Archaeotolithus Stolley, 1912

Schwarzhans, Werner & Keupp, Helmut, 2022, Early teleost otolith morphogenesis observed in the Jurassic of Franconia, Bavaria, southern Germany, Zitteliana 96, pp. 51-67 : 51

Genus Archaeotolithus Stolley, 1912

Type-species.

Designated here as Archaeotolithus trigonalis Stolley, 1912. Stolley (1912) established Archaeotolithus as an otolith-based genus, or, in his words, as a new “typus” (typ. nov.). He may have been considering Archaeotolithus to represent a collective group genus comparable to Otolithus as introduced by Koken (1884; see Schwarzhans 2012 in Addendum). However, we are of the opinion that the otoliths Stolley attributed to Archaeotolithus indeed represent a very specific and unique morphology, and, therefore, a formal otolith-based genus for this pattern is well-justified. This point also generates the need to select a type-species for the redefined otolith-based genus of Stolley (1912), which we represent here.

Diagnosis.

Otoliths with a triangular shape that can reach about 7 mm in length. The three corners are the preventral, postventral and middorsal angles. Inner face convex; outer face flat, often with fine radial furrows starting from the middorsal angle. Otolith nucleus distinctly eccentric, visible on the outer face at the middorsal angle. Inner face with distinctly supramedian sulcus with often vague margins, particularly its ventral margin. Ostium and cauda intergrading and poorly distinguished. Ostium open anteriorly, its ventral margin deeply expanding downward. Cauda narrower, slightly downward-oriented toward posterior, and terminating close to posterior tip of otolith. No dorsal depression or ventral furrow.

Species, distribution and stratigraphic ranges.

Three species are referred here to Archaeotolithus : A. bornholmiensis (Malling & Grønwall, 1909) from the Pliensbachian of the isle of Bornholm, Denmark, and Franconia; A. doppelsteini sp. nov. from the late Pliensbachian of Franconia; and A. trigonalis Stolley, 1912 from the late Pliensbachian of Franconia and the Bajocian of northern Germany. Malling and Grønwall (1909) also reported two additional, presumably Archaeotolithus , otoliths from the Pliensbachian of Bornholm in open nomenclature, which cannot be identified from their documentation.

Relationships.

The relationships of Archaeotolithus are obscure. We are not entirely certain whether it represents a sagittal otolith, although this appears likely because of the presence of a sulcus on what is perceived as the inner face of the otoliths, or a lapillus. In any case its peculiar and highly characteristic morphology does not relate to that of any known teleost.

Three kinds of vaguely similar otoliths have also been reported from the Late Jurassic freshwater sediments of eastern Australia ( Schwarzhans et al. 2019). This Lagerstätte is of interest because it bears four taxa of pholidophoriforms, one macrosemiiform and one chondrostean in addition to the most common fish, Cavenderichthys talbragarensis (Woodward, 1895), a “primitve” teleost. Otoliths in situ are only known from the latter, probably due to a function of its overwhelming abundance ( Schwarzhans et al. 2019). It thus appears likely that the three Australian Archaeotolithus look-alike morphotypes belong to pholidophoriforms instead of chondrosteans (palaeonisciforms) as suggested by Schwarzhans (2018). Indeed, the Archaeotolithus morphotype best resembles the otoliths of extant lepisosteiforms (for figures, see Nolf 2013 and Schwarzhans et al. 2019). Therefore, the most likely candidates for relationships with Archaeotolithus may be expected in Ginglymodi or very basal Teleostei below the Leptolepidiformes level. We hope that otoliths will eventually be found in situ and this enigmatic otolith morphology can be reliably related to a systematic context.