The Fossil Mayflies
The remarkable characters of recent mayfly wing and venation include: 1. The hind wings are much smaller than the fore wings or absent; 2. Forewing with humeral crossvein brace; 3. MA fused with Rs; and 4. Wing with many interclaries and marginal intercalaries. Those can be used to identify the fossil mayflies.
By the end of year 1990, 61 genera of fossil mayflies have been reported. They distributed almost in all families of the Order Ephemeroptera (Hubbard 1990).
The extinct Permian family Protereismatidae is generally considered as direct ancestors of recent mayflies (Kukalová-Peck 1983, 1985, 1994; McCafferty 1990; Sinitchenkova 1984 ; Needham et al. 1935.). The main characters of this family include: fore- and hind wings closely similar, the fore wing slightly longer and wider than the hind wing, but the hind wing broader near the base. Venation complete, both arranged as regular alternation of convex and concave veins right from C to 2A (J?). Rs is a metatriad. Rs normally is connected with MA only by a short basal anastomosis, but sometimes the original basal stem of Rs can be seen arising from R1 and meeting the upwardly arching MA close to its origin. CuA normally connected by a basal Y-vein with both MP above and CuP below it, but sometimes one or other branch may be missing. Upward archings of M and Cu variable (Tillyard 1936; Carpenter 1979).
Kukalová-Peck (1983, 1985, 1994) proposed that the Carboniferous Bojophlebiidae, Syntonopteridae and Triplosobidae are the mayflies or at least the ancestors of Permian Protereismatidae. But some researchers believed that the Triplosobidae may be the processor of Protereismatidae and doubt on Kukalová-Peck's conclusion on the former two families (Carpenter 1987 cited by McCafferty 1990; McCafferty 1990; Sinitchenkova 1984; Hennig 1981). Needham et al. (1935) suggested that the Triplosobidae is not mayfly either.
The Bojophlebia prokopi of Bojophlebiidae is from the Upper Carboniferous of Europe tropical climatic zone (Kukalová-Peck 1985, 1994). The most remarkable character of this species is its gigantic body. It has 45cm wingspan (fig.3). the prothoracic wings are present and large, the hind wings are broader basally than the fore wings.
The family that closely related to Bojophlebiidae is Syntomopteridae, which from the Middle Upper Carboniferous (Westphalian D) to Lower Permian tropic belt of North America and ?Europe. The species of this family have a wingspan of 8.5cm to 19cm. Like the Bojophlebiidae, the fore wing is slightly longer and narrower than hind wing.
The younger but deviant mayfly group from Upper Carboniferous is the Triplosoba pulohellla (Triplosobidae), which has MA arched or fused with R instead with RP and CuA &M possibly fused (Carpenter 1963; Kukalová-Peck 1983, 1985. 1994) (fig.5).
The Carboniferous mayfly sensu Kukalová-Peck does not have the clear humeral crossvein, and MA may not be fused with Rs. The older Bojophlebiidae have MA &RP and CuA &M arched and connected by a strut, but unfused; the younger Syntonopteridae have MA &RP fully fused and CuA &M strongly arched and strutted but unfused; the still younger but deviant Triplosobidae have MA arched or fused with R instead with RP and CuA &M possibly fused; Permian Protereismatidae have MA &RP fully fused and CuA &M sometimes fused and sometimes strutted.
Kukalová-Peck (1985) noted that bracing and fusing of a section of M, or MA &RP or R, Cu or CuA &M, and RA &RP occurs in most Paleoptera and is typical for the odonato-ephemeroid clade. The anal brace of Bojophlebiidae is typically ephemeroid and veinal resembles closely that of Syntonopteridae. The veins involved are the AA stem and AA1-2. The distal end of the anal brace (AA1) is fused with CuP at a meeting point of four veins. This meeting point is prominent and becames important in the ephemerid type of flight. In Protereismatidae it carries a bulla (fig.6).
Syntonopteridae has two autapomorphic characters of venation: 1.the incipient but already specialized gently arched and strong subcostal brace, which is a derivative character in Ephemeroptera; 2. a composite veinal anal brace fused with CuP at an area important for flight. The species of this family have big body which relate them to Bojophlebiidae. So it is possible that Syntonopteridae and Bojophlebiidae are not directly ancestral to Protereismatoidea but represent a sidebranch, albeit not very sepcialized, of the ephemeroid stem group (Kukalová-Peck 1985).
The extinct superfamilies Protereismatoidea and Mesephemeroidea (similar to the former) constitute the known Permian insects that appear to be mayflies, or at least mayfly precursors. Of these Paleozoic groups, only Mesoplectopteridae and Mesephemeridae continued into the Mesozoic.
Mesoplectopteron (Mesoplectopteridae) is the only known Triassic mayfly. The mayflies from Jurassic were in the extinct taxa Aenigmephemeridae, Epeoromimidae, Hexagenitidae, and Mesephemeridae, and the extant taxa Behningiidae, Ephemerellidae, Coloburiscinae, Leptophlebiidae, Palingeniidae, and Sipyhlonuridae (McCafferty 1990; Hubbard 1990). We can see that the main groups of recent mayflies have appeared in Jurassic.
Kukalová-Peck (1968) and Carpenter (1979) also reported the fossil nymphs of Protereismatidae, and Kukalová-Peck (1985) describled those of the families Bojophlebiidae, Syntonopteridae. Some other are reported by several researchers (Needham et al. 1935; Hubbard and Kukalová-Peck 1980). In contrast with adults, the mayfly nymphs can be recognized easily because they have long caudal filaments and abdominal gills.
The main differences between recent and Paleozoic mayfly nymphs are shown in the following table (Kukalová-Peck 1968, 1978, 1983, 1985, 1994).
| Nymphs Characters | Paleozoic | Recent |
|---|---|---|
| Head | Prognathous | Hypognathous |
| Largest thorax segment | Metathorax | Mesothorax |
| Prothorax | With wing pads | Two genera with wing pads |
| Wing articulation | Articulated by sclerites | Completely obliterated |
| Tarsal segment | 5 segments | 1 segment |
| Claw | 2 | 1 |
| Pairs of abdominal gills | 9 | 7 at most |
| Abdominal legs | Present | Absent |
| Metamorphosis instar | Absent | Present |
References
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