Coxoplectoptera

Coxoplectoptera or "chimera wings" is a primitive, extinct order of winged insects containing one family, Mickoleitiidae, discovered in 2007.

Two adult and more than 20 larval fossils of Mickoleitia have been scientifically described from Mesozoic outcrops, mainly from the Lower Cretaceous Crato Formation of Brazil (in total, around 40 fossil larvae have been found). Coxoplectoptera belong to the stem group of mayflies. Both the winged adults and the aquatic larvae were predators with raptorial forelegs, which are reminiscent to those of praying mantids. The larvae had a peculiar freshwater shrimp-like habitus.

Coxoplectoptera
Temporal range: Late Jurassic-Early Cretaceous
~150–120 Ma
Mickoleitia longimanus
Mickoleitia longimanus, imago, holotype
Scientific classification
Kingdom:
Phylum:
Class:
Subclass:
Infraclass:
Superorder:
Panephemeroptera
Order:
Coxoplectoptera

Stanizcek et al. 2011
Families

Etymology

The genus Mickoleitia and family Mickoleitiidae was named in honor of German zoologist Gerhard Mickoleit from the University of Tübingen, who was among the first proponents of Willi Hennig's "Phylogenetic Systematics". The scientific name of the order Coxoplectoptera refers to the prolonged coxal segment of the larval and adult legs, and the old scientific name Plectoptera for mayflies (not to be confused with Plecoptera for stoneflies). The common name "chimera wings" was coined in reference to the strange combination of characters in the morphology of the adult animal, which looks like a kind of chimera built from unrelated insects, with their oblique thorax and broad hind wing shape like a dragonfly, their wing venation like a primitive mayfly ancestor, and their raptorial forelegs like a mantis.

History of discovery

The fossil larvae of the genus Mickoleitia are not especially rare in the limestones of the Crato Formation; the local brick workers even have a common Brazilian name for them ("Abacaxi" = pineapple). These larvae were scientifically discovered and first mentioned by Bechly (2001: fig. 36), who also pointed to their strange morphology. Staniczek (2002, 2003) discussed the larvae as well and claimed that they arguably had been a kind of living fossil in the Lower Cretaceous. The German biologist Rainer Willmann described the larvae in a chapter in Martill, Bechly & Loveridge (2007) and erroneously attributed them to the extinct stem group mayfly family Cretereismatidae that he described based on adult specimens from the same locality. During the work for this monograph on the Crato Formation the German palaeoentomologist Günter Bechly and entomologist Arnold H. Staniczek discovered in the fossil collection of the Stuttgart State Museum of Natural History the very adult specimen that later would become the holotype of Mickoleitia longimanus. They figured this fossil in Martill, Bechly & Loveridge 2007 (Fig. 11.90i,j) as undescribed stem group mayfly and indicated in a brief figure legend the possible relationship to the erratic larvae. The detailed scientific description of Coxoplectoptera and the demonstration of the relationship of fossil adult and larvae was finally published by Staniczek, Bechly & Godunko (2011) in a special issue on Cretaceous insects of the journal "Insect Systematics & Evolution". The authors also determined that two fossil larvae (Mesogenesia petersae = Archaeobehnigia edmundsi) that had been erroneously described by Tshernova (1977) as modern mayfly larvae from the Middle or Upper Jurassic of Transbaikals, can be attributed the order Coxoplectoptera. The discovery of Coxoplectoptera represented one of the more spectacular findings of paleontology in 2011 and was heavily covered by news media around the globe.

