Portal of Graptolite and Pterobranch Hemichordates
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Graptolite Net | Graptolites & Graptoliters | Rhabdopleuroidea | Cephalodiscoidea | Crustoidea | Camaroidea | Tuboidea | Dendroidea | Graptoloidea
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DISCOVERY OF THE OLDEST REMAINS OF CRUSTOID GRAPTOLITES AND ITS PHYLOGENETIC
SIGNIFICANCE
PIOTR MIERZEJEWSKI, ADAM URBANEK and CYPRIAN KULICKI
North American Paleontology Convention 2005, Abstracts, pp. 48-49
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--------Crustoidea rea regarded as encrusting graptolites, morphologically intermediate between the extant
pterobranch Rhabdopleura and extinct Dendroidea. Recently, crustoid stolons have been etched from upper
Tremadoc chert nodules in Wysoczki (Poland) by Mierzejewski et al. (in press). This finding is very significant for
graptolite research because it sheds a new light on the budding patterns in graptolites and their evolution, extends
the lower stratigraphic range of Crustoidea from the Llandeilo to the upper Tremadoc, and clears up the puzzle of
the presence of graptoblasts in the upper Tremadoc. According to Kozłowski (1949, 1962), there are two main
lineages in the graptolite evolution leading from a common ancestors, namely: (1) Crustoidea > Dendroidea >
Graptoloidea and (2) Tuboidea > Camaroidea; lineage (1) is characterized by regular triad budding resulting in
alternating triads of autotheca, bitheca and stolotheca, whereas lineage (2) exhibits diad budding with no regular
succesion and variably distributed nodes. Kozłowski left open the question of what of mode budding and thecal
succesion has been adopted by the common ancestor of graptolites. Our observations make distinct disturbances in
Kozłowski's schemes of stolon system budding because the crustoid system is more complicated and somewhat
sophisticated than that in Dendroidea. The crustoid trifurcation in the material from Wysoczki is only apparent in
character and composed of two bifurcations following in rapid succesion: the first diad of "triad" forms due to
bifurcation of the parental stolothecal stolon into the very long descendant stolon and extremely short prezooidal
stolon, whereas the second diad bifurcates into the autothecal and bithecal stolons. Identical structures were
illustrated but not discussed by Kozłowski. At the present state of knowledge, it seems possible that the regular
triad succesion of thecae in Crustoidea and Dendroidea are different and highly specialized modes of budding.
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GRAPTOLITE NET
is edited and periodically updated by
Dr Piotr Mierzejewski, Count of Calmont
since 2002
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