Main articleAn unusual mayfly from the Upper Triassic near Dordrecht in the Cape Province of South Africa is described as Xenophlebia optata gen. et sp. nov., and is ascribed to a new family, the Xenophlebiidae, as its sole representative.Non

Riek, E. F.

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149 Palaeont. afr., 19. 149-151 (1976) AN UNUSUAL MAYFLY (INSECTA: EPHEMEROPTERA) FROM THE TRIASSIC OF SOUTH AFRICA by E. F. Riek G.S.l.R.O. Division 0/ Entomology, P.O. Box 1700, Canberra City, A.G.T. 2601 ABSTRACT An unusual mayfly from the Upper Triassic near Dordrecht in the Cape Province of South Africa is described as Xerwphlebia optata gen. et sp. nov., and is ascribed to a new family, the Xenophlebiidae, as its sole representative. INTRODUCTION The classification of Recent Ephemeroptera is based, to a considerable extent, on structures other than the wings of the adults. However, the major groups (subfamilies and higher categories) of Recent Ephemeroptera can be defined on differences in vena-tion' with the possible exception of a few Baetoidea (Arnetropodidae and Metretopodidae) in which it is also necessary to know the structure of the adult tarsi, or the structure of the head of the nymph, to dis-tinguish them from Heptageniidae. The major trend in the wings of Ephemeroptera has been reduction in the size of the hind wing. The known Permian species and some early Mesozoic ones had a hind wing that was as long as and slightly broader than the fore wing. Reduction has culminated in the com-plete loss of the hind wing in the more specialised Re-cent species of a number of phyletic lines. In the initial stages of reduction of the hind wing, a complementary tomus, or obtuse angle, formed on the hind margin of the fore wing at a point about level with the apex of the hind wing. The tomus is situated between the two branches of the cubitus, except in the Baetiscidae. Even though the hind wing is relatively large in the Baetiscidae, which retain a very primitive wing vena-tion, the tomus is in the anal field. The Baetiscidae is the only family in which CuA and CuP are subparallel and connected by simple cross veins for all or most of their length. In all other mayflies, the tomus, when pre-sent, is between the branches of Cu. As the hind wing is reduced, there is a greater complementary reduction in the length of CuP as compared with CuA so that the length of the wing margin occupied by the cubital field increases up to a point, and then remains relatively constant. When the hind wing is very reduced or absent, the tomus is lost, and the hind margin of the fore wing is rounded, and slightly to markedly widened in the cubito-anal field. The base of the wing is markedly widened in Caenidae, Baetidae and Tricorythidae but it is not widened in l.eptophlebiidae. The hind wings are not markedly reduced (or absent) in other Ephemeroptera. At no stage in the sequence of reduc-tion do the two main branches of the cubitus become re-oriented and subparallel to one another as they are in the Permian Misthodotidae and Recent Baetiscidae. However, the fossil species under review from the Upper Triassic of southern Africa has a very reduced cubito-anal area, and the two branches of Cu are close and subparallel (and connected by a simple cross vein or veins). The tomus is lost but the wing is not widened at base. The cubito-anal field is markedly reduced and occupies only a minute area at the base of the wing. Reduction in venation resulting in a long relatively narrow wing with a minute cubito-anal field (and a large MP field) had been unknown in any phyletic line, either fossil or Recent. This very unusual mayfly, of which only the wing, almost certainly a fore wing, is known, is referred to a new superfamily without recognisable close phyletic relationship to any known Ephemeroptera. SYSTEMATICS SUPERFAMILY XENOPHLEBIOIDEA superfam. nov. Diagnosis Wing. Stem of Cu distinct to wing base, as in Permian Ephemeroptera, branching into CuA and CuP more basally than the thickened stem of the anal field. Basal thickened stem of anal field curved upwards, mainly at the cross connection between lA and CuP; stem more similar to that in Recent than in Permian species. Rs appearing to arise as a forward branch ofMA, and MP arising very close to the wing