Description: Horseshoe-shaped strongly birefringent ceratolith, with c-axis perpendicular to length. Arms variable in length and in degree of keel development.

Remarks: As noted in the generic description, ceratoliths show very consistent morphology in terms of asymmetry and pattern of development of ridges and teeth. Nonetheless, individual ceratoliths are highly variable in size and degree of ornamentation which has lead to discrimination of several “species”. In particular the forms telesmus and simplex appear to be simply more and less ornate forms of cristatus whilst rugosus appears to be an irregular variant as a result of poor preservation. The rostratus type of ceratolith is a highly ornate form common in modern assemblages.

NB The heterococcolith stage - Ceratolithus cristatus Kamptner, 1950 HET is described on a separate page.

Original description:

Synonyms/Variants

• Ceratolithus rugosus Bukry and Bramlette, 1968 - ceratolith with thick arms and irregular form. These are almost certainly simply overgrown C. cristatus specimens. They are mostly recorded from the Pliocene but, as argued by Bergen (1984), this is probably a function of preservation being worse in older sediments.
• Ceratolithus simplex Bukry, 1979 - small, smooth form. This morphotype occurs throughout the range of C. cristatus and in modern assemblages.
• Ceratolithus separatus Bukry, 1979 - both arms slightly extended beyond the arch, a moderately ornamented form. This morphotype occurs in modern assemblages and is not obviously discrete from normal C. cristatus.
• Ceratolithus cristatus var. telesmus (Norris, 1965) Jordan and Young, 1990 [Cr. telesmus] - variety with long sinuous arms. Range: NN16 to 21, but possibly becomes more common in younger samples.
• Ceratolithus cristatus forma rostratus Borsetti & Cati 1976 [NB this form was not given a formal description and so is invalid]. Ceratolith with high keels and with the rodded keel of the right hand arm extended into an apical beak/rostrum.

Description: Left arm extends into apical spur producing a triangular apical area. Right arm longer than left.

Remarks:

Original description:

Variants:

C. acutus Gartner and Bukry, 1974 - C.armatus and C.acutus were both described in 1974 from Indian Ocean sediments of Early Pliocene age (zone NN12, Sites 242 and 214 respectively). The holotypes, and paratypes, of the two species are very similar. The C. armatus specimens have slightly longer arms and more distinct ornament, but this is almost certainly a result of the much better preservation at Site 242. They are clearly synonyms, and probably not worth distinguishing, even at varietal level. According to the publication dates C. armatus has two months priority (May 1974 vs. July 1974). Nonetheless, several authors use both species.

C. larrymayeri Backman & Raffi, 1998, in Raffi et al. 1998 - this is a delicate variant of C. acutus with elongate arms. It appears to me to be an extreme variant of C. acutus but may prove to be a separate species.

Description: Simple form with short arms, broad arch and weakly developed keels.

Remarks:

Original description:

Description: Ceratoliths non-birefringent or only weakly birefringent. The c-axis is perpendicular to the plane of horseshoe, but spines on the surface may result it in being tilted from the horizontal and so showing some birefringence, but birefringence is lower than in Ceratolithus and extinction is rarely exactly in line with axis of the ceratolth.

In the SEM Amaurolithus ceratoliths (sometimes termed amauroliths) usually come to rest with the more ornamented surface upward, in this orientation the left hand arm is distinctly curved whilst the right hand arm is relatively straight, but more heavily ornamented.

Remarks: Raffi et al. (1998) documented likely evolutionary relationships between Ceratolithus and the fossil genera Amaurolithus and Triquetrorhabdulus. They presented evidence that A. delicatus, A. amplificus and C. acutus all independently evolved from Triquetrorhabdulus. Since this indicated that Amaurolithus was polypyhletic they proposed dividing the genus in two; Amaurolithus and Nicklithus.

Taxa included:

A. primus	A. delicatus	A. tricorniculatus	A. amplificus
Amaurolithus			Nicklithus

Original description: