|Chaunograptus and the Dendroidea
|Chaunograptidae were initially defined as: "Free dendroid or irregularly branching encrusting rhabdosome with free
conical thecae" (Bulman 1955, p. V36). Bulman (1955) assigned to that family the following genera: Chaunograptus
Hall, Mastigograptus Ruedemann and Haplograptus Ruedemann. Chaunograptidae were initially treated as
graptolites of the Order Dendroidea. BouÄŤek (1956, p. 149) held a different point of view, stating that "it would be
better to treat these genera (and the family on the whole) for the present separately as dendroid graptolites
incertae sedis (or i. ordinis)". Subsequently, Obut (1964) allocated this family in the graptolite Order Dithecoidea
Chaunograptidae as interpreted by Bulman (1955) represent clearly artificial groups and as such they were later
treated (Bulman 1970) when he neglected this name and placed the genera previously allocated to the
Chaunograptidae in "Dendroidea, Tuboidea, Crustoidea, Camaroidea and Stolonoidea - taxonomic position uncertain".
|I presented (Mierzejewski 1986) a new concept of the Chaunograptidae and treated this family as Hydroidea,
assigning to it only the type genus with its junior synonyms (Desmohydra KozĹ‚owski and Epallohydra KozĹ‚owski).
The similarity of Chaunograptus to Hydroidea was indicated by Chapman (1919) and Bulman (1938); Ruedemann (1947)
regarded this genus as hydroid. The genus Chaunograptus, to which he assigned several species from the Cambrian,
Ordovician, Silurian and Devonian from various continents, is known from imprints and carbonized remains on rock
surfaces only. The species were assigned here taking into account similarities in shape of colony and tubular form of
thecae. Because of poor preservation, some hydroids, rhabdopleurids (Rhabdopleuroides KozĹ‚owski) or crustoid
graptolites could be described under that generic name. I do no doubt that this was often the case as
Chaunograptus has never been described on the basis of material chemically extracted from rocks and Desmohydra,
Epallohydra and Rhabdopleuroides - on the basis of imprints or carbonized remains. The lack of remains of
representatives of the three last-named genera preserved in a similar form as those of Chaunograptus is simply
improbable, so I suppose here a typical dualism in nomenclature used for a part of hydroids, rhabdopleurids and
crustoid graptolites. The origin of this may be explained in the following way: encrusting, irregularly branching colony
with thecae creeping on their whole length, when preserved as imprints or carbonized remains, used to be assigned
to the genus Chaunograptus, whereas the colony identical in shape and form of thecae, when extracted from rock
could be subjected to studied on morphological details and, therefore, assigned to Hydroida, Rhabdopleuroidea or
Crustoidea. It follows that Chaunograptus is one more "form-genus". The ordering of the taxonomy of species
assigned to this genus is therefore significant but troublesome. The significance of this question is connected with
the fact that several specific names of hydroids, rhabdopleurids and crustoids most probably are junior synonyms of
species of Chaunograptus and the troubles which may be expected in this taxonomical revision arerelated to
difficulties in comparing the specimens of individual Chaunograptus species and forms extracted by chemical
methods due to poor preservation of mictoanatomical details in the former.
|The congeneric character of species assigned to Chaunograptus is questionable, so the taxonomic position of that
genus mabe reconstructed on the basis of an analysis of its type species only. The type species, Ch. novellus (Hall)
from the Silurian of the USA, was originally defined as follows: "Fossils occuring free in the shales, or upon other fossil
bodies, in slender branching fronds. Branches diverging, lax and slender, with numerous branchlets, both marked by
numerous cellules which are usually indicated by the appearence of abrupt expansion and contraction of the
branches. The angular projection of the cell apertures can be observed in many parts of the fossil (Ruedemann 1947,
p. 254). The presence of expansions and contractions of branches and thecae (branchlets) is of marked significance
for discussion on systematic position of this form, as such shapes and thecae are found in neither graptolites nor
pterobranchs, but rather in various hydroids. When this is the case, the species Ch. novellus and thus, the genus
Chaunograptus should be treated as hydroid.
From Ordovician erratic boulders, KozĹ‚owski (1959) described the genera Desmohydra KozĹ‚owski and Epallohydra
KozĹ‚owski, differing in the presence or lack of short stalk of hydrotheca. The rank of this difference is to small for
discrimination the genera. In modern Thecaphora, a single genus may comprise species with hydrotheca seated or
with stalkes. Moreover, the two types of seating may be found even in a single species (e.g. in Thyroscyphoides
biformis Naumov). The type species of Desmohydra and Epallohydra appear strikingly similar to Chaunograptus
novellus. According to me, the names Desmohydra kozlowski, 1959 and Epallohydra Kozlowski, 1959 should be
treated as junior subjective synonyms of the name Chaunograptus Hall, 1883.
In this situation I proposed a new diagnosis of Chaunograptidae:
"Hydroida with encrusting, irregularly branching colonies; thecae creeping along their whole length" (Mierzejewski
1986, p. 163).
Mierzejewski, P. 1986. Ultrastructure, taxonomy and affinities of some Ordovician and Silurian organic microfossils. -
Palaeontologia Polonica 47, 129-220.