Description

Adult

The adult stage of the type species Mickoleitia longimanus had a wing length of 28–29 mm and a probable body length of ca. 35–40 mm (the abdomen is not preserved in the single known fossil holotype specimen). A second unnamed species of the genus Mickoleitia was only of half this size, and is only known by a single adult specimen from a private fossil collection in Japan. The head of Mickoleitia was provided with large compound eyes and functional mouthparts (preserved are 3-segmented labial palps). The thoracic segments are obliquely tilted backwards as in dragonflies, so that the raptorial forelegs are shifted forwards. All legs have a strongly prolonged and free coxal segment. The forelegs are developed as subchelate raptorial devices with a single-segmented tarsus with an unpaired claw. Most likely the abdomen was provided with three caudal filaments (two lateral cerci and the median epiproct) as in modern mayflies and their Permian stem group representatives (Permoplectoptera, e.g. Protereismatidae). Since males of modern mayflies and of Permoplectoptera have gonopods on the 9th abdominal segment that are developed as genital claspers to grip the female for copulation, such a character state and behavior is also likely for Coxoplectoptera, who have an intermediate position as phylogenetic link between these two groups.

Larva

Mickoleitia larva
Mickoleitia spec., larva

The more than 20 described larvae of different stages have a body length of 10 to 32 millimetres (0.39 to 1.26 in). Their laterally compressed body is unique among all known fossil and Recent aquatic insect larvae, and rather resembles the body of gammarid freshwater shrimps. Many of the fossil larvae are preserved in a characteristic posture with arched back, erect antennae and terminal filaments, and forelegs always in catching position similar to a praying mantis. The head was strongly armored and provided with horn- or shovel-like projections. Of the mouthparts only the crossed, sabre-like mandibles and the spoon-shaped labium are known. All legs have a strongly prolonged and free coxal segment as in the adult. Likewise, the forelegs are developed as slender subchelate raptorial legs with nearly identical segment proportions as in the adult stage, but with a shorter tibia that may have been fused with the single-segmented tarsus, which ended in an unpaired claw. Styliform and ventrally directed abdominal gills are developed on abdominal segments 1-7. These gills are composed of a broader, more strongly sclerotized basal part and a slender and rather membranous distal part. The gills articulate dorsally within the abdominal tergites that are distinctly separated from the ventral sternites. The caudal filaments are formed by the two lateral cerci and the slightly longer medial terminal filament. All three appendages are lined with dense rows of long and thin setae.

Ecology and behavior

Adult

Because in the adult holotype specimen well-preserved mouthparts (palps) are visible, the adult animals almost certainly were able to feed. In direct contrast, the adult form of modern mayflies has dramatically reduced, non-functional mouthparts, and lives solely to reproduce. The raptorial forelegs and oblique thorax indicate that Mickoleitia was a predator. The large and broad hinds suggest that they ecologically similar to dragonflies, in that they were swift, flying predators of other flying insects.

Larva

The abundance of fossils, the circumstances of preservation and special anatomical adaptations (7 pairs of abdominal gills, 3 caudal filaments with dense rows of swimming hairs) prove that the larvae have been living in freshwater of streams and rivers, just like those of modern mayflies. They were washed in as allochthonous elements into the brackish Crato lagoon, were the limestones were deposited. The raptorial forelegs, sabre-like mandibles, large eyes and long antennae indicate that the larvae were predators like the adults. On the other hand, the strong, shortened and broadened mid- and hind legs, the strong body armature, and shovel-like projections on the head all suggest that the animals were burrowing. Staniczek, Bechly & Godunko (2011) therefore assumed that the larvae were ambush predators that were hiding, partly burrowed in the river bed, and waiting for small prey passing by.

Evolution and phylogeny

The larvae of Coxoplectoptera provided new clues to the disputed question of the evolutionary origin of insect wings. Before this discovery the paranotal-hypothesis and the leg-exite-hypothesis have been considered as incompatible alternative explanations, which have both been supported by a set of evidences from the fossil record, comparative morphology, developmental biology and genetics. The expression of leg genes in the ontogeny of the insect wing has been universally considered as conclusive evidence in favour of the leg-exite-hypothesis, which proposes that insect wings are derived from mobile leg appendages (exites). However, the larvae of Coxoplectoptera show that the abdominal gills of mayflies and their ancestors, which are generally considered as corresponding structures to insect wings, articulated within the dorsal tergite plates. This cannot be seen in modern mayfly larvae, because their abdominal tergites and sternites are fused, without any traces of separation left even in embryonic development. If larval gills and wings are corresponding ("serial homologous") structures and thus share the same evolutionary origin, the new results from Coxoplectoptera demonstrate that also wings are of tergal origin, as proposed by the classical paranotal-hypothesis. Staniczek, Bechly & Godunko (2011) therefore suggested a new hypothesis that could reconcile the apparently conflicting evidence from paleontology and developmental genetics: wings originated as stiff outgrowths of tergal plates (paranota), and only later in evolution became mobile, articulated appendages through secondary recruiting of leg genes.

