Architecture, growth, and function of ozarkodinid conodonts.
thesisposted on 19.11.2015, 09:04 by Philip Conrad James. Donoghue
Analysis of natural assemblages reveals that the architecture of the ozarkodinid conodont feeding apparatus remained conservative throughout two hundred million years of evolution. The apparatus was differentiated into an anterior array which performed a rasping and/or slicing function and its supporting structures were probably homologous to the dental cartilages of the living agnathans. The taphonomy of the apparatus indicates that the majority of natural assemblages represent carcasses that came to rest at a high angle to the sea floor, suggesting the presence of soupy substrates. Analysis of conodont hard tissue histology has led to a new model of element growth. This is used to reinterpret the affinity of the hard tissues themselves as opposed to the competing methodology which interprets the hard tissues first. Conodont elements are composed from numerous odontodes, and individual elements can be considered as odontocomplexes. Analysis of pattern formation in conodont element growth provides a new means of understanding these structures. The pattern of growth exhibited by many conodont elements is similar to that of the dentigerous jaw bones of acanthodians, and to that of lungfish toothplates. The periodic addition of odontodes to conodont elements provides a mechanism by which the paradox of growth and function may be resolved. The identification of internal discontinuities as representing episodes of function m the growth record of conodont elements indicates that the animal retained its feeding array throughout life rather than periodically shedding and replacing component elements. The functional morphology of pairs of elements dissected from natural assemblages reveals that, even though conodonts lacked jaws, some groups evolved a level of dental occlusion unrivalled before the rise of mammals, occurring in conodonts at least several tens of millions of years earlier. Comparison with the functional morphology of other taxa indicates that this level of occlusion was maintained by an additional unpreserved structure, comparable in function but not homologous to a jaw.