Can denticle morphology help identify southeastern Australian elasmobranchs?

Area of Science:

• Paleontology
• Ichthyology
• Marine Biology

Background:

• Elasmobranchs possess dermal denticles, which vary morphologically within and between species.
• These denticles are shed and preserved in marine sediments, offering potential for paleontological studies.
• Understanding denticle morphology can aid in assessing elasmobranch diversity and abundance.

Purpose of the Study:

• To expand the literature on dermal denticle morphology.
• To investigate intra- and interspecific variability in denticle morphology.
• To assess the viability of using denticle morphology in sediment samples for elasmobranch diversity and abundance assessments.

Main Methods:

• Collected and characterized dermal denticles from deceased shark species.
• Assigned denticles to morphotypes based on morphology.
• Conducted manipulative experiments using denticles from aquaria with known elasmobranchs.
• Utilized visual examination, morphometric measurements, scaled photographs, and reference collections for identification.

Main Results:

• Denticle morphology was more strongly influenced by life-history traits (demersal vs. pelagic/benthopelagic) than by species.
• Demersal species exhibited generalized function and defense denticles; pelagic/benthopelagic species showed drag-reduction denticles.
• Snout denticles (abrasion strength/defense) were common across species, limiting their use for species-level separation.
• Identification to species level from sediment samples was not always precise, though family-level identification is promising.

Conclusions:

• Dermal denticle morphology provides insights into elasmobranch life history and ecology.
• Developing comprehensive denticle reference collections is crucial for accurate identification of past and present elasmobranchs.
• Sediment-based denticle analysis shows potential for assessing elasmobranch diversity, particularly at the family level.