Historically, there were four recognized orders within the class Reptilia: order Testudines (turtles and tortoises), order Squamata (amphisbaenians, lizards and snakes), order Crocodylia (crocodiles, alligators and gharials) and order Rhynchocephalia (tuataras; unique to New Zealand). However, we now know that birds (order Aves) are closely related to dinosaurs and crocodilians, and that crocodilians are more closely related to birds than they are to snakes, lizards and turtles. This means that order Aves is actually nestled deep within the historic class Reptilia, and that based on taxonomic orthodoxy birds are, in fact, reptiles. Despite this, most people continue to use the word “reptile” to refer to what we historically classed as reptiles (turtles, amphisbaenians, snakes, lizards, crocodilians and tuatara), and the Canadian Herpetological Society also uses the name in this historic context.
Like mammals, birds, amphibians and fish, reptiles are vertebrates (animals with a spinal column). Reptiles have dry, non-permeable skin covered in scales or bony plates. Although some reptiles live in aquatic environments (e.g. turtles, sea snakes), they all breathe air through lungs. Reptiles are ectothermic (commonly referred to as cold-blooded), meaning they do not generate their own body heat, but rather, their internal body temperature depends on the surrounding environment. Like birds, reptiles have amniotic eggs, which have a protective membrane, yolk and outer shell. However, some species of snakes and lizards do not lay eggs, but instead the female retains the amniotic egg (embryo and a basic placenta) during development and gives birth to live young.
As of July 2018, there are 10,793 known species of reptiles: 6,512 lizards, 3,709 snakes, 351 turtles, 196 amphisbaenians, 24 crocodilians, and 1 tuatara species (The Reptile Database 2018), and new species are discovered each year. Despite its northern latitude and cool climate, Canada has a reasonably high diversity of reptiles, with 10 extant turtle species (excluding some of the transient Sea Turtles), 33 extant snake species and 5 extant lizard species. Some species, such as the Common Gartersnake, are further broken into multiple subspecies across Canada, which are not reflected in these numbers.
Since reptiles are ectothermic, they regulate their body temperature through behaviour,
such as basking in the sun to warm up or seeking shelter in the shade to cool down. Therefore,
reptile behaviour and activity is largely dictated by environmental conditions. Metabolic
activity and energy levels are dependent on temperature; reptiles are relatively slow and
inactive when they are cold and are most active when they are warm. Reptiles have an optimal
body temperature at which they are able to function most efficiently, and they have to
maintain sufficient body temperature to digest their food, incubate young, and forage for
food or escape from predators. In Canada’s cooler climate, having to spend long periods
basking to maintain high body temperature can limit how much time reptiles have for other
behaviours, such as foraging and mating. However, since they do not expend metabolic energy
to maintain their body temperature, reptiles have much lower energy requirements than mammals
or birds of similar size, and can go long periods of time without eating (sometimes months,
in the case of large snakes).
Canada’s snakes and lizards avoid freezing temperatures during the winter by
hibernating underground below the frost line (in mammal burrows, tree root hollows, rock
crevices or other cavities), while turtles hibernate at the bottom of rivers, lakes or
wetlands, beneath the ice. Since their body temperature drops to that of the surrounding
environment, which may be as low as 1-2°C in the hibernation site, metabolic rate slows
dramatically, allowing reptiles to survive for months with no food and very little oxygen.
Turtles are able to obtain what little oxygen they require from the water by absorbing it
through the lining of their mouth and cloaca. During the active season (e.g. when they are
not hibernating), reptiles are most active during warm weather, when they can easily maintain
optimal body temperatures.
Reptiles are adapted to living in a wide diversity of habitats, from cold northern climates
to deserts and everything in between, as well as freshwater environments and oceans (polar
regions excluded). Despite the diversity of habitats they occupy, all reptiles require access
to areas that receive direct sunlight or are sufficiently warm enough to maintain an appropriate
body temperature. All extant turtle species in Canada are aquatic, living in freshwater ponds,
lakes, rivers and wetlands, and the ocean, in the case of sea turtles that frequent Canadian
coasts. Although they spend most of their time in water, turtles use terrestrial habitats for
nesting or moving between aquatic habitats. Some freshwater species, such as the Wood Turtle,
may spend the majority of the active season on land. The Eastern Box Turtle, which was
historically found in southern Ontario but is now extirpated from Canada, is entirely
terrestrial and lives in woodlands. Most snakes and lizards are terrestrial and inhabit a
wide variety of environments ranging from forests to grassland to deserts. However, some
snake species, such as the Queensnake and Common Watersnake, are semi-aquatic and forage
primarily in lakes, rivers and wetlands.
All reptiles in Canada have internal fertilization, meaning that males and females must
copulate for fertilization to occur. Mating occurs during the active season, with the
specific timing (e.g., spring or summer) varying between species. Reptile eggs are more
resistant to drying out than amphibian eggs and can be laid on land, which has allowed
reptiles to colonize and thrive in dry environments far from water. However, most reptile
eggs will drown if submerged under water for extended periods of time. Female turtles lay
their eggs on land in nest cavities that they excavate in sand, gravel or other soft
substrates, typically close to the water. Sea turtles, which inhabit Canadian waters for
parts of the year, migrate south to nest on beaches in tropical regions. Snakes and lizards
lay their eggs in sites that are protected from predators and the elements, such as under
rocks, logs or vegetation, in rotting logs or underground in animal burrows. Female hog-nosed
snakes, however, also use their upturned snout to excavate nest sites in sandy habitats.
Females of live-bearing snakes and lizards are able to protect the developing young inside
their body and ensure optimal temperature and humidity for development. This strategy helps
these species survive in colder climates, since females can reduce the incubation time of
their eggs by basking.
Most species of snakes do not demonstrate parental care, leaving the eggs or young to fend for themselves; female rattlesnakes, however, remain with their young for a few days to a week after birth, protecting them from potential predators. Some female lizards display parental care and remain with their eggs until they hatch in late summer, protecting them from predators and turning the eggs to ensure optimal moisture levels.
Most turtles in Canada are omnivorous, feeding on vegetation as well as a variety of animal
prey, such as invertebrates, fish, frogs, and carrion. However, some turtles have very
specialized diets, such as Northern Map Turtles, which use strong jaws to crush and eat
mussels and snails, and Leatherback Sea Turtles, which follow warm currents into Canadian
waters to forage for jellyfish. Most of Canada’s turtles feed in the water, where the flow
of water into the mouth helps draw food inwards. Lizards feed on a variety of invertebrates,
such as insects, spiders and earthworms, which they actively hunt with their keen senses of
sight and smell. Some lizard species have specialized diets, such as the short-horned
Lizards, which feed primarily on ants. All snakes are carnivorous, although the type of prey
and how it is captured varies. Canada’s snake species prey on a wide range of animals,
including insects, slugs, worms, fish, frogs, toads, salamanders, small mammals, birds and
their eggs, and other snakes. Some species consume a range or prey, while others are
specialists and have a much narrower diet preference. For example, the Common Gartersnake
will eat almost anything it can swallow, while the Queensnake is a specialist, feeding
entirely on freshly-moulted crayfish. Most snake species in Canada actively search for their
prey, although some species, such as the rattlesnakes, employ a ‘sit and wait’
tactic. Some snake species consume their prey alive (e.g., gartersnakes and watersnakes),
while others employ venom (e.g., rattlesnakes) or constriction (e.g., rubber boas and
ratsnakes) to kill prey before swallowing it. Snakes have highly elastic ligaments between
their jaw bones, enabling the mouth to stretch open wide enough to swallow prey that is much
larger than their head.