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Ceratolithaceae and Triquetrorhabdulaceae

The Ceratolithaceae and Triquetrorhabdulaceae are a rather rare but biostratigraphically valuable pair of nannolith families (see also Neogene range chart). Relationships between them were postulated by several authors and demonstrated by Raffi et al. (1999). The Triquetrorhabdulaceae are extinct (range - Late Oligocene to early Pliocene) but the Ceratolithaceae are extant (range - Late Miocene to Recent). Combination coccospheres indicate that the Ceratolithaceae have a complex life cycle producing in addition to Ceratoliths (horseshoe-shaped nannoliths) two types of heterococcolith - hoop coccoliths and planoliths (formerly assigned to the genus Neosphaera). References Alcober and Jordan 1997, Young et al. (1998), Sprengel and Young (2000).

CERATOLITHACEAE

Informal taxon-based term: Ceratolith - dibrachiate nannoliths formed by the Ceratolithaceae. Includes Amaurolithus nannofossils; does not include the hoop-shaped exothecal heterococcoliths, or the planoliths formed during the alternate life-cycle phase.

Orientation:

Upper / lower The more-ornamented surface is designated upper. This division is arbitrary, but it is useful since there is a consistent polarity to structures. With careful through-focussing it is quite possible to distinguish the two sides by light microscopy. N.B. The terms distal/proximal should not be used since ceratoliths appear to be either intracellular or wrapped around the cell (Norris 1965).
Anterior / posterior Closed end is designated anterior.
Left /right Based on upper view, looking toward anterior end.

ceratolith terms

2. Parts

Apical region anterior end of ceratolith, hence terms such as apical node.
Arch part of apical region connecting the two arms.
Arm rod-like extension back from apical region.
Rod rod-shaped structure attached to the nannolith, (e.g. Amaurolithus bizarrus).
Spur projection from apical region.
Keel lath-like structure running along an arm. Types:
Dentate keel - keel formed of sub-parallel teeth.
Smooth keel - keel without teeth.
Tooth rod-like sub-element of a keel.
Wing plate-like extension from main body of nannolith (e.g. Amaurolithus ninae).

TRIQUETRORHABDULACEAE

 Orientation: There is no obvious proximal/distal differentiation.
Longitudinal parallel to length of nannolith.
Transverse perpendicular to length of nannolith.
Blade one of the three main sub-parts of the nannolith.
Dentate blade blade with transverse sub-structure of rod-shaped teeth.
Lateral blade one of two broader blades nearly in the same plane (e.g. T. rugosus)
Median blade narrowest of three blades.
Ridge subsidiary longitudinal structure on a blade. E.g. T. challengeri.
Wing blade greatly extended in transverse direction. E.g. T. finifer.
Tooth rod-like part of a dentate blade.

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