Chimera wingers

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Chimera wingers
Mickoleitia longimanus, holotype, imago

Mickoleitia longimanus , holotype, imago

Temporal occurrence
Jurassic to Aptium ( Lower Cretaceous )
150 to 120 million years
Locations
Systematics
Over trunk : Molting animals (Ecdysozoa)
Trunk : Arthropod (arthropoda)
Class : Insects (Insecta)
Subclass : Flying insects (Pterygota)
Superordinate : Fixed wing (Palaeoptera)
Order : Chimera wingers
Scientific name
Coxoplectoptera
Staniczek, Bechly & Godunko, 2011
Familys

Mickoleitiidae

Coxoplectoptera (Coxoplectoptera) are a primitive, extinct group of insects from the main line of mayflies , which was not scientifically described until 2011th Winged animals and aquatic larvae were predators and had prehensile paws that at mantises remember. The larvae have a strange, river flea- like shape. The chimeric wings lived in the Mesozoic . So far only fossils of two adults and more than 20 larvae have been scientifically described (a total of at least 30–40 larvae were found).

etymology

The genus Mickoleitia and the Mickoleitiidae family were named in honor of the Tübingen zoologist Gerhard Mickoleit . The scientific name Coxoplectoptera is derived from the elongated hip limbs (coxes) of the larval and imaginal legs and from the old scientific name Plectoptera for mayflies (not to be confused with Plecoptera for stone flies ). The German name Chimärenflügler refers to the adult animals, which because of their unusual combination of characteristics (breast and hind wing shape of a dragonfly, wing veins of a primitive ancestor of the mayflies, and forelegs as catch legs like those of a praying mantis) like a being composed of different, unrelated animals ( chimera of Greek mythology) work.

Discovery story

The larvae of the Coxoplectoptera are not infrequently found in the plate limestone of the Crato Formation, so that they have even been given a special name ("Abacaxi" = pineapple) by the Brazilian quarry workers. The larvae were first depicted by Bechly (2001: Fig. 36) and pointed out to their strange morphology. Staniczek (2002, 2003) also discussed these larvae and mentioned that they were a kind of “ living fossils ” during their lifetime . The Göttingen biologist Rainer Willmann described these larvae in Martill, Bechly & Loveridge (2007) and erroneously assigned them to the Cretereismatidae family , which he described as adult animals from the same site as the core group representative of the mayflies. The German (paleo) entomologists Günter Bechly and Arnold H. Staniczek had already discovered the adult fossil in the collection of the Stuttgart Natural History Museum while working on this monograph of the Crato formation , which would later become the holotype of Mickoleitia longimanus . They pictured it in Martill, Bechly & Loveridge 2007 (Fig. 11.90i, j) as an undescribed core group representative of the mayflies and already mentioned the possible relationship to the larvae in a short legend . The actual description of the Coxoplectoptera and the proof of the affiliation of the larvae was published by Staniczek, Bechly & Godunko (2011) in a special volume on Cretaceous insects in the journal "Insect Systematics & Evolution". The authors also recognized that two mysterious larvae ( Mesogenesia petersae = Archaeobehnigia edmundsi ) from the middle or upper Jurassic of Transbaikalia , which Tshernova (1977) had erroneously described as modern mayfly larvae, also belong to the Coxoplectoptera. The discovery and description of the chimera wing was one of the more spectacular paleontological events of 2011 and generated worldwide media interest.

anatomy

Imago

The adult stage of the type Mickoleitia longimanus has a wing length of 28-29 mm and a presumed (the abdomen is not preserved) body length of 35-40 mm. A second unnamed species of the genus Mickoleitia is only about half the size and is only known from a single fossil in a Japanese private collection. Large complex eyes sit on the head and functional mouthparts are apparently present (3-part lip probes have been preserved ). The breast segments are tilted backwards as in dragonflies , which pushes the front canine legs more forward. All legs have a greatly elongated and exposed hip joint ( coxa ). The forelegs are designed as subchelate fangs with a single-limbed tarsus with an unpaired claw. It is very likely that the abdomen ended in three tail threads ( cerci and terminal filum ), as in today's mayflies and their Permian core group representatives ( Permoplectoptera , e.g. Protereismatidae ). Since the males of today's mayflies and the Permoplectoptera have gonopods that have been transformed into genital grasping pincers in order to grasp the females during mating, this characteristic state and this behavior can also be assumed for the Coxoplectoptera, which historically can be classified as a link between these two groups.

