| Ruedemann (1947) established graptolite family Inocaulidae allocating in it the genera Inocaulis Hall, Thallograptus Ruedemann, Medusaegraptus Ruedemann and Diplospirograptus Ruedemann. Bouček (1957) excluded the genus Thallograptus from that family, allocated the genus Palmatophycus Bouček, and rised its rank to the order Inocaulida with the following characteristics: "Thick main branches, simple or infrequent bifurcating, rarely distally a bundle of secondary branchlets, with abundant filamentous thecal tubes" (Bouček 1957, p. 145). Obut (1964) widened the range of Inocaulidae to comprise also the genera Boucekocaulis Obut, Crinocaulis Obut and Estoniocaulis Obut et Rytzk. According to the latter author, Inocaulidae developed from dendroid graptolites, more precisely those of the family Dendrograptidae. Bulman (1970) assigned the genus Inocaulis to dendroid graptolites (family Acanthograptidae), treating the remaining genera together as "Dendroidea, Tuboidea, Camaroidea, Crustoidea, Stolonoidea - taxonomic position uncertain". |
| I doubt the graptolitic nature of Inocaulis and other forms regarded as related to it by the authors mentioned above. Anatomy of all these genera is very poorly known as they have been described on the basis of imprints or carbonized, flattened remains. The only features in which they may resemble graptolites include: a) a bushy shape of colony displayed by some of them, and b) the presence of long, narrow "thecae". Both features are without much importance for analysis of eventual affiliation of inocaulids and graptolites, as bushy colonies are known from various groups of colonial invertebrates and the so-called ?"thecae" fail to display any traces of fusellar structure. The "thecae" and branches actually somewhat resemble morphology of autothecae of such graptolites as Acanthograptus Spencer or Koremagraptus Bulman but, up to the present, no elements which could be interpreted as bithecae were found in inocaulids. Inocaulis plumulosa Hall, the type species of the genus Inocaulis display branches formed of bunches of undifferentiated long tubes (see Ruedemann 1947, pl. 32 9-11). |
| Bulman (1979: V55) stated that Diplospirograptus displays "superficial resemblance to algal forms, though it is perhaps doubtful whether such delicate filamentous algae could survive under the given conditions of preservation of these fossils". According to me, the algal nature of this genus may be regarded as quite sure. I consider Diplospirograptus as an alga of the class Chlorophyceae, close to Dasycladaceae, especially Batophorereae. In the "rhabdosome" of D. goldringae Ruedemann, type species of Diplospirograptus, it is possible to note morphological elements identical to the thallus of modern Batophora oerstedi Agarth (Fig. 1). |
| Fig. 1. Lateral branches in Diplospirograptus goldringae Ruedemann (a) and Batophora oerstedi Abardh (b). After Ruedemann and Nitecki from Mierzejewski. |
| Elements of the "rhabdosome" of D. goldringae, named as "theciferous branches" by Ruedemann (1947), are essentially identical to lateral branchings of the above-mentioned green alga. These forms essentially differ in the presence of single major axis in Batophora, similarly as in all Dasycladaceae, and double, spirally coiled and branching axis in Diplospirograptus. This make possible treatment of the latter as a representative of the Dasycladaceae which it so closely resembles in morphology of "theciferous branches". It is worth to note here that I found a thallus of alga with polysiphonal axes and lateral branchings similar to those of Dasycladaceae in one of Silurian erratic boulders. According to Dr. J. Kamierczak (1978, oral inf.) the algae represent hitherto unknown group, intermediate between Dasycladaceae and Codiaceae. It seems that the genus Diplospirograptus would be best accomodated in that group. |
| Other inocaulid, Ordovician-Silurian Medusaegraptus Ruedemann may also represent Chlorophyceae. Ruedemann (1925, p. 29) characterized it as follows: "rhabdosome consisting of a simple, not branching stipe, which is a uniformly thick tube, ending in a blunt point at the base and terminating distally in a dense mass of simple, unbranched flexuosus thin tubes, the thecae". Medusaegraptus may be easily classified as representative of Codiaceae. Thallus of Codiaceae is sometimes built of stem and brush -like top part, formed of numerous thallus threads. The so-called thecae of Medusaegraptus I treat as equivalents of these threads, and "not branching stips". In an identical way I interpret the Silurian Palmatophycus Bouček, actually originally described as an alga (Bouček 1941). |
| In considering the systematic position of Diplospirograptus, Medusaegraptus and Palmatophycus, the record of the first fossil representatives of Batophoreae (Archaeobatophora Nitecki) from the Ordovician of the USA (Nitecki 1976) is of marked significance. The morphology and state of preservation of this form are strikingly similar to those of "inocaulid graptolites". |
| Among inocaulids, special attention should be paid to the genus Inocaulis Hall. Ruedemann (1947, p.236) characterized it in the following way: "Very thick branches, bifurcating infrequently, composed of an exteremely large number of fine tubes, which project freely distally as hairlike processes". I suppose that this genus represents hydroids with polysiphonal colonial stem and branches. Species assigned to the genus Inocaulis have hydrosomes simply identical as those of modern hydroid species of the genus Grammaria Stimpson Fig. 2). |
| I do not know of any differences in structure of the hydrosomes of species of the two genera. Both genera are characterized by: (a) identical tree-like shape of colony, (b) stems and branches polysiphonal along their whole length, (c) root-like hydrorhizae, (d) tubular thecae with basal parts embedded in stems and branches of colony, (e) thecae regularly arranged, (f) free part of theca diverging from stem and branches, or (g) distal part of theca embedded up to aperture in stems and branches, and (h) the same diameter of distal parts (0.05-0.4 mm in Inocaulis and 0.15-04 mm in Grammaria. Moreover, the differentiation in morphology within these genera is so similar that it is possible to find fossil equivalents for modern species of Grammaria among those of inocaulids. The species G. immersa Nutting, I. simplex Ruedemann and G. stentor Allman, I. arborescens Ruedemann may serve as examples. In discussing the two genera it is even possible to state that their hydrosomes display no morphological features which would question their congeneric nature. I suppose, however, that in the light of gap in their records, extending from the Devonian to the present times, it will be more appropriate to treat them as separate taxa. I confine the range of the family Inocaulidae to the genus Inocaulis Hall. |
| Fig. 2. Recent species of the genus Grammaria Stimpson: a Grammaria immersa Nutting, B Grammaria stentor Allman. After Naumov from Mierzejewski. |
| Based on: Mierzejewski, P. 1986. Ultrastructure, taxonomy and affinities of some Ordovician and Silurian organic microfossils. - Palaeontologia Polonica 47, 129-220. |
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| GRAPTOLITE NET is editted and periodically updated by Piotr Mierzejewski, the Count of Calmont & Countess Maja A. Korwin-Kossakowska since 2002 |
| - Inocaulis and the graptolite order Inocaulida - ___________________________________________________ |
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| updated July 25, 2005 |
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