Feeding mechanisms and ecology of pycnodont fishes (Neopterygii, Pycnodontiformes)

Abstract

The functional morphology of the jaw apparatus and the skull and the feeding habits of the extinct pycnodont fishes arc reconstructed in comparison with some extant halecostomes. For this, a short review of the functional units of the pycnodont head is given. The feeding mechanisms of pycnodonts exhibit a transition from simple stcrcotypic feeding kinematics. which are characteristic for primitive actinopterygians, to the modulating feeding kinematics of advanced teleosts and is called limited modulating fccding kinematics herein. Two structural specialisations which are found in halecostomes (operculum with distinct ni. levator operculare and the interopercular bone with the interopercular ligament) are supposed to be absent i i i pycnodonts, whereas they maintain the two primitive couplings for direct mandibular depression (epaxial muscles -neurocraniunr. hypaxial muscles -cleithrum-ni. sternohyoideus -hyoid apparatus). Advanced pycnodonts developed a new structure (upper jaw protrusion resulting in an enlargment of the buccopharyngeal cavity), that is absent in halecomorphs (e.g., h i i i r r cnlvn) and basal pycnodonts (e.g.. tArdunfrons, tMesturzis). The premaxillae and maxillae are firmly fixed in basal pycnodonts, whereas the premaxillac and maxillae are free and movable in advanced pycnodonts. Pycnodonts were benthic foragers with a combination of biting or nipping and suction feeding based on the "truncated cone morphology" of the buccopharytigcai cavity. 11 is concluded. that pycnodonts certainly were omnivorous leeders with a general broad range of prey. But they wcrc also a highly specialised group on generic level in respect to their prey. This is indicated by gut contents, as far as thcy are known. which comprise only monospecific remains of shelled invertebrates (e.g., spines of echinoderms. shells of bivalves). The ecological dcmands of pycnodonts are discussed.Keg words: Neopterygii, Pycnodontiformes, fccding, gut contents, ecology. ZusammenfassungDie funktionelle Anatoinie des Nahrungsaufnahmeapparates sowie das Fressverhalten der seit dem Eozan ausgestorbenen Neopterygier-Gruppe der Pycnodontier wird im Vcrgleich zu einigen rezenten Halecostomen (Amin cnlvn. verschiedene Teleosker) untersucht und diskutiert. Dazu wird cine kurze Ubersicht iiber die funktioncllen Einheiten des Pycnodonticrschiidels gegeben. Die Kirrcmatik des Nahrungsaufnahmeappat-ates der Pycnodontier stellt einen Ubcrgang von der einl~iclren. stereotypischcn Kinematik primitiver Actinopterygier z u der modulierenden Kinematik fortschrittlicher Teleosteer dar tind wird hier als limitierte, modulierende Kinematik bezeichnet. Zwei structurellc Spezialisationen, die bei Halecostonii cntwckelt sind (Operculum mit distinkten m. levator operculare und das Interoperculare mit dem interuperculare Ligament) fclrlen bci Pycnodontiern, wogegcn sie die zwei primitiven Verbindungen zwischen den epaxialen Muskeln und dein Neurocranium und zwischen den hypaxialen Muskeln, dem Cleithrum und dcm Sternohyoidmuskel fur die direkte Unterk...

Njoerdichthys dyckerhoffi gen. et sp. nov. (Pycnodontiformes, lower Turonian) northward migration caused by the Cretaceous Thermal Maximum

“…The Late Cretaceous, beginning with the Cenomanian, witnesses further expansion eastwards for the pycnodonts as they appear in high diversity and disparity in Lebanon, displaying their highest disparity in their evolutionary history ( Marramá et al, 2016 ; Cawley and Kriwet, 2019 ). They also migrated further south, where pycnodonts occurred in what now is Croatia, Tunisia, Egypt, Ecuador and Brazil ( Agassiz, 1833–1844 ; Weiler, 1935 ; Leonardi, 1966 ; Kriwet, 2001a , c ; Machado and Brito, 2006 ; Taverne et al, 2015 ). This is by far the widest range in the distribution of pycnodonts during the Cretaceous.…”

A new pycnodont fish,Scalacurvichthys naishigen. et sp. nov., from the Late Cretaceous of Israel

“…Deposition of the finely laminated limestones is considered to have been in a structured, near-coastal area characterized by reefs with interspersed lagoons, and pycnodontiform fishes mainly occupied such habitats (e.g. Kriwet 2001a, b). Consequently, we assume that Scalacurvichthys naishi gen. et sp.…”

“…This kind of dentition is considered characteristic for pycnodonts (e.g. Kriwet 2001a; Poyato-Ariza & Wenz 2002; Nursall 2010). Many taxa were most likely durophagous, consuming heavily armoured invertebrates such as crustaceans and gastropods.…”

Late Triassic pycnodont fish remains (Neopterygii, Pycnodontiformes) from the Germanic basin

“…Although much progress has been made in the last years to establish dental characters of different taxa (e.g. Kriwet 1999, 2000a, 2000b, 2001b, 2002, Kriwet et al 1997) a lot of important data from comparable many taxa is still lacking. In addition, the prearticular dentition of the contemporaneous pycnodont Gibbodon is unknown.…”