Otoliths in situ in the stem teleostCavenderichthys talbragarensis(Woodward, 1895), otoliths in coprolites, and isolated otoliths from the Upper Jurassic of Talbragar, New South Wales, Australia

Abstract

Cavenderichthys talbragarensis (Woodward, 1895) is a common signature freshwater stem teleost in the Upper Jurassic of Australia. Our discovery of numerous otoliths in the Talbragar Fish Bed establishes Cavenderichthys as only the second known Jurassic teleost and the third known stem teleost with otoliths in situ and provides an important calibration point for the interpretation of isolated Mesozoic otoliths. It corroborates the low degree of morphological diversification of stem teleost otoliths. The abundance of otoliths (isolated, in coprolites and in situ) allows the mapping of ontogenetic effects and of intraspecific variability for the first time in attributable stem teleost otoliths. Here, we describe 284 otoliths, mostly from Cavenderichthys. Otoliths in situ in Cavenderichthys document the presence of sagitta, lapillus, and asteriscus. Three other, much rarer otolith types were also found that have a teleost otolith pattern more primitive than that of Leptolepidiformes; the origin of these is unknown, but it is likely that they stem from pholidophoriform fishes of the family Archaeomenidae. If confirmed, this otolith pattern would provide a further highly diagnostic and synapomorphic character to define teleosts at the level of the Leptolepidiformes and above. Different mineral replacement processes in fossils from the Talbragar Fish Bed aided us in finding many otoliths, particularly otoliths in situ. Given their abundance and distinct preservation, it is surprising that otoliths in the Talbragar Fish Bed have not been recognized before.

Early teleost otolith morphogenesis observed in the Jurassic of Franconia, Bavaria, southern Germany

“…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.…”

“…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 andSchwarzhans 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.…”

“…Weiler (1954) noted that the interspecific diversity might have been rather low in such "primitive" otolith morphologies and established a plethora of otolith-based species based on vague, minute morphological differences. Schwarzhans et al (2019) recent study of many otoliths, both in situ and in isolated otolith specimens from the late Jurassic Cavenderichthys talbragarensis, has indeed confirmed a low level of morphological diversity when compared with otoliths of the early Jurassic Leptolepis normandica; however, indications have also shown a "normal" level of intraspecific variability. In conclusion, these observations do not support the excessive number of species described by Weiler.…”

“…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).…”

The taphonomic clock in fish otoliths

“…In contrast to molluscan shells that rapidly accrue damage, resulting in even young specimens appearing old, otoliths can be better preserved. At least some otoliths are deposited through predator feces (Martini 1965; Schwarzhans et al 2018) (Fig. 9).…”