[show abstract][hide abstract] ABSTRACT: The majority of studies on the evolution and function of feeding in sharks have focused primarily on the movement of cranial components and muscle function, with little integration of tooth properties or function. As teeth are subjected to sometimes extreme loads during feeding, they undergo stress, strain, and potential failure. As attributes related to structural strength such as material properties and overall shape may be subjected to natural selection, both prey processing ability and structural parameters must be considered to understand the evolution of shark teeth. In this study, finite element analysis was used to visualize stress distributions of fossil and extant shark teeth during puncture, unidirectional draw (cutting), and holding. Under the loading and boundary conditions here, which are consistent with bite forces of large sharks, shark teeth are structurally strong. Teeth loaded in puncture have localized stress concentrations at the cusp apex that diminish rapidly away from the apex. When loaded in draw and holding, the majority of the teeth show stress concentrations consistent with well designed cantilever beams. Notches result in stress concentration during draw and may serve as a weak point; however they are functionally important for cutting prey during lateral head shaking behavior. As shark teeth are replaced regularly, it is proposed that the frequency of tooth replacement in sharks is driven by tooth wear, not tooth failure. As the tooth tip and cutting edges are worn, the surface areas of these features increase, decreasing the amount of stress produced by the tooth. While this wear will not affect the general structural strength of the tooth, tooth replacement may also serve to keep ahead of damage caused by fatigue that may lead to eventual tooth failure.
Journal of Morphology 02/2011; 272(2):169-79. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: Morphological studies of fossil and extant shark teeth have typically been qualitative in nature, with resulting taxonomic problems due to the complicated forms of heterodonty exhibited by many sharks. This is apparent in the designation of fossil species assigned to Isurus (Lamniformes), where the status of the putative Neogene fossil species Isurus xiphodon and I. hastalis is solely based upon supposed differences in tooth morphology. Here we apply the geometric morphometric techniques of Procrustes superimposition, resampling-based Goodall's F-test, and canonical variates analysis to extant Isurus teeth, with the goal of assessing whether these quantitative analytical techniques provide a more objective basis for taxonomic decisions than do traditional qualitative morphological descriptions. These quantitative techniques are then applied to I. hastalis and I. xiphodon to examine whether I. xiphodon should be considered a junior synonym of I. hastalis or a separate species. Results show that geometric morphometric techniques can differentiate between the two extant species as well as the two extinct species, supporting I. xiphodon as a valid taxon. We suggest that this type of analysis is applicable for examining tooth-based species delimitations of sharks with both extant and extinct members, and has the potential to be applied to other fossil shark species as well.
Journal of Vertebrate Paleontology 03/2010; · 1.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: To date, the majority of studies on feeding mechanics in sharks have focused on the movement of cranial components and muscle function, with little attention to tooth properties or function. Attributes related to mechanical properties, such as structural strength, may also be subjected to natural selection. Additionally it is necessary to characterize these properties in order to construct biomechanical models of tooth function. The goal of this study was to determine hardness and elastic modulus for the shark tooth materials enameloid, osteodentine, and orthodentine. Five teeth each from one carcharhiniform species, the bonnethead Sphyrna tiburo, and one lamniform, the sand tiger shark Carcharias taurus, were utilized for nanoindentation testing. Each tooth was sectioned transversely, air-dried, and polished. Both enameloid and dentine were tested on each tooth via a Berkovich diamond tip, with nine 2 microm deep indentations per material. t-Tests were used to determine if there were differences in hardness and Young's modulus between the tooth materials of the two species. There was no significant difference between the two species for the material properties of enameloid, however both hardness and Young's modulus were higher for osteodentine than for orthodentine. This may be due to differences in microanatomy and chemical composition, however this needs to be studied in greater detail.
Archives of oral biology 03/2010; 55(3):203-9. · 1.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: The application of engineering analysis to new areas, such as nanomechanics and the life sciences, often involves geometric
problem domains defined by discrete point sets as measured from diagnostic equipment. The development of a suitable mesh for
finite element analysis can be a tedious task. One approach to simplifying the geometric description is to use a parametrized
set of basis functions, and fit the parameters to the data set. In this paper, we discuss the problem of determining suitable
parameters for the Reproducing Kernel Element Method representation of discrete point sets, and in particular the solution
of the inverse problem of determining pre-image evaluation points in the parametric space that correspond to a given input
point. We justify our solution by posing a theoretical framework and an error indicator.
