A new assemblage of arthropod cuticles from Upper Silurian rocks in Shropshire, England, includes at least two centipedes and a trigonotarbid arachnid. This unequivocal terrestrial fauna from the Silurian constitutes the earliest direct record of land animals. The presence of predatory arthropods suggests that complex terrestrial ecosystems were in place by the late Silurian (414 x 10(6) years before present) and that the animal invasion of the land occurred earlier than was previously thought.

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The wide range of organs of respiration (book-gills, book-lungs, sieve- and tube-tracheae), reproduction, sensory perception, etc., among the chelicerates indicates that the major groups made the transition to land life independently. The fossil record is patchy for most chelicerate groups, certain intervals (e.g. Westphalian) being particularly rich in chelicerate bearing Lagerstatten while in others (e.g. Mesozoic) they are sparse. Due, apparently, to their unusual hyaline exocuticle, scorpions are better preserved than other arthropods, and show a fairly continuous record from fully aquatic forms in the Silurian, to both aquatic and terrestrial faunas in the Carboniferous. In particular, new and well-preserved material of the earliest demonstrably terrestrial scorpions from the Lower Carboniferous of East Kirkton, West Lothian, suggests that book-lungs, at least in the scorpions, developed directly from book-gills by suturing of the covering plate (Blattfuss of the related eurypterids) to leave stigmata for diffusion of air. This evidence supports the ideas of early authors that the scorpion mesosomal ‘sternites’ are fused plates, contra Kjellesvig-Waering (1986) who envisaged the plates being lost to reveal true sternites beneath. The fossil evidence also indicates that by the Triassic at least two scorpion lineages had evolved intra-‘sternite’ stigmata.

Scorpions from East Kirkton Quarry are represented by abundant cuticle fragments and rarer articulated specimens. Cuticles isolated from their matrix are exquisitely preserved, permitting this fauna to be described in more detail than other Carboniferous scorpion faunas. Most of the material is attributed to Pulmonoscorpius kirktonensis n. gen. n. sp. Specimens possibly indicating the presence of two additional Pulmonoscorpius species are referred to under open nomenclature. Rare fragments of an aquatic ‘archaeoctonoid’, and an orthostern scorpion, also occur. Most specimens of Pulmonoscorpius are juveniles. The range of taphonomic effects observed in these and larger individuals suggests that, as a consequence of poor preservation, the morphology of some Upper Palaeozoic scorpions has been misinterpreted by previous workers. Within the infraorder Mesoscorpionina two groups are recognised. These are distinguished by the position of the posterior pair of coxae. Pulmonoscorpius n. gen. belongs to group A, in which the posterior coxae abut the sternum. This group includes the known Lower Carboniferous mesoscorpions and ranges from the Upper Devonian to the Upper Carboniferous. All group-A mesoscorpions are reviewed here. In group-B mesoscorpions the posterior pair of coxae apparently abut the genital opercula, but confirmation of this derived character and formal taxonomic recognition of these groupings must await a restudy of the group-B mesoscorpions, which are known from the Upper Carboniferous and Triassic.

The hibbertopteroid eurypterid genera Hibbertopterus, Dunsopterus, and Cyrtoctenus occur in the East Kirkton Limestone of Bathgate, West Lothian. Most specimens are fragmentary and appear to have been washed into the depositional area with plant debris and tuffaceous sediment. Nearly all of the identifiable material can be attributed to Hibbertopterus scouleri (Hibbert), but two isolated Cyrtoctenus combs, and a femur comparable with Dunsopterus have also been recognised.New material of Hibbertopterus scouleri (Hibbert) reveals that the posterior legs and telson resemble those of the cyrtoctenids more closely than was previously thought. It is possible that Hibbertopterus, Dunsopterus, and Cyrtoctenus are indistinguishable except by relatively minor characteristics, and that all of the material from East Kirkton Quarry might be derived from a single eurypterid species. However, associations of the diagnostic sclerites which would demonstrate that these taxa are either cogeneric or distinct have not yet been found.

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