Thallograptus christoffersonae, 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 : 325

publication ID	https://doi.org/ 10.3853/j.0067-1975.55.2003.1387
persistent identifier	https://treatment.plazi.org/id/039E87A3-F929-FFBF-7104-476A9EFAE7F6
treatment provided by	Felipe
scientific name	Thallograptus christoffersonae
status	sp. nov.

Treatment

Thallograptus christoffersonae n.sp.

Figs. 18B View Fig , 22A,B View Fig

Material. HOLOTYPE AM F114746 , W885 (approximately = BF14 and F14), Bridge Creek . PARATYPES AM F114644 , W885 and AM F114765 , BF14 ; and numerous other specimens from F14, BF24, BF28, and BF29, all uppermost Llandovery .

Derivation of name. After Ruth Christofferson of “Avon Lea”.

Diagnosis. Thallograptus with very bushy dendroid appearance, fan-shaped; stipes no more than 0.60 mm wide, branching every 1 mm or less; about 10 stipes per cm; twigs at rate of 12 per cm, up to 1 mm long, terminating as one autothecal tube; autothecae 0.10–0.15 mm wide; bithecae 0.03–0.04 mm wide.

Description. The rhabdosome, measuring up to 25 mm wide and 15 mm long on the largest specimens, is probably fanshaped because despite the dendroid, fan-shaped appearance stipes do not overlap but fill the available space. A holdfast has not been identified. At their thickest the stipes are about 0.60 mm wide, and branching takes place regularly, usually with intervals of less than 1 mm between branches. Branches diverge in such a manner that the available space is filled. There is no anastomosis. Twigs occur between branching points and are spaced at around 10–12 per cm with an individual length of up to 1 mm.

They terminate in single autothecal tubes having a diameter of 0.10–0.15 mm and unornamented apertures. Along the main stipes bundles of up to 6 autothecae are visible in the ropy stipe texture, implying that there are considerably more in any one cross section of stipe. Bithecae are seen occasionally as diminutive tubes, 0.03–0.04 mm wide, irregularly positioned.

Remarks. The closest species seems to be T. elegans Bouěek, 1957 , which has a similar growth pattern of the stipes. In this form, however, the stipes are much thicker, and they thin and thicken at branching points which does not occur in T. christoffersonae . Other measurements, such as stipe spacing and branching frequency, also differ. Acanthograptus praedeckeri n.sp. is also similar in rhabdosomal form (and it is interesting that Bouěek (1957: 102) referred his new species A. deckeri inadvertently to Thallograptus !). Acanthograptus praedeckeri n.sp. differs from Thallograptus christoffersonae n.sp. in having a definite twig system where each twig is composed of several thecae, the twigs are shorter, and branching is much less frequent. Thallograptus densus Kraft, 1979 is another similar species but differs in having more parallel and more densely arranged stipes; it occurs in the sedgwickii Biozone (Llandovery). Thallograptus elegans is a Wenlock to Ludlow species.