The changing turtle plastron pattern
Most pet turtles (I’d say they’re mostly aquatic turtles) have beautiful plastron shell patterns that change as the turtle get older, bigger, and matures. Continuous shell shedding and growth ensures that the belly part of the shell (the plastron) changes over time.
Here’s a look at the changes of plastron pattern over time with my male pet red ear slider turtle, Rex.
Here he is a hatchling at around 1″ SCL (straight carapace length):
This picture was taken when he was newly acquired – he’s in the tupperware the little store put him in for me to take home.
Notice the very bold and very clear and distinct patterns. The plastron colors and lines are solid and clearly defined.
The Changing Turtle Plastron
And here he is two months or so later. He’s already grown thanks overfeeding, as advised by the pet turtle food company (don’t follow their feeding schedule – it will overfeed your turtle and cause them to grow too fast and have shell pyramiding).
His nice hatchling plastron pattern is beginning to fade and dark circles are starting to form. He’s probably around 2″ SCL at the time.
He also looks very adorable looking like he’s holding on for dear life – but he’s trying to get free from my hand.
Over time, the hatchling pattern stretched and faded as my pet red ear slider grew and grew. Take a look here at photos of my pet turtles shed shells.
Maturing Shell Pattern
After a few good years of growth and shell shedding, here is what his plastron looked like. At this point he’s obviously not a hatchling anymore and can barely fit in my hand.
The dark spots continued to grow darker and darker, while the hatchling pattern stretched and continued to fade. Notice the four bottom scutes – you can see the movement and growth (and fading) of the dark spots. The direction of fading/blotching coincides with growth direction of the scutes. You can see from the picture the lines in each of those scutes, each one representing a layer of shell that will eventually be shed.
a little later you can see more of the fading of the hatchling pattern.
At some point, all the shell scutes with remainders of the hatchling pattern will completely disappear and all that will be left are the dark splotches. Also, the changing plastron pattern also coincides with a turtles change in skin color from a lighter almost yellow-green color to a darker and darker olive (and even darker) color (skin patterns also fade).
Why do plastron patterns change?
I don’t really know why. Some people, such as those at Turtle Forum speculate that it serves as either a sort of camouflage (but can’t really since some turtle species have non-camo colors) or that they serve as a type of warning to predators (since bright colors in animals usually means “I’m poisonous”, “difficult to eat” or similar).
What is clear is that the patterns change as the turtle grows in size and that the need for a “hatchling pattern” is reduced as the turtle grows.
So, what do you think? Have a thought about why a turtle’s shell plastron pattern changes over time? Share them in the comments.