Before we dive in deeper, it’s important to clarify that turtles are not dinosaurs. This common misconception stems partly from the fact that both groups are reptiles and share a prehistoric past. They’re both reptiles, they’re both creatures that evolved a long time ago. However, their evolutionary paths diverge significantly.
Dinosaurs, which roamed the Earth from about 245 million years ago until their abrupt demise 66 million years ago, belong to a distinct group known as archosaurs. This group also includes modern birds and crocodiles.
Turtles, on the other hand, hail from a different lineage. They are part of the group called ‘Testudines,’ which branched off early from the more familiar reptilian lines. To understand why turtles are not dinosaurs, we need to look at the broader reptilian family tree.
What are dinosaurs
Dinosaurs were a diverse group of reptiles that appeared during the Triassic period, some 245 million years ago. They came in all shapes and sizes, ranging from the size of chickens (like Microraptor), to the enormous Argentinosaurus, which could stretch over 30 meters (98 feet) long and weigh up to 100 tons.
Broadly speaking, the group is categorized into two main groups:
- the ornithischians, which were mostly herbivorous and included dinosaurs like Stegosaurus and Triceratops; and
- the saurischians, which included both herbivores like Diplodocus and carnivores like Tyrannosaurus rex. It’s also from this saurischian lineage that modern birds evolved. But turtles don’t belong to either of these groups.
What are Turtles?
Turtles are a group of reptiles known for their bony or cartilaginous shells, which develop from their ribs and act as a shield against predators. This defining feature is universal among all turtle species.
The story of reptilian evolution is a saga of branching paths and survival. About 310 million years ago, the earliest known proto-turtles emerged, featuring some but not all characteristics of modern turtles. Crucially, these ancient reptiles developed protective shells, setting them apart from other evolutionary lines.
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The lineage of true turtles is still debated, but researchers believe these turtles evolved some 210 million years ago, during the Late Triassic. So, they’re a bit younger than dinosaurs as a group.
Turtles diverged from a group called Archosauromorpha. Crocodiles and birds, which are closely related, also diverged from this group. Archosaurs are also the group that includes the dinosaurs (birds are technically dinosaurs).
To consider turtles and dinosaurs “cousins” rather than “siblings” within the reptilian family is more accurate. While both share a common reptilian ancestor, their paths diverged early on. The archosaurs took one route, leading to crocodiles and eventually the mighty dinosaurs, while another path led to the evolution of turtles.
Turtles are often referred to as “living fossils,” a term that implies they have remained unchanged for millions of years. However, while it is true that turtles have a long evolutionary history and have retained many ancestral features, they are far from static creatures.
Throughout their evolution, turtles have adapted to a wide range of environments, from deserts to oceans. They have developed specialized adaptations for swimming, burrowing, and even climbing trees. Their shells, once thought to be primarily defensive structures, have also evolved to serve a variety of functions, such as thermoregulation, buoyancy control, and even camouflage.
They also have a wide range of sizes, from the small speckled padloper tortoise, which can fit in the palm of a hand, to the massive leatherback sea turtle, which can weigh over 900 kilograms (2,000 pounds). Their diets vary as widely as their habitats — they can be herbivorous, carnivorous, and omnivorous. Despite their slow reputation, turtle evolution has been remarkably efficient.
The evolutionary tree of turtles
Remember when we were saying there’s still some debate regarding the evolutionary history of turtles?
Historically, researchers have analyzed the evolution of animals with fossils. In fact, fossil analyses are the absolute core of our understanding of ancient creatures. But new techniques are enabling us to see ancient creatures in a new way.
For instance, a 2014 study from researchers at the California Academy of Sciences, utilized a new genetic sequencing method called Ultra Conserved Elements (UCE) to examine the vast genetic landscape of turtles, revolutionizing the traditional views held about their evolutionary relationships. The research firmly places turtles in a newly identified group named “Archelosauria,” alongside birds, crocodiles, and dinosaurs, challenging previous theories that aligned them closer to lizards and snakes. This reclassification not only clarifies the genetic lineage of turtles but also marks a pivotal shift in how scientists view the vertebrate family tree.
“Calling this an exciting new era of sequencing technology is an understatement,” says Brian Simison, PhD, Director of the Academy’s Center for Comparative Genomics (CCG) that analyzed the study’s massive amount of data. The CCG is a state-of-the-art facility composed of a sequencing lab, frozen DNA collection, and computing resources that serves as the Academy’s core genetic center. Established in the summer of 2008, the CCG continues to refine Academy research — including new turtle findings — on a global, evolutionary scale.
“In the space of just five years, reasonably affordable studies using DNA sequencing have advanced from using only a handful of genetic markers to more than 2,000 — an unbelievable amount of DNA,” adds Simison. “New techniques like UCE dramatically improve our ability to help resolve decades-long evolutionary mysteries, giving us a clear picture of how animals like turtles evolved on our constantly-changing planet.”
The approach also pushed scientists to reclassify some changes inside the turtle group. For instance, softshell turtles, a unique group of scale-less turtles with distinct snorkel-like snouts, do not share a close relationship with mud turtles as previously thought. Instead, they occupy a distant branch on the evolutionary tree.
No matter how you look at it, turtles are not dinosaurs
Despite the uncertainties in our understanding of turtle evolution, it’s clear that turtles are not dinosaurs. But that’s not to say they’re not just as interesting.
Turtles withstood the massive extinction that wiped out the dinosaurs. They have a rich history that stretches back hundreds of millions of years. Their story is one of resilience and adaptability, traits that have allowed them to thrive across epochs and geographies. So, when you think about a turtle, don’t just think about its shell or it being slow — think that this stunning creature adapted over 200 million years and continues to thrive even now.
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