There are many qualities that set animals apart from each other, but if you really want to simplify things, all species on the planet can be split into two main categories: vertebrates and invertebrates. The vertebrate category contains many of the most popular, beloved animals out there (possibly even your ideal pet!), but what does the term mean, and are reptiles in this group?
Yes, any member of the reptile species is classed as an air-breathing vertebrate. Second to birds and fish, reptiles represent the largest category of vertebrate animals on earth, comprised of over 10,000 species. As vertebrates, reptiles have a backbone but do not have an outer (Exo)skeleton.
As strange as it is to consider, even snakes are included in this category of animals that have a backbone. That isn’t the only interesting fact though. Let’s look at reptile vertebrates in a little more detail including their many characteristics and skeleton structure, plus a look into vertebrate animal species as a whole.
What are Vertebrates?
Vertebrates essentially refer to any living creature with a backbone or a spinal column that protects the nerve cord. Vertebrate animals also have an internal skeleton and the term vertebrate comes from the Latin word ‘vertebratus’ which roughly translates to ‘joint of the spine’.
In addition to reptiles, vertebrate animals also include fish, birds, amphibians, sharks, and mammals (that includes us humans too!). One thing vertebrates don’t have, however, is an exoskeleton e.g. a hard shell or outer casing.
Invertebrates, by comparison, do not possess a backbone or an internal skeleton. They do, however, have an exoskeleton which could be a soft body or a tough outer casing depending on whether they are land or marine animals. Invertebrate animals include crabs, jellyfish, worms, spiders, squids, clams, and coral.
What are the Characteristics of Reptiles Vertebrates?
- Reptiles are classed as tetrapod vertebrates, which essentially means that they possess four limbs or are at least descended from ancestors with four limbs. So this comprises snakes as well as modern-day turtles, lizards, crocodiles, and alligators.
- They are also cold-blooded animals, meaning they cannot regulate their internal body temperature.
- Like other vertebrates, reptiles have a backbone running along the entire back of their body and have a distinct head with a tubular brain and otic, optic, and nasal organs.
- Their internal skeletons or ‘endoskeletons’ are divided into tail and trunk bone sections with a rib cage, sternum, and vertebrae and the chain segment of bones helps them move their limbs fluidly whether in a tiny gecko or a large crocodile.
- Reptile vertebrates possess toughened thick skin made from Keratin (the same substance that human hair and nails are made from). This gives them a waterproof layer that prevents the reptile’s internal moisture from evaporating. This tough outer skin can be in the form of scales (as with snakes), bony armor plates (turtles and tortoises), or a combo of both for crocodiles and alligators.
- Reptilian vertebrates also fertilize their eggs internally and produce either live young or soft-shelled eggs.
Do Reptiles Have Exoskeletons?
No, reptiles do not have an exoskeleton as this is associated with invertebrates like insects and crustaceans with a hard outer shell casing like crabs and beetles. What reptiles have instead are endoskeletons inside their bodies – just as humans do – although unlike ours, their skeletal structure varies wildly across the various reptile species!
Reptile endoskeletons are formed of a protein network delicately mineralized by calcium and across the snake species alone, some may possess as few as 2 or as many as 18 cervical vertebrae (the bone segments connecting the skull to the shoulders).
Another characteristic of the reptile endoskeleton is that some species will either have single-headed or double-headed ribs. The former aligns at the joining of two vertebral bodies and is typically seen in turtles and tortoises, whilst double-headed ribs (often seen on lizards and snakes) allow for mobility.
Are Fish Vertebrates?
Yes, fish count as aquatic vertebrates because, like all vertebrates, they have an internal backbone or ‘endoskeleton’. In fact, fish actually make up 50 percent of all living vertebrates, comprising around 25,000 species in total.
Not to be confused with invertebrate fish species, vertebrate fish consist of the gill-bearing bony fish such as carp, catfish, goldfish, and guppy etc. Invertebrate fish, meanwhile, include lobsters, oysters, prawns, jellyfish, worms, sea cucumbers, and sponges.
Are Birds Vertebrates?
Yes, all bird species on the planet (over 10,000 or so) are vertebrates as there is not a single bird species without an endoskeleton. Their internal skeleton is much lighter than a mammal or reptile’s because the bones are hollow due to air cavities known as ‘pneumatic bones’ which help them to breathe. However, these hollow bones are every bit as strong for their size and function.
Unlike reptiles and fish, birds are warm-blooded vertebrates, so they are able to generate and maintain their internal body temperature by converting their food to energy and warmth. However, like their reptilian vertebrates, birds also lay their young in egg form and often possess scaly skin on their feet and lower legs.
Are Amphibians Vertebrates?
Yes, amphibians are also vertebrates (all 8,226 species to be exact!) as they have internal backbones but no hardened scales on the outside of their bodies. Their name derives from the Greek word ‘amphibious’ which loosely means “double life” in reference to an amphibian’s life spent on land and in the water.
Amphibians are cold-blooded vertebrates meaning that, like reptiles, they are not able to regulate their body heat and rely on their surroundings to help them keep warm or cool off, either by basking in the sunshine or leaping into the water to cool themselves down.
Like fish vertebrates, amphibians are born with gills (though many species outgrow them as they reach adulthood), and unlike reptile vertebrates, amphibians lay very soft, porous eggs that are transparent and have no shell, requiring them to be laid underwater as opposed to on land.