Polymorphic organization in a planktonic graptoloid (Hemichordata: Pterobranchia) colony of Late Ordovician age

Zalasiewicz, Jan; Page, Alex; Rickards, R. B.; Williams, Mark; Wilby, Philip R.; Howe, Michael P. A.; Snelling, Andrea M.

doi:10.1017/s0016756812000349

Cited by 5 publications

(5 citation statements)

References 39 publications

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“…Furthermore, planktonic graptolite colonies may have experienced long post‐mortem drifts before their arrival at the sea floor (Underwood ; Zalasiewicz et al . ).…”

Section: Discussionmentioning

confidence: 97%

Fossilization processes of graptolites: insights from the experimental decay of Rhabdopleura sp. (Pterobranchia)

2017

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Laboratory experiments documenting the decomposition pattern of extant organisms are used to reconstruct the anatomy and taphonomy of fossil taxa. The subclass Graptolithina (Hemichordata: Pterobranchia) is a significant fossil taxon of the Palaeozoic era, represented by just one modern genus, Rhabdopleura. The rich graptolite fossil record is characterized by an almost total absence of fossil zooids. Here we investigated the temporal decay pattern of Rhabdopleura sp. tubes, stolons and single zooids removed from the tubarium. Tubes showed decay after four days, when fuselli began to separate from the tube walls. This rapid loss may explain the absence of fuselli from some graptolite fossils. The black stolon did not show decay until day 155. One day after their removal, zooids quickly decomposed in the following temporal sequence: (1) tentacles; (2) ectoderm; (3) arms; (4) gut; (5) cephalic shield, leading to complete disappearance of recognizable body parts in the majority of experimental zooids within 64-104 h. The most resistant zooid features to decay (61 days) were black-pigmented granules. These results indicate that tubes and the black stolon would persist for weeks across death, transport and burial, whereas a complete decay of zooid features occurs in few days, providing an explanation for the overall poor record of fossil graptolite zooids and suggesting that recorded silhouettes of fossil zooids may be attributed to fossil decay-resistant pigments.

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“…Furthermore, planktonic graptolite colonies may have experienced long post‐mortem drifts before their arrival at the sea floor (Underwood ; Zalasiewicz et al . ).…”

Section: Discussionmentioning

confidence: 97%

Fossilization processes of graptolites: insights from the experimental decay of Rhabdopleura sp. (Pterobranchia)

2017

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“…) and in graptolites from the Late Ordovician strata of southern Scotland (Zalasiewicz et al . ) and has been used for taphonomic analyses.…”

Section: Discussionmentioning

confidence: 99%

Decay and mineralization of soft tissue in Early Devonian boring ctenostome bryozoans

Olempska

2016

LET

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The Early Devonian of Podolia, Ukraine, has yielded phosphatized colonies of the boring ctenostome bryozoan Podoliapora doroshivi with 3‐D preservation of soft tissues. However, the feeding zooids are not anatomically complete, their preserved soft tissues comprising decay‐resistant structures such as the protective cuticular polypide sacs with presumed parietal muscles inside the wall of the sacs, the setigerous collars, the membranous orificial walls and remains of the muscle tissues. Early diagenetic apatite mineralization occured in numerous feeding zooids of Podoliapora at different stages of decay and may be important for the interpretation of decay processes in these colonial soft‐bodied fossil organisms. A setigerous collar, which is a characteristic of extant ctenostomes, occurs in P. doroshivi in several stages of decay showing progressive collapse and eventual complete loss. This study indicates that the morphological changes of collars induced by decay often resulted in connection with the membranous orificial wall, producing false anatomical structures, unrelated to structures observed in the earlier stages of decay or to the anatomical structures of extant ctenostomes. The most decay‐resistant cuticular polypide sacs mineralized as cryptocrystalline apatite in early stage of decay became degraded in later stages of decay. These data provide evidence that the anatomical interpretation of soft‐bodied fossils preserved only in the later stages of decay may have led to imprecise morphological interpretations.

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“…A stolon system is not preserved in isolated specimens of the planktic Rhabdinopora flabelliformis described by Legrand (1974), suggesting that it may have been only weakly, if at all, sclerotized and was not preserved. Zalasiewicz et al (2013) discussed a 'stolonlike system' in the planktic graptoloid Dicranograptus aff. ramosus as an abnormal recalcitrant pectocaulus or a stolonlike system.…”

Section: The Graptolite Stolon Systemmentioning

confidence: 99%

“…3D, F, G) show the organic remains of their tubaria strongly affected by parallel fractures indicating considerable tectonic deformation. The majority of the fossil described by Zalasiewicz et al (2013) represents remains of pressure shadow minerals (cf. Underwood 1992) in a poorly preserved and strongly tectonized graptolite.…”

Section: The Graptolite Stolon Systemmentioning

confidence: 99%

Hemichordata (Enteropneusta & Pterobranchia, incl. Graptolithina): A review of their fossil preservation as organic material

Maletz¹

2020

Bull. Geosci.

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Fossil preservation has been discussed at length in nu merous publications, but still many details are unclear or have not been considered. It is usually discussed in relation to individual fossil groups (e.g. bacteria, brachiopods, graptolites, plants, trilobites, vertebrates) or types of fossil lagerstätten (cf. Seilacher 1970). In the Hemichordata, the preservation of the fossils is especially important, as the involved materials differ considerably between the two groups, the Enteropneusta (Fig. 1A) and the Pterobranchia (Fig. 1B-D).The results found in the fossil preservation are often interpreted from the visual aspects of the fossils only, and without consideration of the composition and reaction of the various materials involved in the decay processes and the subsequent fossilization processes over millions of years. Also a differentiation of originally preserved organic material and replacement of this due to later processes is often not considered. Briggs (2003) suggested replication of the morphology by rapid in situ growth of minerals as essential to preserve labile tissues, which means the loss of the original organic material through geological processes and replacement by secondarily formed minerals.Decayretardation during early biostratinomic proces ses may increase the potential for the preservation of fossils, not just in organically preserved material, but also in mineralic skeletons or shells. Important changes, however, modify the fossils considerably during later geological processes. To gain insight into the preservation of fossils it is necessary to consider the changes through these geological processes and to understand the various paths necessary to produce the final results, to see what happens to materials during numerous geological processes in Earth history. The fossilization of the Hemichordata may serve as a very important and useful example here.

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Polymorphic organization in a planktonic graptoloid (Hemichordata: Pterobranchia) colony of Late Ordovician age

Cited by 5 publications

References 39 publications

Fossilization processes of graptolites: insights from the experimental decay of Rhabdopleura sp. (Pterobranchia)

Fossilization processes of graptolites: insights from the experimental decay of Rhabdopleura sp. (Pterobranchia)

Decay and mineralization of soft tissue in Early Devonian boring ctenostome bryozoans

Hemichordata (Enteropneusta & Pterobranchia, incl. Graptolithina): A review of their fossil preservation as organic material

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