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Turtle Taxonomy Explained In Layman’s Terms

The information is current and up-to-date in accordance with the latest veterinarian research.

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At first, let me tell you why I am writing this post. As I am running this large turtle website, I felt that I need to understand these creatures better, in a more scientific way.

And from a scientific standpoint, understanding the Turtle Taxonomy seemed most logical as the first step.

I am not explaining this taxonomy from an expert POV. In fact, as I am studying the taxonomy, I am explaining here what I learned.

This way, both you and I get to learn turtles and tortoises better, right?

So let’s get started.

Turtle Taxonomy

At first, let’s go through the first 4 stages of turtle taxonomy. Why? Because these 4 stages are common for every turtles and tortoises!

  • Domain: Eukaryota
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Reptilia
  • Order: Testudines (also known as Chelonia)

What is domain?

In biological classification, the domain is the highest taxonomic rank in the hierarchy of classification. There are three domains into which all of life can be divided:

Bacteria

This domain includes what we typically think of as bacteria. These are very small, simple organisms that can be found almost everywhere on Earth, from soil to water to inside the human body.

They are prokaryotic, which means their cells do not have a nucleus. Their genetic material floats freely inside the cell.

Bacteria are different from Archaea (another domain of simple organisms) because they have unique chemical and genetic makeups which influence things like how they metabolize food or how they are structured.

Archaea

Archaea are also tiny, simple organisms, but they are quite different from bacteria even though they look similar under a microscope.

Like bacteria, Archaea are prokaryotic (no nucleus). However, their genetic material and the way their cells function are more similar to eukaryotes (organisms whose cells have a nucleus).

Archaea are known for living in extreme conditions like very hot springs, salty lakes, or deep ocean vents. They can survive environments that would kill most other organisms.

Eukarya

This domain includes all the organisms whose cells have a nucleus enclosed by a membrane. This group is very diverse, ranging from tiny yeasts to plants to animals.

They are eukaryotic, meaning their cells have a nucleus that contains the genetic material, and various other specialized structures (called organelles), each surrounded by membranes.

What is Kingdom?

In biological taxonomy, the kingdom is a major category directly below domain in the hierarchical classification system of organisms. Kingdoms are used to group species with fundamental structural and physiological traits in common.

Here’s a one-line explanation for each of the kingdoms under the domain Eukarya:

Animalia:

Animals are multicellular and eat other organisms for food. They can move around, especially when young, and their bodies are made up of complex cells organized into tissues.

Plantae:

Plants are multicellular and make their own food through photosynthesis using sunlight and chlorophyll. They have sturdy cell walls made of cellulose and don’t move from place to place.

Fungi:

Fungi include mushrooms, molds, and yeasts (which are usually single-celled). They get their food by breaking down substances around them. Their cell walls are made of a tough substance called chitin.

Protista (or Protoctista):

Protists are a mixed group; they can be single-celled or made of many cells, and might make their own food or eat other organisms. They mostly live in water and their bodies aren’t as complexly organized as plants, animals, or fungi.

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      What is Phylum?

      Essentially, a phylum brings together a large group of organisms that share a significant evolutionary trait, often observed in their structural makeup.

      Here’s a simplified one-line explanation for each major phylum under the Kingdom Animalia:

      Phylum Porifera: Sponges are simple, non-moving animals that filter nutrients from water flowing through their porous bodies.

      Phylum Cnidaria: Jellyfish, corals, and sea anemones are aquatic animals known for their stinging tentacles and mostly marine habitats.

      Phylum Platyhelminthes: Flatworms are thin, often parasitic worms that lack a body cavity, including varieties like tapeworms.

      Phylum Nematoda: Roundworms are common, cylindrical worms with a complete digestive tract, found in soil and water.

      Phylum Mollusca: Mollusks include snails, clams, and squids, characterized by their soft bodies, most with hard calcium-based shells.

      Phylum Annelida: Segmented worms such as earthworms and leeches have bodies divided into ring-like segments.

      Phylum Arthropoda: This is the largest phylum, including insects, arachnids, and crustaceans with segmented bodies, jointed limbs, and typically an exoskeleton.

