Ruedemann (1947) established graptolite family Inocaulidae allocating in it the genera Inocaulis Hall, Thallograptus
Ruedemann, Medusaegraptus Ruedemann and Diplospirograptus Ruedemann. BouÄŤek (1957) excluded the genus
Thallograptus from that family, allocated the genus Palmatophycus BouÄŤek, 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" (BouÄŤek 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 ďżż"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. KaĹşmierczak (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 BouÄŤek, actually originally described as an alga (BouÄŤek 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
|- Inocaulis and the graptolite order Inocaulida -