Why Love Turtles or Tortoises?

Well, we think it goes without saying, they are TOR-TALY AWESOME!  They are brady metabolic poikilothermic chelonians! Don’t worry if you looked at that last sentence like it was an ancient forgotten language.  In Zilla’s Guide to Turtles and Tortoises, we’ll discuss what makes these reptiles so amazing.  This three part series starts with Part 1: Biology and Natural History.  In Part 1 we’ll discuss what makes tortoises bodies and systems unique as well as discuss their origins over millions of years and how they live now.  If you’re a turtle nerd like we are, relax in your favorite reading spot and lets learn about these reptile mobile homes.

Part 1: Biology and Natural History
What is a turtle?

Turtles and tortoises belong to the class called Reptilia, more commonly known as Reptiles.  Reptiles are cold-blooded animals with scales and a three chambered heart.  Turtles and tortoises are in the order Testudines (formerly Chelonia) and commonly referred to as Chelonians.  Every living species in this group, and some extinct species, has a bone or cartilage shell.  Chelonians are one of the oldest living groups of reptiles and appeared before snakes and even crocodiles.  There are three groups of animals in the Chelonian order.  First is Turtles.  While some consider every living thing with a shell a turtle, this term actually refers to what we call Sea Turtles.  Turtles are Chelonians that live nearly all of their lives in water, usually only coming onto land to lay their eggs.  Second is Terrapins.  Terrapins are Chelonians that live on both land and water and are generally found in fresh and brackish water such as ponds, rivers, swamps, and lakes.  Terrapins are what we commonly refer to as Turtles.  So technically the terms “Box Turtle” and “Painted Turtle” should actually be Terrapin, not Turtle, but that’s just by definition.  Last is Tortoises.  Tortoises spend all of their time on land and don’t have flippers or webbed feet.  Both Tortoises and Terrapins also have pretty limited home ranges where they live and they don’t travel very far throughout the year.  Turtles are known for their incredible journeys through the oceans of the world over thousands of miles just to return to the beach where they were born to lay their eggs.  Since the scientific definitions aren’t what we commonly refer to these animals as, for the remainder of this article we’ll refer to Turtles as Sea Turtles, Terrapins as Turtles, and Tortoises as….well Tortoises.

A Peak Inside Their Mobile Home

The shell of our favorite Chelonians is an incredible adaptation that has allowed this group of animals to survive for millions of years.  It also makes Chelonians unique compared with all other types of reptiles. Their shell came to be nearly 260 million years ago as the ribs of some lizard like species began to widen.  The first notable animal was Eunotosaurus africanus.  Fifty million years later, Proganochelys quenstedi became one of the first reptilian creatures whose ribs and shell like bones completely encased the shoulder and pelvic girdles giving them the true appearance of modern Chelonians.  The shell is made of three main areas: the carapace (the top); the plastron (the bottom); and the bridge (connection between the two).  Internally, the vertebrae and ribs are part of the inner layer of the shell, which is made of up of around 60 bones.  Unfortunately, this also means the cartoons we grew up with where the turtle leaves his shell were fun but fiction.  Streamlined shells are an indication of a species that swims such as a Sea Turtle or Turtle, while deep domed shells are a characteristic of a land-dwelling species like a Box Turtle or Tortoises. The shape and texture of a Turtle shell’s scales, called scutes, can tell you if it’s a species that swims quickly or spends it’s time sitting on the bottom of the pond.  Smooth scutes indicate an animal that needs to encounter less friction through the water so these are usually quick swimmers.  Large domed shells or spiked shells on turtles indicate a species that doesn’t move quickly or is an ambush predator trying to blend in with its environment. Tortoise shells are generally domed to allow them to roll onto their belly if they become flipped over, but other than a few specific species most tortoise shells are pretty smooth and similar in texture.  While the shell provides a sort of mobile home for the Chelonian, the main reason this adaptation is so important is its ability to protect them from predators.  In box turtles, the front and back portions of the plastron have hinges that allow them to seal themselves completely inside their shell.  Most other Chelonians, especially Tortoises, have incredibly thick and strong scales on their forearms which they use to block the front of their shell and protect their head when it’s pulled into their shell for protection.

Zilla Tip: Make sure your humidity levels in their habitat are correct and you give your tortoises or land turtles different areas with varied humidity.  For turtles, make sure to clean their tank and change the water often to avoid problems from too much bacteria.  Lastly, UVA/UVB bulbs are absolutely necessary for shell development as well as many other biological systems within your pet Chelonian.  Without access to this type of light, they can become sick, paralyzed, and eventually will die.

Emerging to Conquer the World!

Ok, maybe they won’t conquer the world, but they are on every continent except Antarctica.  Chelonians are shy creatures that only bite for food or when threatened.  Outside of those moments, Chelonians are very docile and personable animals.  Before emerging from their nearly impermeable fortress, they peak to make sure there are no predators and they are safe.  When the coast is clear they extend their neck and legs and get on with their daily routine.  While this is just a normal day for any turtle, their legs and necks have amazing adaptations to protect them from predators and allow them to move efficiently through their environment.  

Turtles and Tortoises have characteristic long necks which contain major blood vessels and at the end of it is their head, which is pretty important.  This can be a weak spot for a predator to take advantage of so our amazing Chelonian friends have developed a few methods for protecting this vital piece of their anatomy.  The most common is the Cryptodiran Method.  This method is used by Tortoises and Sea Turtles as well as most Turtles.  This method entails pulling the head straight backwards into the shell.  The spine hinges at the front inside of the plastron and allows for the neck to curl under itself as the head comes into the shell.  The other method is known as the Pleurodiran Method and involves pulling the head to the side of the shell.  Side-Neck and Snake-Neck Turtles are the most common example of this type of head movement.  Space is made in the shell by folding the neck back and forth like an accordion, leaving the neck and head at the front of the shell partially exposed.  It doesn’t seem like the best method for protecting your neck and head, but they’ve evolved for millions of years and humans have only been around for 300,000 years so who are we to judge.

While not as vital as their neck for life, their legs are still a crucial part of how they get around, dig burrows and nests, protect themselves, and is even important for breathing (Read more HERE).  Each of the three groups of Chelonians has different leg anatomy for different reasons.  Sea Turtles have large paddle-like flippers covered with tight skin and smooth scales used to propel them through the oceans of the world.  All of their fingers and toes are inside the flipper as part of the skeletal structure but aren’t visible from the outside.  Sea Turtles are also unable to retract their legs into their shell.  Turtles, while they live a very aquatic life, have a slightly different anatomy to their arms and legs.  A Turtle’s legs generally have a lot of extra skin which allows them to be flexible when moving in and out of their shell.  Their feet have more defined toes with claws at the end and webbing in between.  This allows them to dig for food or for nesting as well as climbing onto logs and rocks to bask out of the water.  The webbing between their toes allows them to paddle through the water quickly to hide or evade predators.  Slow and steady, but coming up last are Tortoises.  A tortoise’s lower legs are covered with thick strong scales that they use as shields at the opening of their shell when they pull themselves inside it.  Like Turtles, Tortoises have defined claws, but their phalanges, tarsals, and metatarsals (finger bones), are hidden within the skin of their foot.  Their feet look similar to an elephant’s foot.  This provides protection for them along with a solid and durable surface for the bottom of their feet.  This is important as tortoises can spend a good amount of time walking around exploring their environment. 

This Is Just the Beginning