Age Estimation in Marine Mammals: the answer lies in a dolphin’s smile

Photo credit: David B. Fleetham at Allposters.com

Photo credit: David B. Fleetham at Allposters.com

Ah, the question we all wonder at one time or another. How old or how young is a certain person? Humans are tricky subjects for age guessing depending on race, sun exposure, dyed hair, plastic surgery and general health upkeep. Unless you are willing to just ask and make it easy; assuming whoever it is tells you the truth.

But what about dolphins or other marine mammals for that matter? Dolphins look ageless, that smooth skin, healthy countenance and generally happy demeanor. I mean they are smiling all the time for crying out loud! Don’t get me wrong, that happy dolphin face is always thrilling to see, but it really messes up the age guessing game. Plus, no visible gray hair, arthritis or limp swimming. So dolphins, what’s your secret?

According to the Encyclopedia of Marine Mammals, the answer lies in a dolphin’s smile or more specifically their teeth. But this doesn’t mean a smiling teeth-baring dolphin discloses its age, a tooth actually has to be pulled out and sawed in half. Once inside the tooth it’s possible to see growth layers that can be counted to determine the dolphin’s age, similar to the growth rings in a tree.

Obviously there are downsides to this approach, but scientists have found this process to be the most accurate technique for finding the numerical truth behind that smile.

However, counting dolphin tooth growth layers is not as easy as counting tree rings. According to Aleta Hohn, author of the Encyclopedia of Marine Mammals’ article on age estimation, there are actually multiple layers visible for every growth year, this is referred to as a growth layer group.

Apparently, this term was coined after linguistic confusion over what growth layer really meant with several tooth layers falling within a year. Instead of referring to in between layers as accessory, incremental or sub-annual it was easier to call all layers within the same year a growth layer group. This is one of the few times I’ve read a new science term that actually makes sense! But with so many layers, it takes a discerning eye to determine the annual layers from the rest. Based on the photos in the encyclopedia, this job would make the average person cross-eyed.

Using teeth to determine age works for most marine mammals species, except for the ones who don’t have teeth. For baleen whales the best strategy is to look at their ear plugs. Based on what I can gather from reading on the internet the ear plug is alternating layers of departed skin cells and ear wax. Gross!

And of course there are always exceptions to the rule, like the manatee who doesn’t have tusks and is constantly losing and replacing teeth. In this case according to Hohn, it’s best to look at the auditory bones. This strategy also works for some of the baleen whales.

Regardless, determining a marine mammal’s age isn’t an easy business. And from now on instead of wondering how old a dolphin is I will contemplate: “How many layers are in those teeth?” and “Why do whales have earwax?”

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  1. […] layer group a year, rather than two.” And just a refresher for those of you who missed the post on figuring out the age of marine mammals, many marine mammals have growth layers in their teeth, similar to the growth rings found within a […]

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