By John Marshall | Feb 12, 2020
Turtles have been around for more than 200 million years, making them among the oldest surviving land animals on Earth. We all have a picture of what a turtle looks like, but what makes a turtle a turtle?
Photo by Adobe Stock/MCE-128
The first distinguishing characteristic is its shell, which is formed by the fusion of the backbone, vertebrae, and ribs to form a box made of bone and cartilage. The top shell is called the “carapace,” and the bottom shell is known as the “plastron.” The two are joined by the “bridge.”
Another feature of turtles, as is the case with most reptiles, is that they lay eggs. Even aquatic and marine turtles that spend most of their lives in the water must come onto dry land to lay their eggs. The eggs are buried in the soil or under decaying vegetation, where they then incubate. Turtles don’t provide any care for their eggs or young; once the eggs are deposited, they’re on their own.
One more characteristic of all modern turtles is that, like birds, they don’t have teeth. Most turtles have beak-like mouths, and food is swallowed whole or crushed by their bony jaws.
There are more than 300 species of turtles worldwide, with more than 50 in the United States and Canada. They can be loosely grouped into five large categories: snapping, soft-shelled, aquatic and pond, box turtles and tortoises, and sea turtles.
These truly ancient-looking animals have large heads, long tails, and hooked snouts, and they’re aquatic, only leaving the water to bask in the sun and lay eggs. There are two species in North America: the common snapping turtle (Chelydra serpentina) and the alligator snapping turtle (Macrochelys temminckii). The alligator snapping turtle is the largest freshwater turtle in the world, capable of reaching 200 pounds and more than 2 feet in length, and it has a distinctively ridged carapace. The smoother-shelled, common snapping turtle, while not as large, may still weigh as much as 35 pounds and have carapace lengths of 1-1/2 feet.
Common snappers are found in slow, freshwater currents throughout the eastern and central U.S. and southern Canada. In peninsular Florida, the common snapping turtle is replaced by a different subspecies called the Florida snapping turtle. When on land, the common snapper is extremely aggressive if confronted by a predator (or human) and can deliver a nasty bite from its powerful jaws and hooked, beak-like mouth.
Photo by AKM Images/Joshua Gahagan
Alligator snapping turtles are found mostly in the southern U.S. They inhabit large, slow-moving rivers and swamps. Adult alligator snappers, while ferocious-looking, are much more docile than common snapping turtles. When cornered on land, alligator snapping turtles simply sit and gape open-mouthed — although their bite can still take off your finger.
Though both species are omnivores, unlike common snappers, alligator snapping turtles don’t pursue their prey. Instead, they catch their food by “fishing” for it with a worm-like appendage at the bottom of their mouth. This “lure” is wiggled to attract a curious fish, tadpole, or crayfish to its doom.
Photo by Getty Images/Zoonar RF
Perhaps the oddest of the turtles are soft-shells, so called because their plastrons are covered with skin instead of hard plates called “scutes.” There are four species of soft-shelled turtles across North America: the spiny (Apalone spinifera), midland (Apalone mutica), Gulf Coast (Apalone calvata), and Florida (Apalone ferox). Soft-shelled turtles are relatively large, some with shell lengths of almost 25 inches, although 12 to 18 inches is more common.
Soft-shells inhabit large creeks, rivers, and farm ponds, where they feed on crayfish, snails, mussels, frogs, and fish. In addition to their distinctive, pancake-like shell, these turtles have long necks and pointed snouts with the nostrils at the very tip. Soft-shelled turtles are extremely aquatic in nature, rarely leaving the water except to lay eggs.
Photo by Getty Images/oceanbounddb
In shallow water, they typically bury themselves in mud or sand and extend their heads to the surface to breathe. In deeper water, soft-shelled turtles can remain submerged for long periods of time, thanks to their ability to absorb oxygen through their skin, and by pumping water in and out of their throats.
