The Kilmaluag Formation is a Middle Jurassic geological formation in Scotland. It was formerly known as the Ostracod Limestone for preserving an abundance of fossil freshwater/low salinity ostracods. Gastropods, bivalves, trace fossil burrows, and vertebrate fossil remains have also been recorded from the formation. Vertebrate fossils include fish, crocodylomorphs, mammals, small reptiles, amphibians, theropod and sauropod dinosaurs and pterosaurs.
Geology The Kilmaluag Formation was deposited during the Bathonian stage ~167 million years ago and is part of the Great Estuarine Group. Like other rock formations within the Great Estuarine Group, the Kilmaluag Formation is composed of a series of fine grained sandstones, silts, mudstones, and dolomitised limestones. The sediments were deposited in a freshwater influenced low salinity closed lagoonal palaeoenvironment subject to lagoon margin transgressions and regressions. During regressions, sediment abandonment ensued and is indicated by the deposition of dolomitised limestones, in which large desiccation cracks can be observed. In contrast, during transgressions, sediment influxes and increases in water depth led to the deposition of finer grained silts and muds. Occasional shoreline conditions are indicated by rippled sandstones.
The Kilmaluag Formation is divided into two facies: the clastic facies deposited in the Sea of the Hebrides basin of northern Skye, and argillaceous limestone facies present in the Inner Hebrides basin, present on the Straithaird peninsula, Isles of Eigg and Muck.Andrews, J. E. 1985 The sedimentary facies of a late Bathonian regressive episode: the Kilmaluag and Skudiburgh Formations of the Great Estuarine Group, Inner Hebrides, Scotland. Journal of the Geological Society of London, 142, 1119-37.
Fossils In many beds, freshwater gastropods and bivalves can be found, including Viviparus and Unio, and freshwater ostracods such as Darwinula and Theriosynoecum.Barron, A. J. M., Lott, G. K. and Riding, J. B. 2012 Stratigraphical framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf. British Geological Survey Research Report, RR/11/06. British Geological Survey, Keyworth
Many vertebrate fossils have been recorded from the argillaceous facies of Straithaird since the 1970s, when the first mammal fossil were found by Michael Waldman. He returned with fellow palaeontologist Robert Savage and named two new species from the area: the Docodont Borealestes serendipitus, and the tritylodontid, Stereognathus hebridicusWaldman, M and Savage, R.J.G 1972 The first Jurassic mammal from Scotland. Journal of the Geological Society of London 128:119-125 (although S. hebridicus is now thought to be a junior synonym to S. ooliticus). Many other fossils are found in the Kilmaluag, including members of other Mesozoic mammal groups, turtles, reptiles, and amphibians.Evans, S., Barrett, P., Hilton, J., Butler R.J., Jones, M.E.H., Liang, M-.M., Parrish, J.C., Rayfield, E.J., Sigogneau-Russell, D., and Underwood, C.J. 2005. The Middle Jurassic vertebrate assemblage of Skye, Scotland. 36-39. In P. Barrett and S. Evans (eds). Proceedings of the Ninth Symposium on Mesozoic Terrestrial Ecosystems and Biota. Natural History Museum, London. Notable vertebrate fossil recent discoveries in the Kilmaluag Formation include Palaeoxonodon ooliticus and Wareolestes rex. A notable dinosaur find includes the tooth of a sauropod dinosaur. The most recent scientifically pre-published find includes a pterosaur found in 2006.
Comparisons between the Kilmaluag Formation and other British and global Middle Jurassic localities suggest that the fauna represented is globally significant, due to the scarcity of similarly aged sediments. The fauna is a subset of the animals represented in the Forest Marble Formation in England, but fossils in the Kilmaliag Formation are substantially more complete.
Exposures of the Kilmaluag Formation are protected by law as SSSIs (Site of Special Scientific Interest) and under the new Scottish NCO (Nature Conservation Order), thus no public collection is permitted. Most fossils found to date are held in the collections of the National Museum of Scotland.
Vertebrate paleobiota
Amphibians Amphibians Genus Species Location Stratigraphic position Material Notes Imagescf. Anoualerpetoncf A. priscumPair of articulated premaxillaAlbanerpetontid Marmorerpeton M. wakei Cladach a'GhlinneSeveral partial skeletons Salamander Caudata Indeterminate Cladach a'Ghlinne Referred to as "Kirtlington 'Salamander A'"
Turtles Turtles Genus Species Location Stratigraphic position Material Notes Images Eileanchelys E. waldmani Cladach a'Ghlinne Partial skull and association of 5-6 individuals with skull and shell material.A mesochelyidian Testudines Indeterminate Cladach a'Ghlinne
Lepidosauromorphs Lepidosauromorphs Genus Species Location Stratigraphic position Material Notes ImagesBalnealacerta B. silvestris"right dentary, partial right maxilla and a partial right prefrontal"SquamateBellairsia B. gracilis "dentary and parts of other bones scattered on a slab"Stem-squamateBreugnathairB. elgolensisElgol Partial skull and skeletonA parviraptorid pan-squamate of uncertain affinities Marmoretta M. oxoniensis Cladach a'Ghlinne Partial associated skeleton Stem-lepidosauromorph cf. Paramacellodus Indeterminate Cladach a'Ghlinne Squamate Parviraptor Indeterminate Cladach a'Ghlinne Squamate Indeterminate Cladach a'Ghlinne Distinct from other taxa known from the British Bathonian, new gen et sp indet.
Choristoderes Choristoderes Genus Species Location Stratigraphic position Material Notes Images Cteniogenys Indeterminate Cladach a'Ghlinne Partial skull
Dinosaurs
Dinosaurs Genus Species Location Stratigraphic position Material Notes Images Cerapoda? Indeterminate S. Carn Mor Fragments including a possible dorsal vertebral neural arch, a dorsal rib, a partial right ilium, and a possible limb bone The first and most complete dinosaur skeleton found in Scotland, potentially the oldest known ornithopod body fossil Eusauropoda Indeterminate Cladach a'Ghlinne Tooth
Pterosaurs Pterosaurs Genus Species Location Stratigraphic position Material Notes Images Ceoptera C. evansae Cladach a'Ghlinne A partial skeleton
Mammaliamorphs Mammaliamorphs Genus Species Location Stratigraphic position Material Notes Images Borealestes B. serendipitus Cladach a'Ghlinne Toothed jaw fragments, referred partial skeleton DocodontB. cuillinensisCladach a'GhlinnePartial skeleton Krusatodon Indeterminate Cladach a'Ghlinne Molar Palaeoxonodon P. ooliticus Cladach a'Ghlinne Three partial left dentaries Amphitheriid Stereognathus S. ooliticus Cladach a'Ghlinne Partial toothed jaw, isolated teeth Tritylodont Wareolestes W. rex Partial left dentary Morganucodont
See also List of fossiliferous stratigraphic units in Scotland
References