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	Loganellia scotica Loganellia scotica (after )
	Loganellia scotica was a jawless fish found in several northern regions, dating from the Late Ordovician period (Sandbian epoch, 458-453 mya) to the Late Silurian period (Pridoli, 423-419 mya). L. scotica is in the phylum Chordata, the subphylum vertebrata, the class Theoldonti, and the order Loganiidae. Thelodonts ("nipple teeth") are distinguished by their protective body covering of tooth-like or spiny scales called denticles, used as a barrier against their main predators, giant sea scorpions. The teardrop-shaped thelodont scales are mounted on a base, often with a small rootlet that attached the scale to the fish. These non-overlapping scales were aligned to point backwards along the fish, in a streamlined direction. Readily dispersed after death, the Thelodont scales are the most commonly found vertebrate fossil of their period. The first fossil of L. scotica was found by Traquair 1898 at Lesmagoh in southern Scotland. The find consisted of well-preserved fins and body parts. Loganellia has also been found in Estonia, Greenland, North America, and Siberia (Märss 2006, Märss and Karatajute-Talimaa 2002).  Loganellia had a large head with frontal eyes. Their swimming was aided by paired pectoral fins, and a single dorsal and anal fins. While it lacked jaws and oral teeth, L. scotica had both dermal scales and pharyngial denticles, joined into sets that resemble teeth.   As in the case of most other Theolodonts, the scales of Loganellia are considered species-diagnostic.  The Loganiid scale is larger than the Thelodontic scale, and has a rather flat crown. The pharyngeal scales, comprising very small denticulated plates, were possibly ancestral to the teeth of gnathostomes (jawed fish). References:            Märss, T.M.  2006. Thelodonts (Agnatha) from the basal beds of the Kuressaare Stage, Ludlow, Upper Silurian of Estonia  Märss, T.M. and Karatajute-Talimaa  2002. Ordovician and Lower Silurian thelodonts from Severnaya Zemlya Archipelago (Russia)     Märss, T.M.  et al.  2007  Traquair 1898 Turner, S. 1991. Monophyly and interrelationships of the Thelodonti. In Early vertebrates and related problems of evolutionary biology (ed. M. M. Chang, Y. H. Liu, and G. R. Zhang), pp. 87-111
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