Tarsophlebiidae


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 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. 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, 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, while the smallest species Tarsophlebia minor reached only a wingspan of about.
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 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 ; 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. 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 : in Zygoptera it is the ligula, an 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.. However, Bechly showed that these alleged male auricles were based on a misinterpretation of the hamuli posteriors, which was confirmed by Fleck et al..
Fleck et al. 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 and no epiproct. 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 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., 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:
All other described taxa are synonyms of the type species Tarsophlebia eximia.

Phylogeny

The monophyly of Tarsophlebiidae is strongly supported by the following set of derived characters :

hindwings with hypertrophied subdiscoidal cell that is developed as "pseudo discoidal cell"; fusion of veins MAb+MP+CuA for a considerable distance before separation of MP and CuA in hindwing; vein AA strongly bent at insertion of CuP-crossing; extremely acute distal angles of forewing discoidal and subdiscoidal cell. The body characters "distinctly prolonged legs, with very long tarsi" and "male cerci with paddle-like distal expansions" are known from one species of the genus Tarsophlebia and Turanophlebia respectively, and thus belonged to the common ground plan of all Tarsophlebiidae. The extremely prolonged female ovipositor could be a further synapomorphy for the family, but it is only known from T. eximia and from a single specimen of T. minor at the Solnhofen museum.
Bechly and Nel et al. proposed a long list of putative synapomorphies that demonstrate a closer relationship of Tarsophlebiidae with crown group Odonata:

presence of a costal triangle as broad and strong sclerotisation of the basal costal margin; the distal discoidal vein MAb and the subdiscoidal vein are aligned and dorsally enforced by a strong sclerotisation, so that this structure appears to cross the vein MP and the concave fold along this vein ; this discal brace is aligned with the arculus in the ground plan ; the midfork is shifted basally, with the RP3/4 generally arising basal of the subnodus and RP2 arising close to the subnodus ; more derived type of nodus, with a kink in ScP; the oblique basal brace is transformed into a transverse “basal bracket” Ax0 which looks like a primary antenodal crossvein; presence of two strong primary antenodal crossveins Ax1 and Ax2 ; pterostigma distinctly braced by an oblique postsubnodal crossvein beneath the basal margin of the pterostigma; presence of a tracheated lestine oblique vein 'O' between RP2 and IR2 ; in the median space the convex vestige of the Media-stem is suppressed since it is fused with the cubital stem to a common medio-cubital-stem, convergent to some Protanisoptera, Triadophlebiomorpha, and Protozygoptera.
Bechly proposed that several unique symplesiomorphic features of all Tarsophlebiidae indicate that this family represents the sister group of all Recent Odonata. These features are the basally open discoidal cell in the hindwing which implies an incomplete arculus, the presence of four tarsomeres of equal length, and the very primitive condition of the male secondary genital apparatus without any intromittent organ. Bechly therefore considered the similarities of Tarsophlebiidae and Epiprocta mentioned by Nel et al., viz the less separated and relatively large eyes, the presence of two cephalic sutures, and the small leg spines, as symplesiomorphies.
However, based on a cladistic study of 14 characters Fleck et al. again suggested that Tarsophlebiidae might rather be the sister group of the clade Epiprocta that includes Epiophlebiidae and Anisoptera. Nevertheless, this result has a very low statistical support and might as well be an artefact of the parsimony computer algorithm, because none of the 14 characters represents an unambiguous synapomorphy for Tarsophlebiidae and Epiprocta.
Huang & Nel presented convincing evidence from a new fossil Tarsophlebiidae from China that the number of tarsomeres is only three as in modern odonates, but that the first tarsomere is about twice as long as the others. Bechly already discussed this possibility and suggested that such a long basal tarsomere, compared to the short basal tarsomere in protodonates and all Recent odonates, could still be a plesiomorphic state that could have resulted by the fusion of two basal tarsomeres. Huang & Nel state that there is no evidence for such a fusion in the fossils and that the elongation of the first segment could as well be a derived feature of Tarsophlebiidae.
The two alternative phylogenetic positions of Tarsophlebiidae
Hypothesis of Fleck et al. :
Hypothesis of Bechly :

Biology

Next to nothing is known about the ecology and behavior of Tarsophlebiidae, but it probably was quite similar to Recent odonates. With their very long ovipositor the females probably inserted their eggs into mud in or close to water, similar to modern Cordulegastridae. It is remarkable that two other groups of Mesozoic odonates had a similarly elongated ovipositor.

Geographical and geological distribution

The fossil record of this family ranges from Upper Jurassic of Kazakhstan and Germany to the Lower Cretaceous of England, Transbaikalia, Mongolia and China. There are no records of Tarsophlebiidae from any fossil locality outside the Eurasiatic region.

History

The first tarsophlebiid fossils were specimens of Tarsophlebia eximia from the Upper Jurassic Solnhofen Plattenkalk of Germany described as "Heterophlebia eximia" and Euphaea longiventris by Hagen. Larger revisions of this family have been provided by Nel et al. and Fleck et al..

Notable specimens

Beside the important type specimens there are also several exceptionally well preserved fossils that contribute to our knowledge of the morphology of Tarsophlebiidae. These include the following specimens: