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88 ADVANCES IN PALAEOICHTHYOLOGY dorsal process of the clavicle (Figs. 5B, C). The ventral part of the anterior edge of the cleithrum is convex. Mesially from the anteroventral process and posteriorly from the anteromedial depression there is a process parallel to the former, named here the ventral anteromedial process. Its mesial surface is smooth; it is straight and the ventral tip projects below the apex of the anteroventral process. The corresponding part of the posterior edge of the cleithrum is, on the contrary, concave and its outline almost follows in parallel that of the anterior edge. The contact with the scapulocoracoid can be easily traced; it follows the sharp ridge of the posteroventral edge. The posterodorsal edge of the bone is less acute and smoothly arched in plan view. The scapulocoracoid (Fig. 5B) is incompletely ossified and only its scapular portion is partly preserved, in accordance with the condition noted by Holmes (1980) in Proterogyrinus. This bone is solidly fused to the mesial side of the cleithrum, however, in contrast to Ichthyostega, Acanthostega and Hynerpeton and in agreement with the condition in Elginerpeton (Ahlberg 1998) its sutures are fairly well discernible. As noted above, the posterolateral suture of the scapulocoracoid runs parallel to the posteroventral edge of the cleithrum. Posterodorsally it is obscured by three shallow muscle attachment pits, possibly for the analogue of the m. levator scapulae. These pits are separated anteriorly from the anterodorsal part of the supraglenoid buttress by a prominent transverse ridge. The anterodorsal crest at this point is robust, ventrally it reduces in height forming a concavity at the anterior edge of the subscapular fossa, which would have been large and comparable in configuration to that in Hynerpeton (Daeschler et al. 1994) and Elginerpeton (Ahlberg 1998). The anteroventral part of the anterior edge of the scapulocoracoid abuts the dorsal part of the ventral anteromedial process of the cleithrum. A small supraglenoid foramen is situated close to the scapulocoracoid-cleithrum suture in the same position as in Hynerpeton and foramen “C” in Acanthostega (Coates 1996). Only the distal part of the left femur (PIN 2657/344) is preserved. The major feature distinguishing it from all other known Devonian tetrapods is the absence of an intercondylar fossa (Figs. 6, 7) and correspondingly distinctly expressed condyles. Instead, the dorsal (extensor) surface of the femur in its distal part is almost flat (Fig. 6B). Two shallow ridges, one running along the posterior edge of the dorsal surface and the other parallel to it roughly in the middle of the surface, form a shallow groove with uneven surface. The rest of the surface adjoining the tibial condyle is also flat and pierced with several large blood vessel foramina. Its anterior edge forms an abrupt bend to the condyle surface. More proximal part of the dorsal surface in the shaft area is rounded and passes smoothly into the shaft portion of the anterior surface of the femur. The massive adductor crest running obliquely towards the anterior bone surface delimits the ventral margin of the anterior surface (Fig. 6A). The distal part of the anterior surface is dominated by the bulky perichondral mass of the tibial condyle strongly overhanging and even partly enclosing ventrally the large and deep triangularshaped popliteal fossa (Figs. 6A, C). The ventral surface of the bone enclosed between the adductor crest and a sharp ridge separating this surface from the posterior one is narrow distally but widens in the proximal direction. The latter ridge is situated topographically in the same position as a well marked unnamed ridge situated at the ventral side of the femur receiving the distal extremity of the adductor crest and separating
O.A. Lebedev. A new tetrapod from Russia 89 Fig. 6. Jakubsonia livnensis gen. and sp. nov., distal part of the left femur, PIN 2657/344. A, anteriorly, B, dorsally, C, ventrally, D, posteriorly. Fig. 7. Distal part of the femur in Tulerpeton curtum Lebedev, 1984 (upper row) and left femur in Jakubsonia livnensis gen. and sp. nov. (lower row). The drawings of Tulerpeton curtum femur reversed from the right to the left for the sake of comparison, distal part directed downwards. A, anterior view, B, dorsal view, C, ventral view, D, posterior view. Abbreviations: ac, adductor crest; fc, fibular condyle; ff, fibular facet; fif, fibular fossa; fr, fibular ridge; icf, intercondylar fossa; pf, popliteal fossa; tc, tibial condyle; tf, tibial facet.
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LATVIJAS UNIVERSITĀTES RAKSTI 679.
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LATVIJAS UNIVERSITĀTES RAKSTI 679.
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Contents Ervīns Lukševičs and Ģ
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ACTA UNIVERSITATIS LATVIENSIS, 2004
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Ervīns Lukševičs, Ģirts Stinkul
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Olga Afanassieva. Microrelief on th
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D.K. Elliott, E. Mark-Kurik, E.B. D
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Page 47 and 48: C.G.Miller, T. Marss, H. Blom. New
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Page 59 and 60: H.-P. Schultze, T. Marss. Revisitin
Page 81 and 82: O.A. Lebedev. A new tetrapod from R
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Page 101 and 102: E. Lukševičs, I. Zupiņš. Sedime
Page 121 and 122: J. Valiukevičius. Silurian acantho
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J. Valiukevičius. Silurian acantho
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V. Pernegre, V. Dupret. Biostratigr
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Ž. Žigaite. New telodont from Tuv
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