Shape-preserving erosion controlled by the graded microarchitecture of shark tooth enameloid

Abstract

The teeth of all vertebrates predominantly comprise the same materials, but their lifespans vary widely: in stark contrast to mammals, shark teeth are functional only for weeks, rather than decades, making lifelong durability largely irrelevant. However, their diets are diverse and often mechanically demanding, and as such, their teeth should maintain a functional morphology, even in the face of extremely high and potentially damaging contact stresses. Here, we reconcile the dilemma between the need for an operative tooth geometry and the unavoidable damage inherent to feeding on hard foods, demonstrating that the tooth cusps of Port Jackson sharks, hard-shelled prey specialists, possess unusual microarchitecture that controls tooth erosion in a way that maintains functional cusp shape. The graded architecture in the enameloid provokes a location-specific damage response, combining chipping of outer enameloid and smooth wear of inner enameloid to preserve an efficient shape for grasping hard prey. Our discovery provides experimental support for the dominant theory that multi-layered tooth enameloid facilitated evolutionary diversification of shark ecologies.

Forced Biomineralization: A Review

“…Our review of numerous recent scientific publications on biomineralization has revealed emphasis of the overall scientific attention towards calcification [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ], biosilicification [ 14 , 15 , 16 ], biomagnetism [ 17 , 18 ], and multiphase biomineralization [ 19 , 20 , 21 , 22 , 23 ]. Traditional objects of study continue to include molluscs [ 24 , 25 , 26 , 27 , 28 ], sea urchins [ 29 ], and skeletal structures such as eggshells [ 30 ], teeth [ 31 , 32 ], and bones [ 33 , 34 , 35 , 36 ]. While it is understandable to focus on the biomineralizing organisms typically encountered by humans on Earth, this focus tends to overlook a variety of distinct biomineralization pathways seen in extremophiles.…”

High Resolution Nanostructure with Two-stages of Exponential Energy Dissipation at the Ultrathin Osteochondral Interface Tissue of Human Knee Joint

“…32 The exponential profile of interface tissues, together with porosity and mineral crystallinity differences, are considered to be the key factors in arresting cracks between the mechanically dissimilar materials. 31,60 FEA results further validate the superiority of exponential profile of tissue modulus in facilitating force transfer. The nanoscale heterogeneity of minerals also contributes to the toughing mechanism of interface tissues.…”

A new cuspidate ptychodontid shark (Chondrichthyes; Elasmobranchii), from the Upper Cretaceous of Morocco with comments on tooth functionalities and replacement patterns

“…imbricated dentitions), redirecting the bite-loads to specific areas of the dentition and improving their overall stability ( Nobiling, 1977 ; Ramsay and Wilga, 2007 ; Huber et al, 2009 ; Shimada, 2012 ; Crofts, 2015 ). Moreover, cuspidate teeth of extant and extinct elasmobranchs can be extremely useful in grasping prey ( Summers et al, 2004 ; Ramsay and Wilga, 2007 ; Dean et al, 2008 ; Huber et al, 2009 ; Shimada et al, 2009 ; Amadori et al, 2019b ; Amini et al, 2020 ). The relevance of dental cusps (e.g.…”

“…Elasmobranch dentitions represent a peculiar object for studying the evolution of teeth in which a wide range of functionally demanding diets and the ability to continuously renew teeth during lifetime coexist (see Botella et al, 2009 ; Cappetta, 2012 ; Maisey et al, 2013 ; Belleggia et al, 2014 ; Underwood et al, 2015 ; Amadori et al, 2020a ; Amini et al, 2020 ). The regular and continuous tooth replacement pattern (poly-phyodont) allows elasmobranchs to preserve a constant functionality and effectiveness of their dentitions (see Cappetta, 2012 ; Crofts and Summers, 2014 ; Amadori et al, 2020a ; Amini et al, 2020 ). In some species, tooth renewal can change during ontogeny with juveniles usually being characterized by a faster replacement rate than that observed in adults (e.g.…”

“…Wass, 1973 ; Reif et al, 1978 ). A slow dental renewal would involve a longer presence of teeth that become gradually abraded, damaged, or blunted and that, probably, are no longer able to fully perform their function within the feeding apparatus (see Amini et al, 2020 ). The ability to maintain functional tooth cusps despite an increased risk of bluntness in high-crowned dentitions may result in a crucial evolutionary advantage (see also Crofts and Summers, 2014 ; Crofts, 2015 ; Amini et al, 2020 ).…”