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Pellets independent of or associated with Bohemian Ordovician body fossils

100%

Bruthansova J., Kraft P.

Acta Palaeontologica Polonica

2003

tom 48

nr 3

Clusters of small cylindrical pellets occur sporadically in Ordovician strata in Bohemia. They are assigned to the ichnogenus Tomaculum and occur in lenticular or elongated accumulations. Similar accumulations are associated with body fossils including the cephala of the trilobites Ormathops atavus, Pricyclopyge binodosa, and Parabarrandia crassa. The clusters are situated under the glabella and in the anterior parts of the cephalon but their exact position is variable in different cases. Accumulations of pellets have also been studied inside shells of hyoliths, bellerophontids, and echinoderm thecae. They probably represent the faeces of either scavengers feeding on soft parts or organisms using cephalic shields and other shells as hiding places. An interpretation of these pellets as trilobite eggs is highly improbable.

New evidence for the protoconodont origin of chaetognaths

100%

Szaniawski H.

Acta Palaeontologica Polonica

2002

tom 47

nr 3

An earlier hypothesis concerning the origin of chaetognaths from protoconodonts found additional support in new discoveries and in recent structural, chemical and molecular investigations. The new findings show that the head armature of protoconodonts was composed not only of grasping spines but also of much smaller spicules corresponding in size and shape to the chaetognath teeth. Grasping spines of protoconodonts were originally built mainly of an organic substance. Their original composition was changed by secondary phosphatisation. The thickest layer of the protoconodont spines was originally constructed of organic fibrils, similar to those in the corresponding layer of chaetognaths. Recent molecular investigations show that the chaetognath lineage separated in the early stage of metazoan radiation, which fits the presented hypothesis. Described are some previously unknown structural details of chaetognath grasping spines, including composition of the outer layer and the origin of their distinctive tips.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Bruthansova J.

1 Kraft P.

1 Szaniawski H.

1 2003

1 2002

Wyniki wyszukiwania

Pellets independent of or associated with Bohemian Ordovician body fossils

New evidence for the protoconodont origin of chaetognaths