Reptiles have always fascinated people with their appearances and behaviors that seem almost alien compared to mammals. One question that often comes up regarding reptiles is whether they stop growing or keep growing indefinitely throughout their lives.
If you’re short on time, here’s a quick answer to your question: Most reptiles do stop growing at some point, but their growth slows down dramatically as they reach adulthood. Their maximum size depends on factors like genetics, food availability, climate conditions, and health.
In this comprehensive article, we will analyze the growth patterns of different reptile groups and the various internal and external factors that affect their development. We will also look at some exceptional reptile species that never cease growing.
Growth Patterns of Major Reptile Groups
Lizards
Lizards exhibit incredible diversity in their growth rates and maximum sizes. Small lizards like anoles may reach adult size in under a year, while the Komodo dragon can take over 10 years to reach its full length of 10 feet.
Most lizards follow an indeterminate growth pattern, meaning they grow continuously through their lives. However, their growth rate slows down dramatically once they reach sexual maturity. Large lizard species like monitors and iguanas experience the most significant slowing of growth rates after reaching maturity, while smaller species like geckos and skinks may not exhibit much deceleration at all.
The factor that likely has the biggest impact on a lizard’s growth rate is its habitat. Lizards in resource-poor environments with limited food availability tend to grow slower and reach smaller maximum sizes.
Species in tropical regions with year-round access to prey generally grow much faster and larger. For example, a Savannah monitor in Africa may reach 5 feet long, while a similar-looking monitor species on a remote Pacific island may max out at 12 inches.
Temperature also plays a role, with lizards in warmer climates able to be more active and feed more often than those in colder regions.
Snakes
Like lizards, most species of snakes exhibit indeterminate growth, meaning they continue to get larger throughout their lives, though at a slowing pace once adulthood is reached. Some snake species have extreme differences in growth rates and maximum lengths depending on geographic location and habitat.
For example, timber rattlesnakes in the northeastern United States may reach only 3 feet long, while the same species in the southeast can attain lengths over 7 feet.
For most snake species, males tend to grow faster and often reach larger maximum sizes than females. The difference can be striking in some cases, like green anacondas where males may reach over 20 feet long but females top out at around 16 feet.
Higher levels of testosterone are likely responsible for increased growth rates in male snakes. As with lizards, snake growth rates also depend heavily on habitat quality and food availability. Snakes with access to calorie-rich prey like birds and mammals generally grow much faster than those dining strictly on insects, worms, or amphibians.
Turtles and Tortoises
Unlike lizards and snakes, the growth of most turtle and tortoise species slows dramatically or even stops completely after they reach maturity. For example, a box turtle may reach adult size at 5-7 years old and then grow little, if at all, for the remainder of its lifetime.
In fact, indeterminate growth is so rare in turtles and tortoises that only 6 species are known to exhibit it: alligator snapping turtles, some softshell turtles, pig-nosed turtles, leatherback sea turtles, green sea turtles, and Galápagos tortoises.
For those turtle species that do exhibit indeterminate growth, maximum lifespan plays a big role in determining their ultimate size. Species like Galápagos tortoises and leatherbacks that can live over 100 years continue growing for decades after reaching maturity.
In 2009, researchers encountered a male Galápagos tortoise estimated to be 170 years old with a shell length of nearly 5 feet and weight of 919 pounds – the largest ever measured for the species. In contrast, snapping turtles, with a lifespan of around 50 years, may grow only 10-20% after reaching maturity.
Crocodilians
Crocodilians, including alligators, crocodiles, and caimans, are the reptile group that exhibits the most consistent indeterminate growth. Most species continue to grow noticeably throughout their lives, up to 40-50 years for medium-sized crocodilians and 80-100 years for larger species.
While growth rates slow down significantly once sexual maturity is reached, an adult crocodilian may still increase around 50% in length and weight over the remainder of its life.
As with other reptiles, maximum lifespan and habitat quality play key roles in limiting crocodilian growth. Dwarf crocodile species in Africa and South America may attain maximum lengths of 5-6 feet in the wild due to their shorter life spans.
In contrast, saltwater crocodiles in Australia and estuarine crocodiles in Indonesia with access to abundant food sources can reach sizes of 20 feet or more. The largest crocodilian ever reliably measured was a 20.3 foot saltwater crocodile caught in Australia in 2011. In captivity with abundant food, crocodilians can grow larger than records from the wild, reaching lengths of up to 23 feet for saltwater crocodiles.
