Lung-books in the Devonian Palæocharinidae (Arachnida)

A fossil trigonotarbid arachnid with a ricinuleid-like pedipalpal claw

“…Critical to placing Trigonotarbida are some exceptionally-preserved fossils assigned to Palaeocharinus Hirst 1923 from the early Devonian Rhynie cherts of Scotland. These three-dimensional and often largely complete specimens preserve details of the cuticular anatomy with extraordinary Wdelity (Hirst 1923;Hirst and Maulik 1926;Claridge and Lyon 1961;Shear et al 1987;Dunlop 1996;Fayers et al 2005;Kamenz et al 2008) and allow Trigonotarbida to be scored for phylogenetic analyses with some conWdence for many external-and even some internal-morphological characters.…”

The youngest trigonotarbidPermotarbus schubertin. gen., n. sp. from the Permian Petrified Forest of Chemnitz in Germany

“…410 Ma) Rhynie and Windyfield cherts of Scotland (Hirst 1923;Hirst & Maulik 1926;Fayers et al 2005). These silicified fossils are unequivocally of terrestrial animals since they exhibit the oldest evidence for air-breathing book lungs (Claridge & Lyon 1961).…”

Microanatomy of Early Devonian book lungs

“…These Rhynie respiratory organs are still the oldest putative record of a lung in any animal group. However, previous accounts (Claridge & Lyon 1961;Størmer 1976) figured only their gross morphology, with stacks of thin, sheet-like lamellae which give the book lung its name. Having established a suite of phylogenetically informative characters in the lung microanatomy of Recent arachnids (Scholtz & Kamenz 2006;Kamenz & Prendini in press), our principal aim here was to use newly available specimens prepared from slices of Rhynie chert to test whether these apomorphies could be resolved, three-dimensionally, in exceptionally preserved Devonian arachnids too; fossils crucially dating from the early phases of arthropod terrestrialization.…”

“…Terrestrialization is widely seen as one of the key events in Earth history and this fundamental ecological shift from water to air undoubtedly made significant new demands on the physiology of early land animals, particularly their respiration. In respect of this, we reinvestigated one of the most important discoveries at Rhynie, the fossilized lungs (Claridge & Lyon 1961) found in the extinct (Silurian-Permian) arachnid order Trigonotarbida. Closely related to spiders, trigonotarbids resolve at the base of the Pantetrapulmonata (Shultz 2007), which, as its name implies, is a clade of arachnids defined by the presence of two pairs of book lungs; one pair of which was subsequently modified into tracheae in more derived spiders (Levi 1967;Bromhall 1987).…”