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Acta Palaeontologica
Polonica 36, 265-323 (1991). Jerzy
Dzik Abstract.
The oldest
well-known conodonts had seven pairs of their phosphatic denticles arranged
into a grasping apparatus closely resembling that of the Chaetognatha. During
the Early Ordovician, apparatuses with three morphologic groups of elements
developed, and a single unpaired element that splits the apparatus into two
parts, the posterior one being presumably enclosed into the throat. Subsequent
evolution resulted in the development of an incisor-like morphology of the
anteriormost pair of elements, a filtratory basket in the remaining exposed
part of the apparatus, and a haevily molarized, hidden platform complex.
Further development resulted in great diversity of forms of the apparatuses,
from secondarily simplified, through robust (of the Myxine type), to
highly sophisticated apparatuses with all the element pairs being
morphologically distinctive. The unusual, ventral location of molarized
surfaces in some advanced conodonts suggests some change in muscular armament
of the throat. Conodonts reached their greatest diversity in the Middle
Ordovician. Co-occurrence of many morphologically similar sympatric species is
typical for the Late Paleozoic. A modified classification of the conodonts is
proposed. |