I have seen many turtles in various places, and they stick in my mind as animals with slow movement and sturdy shells. Their appearance also looks a bit ancient-like, and it is not hard to imagine them as creatures related to dinosaurs. Turtles have been around for more than 200 million years. They survived the mass extinction at the end of the Cretaceous period when most dinosaurs went extinct. If they have been around so long and lived during the Mesozoic era, it makes me wonder – are turtles related to dinosaurs?
Turtles are related to dinosaurs, and the latest genetic studies suggest turtles share the same ancestor. The earliest turtles existed together with the dinosaurs millions of years ago. However, the connection to dinosaurs is somewhat distant and is considered to be closer to birds and crocodiles, than for instance, lizards and snakes. Descendants of ancient turtles are still present today, with most of them being species of sea turtles.
If you haven’t heard of the fossilized dinosaur initially thought of as turtle remains, you will encounter it here too.
Turtles Are Related To Dinosaurs
Turtles are reptiles, too and that alone provides a connection to our huge reptiles from millions of years ago, the dinosaurs. Although not as closely related as birds are to dinosaurs, the turtles still have a distant connection to dinosaurs.
Crocodiles Are More Closely Related To Turtles
Dinosaurs and turtles are indeed distant relatives, and in between the two of them are the crocodiles. Birds are known to be direct descendants of dinosaurs. For a long time, anatomical and fossil studies are leaning toward the concept that birds are the closest living relative of crocodiles and alligators.
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Crocodiles and dinosaurs, along with birds, also belong to the same group, the archosaurs. Meanwhile, even in scientific circles, it was previously believed that turtles are more related to snakes and lizards. (Source)
Now, more advanced genetic studies indicate that turtles are the crocodiles’ closest living relative. It seems that turtles and crocodiles share an almost sibling relationship on a molecular level.
Yes, they are all related to each other, but this shows that turtles are more closely related to crocodiles than dinosaurs. Additionally, it can be stated…” that turtles share a more recent common ancestor with birds and crocodilians than with lizards and snakes.” (Source)
Why Turtles Are Related To Dinosaurs
Believed to have been around a long time ago, turtles are among the oldest and most primitive reptiles today. Scientists claim that ancient turtles lived along with dinosaurs approximately 110 million years ago, until the K-Pg extinction event, which wiped out the dinosaurs.
Crocodilians and extinct dinosaurs, and pterosaurs are all grouped as archosaurs (animals with a hole between the eye socket and nostril). According to a hypothesis backed up with DNA analysis, turtles and these archosaurs have common ancestors. If you would like to learn more about crocodiles, alligators and dinosaurs, check out my article: Are Alligators Related to Dinosaurs? (Classification, Similarities)
Another hypothesis is that turtles are anapsids (creatures with skulls with no side openings) while dinosaurs are diapsids (creatures with skulls with two openings). It is significant because diapsids are believed to have evolved from anapsids.
For both of these hypotheses, turtles are shown to be related to dinosaurs. It can either be that turtles belong to a sister group of dinosaurs under the same ancestor or that dinosaurs are more evolved versions of the turtles’ ancestors.
Ancient Turtles Coexisted With Dinosaurs
As I’ve mentioned earlier, turtles are the earliest reptiles that are still existing today, and that ancient turtles were present millions of years ago together with the dinosaurs. Let us now have a closer look at ancient turtles.
YouTube Video About the Prehistoric Sea Turtle Archelon
The Difference Between Ancient and Modern Turtles
Unlike modern turtles that are toothless, the discovered prehistoric turtles have teeth. The earliest ancient turtles also lacked a shell with plastron and carapace, which modern turtles normally have.
But it is believed that these ancient turtles later evolved to provide stability and locomotion to modern turtles. It is because they possessed broad ribbed structures, which are considered precursors for shells.
The evolution of the carapace (the top part of the turtle’s shell) is a wonderful example of how animals change over time. We can deduce from studying the bone structures in ancient turtles that evolved after the plastron (bottom part).
The modern-day turtle has not changed much from its ancient ancestors, which, in turn, links them to extinct dinosaurs. Fossilized ancient turtles also provided evidence that the two Suborders in modern turtles classification (the Pleurodira and the Cryptodira) are already present during the Triassic period.
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Evidence That Ancient Turtles And Dinosaurs Existed Together
No living witnesses can claim that ancient turtles coexisted with dinosaurs, but scientists can prove it thanks to discovered fossilized turtles. An example of this is the fossilized footprint of a sauropod found along with a smashed Plesiochelys turtle shell.
Based on this, the sauropod was probably walking when it unconsciously stepped on the ancient turtle.
People might question how the turtles remain alive despite the dinosaurs becoming extinct if they truly existed together. Galapagos turtles are among the largest tortoises still existing but now are endangered.
An observation of Galapagos turtles shows that they have a slow metabolism and survive for days without eating. A similar ability with this, plus having a protective shell structure, could have helped ancient turtles survive the K-Pg extinction faced by other prehistoric reptiles.
How Turtles Are Grouped With Dinosaurs
Cladograms relate the evolutionary relationship between species, while biological classifications categorize based on observed similarities. Since turtles and dinosaurs are related, parts of their evolutionary history will also be connected, and some of their characteristics will be similar. The cladogram of turtles encountered various changes along the way, but a closer look at this can show how they are ancestrally linked to dinosaurs.
