Kilmaluag Formation

Kilmaluag Formation
Kilmaluag Formation
Stratigraphic range: Bathonian; ~167.4–166.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Sediments of the Kilmaluag Formation overlain by Paleogene lava on the Isle of Skye
Type	Formation
Unit of	Great Estuarine Group
Underlies	Skudiburgh Formation
Overlies	Duntulm Formation
Thickness	Up to 25 m (82 ft)
Lithology
Primary	Calcareous mudstone, limestone
Location
Coordinates	57°12′N 6°06′W / 57.2°N 6.1°W
Approximate paleocoordinates	46°24′N 4°12′E / 46.4°N 4.2°E
Country	UK
Extent	Throughout Inner Hebrides, including Isle of Skye, Isle of Muck, and Isle of Eigg
Type section
Named for	Kilmaluag Bay in the North of Skye
	Kilmaluag Formation (the United Kingdom) Kilmaluag Formation (Scotland)

The Kilmaluag Formation is a Middle Jurassic geologic 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.^[1]

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. ^[2]

Fossils

In many beds, freshwater gastropods and bivalves can be found, including Viviparus and Unio, and freshwater ostracods such as Darwinula and Theriosynoecum.^[3]^[2]

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 hebridicus^[4] (although S. hebridicus is now thought to be a junior synonym to S. ooliticus^[5]). Many other fossils are found in the Kilmaluag, including members of other Mesozoic mammal groups, turtles, reptiles, and amphibians.^[1]^[6] Notable vertebrate fossil recent discoveries in the Kilmaluag Formation include Palaeoxonodon ooliticus^[7] and Wareolestes rex.^[8] A notable dinosaur find includes the tooth of a sauropod dinosaur.^[9] The most recent scientifically pre-published find includes a pterosaur found in 2006. ^[10]

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.^[1] 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	Images
cf. Anoualerpeton	cf A. priscum			Pair of articulated premaxilla^[11]	Albanerpetontid
Marmorerpeton	M. wakei	Cladach a'Ghlinne		Several partial skeletons^[12]	Salamander
Caudata^[6]	Indeterminate	Cladach a'Ghlinne			Referred to as "Kirtlington 'Salamander A'"

Turtles

Turtles
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Eileanchelys^[13]	E. waldmani	Cladach a'Ghlinne		Partial skull and association of 5-6 individuals with skull and shell material.	A mesochelyidian
Testudines^[6]	Indeterminate	Cladach a'Ghlinne

Lepidosauromorphs

Lepidosauromorphs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Balnealacerta	B. silvestris			"right dentary, partial right maxilla and a partial right prefrontal"	Squamate
Bellairsia	B. gracilis			"dentary and parts of other bones scattered on a slab"	Stem-squamate
Marmoretta^[14]	M. oxoniensis	Cladach a'Ghlinne		Partial associated skeleton	Stem-lepidosauromorph
cf. Paramacellodus^[6]	Indeterminate	Cladach a'Ghlinne			Squamate
Parviraptor ^[6]	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^[6]	Indeterminate	Cladach a'Ghlinne		Partial skull

Dinosaurs

Dinosaurs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Eusauropoda^[9]	Indeterminate	Cladach a'Ghlinne		Tooth

Pterosaurs

Pterosaurs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ceoptera^[15]	C. evansae	Cladach a'Ghlinne		A partial skeleton

Mammaliamorphs

Mammaliamorphs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Borealestes^[16]	B. serendipitus	Cladach a'Ghlinne		Toothed jaw fragments, referred partial skeleton^[17]	Docodont
Borealestes^[16]	B. cuillinensis	Cladach a'Ghlinne		Partial skeleton
Krusatodon^[6]	Indeterminate	Cladach a'Ghlinne		Molar
Palaeoxonodon^[7]	P. ooliticus	Cladach a'Ghlinne		Three partial left dentaries^[18]	Amphitheriid
Stereognathus	S. ooliticus^[5]	Cladach a'Ghlinne		Partial toothed jaw, isolated teeth	Tritylodont
Wareolestes^[8]	W. rex			Partial left dentary	Morganucodont

