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 ...
ACTA UNIVERSITATIS LATVIENSIS, 2004, Vol. 679, pp. 158-165 A new thelodont from Lower Silurian of Tuva and north-west Mongolia ŽIVILĖ ŽIGAITĖ Živile Žigaite, Department of Geology and Mineralogy, Vilnius University, M. K. Ciurlionio 21/27, Vilnius, Lithuania; Institute of Geology and Geography, T. Ševcenkos 13, Vilnius, Lithuania; zigaite@geo.lt The new thelodont genus and species Talimaalepis rimae is described from the upper Llandovery – Wenlock, Silurian of Central Asia (Tuva and north - west Mongolia) based on isolated exoskeletal microremains. Five major morphological types of dentine scales, namely rostral, cephalo-pectoral, postpectoral, precaudal and pinnal, are distinguished. Scales with pores of the sensory-line system are also established. According to morphology of scales and the internal structure of dentine tissue, the new thelodont taxon is considered to take an intermediate position between the genera Loganellia Turner, 1991 and Helenolepis Karatajūte-Talimaa, 1978. Key words: Central Asia, Lower Silurian, Thelodonti. Introduction The Central Asia region yields endemic Lower Silurian vertebrate fauna (Karatajūte – Talimaa 1978; Blieck and Janvier 1993). Lower Silurian vertebrate material from outcrops of north-west Mongolia and Tuva have been studied for the present paper. Six samples with thelodont remains come from north-west Mongolia from the Chargat formation (Minjin, 2001), Lake Basin locality (Upper Llandovery – Wenlock; I. Sodov, P. Kosbayar and K. S. Rozman collections) (in Karatajūte-Talimaa et al. 1990). Ten scale samples from Tuva, the Kyzyl-Tchiraa, Elegest and Kadvoj sequences represent thelodonts from Upper Llandovery to Wenlock beds (V. Karatajūte-Talimaa collections). A new thelodont Talimaalepis rimae gen. et sp. nov. was established and is described below. The form is suggested to take an intermediate position between the thelodont genera Loganellia and Helenolepis. This work is a contribution to IGCP Project 491 “Middle Palaeozoic vertebrate biogeodiversity and climate”.
Ž. Žigaite. New telodont from Tuva and Mongolia 159 Systematic palaeontology Class AGNATHA Cope, 1889 Subclass THELODONTI Kiaer, 1932 Order PHLEBOLEPIDIFORMES (?) Berg, 1938 Family PHLEBOLEPIDAE (?) Berg, 1940 Talimaalepis gen. nov. Etymology. In honour of Habil. Dr. Valentina Karatajūtė-Talimaa; lepis (Greek), scale. Type species. Talimaalepis rimae gen. et sp. nov. Diagnosis. As for type species. Remarks. The description of the new taxon is based on the isolated microremains of exoskeleton, the dentine scales. It has intermediate position between the two thelodont genera – Loganellia (Fam. Loganellidae) and Helenolepis (Fam. Phlebolepidae). Talimaalepis possesses one single pulp canal, which is typical to genus Loganellia. Though well-defined thick dentine canals opened into pulp canal are very specific to genus Helenolepis. Talimaalepis rimae sp. nov. Figs 1-3 1978 Logania ? kadvoiensis, Karatajūtė -Talimaa; p. 82-86; tab. XII, XIII, fig. 3-6; tab. XIX, fig.14; tab. XXII, fig. 1-6; fig. 15, fig. 5-9. 1991 Loganellia ? kadvoiensis, Turner; p. 111. 1991 Helenolepis sp., supposed, Turner; p. 111. 2002 Loganellia sp. nov., Žigaite; p. 229-230; fig. A, B. 2003 Helenolepis sp. nov., Žigaite; p. 57-58. 