Abstract
Conodonts are the first vertebrates to bear a mineralized skeleton, restricted to an array of tooth-like feeding elements. The functional implications for the development of tooth-like elements differentiated into two tissues is tested using 2D finite element modeling, mapping the patterns of stress and strain that elements with differing material properties exhibited during function. Addition of a stiff crown does not change the patterns of stress, rather it reduces the deformation of the element under the same force regime, and distributes stress more evenly across the element. The euconodont crown, like vertebrate dental enamel, serves to stiffen the element and protect the underlying dentine. Stiffness of the crown may be a contributing factor to the subsequent diversity of euconodont form, and logically function, by allowing a greater range of feeding strategies to be employed. The euconodont crown also serves as an analogue to enamel and enameloid, demonstrating that enamel-like tissues have evolved multiple times in independent vertebrate lineages, likely as a response to similar selective pressures. Conodonts can, therefore, serve as an independent test on hypotheses of the effect of ecology on the development of the vertebrate skeleton.
Highlights
Conodonts are an extinct group of eel‐like jawless vertebrates, the earliest known members of the gnathostome lineage (Donoghue et al 2000), and bear the earliest manifestation of a mineralized skeleton in vertebrates
Though conodonts may not be integral to the evolutionary origin of the skeleton inherited by living jawed vertebrates, they constitute a remarkable natural experiment in the evolution of a dental organogenic module, which precisely parallels that of their sister, gnathostome, lineage
Lower basal cavities, such as those seen in the paraconodont Furnishina and the euconodont P. serratus, allow stress to be distributed more evenly, and the stiffness of the functional surface reduces the strain experienced under equivalent loads
Summary
Conodonts are an extinct group of eel‐like jawless vertebrates, the earliest known members of the gnathostome lineage (Donoghue et al 2000), and bear the earliest manifestation of a mineralized skeleton in vertebrates. Conodont dental elements have long been interpreted as the earliest instance of the “odontode” skeletal patterning unit that characterizes the teeth and scales of total‐ group gnathostomes (Donoghue 1998), inspiring the hypothesis that teeth evolved before, and perhaps even independently of dermal scales (Smith and Coates 1998). Are a unique resource in which to test this hypothesis since, though there is evidence for the independent recruitment of enamel‐like tissues to teeth in distinct lineages of gnathostomes (Donoghue 2001), the gradual evolutionary assembly of euconodont dental elements is well documented in the fossil record (Murdock et al 2013). In exploring the functional context of the evolutionary assembly of the canonical suite of enamel‐ and dentine‐like dental tissues that characterize the euconodont dental organogenic module, we aim to obtain general insights that are relevant to understanding the evolutionary origin of this model organogenic system in gnathostomes
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