Trigonotarbida
| Trigonotarbida | ||||||||
|---|---|---|---|---|---|---|---|---|
Anthracomartus hindi Pocock , 1911 |
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| Temporal occurrence | ||||||||
| Pridolium to Sakmarium | ||||||||
| 414 to 290 million years | ||||||||
| Systematics | ||||||||
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| Scientific name | ||||||||
| Trigonotarbida | ||||||||
| Petrunkevitch , 1949 | ||||||||
The Trigonotarbida are an order of arachnids that became extinct in the Paleozoic . On her first fossil occurrence in the Silurian they were among the earliest terrestrial animals at all. They reached the highest density and number of species in the Carboniferous , but with a few species they were still found in the early Permian , for example in Rotliegend in Saxony . Trigonotarbida resembled some spiders in appearance , but in contrast to these, the abdomen was mostly hard-armored (sclerotized) and they had no spinning glands .
At present (as of 2013) 65 species of the Trigonotarbida are recognized, which are distributed over 34 genera . Trigonotarbida are, after the scorpions , the second oldest fossil-proven group of arachnids and the first in which life outside the water could be proven beyond doubt.
anatomy
The body of the trigonotarbida was divided into two sections ( tagmata ), prosoma and opisthosoma .
The prosoma (foreleg) was covered dorsally by an undivided carapace , the shape of which varied greatly between different species; in some species it was drawn out forward into a triangular point. In the middle of the carapace sat an ocular hillock with simple eyes, some morphologically original families also had lateral ocular hillocks. The underside of the prosoma covered an undivided sternum . The mouth opening at the front end was slit-shaped and surrounded by closely spaced filter bristles; this has been demonstrated in unusually well-preserved fossils from the Scottish Rhynie Chert , in which even the smallest details have been preserved. This proves that the Trigonotarbida, like the modern spiders, practiced extraintestinal digestion . The mouth opening was surrounded by hanging, two-part chelicerae , to the side of which sat buttons ( pedipalps ). As with recent spiders, there followed four pairs of legs with small claws at the end, the structure of the legs (in coxa, femur, patella, tibia, metatarsus, tarsus) was also corresponding.
The abdomen (opisthosoma) consisted of twelve segments . Of the narrow first segment, only the tergum was externally visible, which formed a locking mechanism with a fold at the rear edge of the carapace, which stiffened the body. The tergites of the second to eighth (in some species also the ninth) segment were divided lengthways into three or five adjacent plates, some of which were receded or fused together in some families. The tenth to twelfth segments were only visible from the underside. The tenth formed a triangular sternite , to which the last two were attached as a small appendage, collectively called pygidium. The other segments of the opisthosoma also had sclerotized plates (sternites), so that the abdomen was armored; in many Carboniferous forms, like the prosoma, it also wore strong thorns or spines, which probably served as a defense against vertebrate animals as predators. Movable (and also somewhat stretchable) joint membranes sat between the sclerites. The first two plates (according to the findings from Rhynie) were not real sternites, but actually lids (opercula), under which two pairs of book lungs sat as respiratory organs.
Way of life
The book lungs as respiratory organs and the liquefaction of the food in front of the mouth opening (extraintestinal) are reliable indications that the animals lived on land. Similar to the recent arachnids, a predatory diet, presumably from other arthropods, is also considered safe. Since the complex mating apparatus of the spider apparently was missing, external fertilization, through the deposition of a spermatophore , is assumed. The small, dorsally seated eyes certainly made optical hunting impossible. It is assumed that the sense of touch and vibration played a major role in catching prey due to the numerous hairs sitting on the legs. At the latest when the vertebrates went ashore, trigonotarbids themselves became prey for larger predators. The armor and thorns of many carbonic species are interpreted as a protective mechanism against predators.
die out
Although the Trigonotarbida were still among the most common arachnids that have survived in fossil form in the Carboniferous, they soon became extinct. The most recent finds come from Germany and South America (Argentina). The climate change at the beginning of the Permian, when the increasingly arid climate led to the end of the coal forests, was possibly responsible for the extinction, at least in part. However, it is repeatedly assumed that ultimately the competition from the weaving spiders could have been the reason for the extinction.
