Poracanthodes canadensis, BURROW & VERGOOSSEN, 1999, 1999
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publication ID |
https://doi.org/ 10.5070/P940454153 |
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publication LSID |
lsid:zoobank.org:pub:58312615-0833-432E-BF5D-3DFFBF361AAA |
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persistent identifier |
https://treatment.plazi.org/id/B21CD55B-FFD6-FFE8-59ED-8957FB6825AA |
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treatment provided by |
Felipe |
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scientific name |
Poracanthodes canadensis |
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PORACANTHODES CANADENSIS BURROW & VERGOOSSEN,
1999 ( FIG. 2H–2P, T–V View Figure 2 ?2Q–S; TABLE 1; SUPPL. 1, FIGS. 2 View Figure 2 -19)
Poracanthodes canadensis Burrow et al. 1999 , 353– 356, figs. 3A–C, 3F, 3G, 4A–F, 5A, 5B,?3D,?3E,?4G,?7A–D.
“scales ... were assigned by Parkes (1995) to P. punctatus ” in part; Burrow et al. 1999, 355, 358.
“ P. punctatus ... scales ... figured ... are from P. canadensis ” in part; Burrow 2003a, 490.
Diagnosis —see Burrow et al. (1999).
Type material — Holotype scale GSC 116340 View Materials ; Paratype scales: flank scale GSC 116339 View Materials , transitional scale GSC 116343 View Materials ; Locality C-11460, Marshall Peninsula , Cornwallis Island, arctic Canada; Cape Phillips Formation (Late Silurian, Ludlow or Přidolí) .
Referred specimens — Poracanthodes canadensis scales are found at most levels from 395′–518.3′ (120.4-156.8 m) in the BC II section ( Table 1), and include UCR 10750-6 (456.5’= 139.1 m), UCR 10746-5, -6 (430.5’= 131.2 m), UCR 930-4 (395’= 120.4 m), possibly UCR 10768-3 (518.3’= 158 m), and thin sections UCR 930-8 and -9 (395’= 120.4 m); also AMF 97947 (level 513’= 156.4 m) and AMF 97951 (level 402’= 122.5 m), figured by Parkes (1995, fig. 32.1, 32.2, 32.9, 32.10): Roberts Mountains Formation.
Description —The scales have 6–16 short, sharp, mostly even-spaced ridges running back from the anterior edge of the crown. The rest of the crown is relatively smooth, with close-set evenly spaced pores along the margin between growth zones paralleling the zig-zagging posterolateral edges of the crown ( Fig. 2H–2P View Figure 2 ). Unfortunately, the posterior area of most scale crowns has broken off, and the zig-zag orientation of the outer rows of pores, characteristic of P. canadensis , is only rarely preserved ( Fig. 2P View Figure 2 ). Each side of the undersurface of the posterior crown on most scales has three or four large openings to the pore canal system at the crown-neck junction. The neck and base morphology is comparable with that of P. punctatus . One of the scales figured ( Fig. 2Q–S View Figure 2 ) could pos- sibly be from P. punctatus , as the anterior crown ridges are only weakly developed (or alternatively, worn down) and there is a slight anterior median sulcus.
Despite the poor preservation and extensive borings through the scales, thin sectioning shows that the scales have the pore canal layout typical of Poracanthodes canadensis , with six or eight radial pore system canals interconnected by v-shaped arcade canals, from which short canals rise up to the pore openings aligned along the growth zones on the crown ( Fig. 2T–V View Figure 2 ).
Comparison —Scales of P. canadensis can be distinguished from other poracanthodid taxa by their multiple short sharp ridges along the anterior rim of the crown and the alignment of pore openings parallel with the posterolateral edges of the crown, forming a zigzag pattern paralleling the jagged denticulations in younger zones. The taxon is only recorded elsewhere from the Přidolí of the Barlow Inlet Formation ( Märss et al. 1998) and Cape Phillips Formation, Arctic Canadian Archipelago (Burrow et al. 1999), and now from Nevada.
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