A review of Jurassic and Early Cretaceous otoliths and the development of early morphological diversity in otoliths

Teleostean otoliths from the Jurassic and Early Cretaceous represent the earliest records of its kind. They are here comprehensively and critically reviewed based on type material of many previous publications. In the course of the review, several established species are synonymized or are considered as of doubtful nature when they have been based on very small specimens, supposedly from juvenile fishes or on too poorly preserved specimens. New taxa are introduced in fossil otolith-based genera and new species, the latter mostly from previously unpublished material: Xenoleptolepis n. gen., Doggerichthys anguilliformis n. gen. et n. sp., Sphaeronchus rundlei n. sp., Apsopelix? berlinensis n. sp., Protoelops n. gen., Aulothrissus avitus n. gen. et n. sp., Aulothrissus heletzensis n. gen. et n. sp., Palealbula declivis n. sp., Palealbula depressidorsalis n. sp., Protalbula websteri n. sp., Archaeglossus torrensi n. gen. et n. sp., Bicavolithus cavatus n. gen. et n. sp., and Guimarotaichthys problematicus n. gen. et n. sp. Taxonomic allocation of these early teleostean otoliths suffer from the currently very limited knowledge of otoliths in situ. Most of the higher taxonomic allocations of these otoliths have to be considered as tentative and preliminary in the view of the large number of extinct skeleton-based teleost taxa at family and higher levels during the Mesozoic. These will only be resolved once more in situ calibrations of fossil otoliths have been achieved. The possible origin and first occurrence of the teleostean otolith pattern is briefly discussed. The earliest teleostean otoliths are found in the late Sinemurian (Early Jurassic), congruent with the first leptolepidid skeletons. The early teleostean otolith morphology is very uniform throughout much of the Jurassic and even Early Cretaceous, represented by the Leptolepis-type morphology as described and calibrated with one of the very few in situ finds known to date. The Leptolepis-type otolith morphology is found in all environments ranging from freshwater to deepmarine, and therefore, its uniformness likely represents a true phylogenetic signal. Its stratigraphical range coincides well with that of skeletal finds of the Leptolepidiformes and other stem teleosts. New otolith morphologies are first observed in the Bathonian (Middle Jurassic), but gradually gain importance only during Aptian and Albian (Early Cretaceous). First putative elopomorph and osteoglossomorph otoliths occur in the Bathonian and albuliforms in the Kimmerdigian (Late Jurassic), both slightly predating skeletal finds. Putative euteleostean otoliths are first recorded from the Aptian, which is congruent with the skeletal record.