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In Scotland, the base of the Ballagan Formation has traditionally been placed at the first grey mudstone within a contiguous Late Devonian to Carboniferous succession. This convention places the Devonian–Carboniferous boundary within the Old Red Sandstone (ORS) Kinnesswood Formation. The consequences of this placement are that tetrapods from the Ballagan Formation were dated as late Tournaisian in age and that the ranges of typically Devonian fish found in the Kinnesswood Formation continued into the Carboniferous. The Pease Bay specimen of the fish Remigolepis is from the Kinnesswood Formation. Comparisons with its range in Greenland, calibrated against spores, show it was Famennian in age. Detailed palynological sampling at Burnmouth from the base of the Ballagan Formation proves that the early Tournaisian spore zones (VI and HD plus Cl 1) are present. The Schopfites species that occurs through most of the succession is Schopfites delicatus rather than Schopfites claviger. The latter species defines the late Tournaisian CM spore zone. The first spore assemblage that has been found in Upper ‘ORS' strata underlying the Ballagan Formation (Preston, Whiteadder Water), contains Retispora lepidophyta and is from the early latest Famennian LL spore zone. The spore samples are interbedded with volcaniclastic debris, which shows that the Kelso Volcanic Formation is, in part, early latest Famennian in age. These findings demonstrate that the Ballagan Formation includes most of the Tournaisian with the Devonian–Carboniferous boundary positioned close to the top of the Kinnesswood Formation. The Stage 6 calcrete at Pease Bay can be correlated to the equivalent section at Carham, showing that it represents a time gap equivalent to the latest Famennian glaciation(s). Importantly, some of the recently described Ballagan Formation tetrapods are older than previously dated and now fill the key early part of Romer's Gap.
The lower Mississippian Ballagan Formation of northern Britain is one of only two successions worldwide to yield the earliest known tetrapods with terrestrial capability following the end-Devonian mass extinction event. Studies of the sedimentary environments and habitats in which these beasts lived have been an integral part of a major research project into how, why and under what circumstances this profound step in the evolution of life on Earth occurred. Here, a new palaeogeographic map is constructed from outcrop data integrated with new and archived borehole material. The map shows the extent of a very low-relief coastal wetland developed along the tropical southern continental margin of Laurussia. Coastal floodplains in the Midland Valley and Tweed basins were separated from the marginal marine seaway of the Northumberland–Solway Basin to the south by an archipelago of more elevated areas. A complex mosaic of sedimentary environments was juxtaposed, and included fresh and brackish to saline and hypersaline lakes, a diverse suite of floodplain palaeosols and a persistent fluvial system in the east of the region. The strongly seasonal climate led to the formation of evaporite deposits alternating with flooding events, both meteoric and marine. Storm surges drove marine floods from the SW into both the western Midland Valley and Northumberland–Solway Basin; marine water also flooded into the Tweed Basin and Tayside in the east. The Ballagan Formation is a rare example in the geological record of a tropical, seasonal coastal wetland that contains abundant, small-scale evaporite deposits. The diverse sedimentary environments and palaeosol types indicate a network of different terrestrial and aquatic habitats in which the tetrapods lived.
A diverse millipede (diplopod) fauna has been recovered from the earliest Carboniferous (Tournaisian) Ballagan Formation of the Scottish Borders, discovered by the late Stan Wood. The material is generally fragmentary; however, six different taxa are present based on seven specimens. Only one displays enough characters for formal description and is named Woodesmus sheari Ross, Edgecombe & Clark gen. & sp. nov. The absence of paranota justifies the erection of Woodesmidae fam. nov. within the Archipolypoda. The diverse fauna supports the theory that an apparent lack of terrestrial animal fossils from ‘Romer's Gap' was due to a lack of collecting and suitable deposits, rather than to low oxygen levels as previously suggested.
The early tetrapod Crassigyrinus scoticus was a large aquatic predator from the mid Carboniferous (late Viséan or early Serpukovian) of Scotland, around 330 My in age. There are five main specimens with cranial remains: an articulated skeleton; two incomplete skulls; and two lower jaws. Crassigyrinus retains several apparently primitive features of the palatal dentition and lower jaw, and its phylogenetic position is disputed. A partial lower jaw resembling that of Crassigyrinus was discovered at Burnmouth in the Borders region of Scotland. The horizon in which it was found is dated as late Tournaisian, CM palynozone, around 350 My in age. Though it lacks dentition, the jaw preserves much of the postsplenial, angular and surangular, whose appearance externally and internally is almost identical to that of C. scoticus. Internally, the jaw shows a similarly limited extent of the suturing between the splenial series and the prearticular, a primitive condition. Externally, the type and distribution of dermal ornamentation closely matches that of C. scoticus, as does the deeply excavated and marginally positioned lateral line groove. As well as external and internal features, all specimens of C. scoticus are of similar skull size, though the Burnmouth jaw is somewhat smaller. If correctly attributable to Crassigyrinus, this specimen extends the existence of the genus by approximately 20 million years towards the base of the Carboniferous.
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