Soft-shelled turtles can be very aggressive when handled. Their long necks allow them to reach behind them or to the side and deliver a nasty bite. Their soft, leathery shells also make them difficult to hold on to. Like their cousins the snapping turtles, large adults in particular should only be handled by experienced professionals.
Sliders, Sawbacks, and Cooters
The largest group of turtles in North America is pond and river turtles. This diverse group lives in a wide variety of aquatic habitats and includes pond sliders, map turtles, diamondback terrapins, river cooters, painted turtles, red-bellied turtles, sawbacks, bog turtles, Blanding’s turtles, and chicken turtles. Most of these are medium to large in size, with shell lengths from 6 to 12 inches.
Perhaps the best known turtle globally is the red-eared slider (Trachemys scripta elegans), recognizable by the thick red stripe behind each of its eyes. This creature’s native range covers the southern and central U.S., where it inhabits rivers, lakes, swamps, and farm ponds. However, red-eared sliders have also been widely sold as pets throughout the world, which has led to them being released into the wild in far-flung areas. They’re now considered one of the world’s most invasive species. Red-eared sliders feed on a variety of plants and animals, with young turtles requiring more animal protein than adults.
Common map turtles (Graptemys geographica) are medium-sized reptiles found mostly in rivers and large lakes. Their name comes from their ornate carapace patterns that resemble the contour lines on a map.
Closely related to map turtles are diamondback terrapins (Malaclemys terrapin), so-called because of the concentric rings on their carapaces. They’re unique as North American turtles go, in that they live only in brackish coastal marshes and estuaries along the Eastern Seaboard and Gulf Coast. They feed mostly on crabs, clams, and snails. Diamondback terrapins can live in strongly saline waters for extended periods of time and have special glands to secrete excess salt.
Unlike map turtles or red-eared sliders, chicken turtles (Deirochelys reticularia) are named for the flavor of their meat. They’re also known for their unusually long necks and the yellow stripes on their thighs.
While most turtles thrive in warm climates, some species have adapted to cooler environs. The bog turtle (Glyptemys muhlenbergii) is North America’s smallest, with full-grown adults reaching a mere 4 inches. They’re found mostly in the northeastern U.S., with an isolated population in the southern Appalachians of Tennessee, North Carolina, and northern Georgia. As the name implies, their preferred habitat is bogs and wetland areas.
The Blanding’s turtle (Emydoidea blandingii) is a medium-sized reptile found in the north-central U.S. and eastern Canada, especially around the Great Lakes. Blanding’s turtles prefer wetlands and are distinguished by their bright-yellow chin.
Boxy Turtles and Tortoises
While most turtles are associated with water, some have adapted quite well to life on land. Among these are box turtles and tortoises. The box turtles include the eastern box turtle (Terrapene carolina), which is found throughout most of the eastern and central U.S. These 4-1/2-to-7-inch reptiles inhabit forested areas where they feed on a wide variety of foods, such as berries, insects, and mushrooms. The ornate box turtle (Terrapene ornata) inhabits prairies and shrub habitats, primarily in the Great Plains. It can be distinguished from its eastern counterpart by the bright yellow lines decorating its plastron and carapace, and its non-webbed feet.
Photo by Getty Images/JasonOndreicka
All box turtle species get their name from the ability to pull their head and feet inside their shells and close up into a “box.” This is made possible by a hinged plastron. This is the box turtle’s response when in danger, as it protects them against most predators.
Photo by Adobe Stock/Brian E Kushner
Tortoises in North America are represented by four species, all found in the extreme southern U.S.
The gopher tortoise (Gopherus polyphemus) inhabits primarily the dry forests of coastal areas of the southeastern U.S. This is the only North American tortoise found east of the Mississippi River. It feeds on grasses and other herbaceous vegetation.
The desert tortoise (Gopherus agassizii), as its name implies, is found in the Mojave and Sonoran deserts of southern California, Nevada, Utah, Arizona, and northern Mexico. It feeds on succulent plants, such as cacti.