References

^ ^a ^b ^c Panciroli E, RBJ Benson, S Walsh, RJ Butler, TA Castro, MEH Jones, SE. Evans. 2020. Diverse vertebrate assemblage of the Kilmaluag Formation (Bathonian, Middle Jurassic) of Skye, Scotland. Earth and Environmental Transactions of the Royal Society of Edinburgh [online] 1-22
^ ^a ^b 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.
^ 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
^ Waldman, M and Savage, R.J.G 1972 The first Jurassic mammal from Scotland. Journal of the Geological Society of London 128:119-125
^ ^a ^b Panciroli, Elsa; Walsh, Stig; Fraser, Nicholas C.; Brusatte, Stephen L.; Corfe, Ian (2017-09-03). "A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the United Kingdom". Journal of Vertebrate Paleontology. 37 (5): e1351448. Bibcode:2017JVPal..37E1448P. doi:10.1080/02724634.2017.1351448. hdl:10138/230155. ISSN 0272-4634.
^ ^a ^b ^c ^d ^e ^f ^g 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.
^ ^a ^b Close, Roger A.; Davis, Brian M.; Walsh, Stig; Wolniewicz, Andrzej S.; Friedman, Matt; Benson, Roger B. J. (2015-11-13). "A lower jaw of Palaeoxonodon from the Middle Jurassic of the Isle of Skye, Scotland, sheds new light on the diversity of British stem therians". Palaeontology. 59 (1): 155–169. doi:10.1111/pala.12218. ISSN 0031-0239. S2CID 85925908.
^ ^a ^b Panciroli, Elsa; Benson, Roger B. J.; Walsh, Stig (2017-05-04). "The dentary of Wareolestes rex (Megazostrodontidae): a new specimen from Scotland and implications for morganucodontan tooth replacement". Papers in Palaeontology. 3 (3): 373–386. Bibcode:2017PPal....3..373P. doi:10.1002/spp2.1079. ISSN 2056-2802. S2CID 90894840.
^ ^a ^b Barrett, Paul M. (March 2006). "A sauropod dinosaur tooth from the Middle Jurassic of Skye, Scotland". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 97 (1): 25–29. doi:10.1017/S0263593300001383. ISSN 1473-7116. S2CID 129163193.
^ Martin-Silverstone, Elizabeth; Unwin, David M.; Cuff, Andrew R.; Brown, Emily E.; Allington-Jones, Lu; Barrett, Paul M. (2022-02-16). "A new pterosaur from Skye, Scotland and the early diversification of flying reptiles". doi:10.1101/2022.02.14.480264. S2CID 246945717. Retrieved 2023-07-01.
^ Panciroli, Elsa; Benson, Roger B. J.; Walsh, Stig; Butler, Richard J.; Castro, Tiago Andrade; Jones, Marc E. H.; Evans, Susan E. (2020). "Diverse vertebrate assemblage of the Kilmaluag Formation (Bathonian, Middle Jurassic) of Skye, Scotland". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 111 (3): 135–156. Bibcode:2020EESTR.111..135P. doi:10.1017/S1755691020000055. ISSN 1755-6910.
^ Jones, M. E. H.; Benson, R. B. J.; Skutschas, P.; Hill, L.; Panciroli, E.; Schmitt, A. D.; Walsh, S. A.; Evans, S. E. (2022). "Middle Jurassic fossils document an early stage in salamander evolution". Proceedings of the National Academy of Sciences of the United States of America. 119 (30): e2114100119. Bibcode:2022PNAS..11914100J. doi:10.1073/pnas.2114100119. PMC 9335269. PMID 35858401.
^ Anquetin, J.; Barrett, P.M.; Jones, M.E.H.; Moore-Fay, S.; Evans, S.E. (2009). "A new stem turtle from the Middle Jurassic of Scotland: new insights into the evolution and palaeoecology of basal turtles". Proceedings of the Royal Society B: Biological Sciences. 276 (1658): 879–886. doi:10.1098/rspb.2008.1429. ISSN 0962-8452. PMC 2664364. PMID 19019789.
^ Waldman, M.; Evans, S. E. (1994). "Lepidosauromorph reptiles from the Middle Jurassic of Skye". Zoological Journal of the Linnean Society. 112 (1–2): 135–150. doi:10.1111/j.1096-3642.1994.tb00315.x.
^ Martin-Silverstone, Elizabeth; Unwin, David M.; Cuff, Andrew R.; Brown, Emily E.; Allington-Jones, Lu; Barrett, Paul M. (2024-02-05). "A new pterosaur from the Middle Jurassic of Skye, Scotland and the early diversification of flying reptile". Journal of Vertebrate Paleontology. doi:10.1080/02724634.2023.2298741. ISSN 0272-4634.
^ WALDMAN, MICHAEL; SAVAGE, ROBERT JOSEPH GAY (March 1972). "The first Jurassic mammal from Scotland". Journal of the Geological Society. 128 (2): 119–125. Bibcode:1972JGSoc.128..119W. doi:10.1144/gsjgs.128.2.0119. ISSN 0016-7649. S2CID 128622858.
^ Panciroli, Elsa; Schultz, Julia A.; Luo, Zhe-Xi (2018-08-31). "Morphology of the petrosal and stapes of Borealestes (Mammaliaformes, Docodonta) from the Middle Jurassic of Skye, Scotland". Papers in Palaeontology. 5: 139–156. doi:10.1002/spp2.1233. hdl:20.500.11820/4c32b6c2-db3a-4e4d-8c46-cedc3245fac1. ISSN 2056-2802.
^ Panciroli, Elsa; Benson, Roger; Butler, Richard (2018). "New partial dentaries of amphitheriid mammalian Palaeoxonodon ooliticus from Scotland, and posterior dentary morphology in early cladotherians". Acta Palaeontologica Polonica. 63. doi:10.4202/app.00434.2017. ISSN 0567-7920.