Within pterygote insects the Coxoplectoptera represent the sister group of modern mayflies (Ephemeroptera). This relationship is indicated by several synapomorphies, such as: adult wing venation with costal brace (absent in other winged insects), larvae with 7 pairs of abdominal gills (compared to still 9 pairs in Permoplectoptera like Protereisma larvae), and with single-segmented tarsus with unpaired claw (compared to 3-segmented tarsus with paired claw in Permoplectoptera like Protereisma larvae).

Together with mayflies and dragonflies they belong to the clade Palaeoptera, which is characterized by a derived wing articulation with fused sclerites, a vertical resting position of the wings in the groundplan, and a wing venation with intercalary veins between the main longitudinal veins (esp. IR1+ between RP1- and RP2-, and IR2+ between RP2- and RP3/4-).

Because of some very primitive character states, the Coxoplectoptera rather looked like early Paleozoic ancestors of mayflies, e.g. in the wing venation of the adult stage they still had the elongate costal brace that is not fused to the costal margin, and in the larval stage they still had articulated lateral wing pads. The large and broad hind wings are a further plesiomorphy compared to the small hind wing of modern mayflies, and even compared to the slender hind wing of Permian stem group mayflies like Protereisma.

The monophyly of Coxoplectoptera is demonstrated by several autapomorphic characters in the adult stage, such as the raptorial forelegs and single-segmented tarsi with unpaired claw, as well as in the larval stage by the laterally compressed body, the body armature, the raptorial forelegs and burrowing mid- and hind legs, and the styliform shape of the ventrally directed abdominal gills.

Coxoplectoptera are only known from the Jurassic and the Lower Cretaceous. It is not yet known why and when they went extinct.

Systematics

The order Coxoplectoptera only includes a single family Mickoleitiidae with two Mesozoic genera:

Mickoleitia (Early Cretaceous, Crato Formation, Brazil):

  • Mickoleitia longimanus (type species)
  • Mickoleitia spec. (smaller unnamed species, represented by a single adult specimen in a private fossil collection in Japan)

Mesogenesia (Middle or Late Jurassic, Transbaikals):

  • Mesogenesia petersae (= Archaeobehnigia edmundsi)

References

Bibliography

  • Tshernova, O.A. (1977): Distinctive new mayfly nymphs (Ephemeroptera; Palingeniidae, Behningiidae) from the Jurassic of Transbaikal. Paleontologicheskii Zhurnal, 1977(2): 91-96. (in Russian).
  • Bechly, G. et al. (Hrsg.) (2001): Ur-Geziefer - Die faszinierende Evolution der Insekten. Stuttgarter Beiträge zur Naturkunde Serie C, 49: 96 pp., Stuttgart. ISSN 0341-0161 (PDF fulltext).
  • Staniczek, A.H. (2002): Fossile Eintagsfliegen - Einblicke in die Welt urtümlicher Fluginsekten. Fossilien, 19: 297-302.
  • Staniczek, A.H. (2003): Eintagsfliegen - Manna der Flüsse. Stuttgarter Beiträge zur Naturkunde Serie C, 53: 80 pp., Stuttgart. ISSN 0341-0161.
  • Martill, D.M., Bechly, G. & Loveridge, R.F. (Hrsg.) (2007): The Crato Fossil Beds of Brazil - Window into an Ancient World. Cambridge University Press, Cambridge etc. ISBN 978-0-521-85867-0.
  • Staniczek, A.H. & Bechly, G. & Godunko, R.J. (2011): Coxoplectoptera, a new fossil order of Palaeoptera (Arthropoda: Insecta), with comments on the phylogeny of the stem group of mayflies (Ephemeroptera). Insect Systematics & Evolution, 42(2): 101-138, Brill, Leiden. ISSN 1399-560X (author's homepage with link to PDF).