Changes In Cladograms Of Ancient Turtles
Initially, ancient turtles from the Triassic Period are believed to be the only surviving branch of the ancient group, Anapsida. Ancient turtles are considered anapsids, but this was debunked when new phylogenetic studies suggested that they are diapsids.
Scientists then supported this concept with more studies. They also indicated that ancient turtles are closer to Squamata (scaled reptiles including lizards and snakes) than Archosauria (the archosaurs, which include the extinct dinosaurs).
The cladograms became more complicated when ancient turtles were also being grouped in Archosauromorpha, a broader group where archosaurs are based on molecular evidence. Scientists redid analysis, and the turtles were classified again as anapsids. (Source)
Aside from this, a new phylogenetic study emerged which indicated that ancient turtles must belong to a much larger clade, the Lepidosauromorpha (the group of reptiles including lepidosaurs or those closer to lizards than to archosaurs).
At this point, the cladograms of turtles became confusing. Fortunately, after 1000 ultra-conserved elements in the genome are discovered unique to both turtles and dinosaurs. The turtles are finally placed in Archelosauria, which is a newly named clade group. Archelosauria includes the turtles, birds, crocodiles, and even the dinosaurs in its group.
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It’s interesting to note that modern-day sea turtles are the closest descendants of ancient turtles, not the hard-shelled land-dwelling species. So, let’s take a look at sea turtles.
The oldest sea turtle fossils are about 140 million years old. It is around the time when dinosaurs lived on Earth. Ancient turtles like Protostega and Archelon lived during the Late Cretaceous (65 million years ago). Archelon is the largest turtle fossil reaching a length of 15 feet and estimated to weigh 4,900 lbs. Its fossils were found in South Dakota. Interestingly, its shell was not hard but leather-like in texture.
YouTube Video Describing the Sea Turtle from Ancient Times Up Until Now
Sea turtles are reptiles and come from the Chelonioidea family of sea creatures. They were first thought to be a type of lizard, but they belong to their group. Sea turtles are an order of reptiles with approximately 300 species.
Sea turtles live almost exclusively in the sea, but some species wander into brackish water and freshwater habitats. All sea turtle species belong to the superorder Chelonia, which also includes tortoises.
Biological Classification Of Modern-day Turtles
A clade is a group of organisms believed to have evolved from a common ancestor, but it is not a taxonomic ranking used for biological classification. In the 1950s, Testudines became the formal name for turtles. Testudines are under the clade Archelosauria, but in terms of taxonomy, Order Testudines are under the Class Reptilia. Dinosaurs are also under Class Reptilia.
That is why turtles and dinosaurs share common reptilian characteristics such as the ability to lay eggs, be air-breathing vertebrates, and have scaly or bumpy skin.
Under the order of Testudines are two suborders separated based on how the turtle’s neck folds. Suborder Cryptodira is the vertical or S-necked turtles that have a total of 263 species in 11 families.
At the same time, Suborder Pleurodira includes the snake-necked, side-necked, and big-headed turtles, which total 93 species in 3 families. Succeeding classifications after the suborders are based on differences in the modern turtles’ skull and shell.
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Therizinosaurus: The Turtle-Looking Dinosaur
One of the most famous cases where a dinosaur was mistaken for a turtle is Therizinosaurus. This ancient reptile was first thought to be an early turtle, but it turned out that this “turtle” had giant claws on its feet and huge teeth at the end of its snout!
Similar Features With Turtles
When the Therizinosaurus fossils were first discovered in Mongolia, it was thought to be a turtle. In 1954, a Russian paleontologist claimed that the fossils resemble a modern sea turtle. It led to an assumption that the Therizinosaurus fossils were fossils of ancient turtles. Its unique forelimbs are initially believed to be powerful swimming organs, while its large claws for cutting vegetation underwater. These features also made the creature comparable to ancient turtles.
The Therizinosaurus Is Not A Turtle
After some time, experts finally realized that Therizinosaurus fossils are not from a turtle but a dinosaur.
About the Therizinosaurus
After assembling the fossil’s general skeletal structure, the structure showed that it is a theropod dinosaur. The Therizinosaurus has a small head, long neck, and a beaked mouth. It is bipedal with four clawed toes, but only three toes support its weight. It has two hands, each with three gigantic claws.
Although it has huge claws, its diet is believed to be a plant-eating dinosaur. If you want to know more about the Therizinosaurus, check out my articles What Was the Herbivore Dinosaur with Long Claws? Some Surprising Facts and Gobi Desert Dinosaurs – The Amazing Fossil Discoveries
Coming Back to Turtles – Defining Characteristics Of Turtles
The Therizinosaurus is not a turtle because of various reasons. Turtles are reptiles with hard shells for protection which are absent on the discovered Therizinosaurus fossils. A turtle’s shell includes its modified ribcage, and a part of its vertebral column with the top part called the carapace while the bottom part is called the plastron.
Turtles cannot escape their shells nor shed them like skin. Unlike the Therizinosaurus, they use four legs for movement and have short tails.
Technically speaking, turtles only survive in an aquatic environment, tortoises are those surviving inland, and terrapins are those that can live on both. Usually, when you use the term “turtle,” it can represent all the mentioned creatures in the entire Testudines Order.
Turtles and dinosaurs go way back. Millions of years ago, they were living side by side. Genetic evidence shows the two have similarities that can’t be ignored. It’s not just a coincidence that one of them was mistaken for the other!
I feel like turtles can intimidate me now because they are indeed related to dinosaurs. Kidding aside, I’ll probably marvel at their interesting prehistoric ancestry the next time I come across a turtle.
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