      Phylum Echinodermata: Starfish and sea urchins are radial symmetrical marine animals that use a water vascular system for movement.

      Phylum Chordata: Vertebrates like fish, amphibians, reptiles, birds, and mammals belong to this phylum and mostly possess a backbone.

        What is Class?

        In biological taxonomy, class is a major taxonomic rank that falls between phylum and order. It is used to further group organisms within each phylum based on more specific structural and functional characteristics.

        The classification level of “class” allows scientists to group organisms that share key physiological and anatomical traits

        Here’s a simplified overview of the main classes within the Phylum Chordata, which includes a vast range of creatures from fish to mammals:

        1. Class Agnatha (Jawless Fish)

        • Characteristics: These are fish without jaws or paired fins, and they have smooth, slimy bodies.
        • Examples: Lampreys and hagfish.

        2. Class Chondrichthyes (Cartilaginous Fish)

        • Characteristics: Fish with a skeleton made entirely of cartilage, not bone, and they usually have tooth-like scales.
        • Examples: Sharks, rays, and skates.

        3. Class Osteichthyes (Bony Fish)

        • Characteristics: Fish with bony skeletons and scales, they make up the largest class of vertebrates in terms of species count.
        • Examples: Salmon, goldfish, and seahorses.

        4. Class Amphibia (Amphibians)

        • Characteristics: Cold-blooded vertebrates that spend their early life in water and adulthood on land, breathing through skin and lungs.
        • Examples: Frogs, toads, and salamanders.

        5. Class Reptilia (Reptiles)

        • Characteristics: Cold-blooded vertebrates with dry, scaly skin, and they lay eggs with leathery shells.

        6. Class Aves (Birds)

        • Characteristics: Warm-blooded vertebrates with feathers, wings, and beaks; most can fly, and they lay hard-shelled eggs.
        • Examples: Robins, eagles, penguins, and ostriches.

        7. Class Mammalia (Mammals)

        • Characteristics: Warm-blooded vertebrates with hair or fur; females have mammary glands to feed milk to their young.
        • Examples: Humans, whales, elephants, and mice.

        What is Order?

        In biological taxonomy, order is a category used in the classification of organisms that falls between class and family.

        It is a way to group organisms that are even more closely related than those just grouped by class, focusing on more specific structural and genetic similarities.

        The 4 major orders under the class Reptilia are:

        Order Testudines (or Chelonia)

        • Characteristics: This order includes all turtles and tortoises, which are known for their bony shells that act as protective armor.

        Order Squamata

        • Characteristics: The largest order of reptiles, Squamata includes lizards and snakes, which are distinguished by their skin, which is covered in overlapping scales.
        • Examples: Cobras, geckos, iguanas, and monitor lizards.

        Order Crocodylia

        • Characteristics: This order comprises crocodiles, alligators, caimans, and gharials, known for their semi-aquatic lifestyles and long, tooth-filled snouts.
        • Examples: American alligator, Nile crocodile, and Indian gharial.
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        Order Rhynchocephalia

        • Characteristics: This small order is composed of reptiles that resemble lizards and are often called tuataras, which are notable for their “third eye,” a photoreceptive organ on their forehead.
        • Examples: Tuatara (the only surviving member of this order).

        Till now, we discussed 5 stages of the taxonomy that are common for all turtles and tortoises. From onwards, we’ll discuss from the Order Testudines, which includes only turtles and tortoises.

        From this point each specific turtle will fall into different categories.

        14 families under Order Testudines

        The Order Testudines, encompassing all turtles and tortoises, is divided into various families that reflect the diverse ecological niches and evolutionary histories of these reptiles.

        The classification within this order can vary slightly depending on the taxonomy source, but commonly, Testudines is organized into approximately 14 families.

        Cheloniidae

        These turtles live in the ocean and include species like the green sea turtle. They are known for their large flippers and streamlined bodies.

        • Common Name: Sea Turtles
        • Examples: Green sea turtle, hawksbill turtle.

        Dermochelyidae

        This family includes only the leatherback turtle, which is the largest of all sea turtles and doesn’t have a hard shell but a leathery covering.

        • Common Name: Leatherback Turtles
        • Examples: Leatherback turtle.

