Turtles have roamed the Earth since the Triassic Period over 200 million years ago. A new study about their evolution, published in iScience, shows how the scales on turtles’ heads can teach us more about their dinosaur ancestors and their living relatives like crocodiles and birds.
For most vertebrates, genetics control where and how they grow things like feathers, hair, and scales. Crocodiles are an exception to this rule, as their scales form thanks to mechanical processes like skin folding. Researchers have now discovered another exception to the rule, as turtles are the only vertebrates that combine these two processes — genetic and mechanical — to create the scales on their heads.
Read More: The 5 Biggest, Ancient Turtles That Ever Lived Were Among the Dinosaurs
How Do Turtles Make Their Scales?
Typically, animals create their scales or feathers using placodes. Placodes are special areas of the skin controlled by genetic signals. These very specific genetic signals tell the skin to create the required appendage and what area it should grow in.
The other way an animal can produce scales is through purely mechanical processes like skin folding. As the skin grows at different rates, it will fold and bend in particular patterns and create the scales.
Turtles are an anomaly, however, as they use both placodes and mechanical folding to create the scales on their head. On the side of their head, the scales are formed using placode development, similar to birds. But for the top of their head, the scales are formed mechanically, more like a crocodile.
Researchers were able to identify these differences by using 3D light-sheet microscopy and computer modeling. Their findings showed that the diverse and irregular patterns of scales on a turtle’s head were the result of mechanical skin folding.
“This mechanical folding explains the asymmetrical shapes of the scales on the top of the head,” said Rory Cooper, postdoctoral researcher and co-author of the study, in a press release.
Another co-author, Ebrahim Jahanbakhsh, added that the mechanical folding “also accounts for the remarkable variation seen between individuals, and even between the left and right sides of a single individual’s head.”
Turtle Scales and Reptile Evolution
Although it may seem like a small detail, the dual scale-creation processes used by turtles are incredibly significant for the story of reptile evolution. The closest living relatives to tortoises and aquatic turtles are crocodiles and birds. While turtles and crocodiles are now known to share a mechanical process, their other relatives — birds — do not.
What this suggests is that a mechanical process for forming head scales was a trait from a shared ancestor of all three animals that was eventually lost in birds. The common ancestor in question? Likely a dinosaur.
“This reveals a new facet of reptile evolutionary history: the ability to generate head scale patterns through mechanical forces is an ancient trait — predating the emergence of modern turtles, crocodiles, and birds, and therefore most likely present in dinosaurs,” said Michel Milinkovitch, professor in the Department of Genetics and Evolution at the University of Geneva, in the press release.
The evolutionary implications are not the only big news to come out of this discovery. By understanding more about how nature creates complex structures and patterns, such as scales, we can replicate these processes in areas like architecture, tissue regeneration, and innovative material design.
Read More: As Masters of Survival and Evolution, the Crocodile Now Has Two New Species
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
iScience. Chemical and mechanical patterning of tortoise skin scales occur in different regions of the head
As the marketing coordinator at Discover Magazine, Stephanie Edwards interacts with readers across Discover's social media channels and writes digital content. Offline, she is a contract lecturer in English & Cultural Studies at Lakehead University, teaching courses on everything from professional communication to Taylor Swift, and received her graduate degrees in the same department from McMaster University. You can find more of her science writing in Lab Manager and her short fiction in anthologies and literary magazine across the horror genre.
