Titanomyrma gigantea
| Titanomyrma gigantea | ||||||||||
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Titanomyrma gigantea |
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| Temporal occurrence | ||||||||||
| Middle Eocene | ||||||||||
| 47.4 to 46.3 million years | ||||||||||
| Locations | ||||||||||
| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Titanomyrma gigantea | ||||||||||
| ( Lutz , 1986) | ||||||||||
Titanomyrma gigantea is an extinct species of ants, the fossils of which were found in the Messel pit deposit. It is the largest known species of ants and one of the largest hymenoptera. The queens of this species were larger than some species of hummingbird . Since the discovery of the fossil wood wasp Hoplitolyda duolunica in China, however, the species is no longer the largest known hymenoptera. The species is only known from its type locality , but is quite common here.
description
These were animals with the approximate habitus of the recent Formicinae (note that the species belongs to the extinct subfamily Formiciinae, written with two i's!), Whose free abdomen was connected to the trunk section with a transversely oval, scale-shaped stalk ( petiolus ). Only winged sex animals are known, the workers have never been found. Females reached a body length of 4 centimeters (when fossilized in a somewhat swollen state up to 7 centimeters), the forewings were 5.5 to 6.5 centimeters long. Males only reached 2 to 2.5 centimeters in length. The queens' heads were rounded, triangular with large, triangular mandibles , the antennae were unusually short with eleven limbs, and the forehead strips were short and indistinct. The eyes were also quite small with kidney-shaped outlines. The head carried three ocelles , which were noticeably close together. The trunk section (Alitrunk) was short, only a little longer than wide, and arched high. The legs were relatively short but strong. The front legs had unusually small cleaning spurs. The front four phalanxes were flattened, the claws large with a median tooth. The genus is characterized by an unusual wing veins, in which the wing mark (pterostigma) and two small cubital cells sat conspicuously crowded in the middle of the wing. In the species, the wing membrane in the area of the cells was thickened and more sclerotized, so that the cells are difficult to see. The free abdomen showed five free tergites . The spiracles were unusually elongated and slit-shaped. The spine apparatus (ovipositor) is fully developed, but small and weak.
The males were quite similar to females in general shape, but with pronounced sexual dimorphism in the head area. The head was in proportion significantly smaller with very large eyes and ocelles, with long and narrow, only slightly sclerotized mandibles. The antennae were straight (not kneeling) with a very short base member (scapus). The free abdomen was remarkably short and arched, clumsy egg-shaped, with six free tergites.
From other species of the genus and subfamily, the species can be distinguished by its body size and some details of the wing veins.
Taphonomy
As is typical of the fossils from the Messel Pit, the ants are preserved as compression fossils on the layers of the oil slate. Most are preserved in a dorsal view, a few also from the side (lateral) or from the ventral side (ventral). Due to their unusual size, fully preserved specimens are very rare. Since the Messeler oil shale disintegrates into fine scales when it dries out, fossils are prepared under water and stored in glycerine . As is customary with the vertebrate fossils from Messel, some fossils were transferred to epoxy resin and then exposed from the ventral side. Preparations can be obtained that can be examined in transmitted light. The Messel fossils are body fossils, i. H. it is the partially preserved integument, not just impressions on the layer joints.
life situation
The sediments of the Messel Pit are deposits of an isolated freshwater lake about 1.5 kilometers in diameter and 300 to 400 meters deep, possibly a maar , with only the upper 150 meters containing fossils. The current determination of the age of the fossil-bearing strata showed an age of around 47 million years, which means they belong to the Middle Eocene period . Since ants live on land (terrestrial), it can be assumed that the winged sex animals came from the nests of ants that lived somewhere in the vicinity of the lake, possibly at some distance from where they were flown or blown into the lake.
Together with a second Titanomyrma species, Titanomyrma simillimum , the fossils of this species are the most common Messel ant fossils, together they make up more than half of the finds. They were found so often that only particularly well-preserved specimens have been recovered and prepared. After the beetles, ants are the second most common group of Messel insect fossils.
Systematics and ecology
The genus Titanomyrma , like the entire subfamily Formiciinae, is now extinct. It belonged to the "formicoid" ants that u. a. the recent (living) sub-families Formicinae and Dolichoderinae include. Accordingly, conclusions can only be drawn about their way of life on the basis of circumstantial evidence. Due to the largely reduced sting apparatus, it is assumed that they, like the Formicinae, defended themselves against enemies mainly by chemical means (possibly also with formic acid). Compared to the Formicinae, they are characterized by numerous original (plesiomorphic) features, including the quite original wing veins. Is derived u. a. the antennae of the males. Their systematic position is likely that of a sister group to the Formicinae. Grimaldi et al. however, assume a much more basal position of the subfamily, which would therefore possibly be a sister group of the "higher" Formicidae. However, this position is difficult to reconcile with many of the family trees that have been established since then, especially on a molecular basis.
Fossils of the genus Titanomyrma and other Formiciinae are found next to the Messel Pit and the Eckfelder Maar in the Eifel from about the same age in North American fossil deposits (an isolated wing also from England). Due to the circumstances of the find, the overall distribution and the unusual body size, it is concluded that it was a very warmth-loving, probably tropical, group. This raises the question of how the distribution areas of the genus in Europe and North America were related. At the time of the Eocene, the two continents were only connected by an arctic land bridge (over Greenland). It is believed that the spread in this way was possible during an unusually hot period of the earth's climate, when tropical climates prevailed into arctic latitudes.
swell
- Herbert Lutz (1986): A new subfamily of the Formicidae (Insecta: Hymenoptera) from the medium-eozoic oil shale of the "Messel Pit" near Darmstadt (Germany, S-Hessen) . Senckenbergiana lethea 67 (1/4): 177-218.
- GM Dlussky & S. Wedmann (2012): The poneromorph ants (Hymenoptera, Formicidae: Amblyoponinae, Ectatomminae, Ponerinae) of Grube Messel, Germany: high biodiversity in the Eocene . Journal of Systematic Palaeontology, Vol. 10, Issue 4: 725-753.
- S. Bruce Archibald, Kirk R. Johnson, Rolf W. Mathewes, David R. Greenwood (2011): Intercontinental dispersal of giant thermophilic ants across the Arctic during early Eocene hyperthermals . Proceedings of the Royal Society Series B 278, 3679-3686. doi : 10.1098 / rspb.2011.0729
- David Grimaldi, Donat Agosti, James M. Carpenter (1997): New and rediscovered primitive ants (Hymenoptera, Formicidae) in cretaceous amber from New Jersey, and their phylogenetic relationships . American Museum Novitates No. 3208, 43 pp.
- Taiping Gao, Chungkun Shih, Alexandr P. Rasnitsyn, Dong Ren: Hoplitolyda duolunica gen. Et sp. nov. (Insecta, Hymenoptera, Praesiricidae), the Hitherto Largest Sawfly from the Mesozoic of China . PLoS ONE 8 (5), 2013: e62420. doi : 10.1371 / journal.pone.0062420
