Lizards are fascinating creatures that have captured people’s imaginations for centuries. Their reptilian nature and alien-like appearances have led many to wonder – do lizards have bones like other animals? The quick answer is yes, absolutely.
Lizards have skeletal systems made up of bones that provide structure, protect organs, and enable movement. In this detailed article, we will explore the anatomy of lizard skeletons, the types of bones they contain, and how their bones compare to those of other animals.
We will examine the evolution of lizard skeletons and the purposes their bones serve. Pictures and diagrams will provide a visual understanding. By the end, you’ll have a comprehensive overview answering the question – do lizards have bones?
Let’s begin unraveling the mysteries of the lizard skeletal system.
The Basic Structure of a Lizard Skeleton
Skull
Lizards have a specialized skull that houses their brain and sense organs. The skull is made up of many bones that are fused together, including the frontal, parietal, nasal, lacrimal, jugal, squamosal, and quadrate bones. The upper and lower jaws contain rows of teeth for catching prey.
Some lizards have more robust skulls for crushing hard-shelled insects and plant material. The skull provides anchorage for important muscles involved in feeding and moving the head.
Spine
The vertebral column, or spine, runs from the skull to the tail tip. It is made up of many small bones called vertebrae linked together. The vertebrae have projections that interlock for flexibility. Lizards have between 50-100 vertebrae, depending on the species. The spine encloses and protects the spinal cord while providing flexibility for movement.
Some lizards, like chameleons, have highly mobile and specially adapted vertebrae to allow for greater neck rotation and body contortions.
Ribs
Most lizards have ribs attached to the vertebrae that encircle the chest cavity. Ribs provide important protection for vital organs like the heart and lungs while also aiding breathing mechanics. The number of ribs can vary from as few as 2 pairs in some legless species to as many as 30+ pairs in some large lizards.
Many lizards have reduced rib cages or even lack ribs entirely, like snakes and other legless squamates that have elongated bodies for burrowing.
Limbs
Lizards have four limbs, with front legs attached to pectoral girdles coming off the spine and back legs attached to pelvic girdles. The limb bones include a humerus/femur, radius/ulna or tibia/fibula, and fingers/toes.
The number of digits can range from 0 in some legless lizards to as many as 12 in species with extra-long digits for increased surface area, like the collared lizard (Crotaphytus collaris). Specially adapted limbs allow lizards to run, climb, dig, swim, and grasp prey.
For example, chameleons have fused digits for gripping branches, while other species have limb bones adapted for speed and agility.
Types of Bones Found in Lizards
Long Bones
Lizards have many long bones that give their bodies structure and enable limb movement. The humerus, radius, ulna, femur, tibia, and fibula are all examples of long bones in lizards. Made of a diaphysis or hollow shaft and epiphyses or rounded ends, long bones grow mostly lengthwise to form limbs.
For instance, a lizard’s femur extends from the knee to the hip. Long bones contain bone marrow and are adaptable to allow for the great range of motion exhibited by lizards.
Flat Bones
Flat bones provide protection and structure while requiring less weight. Lizards have flat bones such as their skull, ribs, sternum, and scapulae or shoulder blades. Rather than a hollow shaft, flat bones are composed of two thin layers of compact bone surrounding a spongy cancellous bone interior.
Many of the flat bones of lizards serve as attachment points for muscle and ligaments. For example, strong jaw muscles anchor to the temporal bone on the side of a lizard’s skull which allows them to bite powerfully.
Short Bones
Numerous small, cube-shaped short bones form lizards’ wrists and ankles. Made of spongy bone tissue covered by a thin layer of compact bone, bracing short bones enable flexibility and range of motion at joints.
For instance, short bones in the wrists and hands provide remarkable adaptability that allows certain lizards like geckos to adhere to and climb smooth vertical services. Short bones also reinforce the tail for balance and signaling purposes in lizards.
Irregular Bones
Irregular bones such as the mandible or lower jaw bone have complex shapes tailored to perform unique functions. With protruding points, notches, and hollows as muscle and ligament anchors, the lower jaw permits the sharp teeth and powerful bites of lizards.
Other highly irregular bones of lizards include vertebrae and hip bones. Vertebrae encase and protect the spinal cord while enabling head motion and articulation of the tail. Meanwhile, complex hip bones made of the ilium, ischium, and pubis provide robust pelvic structure and musculature anchors enabling hindlimb motion.
Sesamoid Bones
Miniature sesamoid bones act like pulleys providing mechanical advantage to muscles and reducing friction at joints. As many as 50 tiny sesamoid bones less than 2mm long may be embedded in the tendons of some lizard species.
Located in limb joints, these round or oval-shaped bones alter connective muscle forces enabling more effective function. For example, previous research has identified 10 sesamoid bones in the feet and toes of green iguanas that aid digital grasping and running on vertical and inverted surfaces.
Unique Skeletal Adaptations in Lizards
Tail Breaking and Regrowth
One of the most amazing adaptations in lizards is their ability to detach and regrow their tails. When grasped by a predator, lizards can voluntarily detach their tails through a process called autotomy.
The tail will then continue to wriggle after detachment, distracting the predator while the lizard makes its escape. Lizards can later regrow a new, but shorter, tail over a period of weeks or months. This regenerated tail contains cartilage instead of bone, so it is more flexible.
