Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

58 ADVANCES IN PALAEOICHTHYOLOGY
University of Queensland, Brisbane, Queensland, Australia. All previous numbers of
type specimens have been changed in the collections of the Institute of Geology at
Tallinn Technical University during the process of creating the computerised database
(for Lophosteus see Appendix 1).
Systematic description
OSTEICHTHYES Huxley, 1880
LOPHOSTEIFORMES Gross, 1969
LOPHOSTEIDAE Gross, 1969
Diagnosis (after Gross 1969): Osteichthyan fishes with rhombic scales that have a keel
on the inner side, but lacking peg on dorsal margin (sometimes broad based “peg”);
different sculpture on scales (with ridges) and head bones (with star-like tubercles);
ridges formed by dentine (orthodentine) on bony base.
Included genera: Lophosteus Pander 1856.
Lophosteus Pander, 1856
Type species: Lophosteus superbus Pander 1856.
Geographic distribution: Arctic Canada, Baltic region, Central Urals, E-Australia,
Timan-Pechora region.
Time: Ludlow-Pridoli, Late Silurian – Lochkovian, Early Devonian.
Diagnosis (after Gross 1969): Rhombic scales with broad based “peg”; free field of
scales covered with elevated, obliquely arranged ridges which are widely separated.
Ridges can be overgrown during size increase, but they rarely form a continuous dentine
layer. They bear ridgelets oblique to the crest. – Long symmetrical spines triangular in
cross-section without cavity and proximal with a smooth marginal area; ridges run
parallel to its length, and are sometimes fused to a median ridge; posterior side furrowlike
proximally whereas arched distally. Some asymmetrical long and flattened spines
present. – Bones with ridge-like or star-like tubercles. Sensory lines in the form of open
furrows on the bones.
Included species: Lophosteus superbus Pander, 1856; Lophosteus cf. superbus Burrow
and Turner, 2000; Lophosteus canadensis n. sp.; Lophosteus connexus Märss, 1986;
Lophosteus incrementus Burrow, 1995; Lophosteus ohesaarensis n. sp.; Lophosteus
uralensis n. sp.; Lophosteus sp. indet. Turner, 2000.
Remarks: Species are distinguished mainly on the arrangement of ridgelets. The
important characters are the angle between crest (= the highest line on the ridge) and
ridgelets (= small ridges on the sides of the ridges), and the posterior extension of the
ridges (= raised structures on the scale).