What Causes Reptiles to Stop Growing
Reaching Physical Maturity
Like all animals, reptiles go through a growth phase early in life before reaching full physical maturity. The age at which reptiles stop growing varies by species, but generally occurs once they reach adult size and sexual maturity (when they can reproduce).
For example, bearded dragons typically reach full maturity around 18-24 months, while large snakes like pythons may take 3+ years before their growth plates close.
Once a reptile reaches maturity, their skeletal system ossifies (hardens), the growth plates close, and most of their body systems level off. At this point, they’ve achieved their natural maximum size that evolution has «finely tuned» for their species to thrive.
While they’ll continue to put on modest weight as adults, significant growth in length and height stops as resources shift toward reproduction rather than structural development.
Limited Food Supply
Food availability directly correlates with a reptile’s health and consequent physical growth. In the wild, when resources are scarce due to drought, migration, overpopulation or other factors, reptiles may fail to reach maximum adult size for their species.
They channel limited nutrients toward survival functions rather than optimal growth. In essence, their bodies prioritize keeping them alive over getting bigger.
For pet reptiles, improper, insufficient, or monotonous diets prevent them from obtaining all the «building blocks» they need to reach full maturity. Providing balanced, vitamin-rich nutrition with diversity supports a reptile’s growth potential.
But malnutrition «places a ceiling» on how large that reptile ultimately grows – and can even cause stunted development.
Climate and Seasonal Changes
Reptiles are ectothermic, meaning external temperatures significantly impact their biological processes. As cold-blooded animals, most reptiles exhibit higher metabolism and activity levels in warm weather.
But when the mercury drops in winter (or if they don’t receive adequate heat in captivity), their digestion and growth rates may decline or halt altogether during brumation.
Extreme highs also place physiological limitations on reptiles in summer months. Seeking shade, reducing activity, and adjusting food intake enables survival but provides fewer resources for growth. So, while temporary stunting may occur seasonally, once optimal temperatures and photoperiod return annually, most healthy reptiles resume progress toward mature dimensions.
Health Issues and Injuries
When weakened by illness or injury, a reptile’s system directs resources toward recovery before growth. Parasites, respiratory infections, mouth rot, and other conditions tax their immune systems. Healing fractures, wounds, or lost limbs obviously also delays physical development.
Even if the underlying health problem resolves, the energy expended fighting it leaves less raw material for the growth process.
Additionally, research shows long term or highly stressful captivity often correlates with maximal size reduction in various reptiles. Though the exact causes remain speculative, factors like depression of feed/growth drives could inhibit their ability to reach potential.
By promoting low stress handling and housing enriched by habitat furnishings, herp enthusiasts help counteract this effect.
Reptiles That Grow Indefinitely
Green Anaconda
The green anaconda is one of the largest snakes in the world, growing up to 30 feet long and weighing over 500 pounds. These massive constrictors are found in tropical South America near swamps, marshes, and slow-moving streams.
Green anacondas never stop growing throughout their life, which can span over 20 years in the wild.
While most snakes have average lifespans of 15-20 years, anacondas continue growing well past this age due to their slow metabolisms. Their cells continue dividing and enlarging as the snakes age. Females tend to be about 20% larger than males on average.
The largest anaconda ever measured was a female that stretched 28 feet long and weighed over 500 pounds.
A green anaconda’s age can be estimated by its size. Newly hatched babies are around 24-30 inches long. At around 3-4 years old, they reach 6 feet. By 7-9 years old, green anacondas exceed 13 feet and truly begin their massive growth.
The largest specimens are likely at least 20 years old based on their tremendous proportions.
Due to their prodigious appetites and rapid growth throughout life, green anacondas require large territories and abundant prey sources. They are apex predators in their ecosystem and vital to balancing populations of their prey.
Aldabra Giant Tortoise
The Aldabra giant tortoise is one of the largest reptiles on Earth, weighing over 550 pounds on average as adults. These gentle giants originate from the Aldabra Atoll in the Indian Ocean and can live over 100 years.
Their extremely slow metabolism allows them to grow continually throughout their long lives.
Aldabra tortoises hatch from eggs at only 3-5 inches long. Slow growth begins from birth but accelerates with maturity. Once they reach adulthood after 25-30 years, they continue expanding, adding weight and thickening their shells. The oldest known Aldabra tortoise was over 250 years old.
Due to their slow metabolisms, Aldabra tortoises can survive up to a year without food or water. This helps them endure the atoll’s dry seasons when vegetation is scarce. Their long lifespan also aids their survival during harsh conditions and droughts.
