East Kirkton Quarry

East Kirkton tetrapod fossils have all been preserved in aquatic sediments of the East Kirkton Limestone. A majority of the fossils come from laminated spherulitic limestone slabs (units 70 and below), though the best-preserved specimens come from a thin black shale layer (unit 82). Fish fossils do not occur alongside tetrapod fossils, suggesting that the tetrapods lived in or around shallower bodies of water than those supporting the local freshwater fish.[15]

The tetrapod species of East Kirkton are all endemic, though some broader groups (dendrerpetontids, aistopods, "anthracosaurs", etc.) can be found at other Carboniferous locales. Notably absent are adelogyrinids, Crassigyrinus, and lysorophians, all of which are considered fully aquatic. The absence of lysorophians could be explained by the age of East Kirkton, which is much older than the known aquatic members of the group.[15] True amniotes are also absent, and only a single microsaur fossil has been discovered.[14] The rarity of microsaurs may be due to geographic rather than environmental factors, since few fossils of the group are known from other British sites. Overall, East Kirkton has a more terrestrial character than other Scottish fossil sites, though a few aquatic or semi-aquatic species certainly inhabited the area as well.[15]

Tetrapods of East Kirkton
Genus / Taxon	Species	Strata	Material	Notes	Images
Balanerpeton[16]	B. woodi	East Kirkton Limestone	Over 30 specimens, including skulls and nearly complete skeletons	A medium-sized terrestrial temnospondyl similar to Dendrerpeton.
Eldeceeon[17]	E. rolfei	East Kirkton Limestone	Four partial skeletons, two of which are nearly complete[18]	A medium-sized "anthracosaur" with proportionally large hindlimbs and proposed terrestrial habits.
Embolomeri		East Kirkton Limestone	Skull fragments (pterygoid, quadratojugal, lower jaw)[19]	A large indeterminate embolomere with an estimated skull length of 20 cm (7.8 inches), the largest reported for a Mississippian embolomere.[19]
Eucritta[20]	E. melanolimnetes	East Kirkton Limestone	Four partial skeletons and an isolated skull roof[21]	A small baphetoid with a mosaic of features from other tetrapod groups.
Kirktonecta[14]	K. milnerae	East Kirkton Limestone	Single nearly complete skeleton	A very small newt-like aquatic microsaur, with soft tissue of a deep tail fin.
Ophiderpeton	O. kirktonense[22]	East Kirkton Limestone	Five partial skeletons, including skull material	A small aistopod, a type of snake-like legless tetrapod.
Silvanerpeton[23]	S. miripedes	East Kirkton Limestone	Nine partial skeletons, including skull material[24]	A small "anthracosaur" with short limbs.
Westlothiana[11]	W. lizziae	East Kirkton Limestone	Two nearly complete skeletons[12]	A small, slender reptiliomorph.[12] When the holotype specimen, "Lizzie", was discovered in 1988, it was reported to be the oldest known reptile[10][11] (or, more precisely, the oldest known amniote). Subsequent studies have reinterpreted it as a stem-amniote tetrapod close to the ancestry of amniotes[12] and/or lepospondyls.[13]
Temnospondyli		East Kirkton Limestone	Isolated ribs[16]	A large (~2 meter, 6.6 feet) indeterminate temnospondyl, possibly related to Edops.[16][25]
Termonerpeton[26]	T. makrydactylus	East Kirkton Limestone	Single partially articulated posterior torso	A large "anthracosaur"-like tetrapod with a foot similar to Eldeceeon and amniotes.

