In the intricate world of marine biology, few materials capture the imagination quite like shark skin. Far from the simplistic perception of smooth aquatic texture, shark skin is intricately armored with microscopic structures known as dermal denticles. These tiny, tooth-like scales, constructed from the same robust biological material as shark teeth, form a natural exoskeleton that serves multiple crucial purposes. Their unique shape and surface grooves contribute to the remarkable hydrodynamics and durability of sharks, enabling fluid movement through water with minimal resistance while providing critical protection from environmental hazards and physical trauma. Yet, despite decades of research, scientists have only begun to unravel the complexities of how these denticles adapt and change as sharks grow and mature.
Recent scientific efforts led by researchers at Florida Atlantic University have employed pioneering high-resolution imaging techniques to explore the skin morphology of bonnethead sharks (Sphyrna tiburo), a smaller kin of the iconic hammerhead family. By turning to advanced scanning electron microscopy, the team achieved unprecedented magnification and clarity, unveiling the minuscule details of denticle shape, size, and ridge patterning that evade conventional microscopy. This detailed visualization offered novel insights into how denticle structures evolve in individual sharks over time, particularly in relation to developmental stages and sexual maturity.
The investigation involved detailed examination of skin samples from a diverse cohort of 24 bonnethead sharks representing various growth phases, from juveniles to mature females. This cohort was strategically selected due to bonnetheads’ known gradational denticle modifications and apparent sexual dimorphism in dermal features, especially in regions implicated in mating behavior. The research focused extensively on the abdominal skin area, looking at denticles’ morphological characteristics and assessing changes linked to age, size, and sex.
The results revealed significant transformations in denticle morphology associated with maturation. Notably, as the bonnethead individuals aged, their denticles exhibited progressively complex ridging, increased overlap, and larger ridge angles, although the overall denticle length remained consistent across developmental stages. Such modifications are theorized to optimize swimming efficiency and reinforce skin defense mechanisms against both predatory threats and mating-inflicted abrasions. The intricate ridges may help reduce hydrodynamic drag, a vital advantage in the energy-demanding activity of sustained swimming, while enhanced overlap contributes to creating a tougher, more resilient outer covering.
Furthermore, the investigation found minimal sexual dimorphism in denticle morphology beyond slight differences in ridge angles, which were marginally more pronounced in males. Contrary to some earlier studies suggesting that female sharks develop thicker and denser denticles for protection against mating injuries, the bonnethead sharks in this study displayed largely similar denticle traits across sexes. Additionally, denticle features were consistent across different zones of the abdominal skin, dispelling hypotheses that denticle variation is region-specific within the trunk area.
These findings underscore the adaptive plasticity of shark dermal denticles, portraying shark skin not simply as a static protective layer but as a dynamically evolving biological structure tailored to the functional needs imposed by growth and reproductive pressure. Dr. Marianne E. Porter, senior author and a specialist in biological sciences, emphasized the evolutionary sophistication revealed by the study. She noted that these incremental skin transformations enhance both aquatic locomotion and protective resilience, aligning precisely with the multifaceted evolutionary demands imposed on sharks throughout their life cycle.
The synthesis of high-resolution electron microscopy and cutting-edge morphometric analytical tools was instrumental in enabling this research breakthrough. Tricia Meredith, Ph.D., co-author and director of research at Florida Atlantic Laboratory Schools, highlighted how these technologies allowed the team to meticulously quantify features such as ridge patterns and denticle spatial distribution. This leap forward in imaging and analytic precision broadens possibilities for future explorations into shark biomechanics and evolutionary development, promising deeper understanding of the interplay between form and function in aquatic environments.
An intriguing aspect of the research is its wider biological significance. Insights about dermal denticles extend beyond marine biology into disciplines such as bioengineering, where biomimetic applications inspired by shark skin’s drag-reducing capabilities could lead to innovative design in swimwear, watercraft surfaces, and other fields requiring optimization of fluid dynamics. The study’s corresponding author, Hannah Epstein, now a student at FAU’s Harriet L. Wilkes Honors College, underscored this translational potential, suggesting that the profound biological design refined by millions of years of evolution could fuel technological advancements that enhance human performance in aquatic settings.
The study also integrates with broader comparative biological research across other shark species. For example, Portuguese dogfish sharks possess at least eleven distinct denticle forms that manifest at different life stages, echoing the patterns observed in bonnetheads, where juveniles typically have simpler, smaller denticles compared to the more complex morphologies of adults. These consistent developmental trajectories underscore a fundamental evolutionary blueprint regulating denticle differentiation linked to survival imperatives and locomotor efficiency.
Integral to this research endeavor was the utilization of the Berlin Family Bioimaging Lab at Florida Atlantic University, a pioneering facility offering students and researchers alike access to state-of-the-art imaging technologies. This lab’s combination of micro-computed tomography scanners, scanning electron microscopes, histology suites, and stereoscopic and compound microscopes furnishes an unparalleled toolkit to dissect biological structures at microscale levels. Such high-resolution capabilities foster early engagement with complex scientific questions among emerging scientists, enabling original contributions to peer-reviewed literature even from high school and undergraduate students.
The research was financially supported in part by a National Science Foundation CAREER Award and an FAU Office of Undergraduate Research and Inquiry grant, attesting to the high-caliber interdisciplinary collaboration and institutional commitment driving this project. The published findings appear in the August 2025 issue of the journal Integrative and Comparative Biology, underlining their significance to the domains of organismal biology, biomechanics, and evolutionary developmental biology.
In summary, this study provides a compelling glimpse into the microscopic transformations underpinning the macroscopic agility and resilience of the bonnethead shark. It enriches our understanding of how evolutionary pressures sculpt biological materials at both micro and macro scales, highlighting the remarkable dynamic interplay between growth, function, and environmental adaptation in one of the ocean’s most fascinating predators. The implications resonate far beyond marine ecology, offering inspiration for scientific and technological advances that emulate nature’s time-tested designs.
Subject of Research: Animals
Article Title: Zooming in on Bonnetheads: Quantifying Impacts of Maturity on Denticle Morphology
News Publication Date: 23-Aug-2025
Web References:
DOI 10.1093/icb/icaf115
Image Credits: Florida Atlantic University
Keywords:
Marine fishes, Skin, Evolutionary developmental biology, Biomechanics, Locomotion, Mating behavior, Morphology, Body size, Functional morphology, Body weight, Swimming, Animal locomotion, Bioengineering, Developmental stages