Tail autotomy and regrowth helps lizards survive predator attacks. According to a 2018 study, tail loss occurred in 48% of marked lizards over a 5-year period. The new regenerated tails allow lizards to maintain critical fat reserves in their original tails.
This incredible ability highlights the adaptability of lizard skeletal systems.
Arboreal Lizards Have Strong Limbs for Climbing
Lizards like chameleons and anoles that live primarily in trees have evolved specialized adaptations for climbing and grasping branches. Their limb bones are generally longer and more robust compared to terrestrial lizards. Longer forelimbs provide greater reach while climbing.
Grasping feet, with specialized toe pads, provide traction on bark and leaves.
For example, chameleons have fused digits on each foot that form tong-like grasping claws. Their prehensile tails can also coil around branches for added stability. Even chameleons’ turret-like independently rotating eyes help them visually scan their arboreal environments.
These skeletal adaptations allow arboreal lizards to thrive in treetop habitats.
Burrowing Lizards Have Splayed Legs
Fossorial or burrowing lizard species like skinks and amphisbaenians have evolved short, stout bodies and splayed legs to help them maneuver underground. Their wedge-shaped skulls, reinforced by bony deposits, allow them to push through compact soil.
Splayed leg postures increase surface area contact, providing traction against tunnel walls. Compact skulls and reduced ear openings also prevent dirt from entering while burrowing.
For example, the Florida sand skink’s flattened head and streamlined body shape is perfectly adapted for subterranean living. Mexico’s Bipes lizard has tiny vestigial limbs but makes up for it with its powerful shovel-like head.
These types of musculoskeletal adaptations enable fossorial lizards to thrive below ground.
How Lizard Skeletons Compare to Other Animals
Similarities and Differences vs. Amphibians
Lizards and amphibians share some common skeletal features as tetrapods, including having four limbs and a backbone. However, lizard skeletons differ in being better adapted for life on land. While amphibians have cartilage and bone in their skeletons, lizards only have bone, making their frames more rigid and supportive out of water.
Lizards also have specialized vertebrae and pelvic structures not found in amphibians.
Similarities and Differences vs. Mammals
The most noticeable difference between lizards and mammals is that mammals have an enclosed rib cage surrounding their hearts and lungs, while lizards’ ribs simply attach to the backbone and belly scales. However, some lizards and mammals share having a diaphragm muscle important for breathing.
Their limb structures also differ, with mammals having more specialized bone arrangements optimized for running, climbing or other locomotion.
Similarities and Differences vs. Birds
Birds and lizards both are reptiles, giving them major skeletal commonalities including scales, four-chambered hearts, and some features of vertebrae and pelvic bones. However, a bird’s skeleton must be lightweight with some bone fusions to enable flight.
A lizard does not share these specialized avian skeletal traits. For example, birds have hollow bones, swivel wrists, and keeled breastbones to which flight muscles attach – structures lizards lack.
The Evolution of Lizard Skeletons
Early Lizards Looked Very Different
The earliest lizard ancestors looked vastly different from their modern-day descendants. More than 280 million years ago, ancestral lizards had dense, heavy skulls and teeth designed primarily for cracking hard-shelled insects and invertebrates (Taylor, 2021).
Their skeletons were still evolving for a life spent underground, with relatively short limbs and thickset bodies. However, as lizards began to adapt to new environments and food sources, their skeletons evolved rapidly.
Adapting to New Environments Shaped Skeletons
The skeleton is very responsive to environmental pressures, and as lizards adapted to new climates and terrain their bones changed dramatically. Tree-dwelling species like chameleons grew curved nails for clinging to bark and tails for gripping branches.
Swift predators like monitor lizards evolved extremely lightweight skulls and vertebrae to keep their heads level when running. And burrowing desert lizards like sandfish snakes developed reinforced skulls to withstand pushing through compact soil and sand (Reilly et al., 2017).
The same evolutionary progression is reflected across dozens of lizard families – more arboreal species have longer limbs and digits for climbing, terrestrial lizards show fusion of skull bones as strength becomes less important than lightness, and so on (Bergmann and Russell, 2017).
As environments and food sources changed, natural selection quickly acted upon lizard skeletal adaptations to refine them.
Convergent Evolution in Lizard Skeletons
Interestingly, distantly related lizard groups often evolved very similar skeletal changes when adapting to comparable habitats. For example:
| Species 1 | Species 2 | Shared habitat | Convergent skeletal adaptation |
|---|---|---|---|
| Marine iguana | Marine monitor lizard | Coastal marine | Flattened tail for swimming |
| Chameleons | Anoles | Arboreal trees/shrubs | Grasping hands and feet |
| Thorny devil | Horned lizards | Arid deserts | Spiked armored plating |
This phenomenon, known as convergent evolution, reveals the power of natural selection in shaping skeletal structure to match habitat and lifestyle across phylogenetically distant species (Losos, 2011).
Conclusion
In conclusion, lizards absolutely have bones as part of their skeletal system, just like all vertebrates. Their bones provide structural support and protection for muscles and organs. While lizard skeletons share some characteristics with other animals, they have also evolved unique adaptations for the environments and lifestyles of different lizard species.
Hopefully this detailed overview has shed light on the anatomy, purpose and evolution of lizard bones. Lizards have fascinating, intricate skeletal systems that help explain their success across diverse habitats. Their bones allow them to thrive and reveal just how marvelous nature can be.
