadinichthys Traquair, 1877 as re-defined

by Moy-Thomas and Dyne (1938). These features, as well as the larger oper-

cular, distinguish Mentzichthys from the genus Cycloptychius Young, 1865, as

re-defined by the same two authors. Of the known palaeoniscids it would

appear that Mentzichthys is most closely related to those of the Lower Carbonife-

rous assigned to the genus Cycloptychius.

ACKNOWLEDGMENTS

I wish to thank Professor Orvar Nybelins of Stockholm, Sweden, for

reading this paper in its draft form and for providing valuable comments.

Dr. H. V. Eales of the Department of Geology, Rhodes University, assisted by

his team of senior students, provided the material from which the holotype of

M. walshi was selected. This project, carried out in collaboration with Dr.

T. H. Barry, was part of a research programme sponsored by the C.S.1.R.,

who also granted funds for the publication of this work.

SUMMARY

A new palaeoniscid fish Mentzichthys walshi n. gen. et sp. is described from

the Witteberg Series (Lower Carboniferous) of South Africa, just south of

Lake Mentz in the eastern Cape. It is suggested that a mass mortality of these

fishes took place in lacustrine conditions under ice.

REFERENCES

Du Torr, A. L. 1954. The geology of South Africa. 3rd ed. Edinburgh & London: Oliver & Boyd.

Haucuton, S. H. 1963. Stratigraphic history of Africa south of the Sahara. Edinburgh & London:

Oliver & Boyd.

Moy-Tuomas, J. A. & Dyne, M. B. 1938. The actinopterygian fishes from the Lower

Carboniferous of Glencartholm, Eskdale, Dumfriesshire. Trans. roy. Soc. Edinb. 59: 437-480,

Rayner, D. H. 1958. The geological environment of fossil fishes. In WeEsTOLL, T. S., ed. Studies

on fossil vertebrates: 129-156. London: Athlone Press.

Woopwarp, A. S. 1891. Catalogue of the fossil fishes in the British Museum (Natural History). 2.

London: British Museum.

Ann. S. Afr. Mus., Vol. XLVIII. Plate VI

A. Portion of a skull of Mentzichthys walshi, partly obliquely crushed, showing pronounced

postorbital bone and ornamentation.

B. Holotype of Mentzichthys walshi.

INSTRUCTIONS TO AUTHORS

MANUSCRIPTS

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REFERENCES

Authors’ names and dates of publication given in text; full references at end of paper in

alphabetical order of authors’ names (Harvard system). References at end of paper must be

given in this order:

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not ‘and’. Year of publication; several papers by the same author in one year designated by

suffixes a, b, etc. Full title of paper; initial capital letters only for first word and for proper

names (except in German). Title of journal, abbreviated according to World list of scientific

periodicals and underlined (italics). Series number, if any, in parenthesis, e.g. (3), (n.s.), (B.).

Volume number in arabic numerals (without prefix ‘vol.’), with wavy underlining (bold type).

Part number, only if separate parts of one volume are independently numbered. Page numbers,

first and last, preceded by a colon (without prefix ‘p’). Thus:

Smitu, A. B. 1956. New Plonia species from South Africa. Ann. Mag. nat. Hist. (12) 9: 937-945.

When reference is made to a separate book, give in this order: Author’s name; his initials;

date of publication; title, underlined; edition, if any; volume number, if any, in arabic numerals,

with wavy underlining; place of publication; name of publisher. Thus:

Brown, X. Y. 1953. Marine faunas. 2nd ed. 2. London: Green.

When reference is made to a paper forming a distinct part of another book, give: Name of

author of paper, his initials; date of publication; title of paper; ‘In’, underlined; name of

author of book; his initials; title of book, underlined; edition, if any; volume number, if any,

in arabic numerals, with wavy underlining; pagination of paper; place of publication; name

of publisher. Thus:

SmirH, C. D. 1954. South African Plonias. Jn Brown, X. Y. Marine faunas. 2nd ed. 3: 63-95.

London: Green.

SYNONYMY

Arranged according to chronology of names. Published scientific names by which a species

has been previously designated (subsequent to 1758) are listed in chronological order, with

abbreviated bibliographic references to descriptions or citations following in chronological

order after each name. Full references must be given at the end of the paper. Articles and

recommendations of the International code of zoological nomenclature adopted by the XV International

congress of zoology, London, July 1958, are to be observed (particularly articles 22 and 51).

Examples: Plonia capensis Smith, 1954: 86, pl. 27, fig. 3. Green, 1955: 23, fig. 2.

When transferred to another genus:

Euplonia capensis (Smith) Brown, 1955: 259.

When misidentified as another species:

Plonia natalensis (non West), Jones, 1956: 18.

When another species has been called by the same name:

[non] Plonia capensis: Jones, 1957: 27 (= natalensis West).