Acanthograptus praedeckeri, Rickards, R. B., Chapman, A. J., Wright, A. J. & Packham, G. H, 2003

Rickards, R. B., Chapman, A. J., Wright, A. J. & Packham, G. H, 2003, Dendroid and Tuboid Graptolites from the Llandovery (Silurian) of the Four Mile Creek Area, New South Wales, Records of the Australian Museum 55 (3), pp. 305-330 : 322-324

Acanthograptus praedeckeri n.sp.

Figs. 17C,D , 18A , 19C , 20A–E

Material. HOLOTYPE AM F114792 a-b, from BF28, Bridge Creek . PARATYPES AM F114629 a, AM F114718 , AM F114740 a-b, AM F114741 , AM F114785–89 and AM F114791 , all from F14; AM F114742 from BF29, W tributary of Bridge Creek ; AM F114630 from F6, Wallace Creek ; AM F114568 a-b, AM F114741 , AM F114790–1 and AM F114793–4 , all from BF28, W tributary of Bridge Creek .

Derivation of name. To reflect its earlier occurrence than the low Ludlow species A. deckeri , which it resembles.

Diagnosis. Large, flabelliform Acanthograptus in which the main stipes grow from a robust stem region; twigs and secondary branches spread to all available space; 8–14 twigs in 10 mm; twigs 0.70–1.0 mm long; main stipe 0.40– 0.50 mm wide; branching every 0.50–1.50 mm.

Description. In the best preserved specimens there is no physical overlap of adjacent stipes. Rather, the overall branching pattern grows and spreads in all directions to fill the available space. Thus the rhabdosome, although bushlike in appearance, is actually flabelliform. In sections of stipe where no branching takes place the twigs alternate from side to side in classic Acanthograptus fashion. Each twig usually comprises more than one autothecal tube although some seem to terminate in a single tube. However, the twig arrangement breaks down frequently because numerous dichotomies of the stipes occur, spaced at 0.50– 1.50 mm intervals. All the stipes appear to be compound with numerous elongate tubes visible.

Remarks. Acanthograptus praedeckeri n.sp. has too few twigs and too great a stipe width for comparison with A. aculeatus Poěta , as well as having a bushier rhabdosome altogether. Acanthograptus deckeri from the low Ludlow has a similar rhabdosomal appearance, but the twig arrangement is less regular and all the stipes more compound and more robust. Acanthograptus praedeckeri is very similar to Thallograptus christoffersonae described below, and the differences are listed under the Remarks section of the latter.

Figures

Fig. 17. A, Callograptus ulahensis n.sp., AM F114760, holotype, BF15; B, Stelechocladia praeattenuata n.sp.,AM F114743, holotype, BF28; C,D, Acanthograptus praedeckeri praedeckeri n.sp., respectivelyAM F114792, holotype, BF28 and AM F114568a, F14. Scale bars 1 mm.

Fig. 18. A, Dictyonema warrisi n.sp., AM F114629b, F14; B, Thallograptus christoffersonae n.sp., AM F114644, W885. Scale bars 1 mm.

Fig. 19. A,B, Stelechocladia praeattenuata n.sp.: A, AM F114743, holotype, and B, AM F114744, both BF18; C, Acanthograptus praedeckeri praedeckeri n.sp., AM F114629a, F14. Scale bars 1 mm.

Fig. 20. A–E, Acanthograptus praedeckeri praedeckeri n.subsp., respectively AM F114568, AM F114568, AM F114741,AM F114742 and AM F114740, all from F14; F, Acanthograptus praedeckeri minimus n.subsp.,AM F114630, F6. Scale bars 1 mm.