base, before the separa-tion of Rs + MA from the stem of R, as in Recent Ephemeroptera. Bullae present, on Sc and the upper branch of Rs. Posterior branch of MP arising close to base, not deflected towards CuA close to its origin from the stem of MP, but more or less straight throughout its length. Notes. The basal origins of the main veins are partly as in Recent Ephemeroptera and partly as in the Per-mian Proterismatidae and Misthodotidae. The more or less straight posterior branch of MP is similar to that in Baetoidea, Heptagenioidea and l.eptophlebioidea, as distinct from Ephemeroidea, but the triad is developed very close to the wing base, as in Ephemeroidea. The absence of cubital intercalary veins may be due entirely to the very marked reduction in the cubito-anal field of 150 the wing, and may not relate the group to the Baetiscidae in which this area of the wing is fully developed. The absence of a tornus indicates that the hind wing was absent or minute, at least in the one known species. However, development of the hind wing is variable in Recent Ephemeroptera. The superfamily represents a line of development distinct from any that lead to the Recent Ephemerop-tera, in which such a marked reduction in the cubito-anal field is unknown. One included family, from the Upper Triassic of southern Africa. FAMILY XENOPHLEBIIDAE fam. nov. Diagrwsis Wing. MP forming a simple triad, or at most with a tendency towards attached marginal intercalary veins. Without intercalary veins between MP and CuA. Without cubital intercalary veins (CuA and CuP con-nected by a simple cross vein or veins). CuP straight. Rs arising from close to wing base. Cross venation well developed. Wing without short marginal intercalaries. One included genus. Genus Xerwphlebia gen. nov. Etymology Xenos = stranger, and phleps = vein, from the very unusual venation. Type species Xerwphlebia optata sp. nov. Diagrwsis Wing. Almost certainly fore wing: hind wing almost certainly absent. Tornus absent. Cubito-anal area minute. Triad on MA arising about middle of vein. Rs forking moderately close to origin, but about level with triad on MA. CuA and CuP very short, connected by only a basad cross vein. Three distinct anal veins, all minute, simple. MP with convex middle branch forking close to wing margin (possibly a variable character). Cross veins complete over whole wing, simple, except in part, close to margin. Cross veins simple in pterostigrnatic area. Bulla on upper branch of Rs very close to origin of branch. Type Xerwphlebia optata sp. nov. (Figures 1-3) C- Dt II 752 a, band paratypes 754 a, b and 755 a, b, in Bernard Price Institute. Type locality Bird's River, Dordrecht, Eastern Cape Province. Molteno Formation. Upper Triassic. Description In Recent Ephemeroptera specific characters are recognised mainly in the ter!fiinalia which are unknown for the species. Holotype Fore wing, complete. Length c. 21 mm. Cross veins not appreciably closer in the pterostigrnatic area than more basally and, thus, pterostigrna not defined. Triad on MP arising from basal fork in vein. Bulla on upper branch of Rs at the level of the first cross vein to the basad triad. Short cross connection from CuA near its base to the stem ofM before separation ofMP. 1A very widely separated from CuP, with a strong cross connec-tion appearing as an upward continuation of the stem of A. Only three anal veins, simple, the third very short. C- Dt II 754 a, b is a complete wing, slighdy weathered and therefore the impression is pale but venation distinct, including basal swellings of the veins. Costal margin thickened at base. Humeral vein simple, humeral space not widened but rather long. C-Dt I I 755 a, b is the distal half of a wing from the bullae to apex. This wing is very slighdy larger than the other two wings. Note. The venation of the almost perfecdy preserved holotype wing is accentuated by mineral staining. ACKNOWLEDGEMENTS I am grateful to John Green, CSIRO, Canberra for the photographs. Figures 1-3. Xerwphlebia optata gen. et sp. nov. I. C-Dt II 752 a, reversed. 2. C-Dt II 754 b. 3. C-Dt II 754b. Base of wing enlarged. (For size of specimens, see text.) 151 

An unusual mayfly (Insecta: Ephemeroptera) from the Triassic of South Africa

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