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 ...
62 ADVANCES IN PALAEOICHTHYOLOGY The main visible difference between spines with a triangular cross-section as depicted by Rohon (1893) and Otto (1991) is in the arrangement of ridge-like tubercles, which are arranged either in rows or irregularly, and in the difference in depth. The spine described by Gross (1969: text-fig. 5 E) is of the same type as that from the Ruhnu bore hole. They are flattened, sculptured on both flattened sides and distally around the whole spine. Proximally they have a cavity that extends one third of their length. This spine has some similarities with the cornual plate of placoderms. Other spine-like elements described by Gross and also those in the Tallinn collection, were attached to tesserae-like elements in the skin. These have a concave visceral side and are not fin-spines. The spine assigned to the sarcopterygian Psarolepis (Zhu and Schultze 1997) has a very narrow overlapped area. These spines are not inserted deeply in the skin in contrast to spines of sharks and most acanthodians. Zhu et al. (1999) emphasized the occurrence of spines in basal osteichthyans (including Lophosteus), acanthodians and sharks. Advanced sharks and the Early Devonian chondrichthyan Leonodus (Soler- Gijón and Hampe 2003) possess only symmetrical spines, whereas spines in front of paired fins are known in Early Devonian sharks (Sahney and Wilson 2001: putative chondrichthyan; Miller et al. 2003: Doliodus). A convex plate (GIT 382-25, Fig. 1 B, C) represents a new element. Its maximum preserved length is 6.6 mm. The plate is convex externally and concave internally; the lateral margins are broken. It has a short anterior overlapped area. Oval, smooth, abraded tubercles are distributed in indistinct rows posterior to that area (Fig. 1 C); smaller tubercles are placed between larger ones. Fine ridgelets occur radially at the margin of each tubercle. The deeper part of an elongate narrow keel on the concave inner side is partly broken off (Fig. 1 B). Lineations that may represent growth lines are visible in front of the keel. The plate is symmetrical, belongs to the dorsal midline, and may be comparable to a fulcrum. An interesting head plate (GIT 232-16 = Pi 6186, Fig. 2) of L. superbus was described and figured by Märss (1986: 58, pl. 35, fig. 1 a, b). The arched plate shows an open lateral line canal which bifurcates anteriad around the anterior invagination. The course of the lateral line nerve is picked out on the inner side by pores that transmitted branching nerves to the neuromasts in the lateral line canal. The course of the pores and thus the course of the lateral line nerve on the inner side from a posterior to an anterior invagination does not show the bifurcation of the canal on the outer side of the plate. Such plates with an open lateral line canal have already been described and figured by Gross (1969: figs 5 H, 6 D, 7 A, B). Lophosteus cf. superbus 2000 Lophosteus sp. cf. L. superbus — Burrow and Turner: 170, 172; fig. 3.3. Material: part of one scale UQY 8667 (Burrow & Turner 2000: fig. 3.3). Locality: Bullock Creek, northern Queensland, Australia. Horizon: Ancoradella ploeckensis Conodont Zone, Jack Formation, lower Ludlow, Upper Silurian. Description: Burrow and Turner (2000) gave no description. The scale is reminiscent of those of L. superbus and have a pustulate anterior field and elevated oblique ridges
H.-P. Schultze, T. Marss. Revisiting Lophosteus 63 Fig. 2. Lophosteus superbus; head plate GIT 232-16; upper Pridoli, Upper Silurian; Ohesaare cliff, Saaremaa, Estonia. A, external side; B, inner side. with strong ridgelets. The angle between crest and ridgelets at around 20° is lower than in L. superbus. – This is the oldest record of Lophosteus. Lophosteus canadensis n. sp. Fig. 3 1998 Lophosteus sp. — Märss et al.: 60, 62. 1998 Lophosteus spp. — Märss et al.: fig. 4. 2000 Lophosteus sp. — Märss: 68. Holotype: scale UALVP 447 66 (Fig. 3 A, B). Etymology: Named after region of origin (Canada). Type locality: 141.0 m in the Read Bay southern section, Cornwallis Island, Arctic Canada (Märss et al. 1998). Type horizon: Barlow Inlet Formation, Pridoli, Upper Silurian. Additional material: two more scales, one scale is figured herein (UALVP 447 85; Fig. 3 C), one short spine (UALVP 447 90; Fig. 3 D), one plate (UALVP 447 65; Fig. 3 E, F), and head plate and tooth plate fragments. Localities: Two samples at 87.0 m in the Read Bay southern section, Cornwallis Island, Arctic Canada (Märss et al. 1998). Horizon: Barlow Inlet Formation, Pridoli, Upper Silurian. The material occurs together with conodonts Ozarkodina confluens, Oz. excavata, ?Ligonodina confluens, Pelekysgnathus sp,. and Ctenognathodus sp. (Männik in Märss et al. 1998: fig. 4).
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H.-P. Schultze, T. Marss. Revisiting Lophosteus<br />
63<br />
Fig. 2. Lophosteus superbus; head plate GIT 232-16; upper Pridoli, Upper Silurian; Ohesaare<br />
cliff, Saaremaa, Estonia. A, external side; B, inner side.<br />
with strong ridgelets. The angle between crest <strong>and</strong> ridgelets at aro<strong>un</strong>d 20° is lower than<br />
in L. superbus. – This is the oldest record of Lophosteus.<br />
Lophosteus canadensis n. sp.<br />
Fig. 3<br />
1998 Lophosteus sp. — Märss et al.: 60, 62.<br />
1998 Lophosteus spp. — Märss et al.: fig. 4.<br />
2000 Lophosteus sp. — Märss: 68.<br />
Holotype: scale UALVP 447 66 (Fig. 3 A, B).<br />
Etymology: Named after region of origin (Canada).<br />
Type locality: 141.0 m in the Read Bay southern section, Cornwallis Isl<strong>and</strong>, Arctic<br />
Canada (Märss et al. 1998).<br />
Type horizon: Barlow Inlet Formation, Pridoli, Upper Silurian.<br />
Additional material: two more scales, one scale is figured herein (UALVP 447 85;<br />
Fig. 3 C), one short spine (UALVP 447 90; Fig. 3 D), one plate (UALVP 447 65; Fig.<br />
3 E, F), <strong>and</strong> head plate <strong>and</strong> tooth plate fragments.<br />
Localities: Two samples at 87.0 m in the Read Bay southern section, Cornwallis Isl<strong>and</strong>,<br />
Arctic Canada (Märss et al. 1998).<br />
Horizon: Barlow Inlet Formation, Pridoli, Upper Silurian. The material occurs together<br />
with conodonts Ozarkodina confluens, Oz. excavata, ?Ligonodina confluens,<br />
Pelekysgnathus sp,. <strong>and</strong> Ctenognathodus sp. (Männik in Märss et al. 1998: fig. 4).
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