larva

Mickoleitia spec. larva

The more than 20 fossil larvae described have a body length of 10–32 mm, depending on the stage. They are unique among all known fossil and recent aquatic insect larvae due to their laterally flattened physique, which is more reminiscent of river fleas. Many of the larvae are embedded in a characteristic position, with a concave arched back and highly erect antennae and tail threads, the front legs always in a trapping position like a praying mantis. The head is heavily armored and provided with horn- or shovel-like outgrowths. Crossed, saber-like jaws ( mandibles ) and a shovel-shaped lower lip ( labium ) are known of the mouth parts . All legs have a greatly elongated hip joint like the adult animals. The forelegs are slender tentacles with an almost identical structure as in the adult animals, but the tibia is shortened and possibly fused with the one-limbed tarsus. There is only one unpaired claw on all tarsi. The handle-shaped and downwardly directed abdominal gills are located on the 1st to 7th abdominal segment. These gills have a broad, more sclerotized base section and a narrow, more membranous distal section . The gills start within the abdominal back shields ( tergites ), which are clearly separated from the ventral shields ( sternites ). The lateral cerci and the median terminal filum form three long tail threads that are densely lined with fine, long hairs.

Way of life

Imago

Since the mouthparts (palps) are clearly visible on the head of the holotype specimen , the adult animals have certainly consumed food. This is in contrast to the modern mayflies, whose adult stage is a pure reproductive stage, which no longer eats and whose mouthparts are therefore severely reduced. The front legs, which are designed as catch legs, and the inclined chest show that they were predators who presumably actively preyed on other insects in flight. The dragonfly-like wings and large hind wings also indicate that the chimera wings were skillful and fast fliers.

larva

The frequency of finds and certain anatomical adaptations (7 pairs of gill appendages on the abdomen, three tail threads densely lined with webbing hair) prove that the larvae, like today's mayfly larvae, must have lived in flowing fresh water and in the brackish lagoon where the plate limestone with the fossils was deposited when allochthonous elements were washed in. The front legs, which are designed as catch legs, as in the adult animals, and the strong and curved jaws (mandibles) as well as large eyes and long antennae show that the larvae also lived predatory. On the other hand, the strong, shortened and widened middle and rear legs, the strong body armor and shovel-like extensions on the head indicate that the animals have been digging. The descriptors therefore suspect that the larvae lived half buried in the bottom of the water as ambulance hunters and seized small aquatic animals swimming by or passing by.

Evolution and tribal history

The larvae of the Coxoplectoptera provided new clues to clarify the evolutionary origin of the insect wings . So far, two theories, Paranotal theory and Exit theory, were considered incompatible alternatives, each of which was supported by different evidence from the fossil record, comparative morphology, developmental biology and genetics. The proof that leg genes are expressed during the ontogenesis of the larval wing anlage was considered convincing evidence of the exit theory, which derives the insect wing from transformed, movable branches (exits) of the split legs. The larvae of the Coxoplectoptera show, however, that the abdominal gills of the mayflies and their ancestors, which are regarded as organs serially corresponding to the wings, arise within the dorsal shields. This is not recognizable in modern mayflies, since the back and belly shields in the larvae's abdomen are always fused into rings, and there are no indications in the embryo either. If the larval gills and wings are corresponding ( serially homologous ) structures and thus have the same evolutionary origin, the finding of the Coxoplectoptera larvae means that the wings are also of Tergal origin, as the classical Paranotal theory said. Staniczek, Bechly & Godunko (2011) therefore proposed a new hypothesis that could reconcile the new paleontological findings with the results of developmental genetics. According to this, wings were initially formed as rigid outgrowths of the back shields (Paranota), and only later in evolution would these outgrowths have become mobile through the secondary "recruitment" of legs.

