At first glance these two shark dermal denticles appear quite similar, right? Sure, one is a little wider than the other, but they both have distinct peaks, ridges, and intriguing honeycombed ornamentation on their crowns. What if I was to tell you that they are separated in time by about 7,000 years. Which do you think came from the fossil reef?
Did you guess A?
Denticle A looks much more worn than the other. The base is missing, the peaks at the top are eroded, and there are two small cracks running up the crown. Fortunately, its primary characteristics, such as the number of ridges and distances between them, are still intact and distinguishable, permitting classification. Surprisingly, though, this denticle was extracted from sand on a modern reef. However, because the rates of sedimentation and reef accretion are slower today in Bocas del Toro than they were in the past, this denticle may have spent more time on the surface of the reef exposed to things like wave energy and chemical dissolution before it was buried. These mechanical and chemical modifications reduce preservation, as you can imagine, giving the denticle a more weathered look despite being shed within the last 50 or so years.
Or maybe you guessed B?
Well done. Despite appearing more pristine, this denticle is around 6,600 years old! It’s incredible how exquisitely the microstructures are preserved, right?