Frogs have evolved to have some truly strange anatomy! From their massive eyes and wide mouths to their long, strong, and flexible legs, they look downright otherworldly–and almost as if a skeleton would just weigh them down. Do frogs even have bones, and if so, what are their skeletal systems like?
Read on to learn more about the unusually fascinating skeletal anatomy of frogs below. We’ll cover the general structure of their skeletons as well as many specific bones’ functions. Finally, we’ll also go over why and how frogs’ bones have evolved in such extraordinary ways to suit their amphibious lifestyles.
Do Frogs Have Bones?
Frogs and all amphibians in general are vertebrates with endoskeletons, or internal skeletons made up of many different interconnected bones and cartilage. However, their skeletons are among the most heavily modified, lightweight, and uniquely structured amongst all four-legged animals!
The short answer is, yes, frogs have bones. But It gets way more interesting from here!
For starters, their bones are very thin and lightweight to make swimming and jumping long distances easier. Their skulls are wide with absolutely enormous openings, or orbital cavities, for their large eyes. Their chest cavities have no ribs since frogs don’t need them to assist with breathing like we do. Frogs’ vertebral columns, or spines, are heavily arched and made up of only nine individual vertebrae, making them extremely short. They have remnants of a tail bone, called a urostyle, but obviously no tails since they don’t need them, either!
Overall, frogs’ skeletons are heavily modified to be as lightweight as possible. Over time, their bodies have eliminated various unnecessary structures to make them even more flexible and agile. However, they still have plenty of striated muscle, or skeletal muscle, to assist with moving and, of course, jumping. This brings us to the frog’s leg bones, which are perhaps the most unique of all.
Frogs’ legs are long and strong, so their leg and foot bones are also pretty lanky. They have extra joints in their back legs so they can fold them up close to their bodies when they aren’t moving from place to place. Despite having such thin and fragile bones, their limbs, especially their back legs, are heavily muscled and powerful. Their radius and ulna bones are fused into a single reinforced structure known as a radioulna.
Finally, frogs’ five-toed back feet are elongated, thin, and perfectly spaced for their webbed skin. They also have many extra joints to make them flexible for climbing, swimming, and grabbing onto branches.
Do Tadpoles Have Bones?
Most (but not all) species of frogs start life as fully aquatic tadpoles with extremely simplified skeletal systems. Their skeletons at this age are actually soft, flexible cartilage rather than bone. Their most prominent feature is their notochord, a long rod of cartilage that supports the tadpole’s body until they later transform into frogs with more complex skeletons.
Tadpoles’ bodies at this stage of life are very soft and fragile. Though they have long tails, they don’t have any bones or much structure in them aside from their primitive notochord to help with swimming. Thankfully, they only spend a few weeks in this very vulnerable stage before they begin to transform into froglets. Eventually, their tails absorb into their bodies in a process known as apoptosis, and their much bonier limbs begin to develop.
Interestingly, because tadpoles’ skeletons are so soft and cartilaginous, our fossil record of them is very sparse!
Do Frogs Have Backbones?
Frogs have very short backbones made up of only nine individual vertebrae (compared to the 24 that adult humans have!). Their backbones are short and heavily arched and have no ribs attached to them. Frogs’ spines are connected to their wide hip bones, which form the basis of support for their long and flexible legs.
The structure of a frog’s backbone also helps with more agile movement. Their pelvic girdles can move freely up and down their spines to assist with jumping and swimming. Frogs lack tails, despite having them as tadpoles. The last two bones in their vertebral column fuse into the urostyle, which is sort of analogous to our tailbones.
With such a short, strong, and reinforced backbone and pelvis, frogs are able to not only leap long distances but also safely absorb the impact of any falls!
Do Frogs Have Teeth?
Not all frogs have teeth; some species have none at all. For the most part, though, frogs have very tiny tooth-like protrusions along either their upper or lower jaws, but rarely both. They have two different types of teeth: maxillary and vomerine. Maxillary teeth are pedicellate teeth attached to the jaws, and the crowns and roots of the teeth are separated by fibrous tissue. Vomerine teeth are tiny protrusions along the roof of a frog’s mouth.
Both maxillary and vomerine teeth are very small. Maxillary teeth are only around a millimeter long, and vomerine teeth aren’t much larger. Both types of teeth have a pointy, triangular cone shape.
Instead of using their teeth to chew food like most animals, frogs mainly use theirs to grab and hold onto their prey. The number of teeth frogs have varies significantly from species to species. Most have somewhere between 30 and 40 maxillary teeth on their upper jaw and four or five vomerine teeth. They lose and regenerate these teeth often as they wear down over time.
Currently, only one species, Gastrotheca guentheri, has true teeth along both its upper and lower jaws.