X-ray examination
Fossil trigonotarbides from English coal deposits are enclosed in tubers of the iron mineral siderite and are spatially preserved in them (not just as an impression). A non-destructive examination of the fossils was hardly possible because of the dense, opaque material. This was achieved for the first time in 2009 using X-ray tomography . In the case of the species Anthracomartus hindi (sub Cryptomartus hindi , for synonymy cf.) the probable leg position in life could be reconstructed. Accordingly, the animals carried the first pair of legs turned up and stretched out. This makes an attitude and hunting technique as an ambulance hunter, just like with the recent crab spiders , likely.
Phylogeny and Systematics
The existence of book lungs, which in their anatomical fine structure matched those of the recent weaving spiders, flagellum spiders (Amblypygi) and flagellated scorpions (Uropygi), makes a common descent of these groups, with this characteristic as autapomorphy , very likely. These groups were therefore combined with the also extinct Haptopoda in a taxon Pantetrapulmonata. According to this hypothesis, the Trigonotarbida within this group would be basal, with all others together as a sister group . Another hypothesis suspects, with otherwise comparable phylogenetic classification, the hooded spiders (order Ricinulei) as a sister group , with which they have numerous physical features in common. However, these are viewed by many systematics as a sister group of the mites .
Research history
The first fossil trigonotarbide was discovered in England in 1837 by one of the pioneers of modern geology, the naturalist and priest William Buckland and described as Curculioides prestvicii (today Eophrynus prestvicii ). However, he completely misunderstood the find and mistook it for a weevil . In 1871 Henry Woodward recognized the fossil as an arachnid and assigned it to the pseudoscorpions . Ferdinand Karsch discovered another species, Anthracomartus voelkelianus, in 1892 and established a new order Anthracomarti for it. Later editors changed the status several times, introduced new names and described other species. On the basis of this now more extensive material, Alexander Iwanowitsch Petrunkewitsch reworked the material and divided the present finds in 1949 into two orders of Anthracomartida, and the Trigonotarbi newly described by him, whose name he changed to Trigonotarbida in 1955. William A. Shear and colleagues suggested in 1987 that anthracomartida and trigonotarbida be reunited, since the characteristics cited by Petrunkewitsch turned out to be misinterpretations due to poor preservation. Jason Dunlop took over the younger name Trigonotarbida for this united group in 1996, which has established itself in research.
The name Trigonotarbida is actually a younger synonym of Anthracomartida Karsch, 1892. Because the nomenclature rules of the ICZN , including the priority rule, are only used in zoology up to the family (group) level, it is still possible, as in research now common to get the younger name.
Individual evidence
- ↑ Jason A. Dunlop & Ronny Rößler (2013): The youngest trigonotarbide Permotarbus schuberti n. Gen., N. Sp. from the Permian Petrified Forest of Chemnitz in Germany. Fossil Record 16 (2): 229-243. doi : 10.1002 / mmng.201300012
- Jump up ↑ JA Dunlop, D. Penney, D. Jekel (2013): A summary list of fossil spiders and their relatives. In NI Platnick (editor): The world spider catalog, version 13.5. American Museum of Natural History ( PDF ) doi : 10.5531 / db.iz.0001
- ^ A b Russell J. Garwood & Jason A. Dunlop (2010): Trigonotarbids. Fossils Explained 58. Geology Today, Vol. 26, No. 1: 34-37.
- ↑ Russell Garwood, Jason A. Dunlop, Mark D. Sutton (2009): High-fidelity X-ray microtomography reconstruction of siderite-hosted Carboniferous arachnids. Biology Letters 5: 841-844 doi : 10.1098 / rsbl.2009.0464
- ↑ Russell Garwood & Jason A. Dunlop (2011): Morphology and systematics of Anthracomartidae (Arachnida: Trigonotarbida). Palaeontology 54: 145-161. doi : 10.1111 / j.1475-4983.2010.01000.x
- ↑ Jeffrey W. Shultz (2007): A phylogenetic analysis of the arachnid orders based on morphological characters. Zoological Journal of the Linnean Society 150: 221-265.
- ^ Jason A. Dunlop (1996): Systematics of the fossil arachnids. Revue Suisse de Zoologie volume hors série 1: 173-184. therein further references on the history of research.