Within the flying insects, the Coxoplectoptera represent the sister group of the modern mayflies. The following characteristics speak as synapomorphies for a closest relationship with the mayflies : wing veins with costal brace ("costal brace", absent in all other flying insects), larvae with 7 pairs of abdominal gills (in contrast to 9 pairs in the Permoplectoptera, e.g. larvae of Protereisma ), larvae with single-limbed and single-clawed tarsus (in contrast to still 3-limbed tarsus with paired claws in the Permoplectoptera, e.g. larvae of Protereisma ).

Together with the mayflies and the dragonflies , the Coxoplectoptera belong to the monophyletic group of the Palaeoptera , which are characterized by a derived structure of the wing joint with fused sclerites and a vertical wing restraint in the basic plan, as well as by arteries between the actual longitudinal arteries (especially IR1 + between RP1- and RP2-, and IR2 + between RP2- and RP3 / 4-).

The Coxoplectoptera were very original and resembled the early ancestors of the mayflies from the ancient world, for example in the plesiomorphic expression of the costal spantung in the wing veins of the adult animals and the clearly separated, probably movable wing sheaths of the larvae. The large and wide hind wings are also an original feature state compared to the smaller hind wings of the mayflies and the slender hind wings of the Permoplectoptera.

The monophyly of the Coxoplectoptera is evidenced by a number of autapomorphic features of the group, such as B. in the adult stage through the muzzle bones and the one-limbed feet with unpaired claws, as well as in the larval stage through the laterally flattened body shape, the body armor, the muzzle bones and grave bones and the handle-shaped shape of the abdomen gills pointing downwards.

The Coxoplectoptera are proven in the Jura and in the Lower Cretaceous Period. When and why they became extinct is not yet known.

Systematics

The extinct order of the chimera winged (Coxoplectoptera) includes only one family (Mickoleitiidae) with two genera:

Mickoleitia (Lower Cretaceous, Crato Formation, Brazil):

  • Mickoleitia longimanus (type species)
  • Mickoleitia spec. (smaller unnamed species, only one adult fossil specimen in a Japanese private collection)

Mesogenesia (Jura, Transbaikalia):

  • Mesogenesia petersae (= Archaeobehnigia edmundsi )

literature

  • OA Tshernova: Distinctive new mayfly nymphs (Ephemeroptera; Palingeniidae, Behningiidae) from the Jurassic of Transbaikal. In: Paleontologicheskii Zhurnal. 1977 (2), 1977, pp. 91-96. (Russian).
  • Günter Bechly et al. (Ed.): Ur-Geziefer - The fascinating evolution of insects. (= Stuttgart contributions to natural history. Series C. 49). Stuttgart 2001, DNB 964675013 . ( Full text as PDF; 4.5 MB ).
  • Arnold H. Staniczek: Fossil Mayflies - Insights into the world of primeval flying insects. In: fossils. 19, 2002, pp. 297-302.
  • Arnold H. Staniczek: Mayflies - Manna of the rivers. (= Stuttgart contributions to natural history. Series C. 53). Stuttgart 2003, DNB 972757562 .
  • David M. Martill, Günter Bechly, Robert F. Loveridge (Eds.): The Crato Fossil Beds of Brazil - Window into an Ancient World. Cambridge University Press, Cambridge et al. 2007, ISBN 978-0-521-85867-0 .
  • Arnold H. Staniczek, Günter Bechly, Roman J. Godunko: Coxoplectoptera, a new fossil order of Palaeoptera (Arthropoda: Insecta), with comments on the phylogeny of the stem group of mayflies (Ephemeroptera). In: Insect Systematics & Evolution. 42 (2), Brill, Leiden 2011, pp. 101-138. ISSN  1399-560X ( author homepage with link to PDF ).

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