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Trigonotarbida |
| Trigonotarbida Fossil range: late Silurian–early Permian |
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Anthracomartidae |
The Order Trigonotarbida is an extinct group of arachnids whose fossil record extends from the Silurian to the Lower Permian. These animals are known from several localities in Europe and North America, as well as a single record from Argentina. They superficially resemble spiders, to which they were clearly related as part of the Pantetrapulmonata hypothesis.
Like primitive spiders, trigonotarbids have two pairs of book lungs and chelicerae shaped like a 'pocket knife' in which the fang articulates against the basal segment.
These early arachnids seem to have been adapted to stalking prey on the ground. They have been found within the very structure of ground-dwelling plants, but it is unclear whether this is a chance occurence or whether they actively lived and hunted here.
They are characterized by opisthosomal tergites divided into median and lateral plates 1. a feature which they share with the rare and unusual living order Ricinulei2. Supporting the sister group relationship between these two taxa recently reported by cladistic analysis 3.
There is also a proposal that the Trigonotarbida are members of the Tetrapulmonata 4.
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