Nature of the graptolite order Stolonoidea

by Piotr Mierzejewski
The order Stolonoidea has been proposed on the basis of material from the Tremadoc in the Wysoczki locality by
Kozlowski (1938) without diagnosis, next defined by Bulman (1938) and described adequately by Kozlowski (1949).
The stolonoid forms, fairly fragmentary and rare, are placed in  a single genus
Stolonodendrum Kozlowski,
comprising two species, i.e.
S. uniramosum Kozlowski, 1949 (type species)  and S. parasiticum Kozlowski, 1949.
     
Bulman (1970, p. V53) defined the Stolonoidea as follows: "Sessile or encrusting Graptolithina
composed essentially of stolothecae and ?autothecae; stolothecae containing an exaggerated
development of stolons dividing at irregular intervals and quite irregular in form".
Kozlowski (1949) regarded the Stolonoidea as a group of primitive graptolites, which developed independently of
other orders. In turn, Obut (1964) assumed that the Stolonoidea evolved from the same ancestors as dendroid
graptolites of the family Dendrograptidae. Urbanek (
in: KuĹşnicki & Urbanek 1967) noted that there are no
marked differences in the morphology of the Stolonoidea and the
Rhabdopleuroidea. Similarly the Stolonoidea
are characterized by the lack of apertural modifications, the presence of autho- and stolothecae, and a
perforational mode of budding. According to him "Stolonoidea presumably represent an offshoot which evolved
from a groups close to the Rhabdopleurida, independently of other graptolites, to form a tribe subjected to
minor modifications only" (Urbanek
in: KuĹşnicki & Urbanek 1967, p. 433).
The hypothesis of affiliation of the Stolonoidea to graptolites may be very seriously questioned in the light of
the present state of knowledge of fossil Rhabdopleurida. It should be noted that colonies of
Rhabdopleurites
primaevus
and Stolonodendrum parasiticum appear strikingly similar. The fragment of Stolonodendrum
parasiticum
colonies found hitherto have the form of branching creeping tubes. The tubes, initially nonfusellar,
gradually widen and smoothly pass into fusellar ones. Nonfusellar parts of the tubes were interpreted by KozĹ
‚owski (1949) as stolons and the fusellar - as thecae. Bulman (1955, 1970) also regarded Stolonoidea as graptolites
but ne noted that such smooth transition between stolon and theca is not known  in other graptolites. It is
worth noting here that such transition is also unknown in the
Rhabdopleuroidea.
I think that the known fragments of S. parasiticum colonies should be interpreted in an entirely different way
then in Kozlowski (1949). I regard the supposed stolons of this species as homologues to nonfusellar stolonal
tubes in
Rhabdopleurites primaevus and the supposed thecae to fusellar stolonal tubes in the latter. Therefore,
I do not regard
Stolonodendrum parasiticum as a primitive graptolite but rather a rhabdopleurid of the family
Rhabdopleuritidae.
The above interpretation of fragments of Stolonodendrum parasiticum colony makes it possible to assume that
stolons and zooidal tubes of that species are not represented in its type series. I think that stolons have been
independently described as such elements of
Stolonodendrum sp. A-F by Kozłowski (1949) and erect fusellar
parts served as the type material for describing the tuboid graptolite
Conitubus siculoides Kozlowski, 1949. The
stolons of
Stolonodendrum sp. A-F do not differ from those of Rhabdopleurites primaevus. In turn, the presence
of a nonfusellar part of periderm in tha basal part of "autotheca" and its transition into the creeping tube,
markedly smaller in diameter, were interpreted as characteristic morphological features of
Conitubus siculoides
Kozłowski (see Kozlowski 1949, fig 46b and pl 15, fig. 9). Doubts concerning the graptolitic nature of
Conitubus
siculoides
Kozlowski and some reservations in relations to the taxonomy of the genus Epigraptus Eisenack
(=
Idiotubus Kozlowski), put forward elsewhere (Mierzejewski 1978), show that it would be desirable to revise the
Tuboidea described by Kozlowski (1949).
Based on:

Mierzejewski, P. 1986.
Ultrastructure, taxonomy, and affinities of some Ordovician and Silurian microfossils.-
Palaeontologia Polonica 47, 129-220.
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