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The Tillywhandland fish bed of the Lower Old Red Sandstone in the Strathmore area of the Scottish Midland Valley accumulated in a lake, here called Lake Forfar, which was created suddenly following a period of fluvial deposition. Lake creation may have been due to basin faulting or the disruption of drainage patterns by contemporaneous volcanic activity. The fish bed laminites accumulated in a hydrologically open lake under a seasonal climatic regime. When fully developed, laminites comprise repeated quadruplets of clastic silt/carbonate/organic/green clay–shale laminae averaging 0·5 mm in thickness. Following 2000 years of laminite deposition an increasingly silty succession with thin current-rippled sandstones provided the lake-fill.
The fish fauna is dominated by Mesacanthus and Ischnacanthus with rare Euthacanthus, Parexus, Climatius, Vernicomacanthus and Cephalaspis. Most fish carcasses were partially decayed before deposition in the laminites on the poorly oxygenated lake floor. Abundant coprolites are the result of predation on Mesacanthus and small Ischnacanthus, probably by larger Ischnacanthus. Arthropods present include eurypterids (Pterygotus), washed in as near complete exuviae and fragments, and millipeds which were washed in from surrounding terrestrial environments along with plants, of which Parka and Zosterophyllum are common. Bioturbation indicates that conditions were not permanently anoxic during deposition of the laminites.
Comparison of our collections with the Mitchell Collection accumulated in the 19th century indicates that Tillywhandland Quarry was the main source of specimens in laminite lithologies labelled ‘Turin Hill’.
The restoration of deformed specimens of the trilobite Conocoryphe abdita Salter from the late Cambrian of Wales allows a re-evaluation of their systematics, synonymy with other species described from Siberia and Iran, and assignment to the idahoiid genus Maladioidella. Maladioidella abdita is from the Parabolina spinulosa Biozone, and most species similar to it occur in equivalent strata near the lower part of the Iverian Stage. Widespread homeomorphy in primitive libristomates is documented and presents difficulties for assessing relationships within Maladioidella and among related taxa. Both the genus as a whole and the species M. abdita show a widespread peri-Gondwanan distribution that crosses a range of latitudes and lithofacies and, to a limited extent, oceanic basins. No morphological features were discerned that might account for its unusual dispersal ability.
Most species of calymenid trilobite from the Wenlock Series of Britain are revised. In total, British trilobites of this family and epoch comprise nine species and three genera, with a further six species being referred to under open nomenclature: Calymene is represented by five species, Tapinocalymene by three and Diacalymene by one. One new subspecies, C. neotuberculata ludicra, and one new species, C. fuliginata, from the lower and upper Wenlock, respectively, are established. The previously monotypic D. allportiana (Salter, 1865) is now known from about 50 specimens. The upper Wenlock Much Wenlock Limestone Formation yields five species, the most for any formation. Calymene occurs mostly in the shallower water facies on the western edge of the Midland Platform and eastern and southern margins of the Welsh Basin, Tapinocalymene essentially in the more offshore carbonate muds of this basin and D. allportiana on the fringe of the Midland Platform and more offshore carbonate muds. British Wenlock calymenids show some affinity with those of the Scandinavia-Baltic area. C. tuberculosa Dalman, 1827 is recorded with certainty in situ outside Gotland for the first time.