Though few of East Kirkton's fish species have been formally described, available information suggests that the East Kirkton lake hosted a diverse freshwater ecosystem. Body types seen in East Kirkton fish include fusiform (tuna-shaped) generalist predators and deep-bodied durophages (Eurynotus). The fish fauna is comparable to other sites in the Mississippian Oil Shales of Scotland. Only the Granton shrimp bed, a fully marine environment, lacks freshwater fish and tetrapods.[27]

Beside direct body fossils of fish, coprolites are also found in several layers near the Little Cliff Shale-East Kirkton Limestone transition. Small pellet- bullet- and cigar-shaped coprolites are common, often containing ostracod shells, and in one case, bone fragments. One irregular mass, containing ostracods and plant fragments, may be a regurgitate. Elongated spiralling coprolites are rarer and would have been produced by elasmobranchs akin to modern sharks. Irregular or strand-like coprolites may have been produced by tetrapods, though fish cannot be excluded. Massive clusters of phosphatized grains were probably produced by large omnivorous eurypterids like Hibbertopterus, or less likely large rhizodont fish.[28]

Apart from arthropods, other identified invertebrates include freshwater ostracods (Carbonita) and bivalves (Curvirimula?). Ostracods likely formed the base of the aquatic food chain, since they have been found as stomach contents in several fish and tetrapod fossils.[25]

Arthropods of East Kirkton
Genus / Taxon	Species	Strata	Material	Notes	Images
Brigantibunum[30]	B. listoni	East Kirkton Limestone	Single compressed partial specimen[25]	A small harvestman (Opiliones) with very long thin legs, possibly a member of the suborder Eupnoi.
Hibbertopterus	H. scouleri	East Kirkton Limestone	Partially articulated specimens and isolated fragments	A massive semi-terrestrial hibbertopterid eurypterid, with a carapace up to 65 cm (26 inches) in diameter. Some specimens were previously placed in the genera Cyrtoctenus and Dunsopterus.[31][25]
Myriapoda		East Kirkton Limestone	Multiple specimens, six of which are complete enough to describe	At least three species of many-legged arthropods, including a possible glomeridesmid (slug millipede), another millipede with ozopores (scent glands), and a putative non-millipede myriapod.[25][32]
Pulmonoscorpius[33]	P. kirktonensis	East Kirkton Limestone, Little Cliff Shale	16 complete specimens and hundreds of cuticle fragments	A large basal scorpion up to 70 cm (28 inches) in length, the largest terrestrial scorpion known. Two distinctive specimens may represent additional species of Pulmonoscorpius.
Scorpionida		East Kirkton Limestone, Little Cliff Shale	Cuticle fragments	At least two species of indeterminate scorpions, including an aquatic "archaeoctonoid" and a terrestrial "orthostern". One piece of scorpion cuticle apparently sheltered a mite.[33]

The plant fossils of East Kirkton are fragmentary but diverse, and small fragments of fusain (fossilized charcoal) are common in the East Kirkton Limestone. The area was likely forest or open woodland frequented by wildfires. There are few aquatic plants apart from algal laminations, and lycopsid fragments (an indicator of swamp forests) are only common in the Geikie Tuff. The surrounding woods were probably drier during the deposition of the Little Cliff Shale and East Kirkton Limestone. The East Kirkton flora is fairly typical among Viséan Scotland, most species found here have been reported previously from the Midland Valley.[34]

Gymnosperm wood and fern leaves (particularly Spathulopteris and Sphenopteridium) are the most common plant fossils at East Kirkton. These plants are also abundant at Weaklaw, a Viséan-age volcanic ash deposit in East Lothian. It is uncertain whether this similarity betrays a preference for volcanic areas or simply broader biostratigraphy.[34]

Plant fossils have been fossilized through several different chemical pathways. In the East Kirkton Limestone, robust plant parts such as gymnosperm branches and Stigmaria roots are often preserved by permineralization (petrification). During permineralization, the original organic material is sequentially replaced with silica and/or carbonate carried by alkaline groundwater. More commonly, heat and pressure compresses organic matter into carbonaceous films. These coalified compressions of wood and foliage can be found in practically every layer of the site. Some fossils are both compressed and permineralized, particularly in the early layers (units 44–48) of the East Kirkton Limestone.[35]