The leading cause of death for Aldabra tortoises is not old age – they are extremely resilient when healthy. Instead, mortality often occurs when their shells crack due to human activity, animal attacks, or crushing by tree branches.
American Alligator
American alligators are large crocodilians found throughout the southeastern United States. They continue growing their entire lives, which allows them to reach tremendous sizes. American alligators live 35-50 years on average and can exceed 14 feet in length as adults.
Newly hatched alligators measure around 8-10 inches long. Exceptional growth occurs in their first 8 years, where they gain about 1 foot in length annually. Their growth slows around sexual maturity at 6-10 years old but does not stop.
Mean adult length is around 11 feet for males and 8 feet for females.
The largest alligator ever recorded was over 19 feet long and weighed over 2,000 pounds. Only a tiny fraction of the population reaches such mammoth proportions. Based on its size, it was estimated to be at least 80-100 years old. Truly ancient alligators over 100 years old may exceed 16 feet long.
Lifelong growth allows alligators to keep dominating their ecosystems as apex predators. It also aids their survival during lean times when prey is scarce. Overall, their continuous expansion helps them thrive in swamps and marshes across the southern U.S.
Growth Rate Comparison with Other Animals
When it comes to growth rates, reptiles are quite different from other animal groups like mammals and birds. Here’s an overview of how the growth rates of reptiles compare:
Reptiles vs. Mammals
Mammals typically have a faster growth rate than reptiles in early life stages. For example, kittens and puppies reach adult size in a year or less. In contrast, small reptiles like geckos can take 2-3 years to fully mature.
Large reptiles like crocodiles and tortoises can take well over a decade to finish growing.
However, the maximum lifespan and total body size of reptiles is often greater than similarly-sized mammals. For instance, Galapagos tortoises can live over 100 years and reach 600 lbs, much larger than other turtles.
Reptiles vs. Birds
Birds exhibit rapid growth initially but reach adult size quickly, within months for small birds and 1-2 years for large birds like ostriches. Reptiles tend to have a slower but more steady rate of growth over a longer period.
Additionally, birds have indeterminate growth – they continue to put on weight each year as adults. Reptiles stop growing altogether once they reach mature size.
Factors Influencing Reptile Growth
Several key factors impact growth rates in reptiles:
- Genetics – Species with larger maximum sizes tend to have longer growth periods.
- Climate – Warmer temperatures speed up metabolic and growth rates.
- Food availability – Abundant food resources enable faster growth.
- Sex – In some species, males and females grow at different rates.
Measuring Reptile Growth
Snout-to-Vent Length
Snout-to-vent length (SVL) is a common measurement used to track the growth of reptiles over time. It is measured from the tip of the snout to the cloaca or vent. SVL can be useful for estimating age, determining growth rates, and monitoring the health of captive reptiles.
Researchers and veterinarians may take regular SVL measurements of the same individual to assess normal growth and development or issues like malnutrition.
Total Length
Total length measures the reptile from snout to the tip of the tail. This measurement provides an overall size perspective but does not necessarily reflect body mass or growth like SVL. Total length can vary a lot based on tail breaks, so it is not as useful for precision monitoring.
Still, total length provides helpful supplementary data and can allow estimations of age for some species based on published age/length data.
Body Mass
Tracking the body mass of a reptile over time can give precise insight into growth, development, and health status. Mass is measured in grams or kilograms using a scale accurate to at least the nearest gram.
Researchers may take regular body mass measurements of captive reptiles to quantify growth rates at specific ages or under certain conditions. A healthy reptile’s mass should steadily increase over time as it grows. Significant loss of mass may signal health issues like disease or malnutrition.
Skeletochronology
Skeletochronology examines the growth rings or lines of arrested growth (LAGs) in a reptile’s bones to estimate age and historical growth rates. Researchers can take very small bone samples and make thin sections to count the LAGs under a microscope.
Each complete LAG generally represents a full cycle of growth and dormancy, though environmental factors can affect the number produced each year. This technique provides precise age and growth data that can validate or calibrate other measuring techniques.
However, it does require specialized laboratory equipment and training.
Conclusion
In conclusion, while the vast majority of reptiles do stop growing at some point in their lives, the maximal size they reach can vary greatly depending on species as well as environmental factors. Certain exceptional reptiles like large snakes, tortoises and crocodiles have indeterminate growth, enabling them to continue expanding in size albeit at a slowed pace.
Understanding reptile growth dynamics can help herpetology experts provide better care guidelines as well as contribute to conservation efforts for endangered reptiles.