The Texas tortoise (Gopherus berlandieri) lives in extreme southern Texas and areas of northeastern Mexico. At about 8-1/2 inches long, Texas tortoises are the smallest North American tortoises. They feed on grasses and whatever succulent plants might be available, such as the prickly pear cactus.
Photo by Getty Images/Paulbr
The Bolson tortoise (Gopherus flavomarginatus) is the largest North American species, with a carapace length of about 1-1/2 feet. Sometimes called the giant Mexican tortoise, this herbivore lives in the isolated deserts of north-central Mexico. It’s only been known to science since 1959.
As the scientific name implies, these tortoises dig like gophers, making burrows in which they live and escape heat, cold, and fire. The one exception is the Texas tortoise; it either uses the burrows of existing animals (such as armadillos), or digs a shallow depression at the base of a tree or shrub.
Photo by Getty Images/IsaacGolding
Deep Sea Divers
The largest of all turtles are the sea turtles, of which there are seven species. Six of these are found in North American waters: the leatherback (Dermochelys coriacea), the green sea turtle (Chelonia mydas), the loggerhead (Caretta caretta), the hawksbill turtle (Eretmochelys imbricata), Kemp’s ridley (Lepidochelys kempii), and the olive ridley (Lepidochelys olivacea).
By far the largest species of sea turtle — and indeed, one of the largest living reptiles on Earth — is the leatherback, reaching up to 8 feet long and weighing as much as 2,000 pounds. As the name implies, leatherbacks don’t have a bony carapace and plastron. They have thick, leathery skin ridged with bone, and though they’re mostly black, each adult has a pink spot on the top of its head. Leatherback sea turtles are masters of the deep, having been documented diving to depths of up to 4,000 feet. They cover vast distances in their travels and can range from the Caribbean to New England and the Maritime Provinces. Jellyfish are the main staple of their diet.
The other species of sea turtles are found mostly in tropical and warm, temperate waters. They live most of their lives in the ocean, coming ashore only to lay their eggs. As with most other turtles, the sex of the young is determined by the temperature at which the eggs incubate. Warm temperatures produce mostly females, and cooler temperatures result in mostly males.
Green sea turtles are tropical and found mostly in shallow seas offering plenty of algae and seagrass to eat. This green diet gives the turtle the green body fat for which it’s named.
Characterized by a large head with blunt jaws, loggerhead sea turtles are wide-ranging and might live near shore or hundreds of miles out at sea. They feed on a wide range of marine organisms, including the Portuguese man-of-war with its stinging tentacles.
Decorated with splashes of yellow, orange, and reddish-brown, by far the most colorful and tropical species of sea turtle is the hawksbill. Hawksbill turtles are most associated with coral reefs, where they use their long, pointed beaks to pry food from the crevices of corals and feed on sponges.
The Kemp’s ridley turtle is considered the smallest of the sea turtles, with a maximum carapace length of less than 30 inches. It feeds on a wide variety of marine invertebrates in shallow coastal waters.
The olive ridley is found throughout the Pacific, Indian, and southern Atlantic oceans. They’re the second smallest of the sea turtles, behind the Kemp’s. They feed on fish, invertebrates, and algae. Along with the Kemp’s, olive ridley sea turtles are especially known for their unique and synchronized nesting ritual known as arribada, meaning “arrival by sea,” during which thousands of females nest simultaneously over small stretches of beach.
Turtles in Trouble
Many turtle species are in trouble, both in North America and around the world. The causes include the over-hunting of both adults and eggs for food; over-collection of the animals for the pet trade; pollution; and most notably, habitat loss. Other species, such as the red-eared slider, are doing quite well and have even become pests in the parts of the world where they were introduced.
Species with limited habitat requirements and geographic distributions are especially susceptible to population declines. But even widespread species, such as the sea turtles, have declined dramatically throughout their range.
John Marshall is a stormwater inspector for the city of Mobile, Alabama. He lives on the eastern shore of Mobile Bay with his wife and family.
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