Data from: Dermal denticle shedding rates vary between two captive shark species

Shark dermal scale (denticle) accumulation in the fossil record can
provide information about the abundance and composition of past shark
communities. Denticles are shed continuously, such that a single shark
leaves a scattered composite of many isolated denticles in sediments.
However, the rate of denticle shedding as well as how these rates vary
among shark species with different life modes and their consistency over
time are unknown, limiting the interpretation of denticle assemblages. To
better understand the process of denticle shedding and calibrate the
relationship between absolute shark abundance in the environment and
denticle deposition in sediments, we captured denticles shed by two shark
species in a large aquarium over nine months. We then simulated how these
aquarium-derived shedding rates shape the relationship between shark
abundance and denticle accumulation. Bonnethead sharks (Sphyrna tiburo) –
a more active, benthopelagic species with small, thin denticles – shed 3.6
times faster on average than zebra sharks (Stegostoma fasciatum) – a more
sedentary, demersal species with large, robust denticles. This pattern
persisted when shedding rates were corrected by estimated denticle
quantities, shark space use, and methodological factors (2.2- to 3.8-fold
difference). Over the study, bonnethead shark shedding rates declined
while zebra shark shedding rates increased slightly. Finally, denticle
assemblage composition corresponded with the relative abundance of
denticles on each species’ body, consistent with natural shedding rather
than selective loss. Overall, we show that shark taxa contribute unevenly
to the denticle record, indicating that shedding rate measurements can
help inform and constrain ecological interpretations of denticle
assemblages.

化石记录中的鲨鱼真皮小齿（denticle）堆积情况，可为古鲨鱼群落的丰度与组成提供关键信息。小齿会持续脱落，因此单只鲨鱼会在沉积物中留下大量分散的孤立小齿复合体。然而，鲨鱼小齿的脱落速率、不同生活型鲨鱼间的脱落速率差异，以及该速率随时间的稳定性目前尚不明确，这极大限制了对小齿组合（assemblage）的生态学解释。为更好地理解小齿脱落过程，并校准环境中鲨鱼绝对丰度与沉积物中小齿沉积量之间的定量关系，我们在大型水族箱中对两种鲨鱼的脱落小齿开展了为期9个月的收集工作。随后我们模拟了基于水族箱实测数据得到的脱落速率，如何塑造鲨鱼丰度与小齿堆积量之间的关联。窄头双髻鲨（Sphyrna tiburo）是一种活跃的底中水层（benthopelagic）物种，其体表小齿小巧纤细，平均脱落速率约为豹纹斑竹鲨（Stegostoma fasciatum）的3.6倍；后者为行动迟缓的底栖（demersal）物种，小齿宽大粗壮。在校正了估算的小齿种群数量、鲨鱼空间利用模式以及实验方法学因素后，该脱落速率差异依然存在（差异倍数为2.2至3.8倍）。在整个研究周期内，窄头双髻鲨的脱落速率呈逐步下降趋势，而豹纹斑竹鲨的脱落速率则略有上升。最后，小齿组合的组成与各物种体表小齿的相对丰度高度匹配，这表明该模式符合自然脱落过程，而非选择性丢失。总体而言，本研究证实不同鲨鱼类群对小齿化石记录的贡献并不均匀，这意味着脱落速率测量结果可为小齿组合的生态学解释提供有效依据并加以约束。