The Tarsophlebiidae is an extinct family of medium-sized fossil odonates from the Upper Jurassic and Lower Cretaceous period of Eurasia. They are either the most basal member of the damsel-dragonfly grade ("anisozygopteres") within the stem group of Anisoptera, or the sister group of all Recent odonates. They are characterized by the basally open discoidal cell in both pairs of wings, very long legs, paddle-shaped male cerci, and a hypertrophied ovipositor in females.
Description
Adult
Body
The head is similar to that of Recent Gomphidae with two large and globular compound eyes that are distinctly separated, but closer together than in damselflies (Zygoptera). There are also two cephalic sutures. The pterothorax seems to be even more strongly skewed than in damselflies. The legs are extremely long with short and strong spines, and with very elongate tarsi. There are three tarsal segments (tarsomeres), of which the most basal one is twice as long as the others. The pair of tarsal claws lack the ventro-apical hook of modern odonates.
Wings and wing venation The largest species Turanophlebia sinica reached a wingspan of about 10.3 centimetres (4.1 in), while the smallest species Tarsophlebia minor reached only a wingspan of about 5.5 centimetres (2.2 in).
The wing venation is characterized by the following features: wings hyaline, slender, and not stalked; discoidal cell basally open in both pairs of wings, so that the arculus is incomplete; forewing discoidal cell very acute; large and acute subdiscoidal cell in hindwing; primary antenodal braces Ax1 and Ax2 stronger than the secondary antenodal crossveins; nodus in distal position at 44-47% of wing length; nodus with terminal kink of CP and a strong nodal furrow; pterostigma elongate (covering several cells) and with oblique brace vein; one lestine oblique vein 'O' present between RP2 and IR2; in all wings there are pairs of secondary longitudinal concave intercalary veins anterior and posterior of the convex veins CuA, MA, and IR2, and closely parallel to them (the postero-intercalaries are always longer than the associated antero-intercalaries); hindwings without vein CuAb; crossvein-like remnant of vein CuP is curved and rather looks like a branch of AA.
Sexual dimorphism
Males are distinguished by paddle-like cerci, while females are distinguished by very long and thin, hypertrophied ovipositor that projects far beyond the abdomen.
The male secondary genitalia were of a unique primitive type, with a small sperm vesicle on sternite 3, two pairs of small plate-like hamuli on sternite 2, and a very short median ligula on sternite 2. Obviously, none of these structures is hypertrophied as sperm intromittent organ (functional penis). In each of the three suborders of Recent odonates, a different part of this apparatus is enlarged and developed as intromittent organ and device for removal of foreign sperm (sperm competition): in Zygoptera it is the ligula, a median process of sternite 2; in Epiophlebiidae it is the lateral pair of posterior hamuli on segment 2; and in Anisoptera it is the unpaired sperm vesicle on the anterior part of sternite 3. The structure of the apparatus in Tarsophlebiidae is suggestive of an intermediate state between protodonates and modern odonates. An exceptionally well-preserved male specimen of Namurotypus sippeli showed that protodonate Meganisoptera completely lacked a secondary genital apparatus on abdominal segments 2 and 3 and still had primary genitalia on segment 9 that strongly resemble those of wingless silverfish, who do not copulate but deposit external spermatophores. Only on the basis of such a mating behaviour is the evolution of the odonate secondary copulation conceivable at all. A first step probably was the attachment of a spermatophore to the basal sternites of the male abdomen instead of a deposition on substrate. The female now had to fetch the spermatophore from the male venter. This created an adaptive pressure to create storage structures for the spermatophore and attachment structures for the female genitalia. Tarsophlebiidae probably represent this state of evolution. The development of liquid sperm and intromittent organs for copulation apparently evolved three times in parallel in the three extant suborders. Lateral auricles on the sides of the basal abdomen in male Tarsophlebia eximia had been described by Nel et al. (1993). However, Bechly (1996) showed that these alleged male auricles were based on a misinterpretation of the hamuli posteriors, which was confirmed by Fleck et al. (2004). Fleck et al. (2004) demonstrated that male Tarsophlebiidae did possess a unique type of anal appendages. The description of calopterygoid-like appendages of Tarsophlebia eximia, with apparently two pairs of claspers, was based on misinterpretations due to artifacts of preservation. The cerci are very long, with a double-barreled basal petiole and a distal plate-like expansion. The broken double-barrelled petioles of the two cerci have been commonly misinterpreted as two pairs of claspers, while the distal plates have been overlooked or regarded as artifacts. Indeed, Tarsophlebia does neither possess zygopteroid- nor anisopteroid-like appendages. There are no visible paraprocts (as in Zygoptera) and no epiproct (as in Epiophlebiidae and Anisoptera). If these structures are secondarily reduced or primarily missing is not clear.
Larva No fossil larvae of this extinct family have yet been discovered.
Classification The family was established by Handlirsch (1906) on the basis of the type genus Tarsophlebia Hagen, 1866. Tarsophlebiopsis mayi was recognized as valid by most authors until the most recent revision of the family by Fleck et al. (2004), who demonstrated that the holotype of this taxon most probably is only an aberrant specimen of Tarsophlebia eximia. The family contains 2 described genera with totally 9 valid species:
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