Finite element, occlusal, microwear and microstructural analyses indicate that conodont microstructure is adapted to dental function

Abstract

Conodonts constitute the earliest evidence of skeletal biomineralization in the vertebrate evolutionary lineage, manifest as a feeding apparatus of tooth-like elements comprised of enamel-and dentine-like tissues that evolved in parallel with these canonical tissues in other total-group gnathostomes. As such, this remarkable example of evolutionary parallelism affords a natural experiment in which to explore the constraints on vertebrate skeletal evolution. Using finite element analysis, informed by occlusal and microwear analyses, we tested the hypothesis that coincidence of complex dental function and microstructural differentiation in the enamel-like tissues of conodonts and other vertebrates is a consequence of functional adaptation. Our results show topological co-variation in the patterns of stress distribution and crystallite orientation. In regions of high stress, such as the apex of the basal cavity and inner parts of the platform, the crown tissue comprises interwoven prisms, discontinuities between which would have acted to decussate cracks, preventing propagation. These results inform a general occlusal model for platform conodont elements and demonstrate that the complex microstructure of conodont crown tissue is an adaptation to the dental functions that the elements performed.

Evolutionary convergence in conodonts revealed by Synchrotron-based Tomographic Microscopy

“…Functional analyses have advanced to an extent where conodont taxonomy, based on dental morphology, can be interpreted in terms of feeding ecology (Jones et al, 2012a(Jones et al, , 2012bPurnell and Jones, 2012;Martínez-Pérez et al, 2014a, 2014b, 2016Murdok et al, 2014). This opens the possibility of interpreting the conodont fossil record as a detailed and comparatively complete record of the evolution of feeding ecology through much of the Phanerozoic, including across some of the most dramatic ecological and environmental crises that have impacted animal life, such as the end-Ordovician, Frasnian-Fammenian, Hangenberg, and PermianTriassic mass extinction events.…”

There is no general model for occlusal kinematics in conodonts

“…; Martínez‐Pérez et al . ) and demonstrated in the P 1 elements of all other species investigated, culminating in what has been considered a general occlusal model (Jones et al . ; Martínez‐Pérez et al .…”

“…), and the molariform gnathodids Idiognathodus and Gnathodus (Purnell ; Donoghue & Purnell ,b; Martínez‐Pérez et al . ). Indeed, the gnathodids evolved from the Ozarkodina lineage, elaborating the morphology of the P 1 elements from simple blade dorsal (‘posterior’) and ventral (‘anterior’) processes to possess a dorsal molariform occlusal platform.…”

“…; Martínez‐Pérez et al . ). Testing the generality of this functional interpretation is limited because occlusal kinematics can be studied only in elements from articulated skeletal remains of single individuals, which are scarce and rarely occur in the abundance required for destructive analysis (e.g.…”

Testing hypotheses of element loss and instability in the apparatus composition of complex conodonts: articulated skeletons ofHindeodus

“…Increasingly, functional morphology of the elements and patterns of damage and wear are being used to interpret aspects of the ecology and feeding of conodonts (Purnell & von Bitter ; Purnell, ; Donoghue & Purnell ; Purnell & Jones ; Martínez‐Pérez et al . , ) and these too are underpinned by knowledge of the arrangement of elements in the feeding apparatus. Direct evidence of skeletal anatomy comes from fossils that preserve together the articulated remains of the conodont apparatus, either collapsed onto a bedding plane or as clusters of elements in which juxtaposed and overlapping elements have been fused together by diagenetic minerals.…”