Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
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ACTA UNIVERSITATIS LATVIENSIS, 2004, Vol. 679, pp. 158-165<br />
A new thelodont from Lower Silurian of Tuva <strong>and</strong><br />
north-west Mongolia<br />
ŽIVILĖ ŽIGAITĖ<br />
Živile Žigaite, Department of Geology <strong>and</strong> Mineralogy, Vilnius University, M. K. Ciurlionio<br />
21/27, Vilnius, Lithuania; Institute of Geology <strong>and</strong> Geography, T. Ševcenkos 13, Vilnius,<br />
Lithuania; zigaite@geo.lt<br />
The new thelodont genus <strong>and</strong> species Talimaalepis rimae is described from the upper Ll<strong>and</strong>overy<br />
– Wenlock, Silurian of Central Asia (Tuva <strong>and</strong> north - west Mongolia) based on isolated exoskeletal<br />
microremains. Five major morphological types of dentine scales, namely rostral, cephalo-pectoral,<br />
postpectoral, precaudal <strong>and</strong> pinnal, are distinguished. Scales with pores of the sensory-line<br />
system are also established. According to morphology of scales <strong>and</strong> the internal structure of<br />
dentine tissue, the new thelodont taxon is considered to take an intermediate position between<br />
the genera Loganellia Turner, 1991 <strong>and</strong> Helenolepis Karatajūte-Talimaa, 1978.<br />
Key words: Central Asia, Lower Silurian, Thelodonti.<br />
Introduction<br />
The Central Asia region yields endemic Lower Silurian vertebrate fa<strong>un</strong>a (Karatajūte –<br />
Talimaa 1978; Blieck <strong>and</strong> Janvier 1993). Lower Silurian vertebrate material from outcrops<br />
of north-west Mongolia <strong>and</strong> Tuva have been studied for the present paper. Six<br />
samples with thelodont remains come from north-west Mongolia from the Chargat formation<br />
(Minjin, 2001), Lake Basin locality (Upper Ll<strong>and</strong>overy – Wenlock; I. Sodov, P.<br />
Kosbayar <strong>and</strong> K. S. Rozman collections) (in Karatajūte-Talimaa et al. 1990). Ten scale<br />
samples from Tuva, the Kyzyl-Tchiraa, Elegest <strong>and</strong> Kadvoj sequences represent<br />
thelodonts from Upper Ll<strong>and</strong>overy to Wenlock beds (V. Karatajūte-Talimaa collections).<br />
A new thelodont Talimaalepis rimae gen. et sp. nov. was established <strong>and</strong> is described<br />
below. The form is suggested to take an intermediate position between the<br />
thelodont genera Loganellia <strong>and</strong> Helenolepis.<br />
This work is a contribution to IGCP Project 491 “Middle Palaeozoic vertebrate<br />
biogeodiversity <strong>and</strong> climate”.