External links

Amphiesmenoptera

Amphiesmenoptera is an insect superorder, established by S. G. Kiriakoff, but often credited to Willi Hennig in his revision of insect taxonomy for two sister orders: Lepidoptera (butterflies and moths) and Trichoptera (caddisflies). In 2017, a third fossil order was added to the group, the Tarachoptera.Trichoptera and Lepidoptera share a number of derived characters (synapomorphies) which demonstrate their common descent:

Females, rather than males, are heterogametic (i.e. their sex chromosomes differ).

Dense setae are present in the wings (modified into scales in Lepidoptera).

There is a particular venation pattern on the forewings (the double-looped anal veins).

Larvae have mouth structures and glands to make and manipulate silk.Thus these two extant orders are sisters, with Tarachoptera basal to both groups. Amphiesmenoptera probably evolved in the Jurassic. Lepidoptera differ from the Trichoptera in several features, including wing venation, form of the scales on the wings, loss of the cerci, loss of an ocellus, and changes to the legs.Amphiesmenoptera are thought to be the sister group of Antliophora, a proposed superorder comprising Diptera (flies), Siphonaptera (fleas) and Mecoptera (scorpionflies). Together, Amphiesmenoptera and Antliophora compose the group Mecopterida.

Archodonata

Archodonata is an extinct order of palaeozoic paleopterous insects, sometimes included in Odonata.

Coniopterygoidea

Coniopterygoidea is a lacewing superfamily in the suborder Hemerobiiformia. In some classifications, Coniopterygoidea is an expansion used to signify that the spongillaflies (Sisyridae) and the dustywings (Coniopterygidae) are each other's closest relatives.

Diaphanopterodea

The Diaphanopterodea or Paramegasecoptera are an extinct order of moderate to large-sized Palaeozoic insects. They are first known from the Middle Carboniferous (late Serpukhovian or early Bashkirian in age), and include some of the earliest known flying insects.

Dicondylia

The Dicondylia are a taxonomic group (taxon) that includes all insects except the jumping bristletails (Archaeognatha). Dicondylia have a mandible attached with two hinges to the head capsule (dicondyl), in contrast to the original mandible with a single ball joint (monocondyl).

Dictyoptera

Dictyoptera (from Greek δίκτυον diktyon "net" and πτερόν pteron "wing") is an insect superorder that includes two extant orders of polyneopterous insects: the order Blattodea (termites and cockroaches together) and the order Mantodea (mantises), along with one extinct order, the Alienoptera. While all modern Dictyoptera have short ovipositors, the oldest fossils of Dictyoptera have long ovipositors, much like members of the Orthoptera.

Endopterygota

Endopterygota (from Ancient Greek endon “inner” + pterón, “wing” + New Latin -ota “having”), also known as Holometabola, is a superorder of insects within the infraclass Neoptera that go through distinctive larval, pupal, and adult stages. They undergo a radical metamorphosis, with the larval and adult stages differing considerably in their structure and behaviour. This is called holometabolism, or complete metamorphism.

The Endopterygota are among the most diverse insect superorders, with over 1 million living species divided between 11 orders, containing insects such as butterflies, flies, fleas, bees, ants, and beetles.They are distinguished from the Exopterygota (or Hemipterodea) by the way in which their wings develop. Endopterygota (meaning literally "internal winged forms") develop wings inside the body and undergo an elaborate metamorphosis involving a pupal stage. Exopterygota ("external winged forms") develop wings on the outside their bodies and do not go through a pupal stage. The latter trait is plesiomorphic, however, and not exclusively found in the exopterygotes, but also in groups such as Odonata (dragonflies and damselflies), which are not Neoptera, but more basal among insects.

The earliest endopterygote fossils date from the Carboniferous.

