Frogs are unique animals that have fascinated people for centuries. Their ability to live both on land and in water makes them a wonder of nature. But are frogs vertebrates like mammals, birds and reptiles or invertebrates like insects and worms? Read on to uncover the answer.
If you’re short on time, here’s the quick answer: Frogs are vertebrates, meaning they have a backbone and spinal column like other vertebrates.
In this nearly 3000 word guide, we’ll explore frog anatomy in detail to definitively answer whether frogs have a backbone and spinal column, making them vertebrates, or if they lack these traits which would make them invertebrates.
Defining Vertebrates and Invertebrates
Vertebrate Characteristics
Vertebrates are animals that have a backbone or spinal column. The backbone is made up of small bones called vertebrae that protect the spinal cord. Vertebrates share several other key characteristics:
- Vertebrates have an internal skeleton made up of bone or cartilage.
- They have a central nervous system consisting of a brain and spinal cord.
- They have a closed circulatory system with a heart that pumps blood to transport oxygen and nutrients.
- Vertebrates have a segmented body plan with a head, neck, trunk and tail in many species.
- They have a muscular system for locomotion.
There are around 75,000 known species of vertebrates. Major vertebrate groups include mammals, birds, reptiles, amphibians and fish. Humans are vertebrates, as are other well-known animals like dogs, chickens, lizards, frogs and sharks.
Invertebrate Characteristics
Invertebrates are animals that lack a vertebral column or backbone. This is the key distinguishing feature between vertebrates and invertebrates. Here are some other general invertebrate characteristics:
- Invertebrates do not have an internal skeleton made of bone. Some have an exoskeleton like an insect’s hard outer shell or a mollusk’s shell.
- They have more simple nervous system organization compared to vertebrates.
- Many invertebrates have an open circulatory system without true blood vessels.
- Their body plans are more variable than vertebrates.
- Some invertebrates use locomotion methods like cilia, flagella or jet propulsion.
It’s estimated that around 97% of all animal species are invertebrates, so they greatly outnumber vertebrates in diversity. Familiar invertebrate groups include insects, spiders, crabs, clams, squid, starfish, worms, sponges and jellyfish.
Key Aspects of Frog Anatomy
The Frog Skeleton
One of the defining characteristics of a vertebrate is the presence of a backbone, which frogs have. The frog skeleton is made up of a skull, a backbone, ribs, and bones in the arms and legs.
The frog backbone, also called a spinal column, is made up of a series of small bones called vertebrae. There are typically nine fused vertebrae in adult frogs that give them structure and support. This spinal column allows a frog to be flexible for jumping and swimming.
The Frog Spinal Column and Backbone
The frog spinal column surrounds and protects the spinal cord which runs from the brain down the center of the back. Each vertebra has a hole in the center so the cord can pass through.
additionally, frogs have a cervical vertebra that connects the skull to the backbone and allows side-to-side head rotation. This is another vertebrate feature possessed by frogs.
Other Vertebrate Traits in Frogs
Along with a backbone, frogs also share other traits with vertebrates:
- Closed circulatory system with a heart that pumps blood, unlike insect open circulatory systems
- Advanced nervous system with a brain and specialized sensory organs
- Jaws with teeth to grip prey, unlike invertebrates like worms or jellyfish
- Paired appendages (arms and legs) with joints for movement
When comparing the anatomy, it becomes clear frogs have much more in common with vertebrates like fish, reptiles and mammals than with invertebrates like insects or mollusks.
Vertebrate Trait | Frogs | Invertebrates |
---|---|---|
Backbone | Yes | No |
Spinal cord | Yes | No |
Closed circulation | Yes | No |
Paired appendages | Yes | No |
Evidence That Frogs Are Vertebrates
The Frog Backbone and Spinal Column
One of the defining features of a vertebrate is the presence of a backbone. Frogs have a backbone made up of short vertebrae joined together into two main regions: the vertebral column and the caudal vertebrae.
The vertebral column contains 8 or 9 small vertebrae and extends from the skull to the pelvis, providing support for the head and trunk. The caudal vertebrae, numbering over 50, extend into the hindlimbs and tail region providing flexibility.
This spinal column surrounding and protecting the spinal cord is a key characteristic of the vertebrate subphylum.
Similarities to Other Vertebrates
Frogs share other commonalities with vertebrates in terms of anatomical structure and organ systems:
- Well-developed brain enclosed within a bony skull
- Closed circulatory system with heart pumping blood to tissues and organs
- Advanced sensory organs like eyes, ears, nose and specialized receptors in skin
- Paired appendages or limbs
- Pancreas, liver, kidneys and advanced digestive system
The sophisticated organ systems and sensory capabilities are much more advanced than what is found in invertebrates like insects or mollusks. Frogs also undergo indirect development, with free-living larval forms very different from the adults.
This metamorphosis between egg, tadpole and adult is another similarity to other vertebrates.
Vertebrates | Invertebrates | |
---|---|---|
Early Development | Undergo indirect development via larval forms, like tadpoles in frogs | Direct development from egg to adult form |
Embryo Nourishment | Embryos receive nutrients from yolk or specialized tissues | Embryos receive nutrients from egg exterior |
Key Differences From Invertebrates
While frogs share much in common with other vertebrates, they lack key features found in invertebrates like insects or clams:
- No hard exoskeleton or insect shell
- Do not undergo molting/ecdysis to shed rigid external skeleton
- Lack compound eyes and jointed bodies divided into segments
- Do not possess open circulatory system or hemolymph
Common Misconceptions About Frogs
Myth: Frogs Shed Their Backbones
A common myth is that frogs can shed or lose their backbones as they grow and develop. This likely stems from the fact that tadpoles lack backbones early on. However, once a tadpole metamorphoses into an adult frog, the backbone remains intact throughout its life.
The backbone, made up of small interlocking bones called vertebrae, is a defining feature of all vertebrates including frogs. Vertebrates differ from invertebrates in that they possess these internal supportive structures.
So while tadpoles may start life without backbones, mature frogs maintain this structure permanently according to experts at frog research organizations like Save The Frogs.
Myth: Some Frogs Lack Backbones
Connected to the myth about shedding backbones is the idea that certain frogs actually lack backbones at all stages of life. However, this claim has no factual basis. All frog species possess backbones and are therefore classified as vertebrates.
Their skeletal anatomy enables essential functions like jumping on land or swimming through water. According to animal classification resources, over 7,000 amphibian species exist globally, but there are no known backbone-less frog varieties among them.
While frogs display amazing adaptability and variation in their life cycles and habits, all maintain the vertebrate distinction of an internal skeleton. So rest assured, even the most adept jumping frog has a sturdy backbone to thank! 🐸
Conclusion
As we’ve explored, frogs clearly share the same vertebrate traits as mammals, birds, reptiles and other backboned creatures. Their skeleton, spinal column and backbone identifies frogs solidly as vertebrates rather than the invertebrates they are sometimes confused with.
Understanding the vertebrate nature of frogs sheds light on their evolutionary history and relationship to other animals. It also highlights the diversity of vertebrate life on Earth. So next time you encounter a frog, you can confidently say you are looking at a unique vertebrate wonder.