[show abstract][hide abstract] ABSTRACT: The nurse shark, Ginglymostoma cirratum, is an obligate suction feeder that preys on benthic invertebrates and fish. Its cranial morphology exhibits a suite of structural and functional modifications that facilitate this mode of prey capture. During suction-feeding, subambient pressure is generated by the ventral expansion of the hyoid apparatus and the floor of its buccopharyngeal cavity. As in suction-feeding bony fishes, the nurse shark exhibits expansive, compressive, and recovery kinematic phases that produce posterior-directed water flow through the buccopharyngeal cavity. However, there is generally neither a preparatory phase nor cranial elevation. Suction is generated by the rapid depression of the buccopharyngeal floor by the coracoarcualis, coracohyoideus, and coracobranchiales muscles. Because the hyoid arch of G. cirratum is loosely connected to the mandible, contraction of the rectus cervicis muscle group can greatly depress the floor of the buccopharyngeal cavity below the depressed mandible, resulting in large volumetric expansion. Suction pressures in the nurse shark vary greatly, but include the greatest subambient pressures reported for an aquatic-feeding vertebrate. Maximum suction pressure does not appear to be related to shark size, but is correlated with the rate of buccopharyngeal expansion. As in suction-feeding bony fishes, suction in the nurse shark is only effective within approximately 3 cm in front of the mouth. The foraging behavior of this shark is most likely constrained to ambushing or stalking due to the exponential decay of effective suction in front of the mouth. Prey capture may be facilitated by foraging within reef confines and close to the substrate, which can enhance the effective suction distance, or by foraging at night when it can more closely approach prey.
Journal of Morphology 06/2008; 269(9):1041-55. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a new method for representing smooth geometry using the reproducing kernel element method. Further, the formulation provides a simple method to modify geometry that does not require modification of the underlying RKEM mesh. We develop a method for determining the representation from a discrete point set that is applicable to both traditional engineering domains, as well as applications where only discrete point sets are available, such as biology and medicine. Geometry representation and modification are demonstrated using examples of analytic functions and on a digitized shark tooth. Finally, we develop an isogeometric analysis capability for modified and un-modified geometry. The isogeometric capability on modified geometry may be useful in an iterative design-analyze cycle or shape optimization.
Computer Methods in Applied Mechanics and Engineering 09/2007; 196(s 41–44):4304–4320. · 2.62 Impact Factor
[show abstract][hide abstract] ABSTRACT: The silver arawana, Osteoglossum bicirrhosum, hunts along shorelines and within flooded forests in the Amazon River basin and supplements its limited consumption of aquatic vertebrates by leaping from the water to obtain terrestrial and arboreal prey. We offered O. bicirrhosum prey both suspended above and submerged below the surface of the water. From high-speed digital recordings, we measured kinematic variables associated with the jaws, cranium, pectoral fins, and body during orientation and prey capture. Aquatic and aerial feeding events were kinematically distinct, with aerial events generally involving faster, larger movements and a distinct delay in the onset of lower jaw depression until the head had left the water. The comparatively large gape during leaping may facilitate prey capture by overcoming variability in the apparent position of the prey due to refraction, while the delayed onset of mouth opening may serve to reduce the effects of drag. This distinctive leaping behaviour allows exploitation of the terrestrial prey base, especially during seasonal inundation of the Amazon River basin when the aquatic food base is widely dispersed.
Environmental Biology of Fishes 07/2005; 73(4):453-462. · 1.31 Impact Factor
[show abstract][hide abstract] ABSTRACT: Bite damage patterns have long been used to estimate shark species and body size, with somewhat limited success. The lack
of fit between damage patterns and shark size is partially due to variation in tooth size and shape within an individual.
The ability to accurately predict body size from bite patterns is important for better understanding the ecological and behavioral
underpinnings of shark bites/attacks on marine organisms, humans, and submarine equipment. To this end, we measured interdental
distance (IDD) between the most labial teeth in the first six tooth files on both the upper and lower jaws, as well as the
circumference of the portion of each jaw that bears teeth, for prepared jaw sets from fourteen shark species and regressed
these data against total length. IDD is allometric as well as an accurate predictor of total length in all species examined,
except Carcharhinus acronotus. Tooth-bearing circumference is also allometric and predictive of total length in all species. Though considerable overlap
exists in IDD and circumference ranges among species for the total length ranges examined, Carcharodon carcharias and Isurus sp. can be differentiated from Carcharhinus limbatus, Carcharhinus brevipinna, and C. acronotus based on these values alone. When combined with knowledge of species-specific feeding behavior, geographic distribution,
and habitat preferences, these simple measures from bite damage patterns allow quick, accurate assessment of shark size and