Fossils explained 51

Abstract

The Earth???s oldest terrestrial ecosystems date from the Late Silurian period, about 414 million years ago. Amongst primitive plants lived the first land-based animals; invertebrate invaders of a new world, some 30 million years before vertebrates made the very same transition. The fossil record suggests many early land animals were arthropods, belonging to subgroups such as Myriapoda (e.g. millipedes and centipedes) and Arachnida (e.g. spiders, scorpions, mites, etc.). Trigonotarbids belong to the latter. They are appar- ently primitive arachnids, superficially similar in ap- pearance to spiders, but lacking the ability to produce silk. Their presence at Ludford Lane in the Welsh Borderlands in the UK (P??\'{\i}dol\'{\i}, Late Silurian) places the group amongst the earliest terrestrial animals, and their anatomy is well known from exception- ally preserved, silicified fossils in the slightly younger Early Devonian Rhynie Chert of Scotland (Fig. 1). By the Late Carboniferous, trigonotarbids seem to have been amongst the most abundant arachnids; at least their fossils are relatively common throughout the Coal Measures deposits of Europe and North America. They have also been recorded in South America. Such success didn???t last???the group became extinct in the Permian.