2004 Helenolepis ? sp. nov., Žigaite; p. 37-38. Etymology. Rima, ae, f. (Latin) meaning a gap, a slot. Name emphasizes the type species of genus Talimaalepis gen. nov. placed between thelodont genera Loganellia and Helenolepis. Holotype. LGI M-1/224, cephalo-pectoral scale, Fig. 1 herein. Type locality and stratigraphy. South-east slope of mount Chargat, 80 km north from lake Khara-Ubs-Nuur, Lake Basin outcrop No 21, north-west Mongolia; Chargat Formation, Salhit Regional Stage, upper Llandovery – Wenlock, Silurian. Material. About 800 scales stored in the Institute of Geology and Geography, Lithuania; collection numbers LGI M-1 and LGI T. Diagnosis. Elongated scales of medium size, up to 1.4 mm long, 0.6 – 0.8 mm on the average. The elongate and flattened crown of most common cephalo-pectoral scales divided into main central and paired shorter lateral parts. Crown surface with longitudinal sculpture composed of central groove and lateral pairs of ribs. Wedge-shape base usually
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Ž. Žigaite. New telodont from Tuva <strong>and</strong> Mongolia 159<br />
Systematic palaeontology<br />
Class AGNATHA Cope, 1889<br />
Subclass THELODONTI Kiaer, 1932<br />
Order PHLEBOLEPIDIFORMES (?) Berg, 1938<br />
Family PHLEBOLEPIDAE (?) Berg, 1940<br />
Talimaalepis gen. nov.<br />
Etymology. In honour of Habil. Dr. Valentina Karatajūtė-Talimaa; lepis (Greek),<br />
scale.<br />
Type species. Talimaalepis rimae gen. et sp. nov.<br />
Diagnosis. As for type species.<br />
Remarks. The description of the new taxon is based on the isolated microremains of<br />
exoskeleton, the dentine scales. It has intermediate position between the two thelodont<br />
genera – Loganellia (Fam. Loganellidae) <strong>and</strong> Helenolepis (Fam. Phlebolepidae).<br />
Talimaalepis possesses one single pulp canal, which is typical to genus Loganellia.<br />
Though well-defined thick dentine canals opened into pulp canal are very specific to<br />
genus Helenolepis.<br />
Talimaalepis rimae sp. nov.<br />
Figs 1-3<br />
1978 Logania ? kadvoiensis, Karatajūtė -Talimaa; p. 82-86; tab. XII, XIII, fig. 3-6; tab. XIX,<br />
fig.14; tab. XXII, fig. 1-6; fig. 15, fig. 5-9.<br />
1991 Loganellia ? kadvoiensis, Turner; p. 111.<br />
1991 Helenolepis sp., supposed, Turner; p. 111.<br />
2002 Loganellia sp. nov., Žigaite; p. 229-230; fig. A, B.<br />
2003 Helenolepis sp. nov., Žigaite; p. 57-58.<br />
2004 Helenolepis ? sp. nov., Žigaite; p. 37-38.<br />
Etymology. Rima, ae, f. (Latin) meaning a gap, a slot. Name emphasizes the type<br />
species of genus Talimaalepis gen. nov. placed between thelodont genera Loganellia<br />
<strong>and</strong> Helenolepis.<br />
Holotype. LGI M-1/224, cephalo-pectoral scale, Fig. 1 herein.<br />
Type locality <strong>and</strong> stratigraphy. South-east slope of mo<strong>un</strong>t Chargat, 80 km north from<br />
lake Khara-Ubs-Nuur, Lake Basin outcrop No 21, north-west Mongolia; Chargat<br />
Formation, Salhit Regional Stage, upper Ll<strong>and</strong>overy – Wenlock, Silurian.<br />
Material. About 800 scales stored in the Institute of Geology <strong>and</strong> Geography, Lithuania;<br />
collection numbers LGI M-1 <strong>and</strong> LGI T.<br />
Diagnosis. Elongated scales of medium size, up to 1.4 mm long, 0.6 – 0.8 mm on the<br />
average. The elongate <strong>and</strong> flattened crown of most common cephalo-pectoral scales<br />
divided into main central <strong>and</strong> paired shorter lateral parts. Crown surface with longitudinal<br />
sculpture composed of central groove <strong>and</strong> lateral pairs of ribs. Wedge-shape base usually
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