Eumetabola

Eumetabola is an unranked category of Neoptera. Two large unities known as the Paurometabola and Eumetabola are probably from the adelphotaxa of the Neoptera after exclusion of the Plecoptera. The monophyly of these unities appears to be weakly justified.

Myrmeleontoidea

Myrmeleontoidea is a lacewing superfamily in the suborder Myrmeleontiformia.

Neoptera

Neoptera is a classification group that includes most orders of the winged insects, specifically those that can flex their wings over their abdomens. This is in contrast with the more basal orders of winged insects (the "Palaeoptera" assemblage), which are unable to flex their wings in this way.

Odonatoptera

The Odonatoptera are a superorder (sometimes treated as an order) of ancient winged insects, placed in the Palaeoptera which probably form a paraphyletic group however. The dragonflies and damselflies are the only living members of this group, which was far more diverse in the late Paleozoic and contained gigantic species, including the griffinflies (colloquially called "giant dragonflies", although they were not dragonflies in the strict sense) of the order Protodonata. This lineage dates back at least to the Bashkirian, not quite 320 million years ago.

Palaeoptera

The name Palaeoptera has been traditionally applied to those ancestral groups of winged insects (most of them extinct) that lacked the ability to fold the wings back over the abdomen as characterizes the Neoptera. The Diaphanopterodea, which are palaeopteran insects, had independently and uniquely evolved a different wing-folding mechanism. Both mayflies and dragonflies lack any of the smell centers in their brain found in Neoptera.

Panorpida

Panorpida or Mecopterida is a proposed superorder of Endopterygota. The conjectured monophyly of the Panorpida is historically based on morphological evidence, namely the reduction or loss of the ovipositor and several internal characteristics, including a muscle connecting a pleuron and the first axillary sclerite at the base of the wing, various features of the larval maxilla and labium, and basal fusion of CuP and A1 veins in the hind wings. The monophyly of the Panorpida is also supported by recent molecular data.

Paraneoptera

Paraneoptera is a monophyletic superorder of insects which includes four orders, the bark lice, true lice, thrips, and hemipterans, the true bugs. The mouthparts of the Paraneoptera reflect diverse feeding habits. Basal groups are microbial surface feeders, whereas more advanced groups feed on plant or animal fluids.

Protelytroptera

Protelytroptera is an extinct order of insects thought to be a stem group from which the modern Dermaptera evolved. These insects, which resemble modern Blattodea, or Cockroaches, are known from the Permian of North America, Europe and Australia, from the fossils of their shell-like forewings and the large, unequal, anal fan. None of their fossils are known from the Triassic when the morphological changes from Protelytroptera to Dermaptera presumably took place.

Protodiptera

Protodiptera is an extinct order of insects containing the two genera Permotipula and Permila.

Psocodea

Psocodea is a taxonomic group of insects comprising the bark lice, book lice and true lice. It was formerly considered a superorder, but is now generally considered by entomologists as an order. Despite the greatly differing appearance of lice, they are believed to have evolved from within the former order "Psocoptera", which contained the bark lice and book lice. Psocodea contains around 11,000 species, divided among seven suborders.

Pterygota

The Pterygota are a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless (that is, insect groups whose ancestors once had wings but that have lost them as a result of subsequent evolution).The pterygotan group comprises almost all insects. The insect orders not included are the Archaeognatha (jumping bristletails) and the Zygentoma (silverfishes and firebrats), two primitively wingless insect orders. Also not included are the three orders no longer considered to be insects: Protura, Collembola, and Diplura.

Titanoptera

Titanoptera is an extinct order of neopteran insects from the Triassic period. Titanopterans were very large in comparison with modern insects, some having wingspans of up to 36 centimetres (14 in).They were related to modern grasshoppers, but were much larger, had proportionally weaker hindlegs that could not allow the animals to leap, and grasping forelegs and elongated mandibles. Another distinctive feature was the presence of prominent fluted regions on the forewings, which may have been used in stridulation. The general shape and anatomy of the Titanopterans suggests that they were predators.

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