        Testudinidae

        These are land-dwelling turtles with dome-shaped shells and sturdy, elephant-like legs. They are not fast movers and do not swim.

        • Common Name: Tortoises
        • Examples: Galápagos tortoise, African spurred tortoise.

        Emydidae

        Commonly found in ponds and streams, these turtles have hard, bony shells and can close their shells tightly to protect themselves.

        • Common Name: Pond and Box Turtles
        • Examples: Eastern box turtle, painted turtle.

        Geoemydidae

        These turtles live mostly in rivers and streams in Asia. They often have colorful markings and vary widely in shell shape and size.

        • Common Name: Asian River Turtles, Leaf Turtles
        • Examples: Red-crowned roof turtle, black marsh turtle.

        Trionychidae

        Known for their flat, soft shells that feel leathery. They are fast swimmers and often bury themselves in sand.

        • Common Name: Softshell Turtles
        • Examples: Smooth softshell turtle, spiny softshell turtle.

        Kinosternidae

        Small, often mud-colored turtles that live in muddy or marshy waters. They have small, tough shells.

        • Common Name: Mud Turtles
        • Examples: Common mud turtle, yellow mud turtle.

        Chelydridae

        These turtles have strong, sharp beaks and large, rugged shells. They are often aggressive if threatened and live in freshwater.

        • Common Name: Snapping Turtles
        • Examples: Common snapping turtle, alligator snapping turtle.

        Pelomedusidae

        These turtles fold their necks sideways under their shell instead of pulling it directly back. They are mostly found in fresh waters of Africa.

        • Common Name: African Side-necked Turtles
        • Examples: African helmeted turtle.

        Podocnemididae

        Like African side-necked turtles, these also fold their necks sideways. They inhabit rivers and streams in South America.

        • Common Name: American Sideneck River Turtles
        • Examples: South American river turtle.

        Carettochelyidae

        Named for their pig-like, fleshy nose, these turtles have a leathery shell and are excellent swimmers, found in Australia and New Guinea.

        • Common Name: Pig-nose Turtles
        • Examples: Pig-nosed turtle.

        Chelidae

        These turtles, found in Australia and New Guinea, also fold their necks sideways. They have wide, flat shells and are mostly aquatic.

        • Common Name: Australasian Side-neck Turtles
        • Examples: Eastern long-necked turtle, snake-necked turtle.

        Platysternidae

        This family has only one member, the big-headed turtle, which has a disproportionately large head that cannot retract into its shell.

        • Common Name: Big-headed Turtle
        • Examples: Big-headed turtle.

        Caretta

        These are robust sea turtles known for their large heads and powerful jaws, named after their reddish-brown shell color.

        • Common Name: Loggerhead Turtles
        • Examples: Loggerhead sea turtle.

        Now, we cannot discuss each of these 14 families in details as this blog post will turn into a short novel.

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        Let’s choose one family and discuss it further. I am feeling a bit adventurous today, so I am choosing Chelydridae family, also known as the family of Snapping Turtles!

        2 genera under the family Chelydridae (Snapping Turtles)

        The family Chelydridae primarily consists of snapping turtles, known for their large size, aggressive nature when threatened, and powerful jaws.

        This family is relatively small and is generally divided into two genera:

        1. Chelydra
        2. Macrochelys

        These two genera, Chelydra and Macrochelys, encompass the known varieties of snapping turtles, with distinctly adapted features suited to their predatory lifestyle in aquatic environments.

        The separation into two genera reflects significant evolutionary and physical differences, particularly in size, shell shape, and jaw mechanics, which highlight their specialized ecological roles as ambush predators.

        Chelydra

        Chelydra is the genus of the well-known common snapping turtle, which is widespread in North America. It features a rugged, muscular build with a serrated shell and a notably fierce demeanor when provoked.

        Species Examples: Chelydra serpentina (Common Snapping Turtle)

        Macrochelys

        Macrochelys includes species like the alligator snapping turtle, which is one of the largest freshwater turtles in the world. It is distinguished by a heavily spiked shell and a worm-like appendage on the tongue used to lure fish—a form of aggressive mimicry.

        Species Examples: Macrochelys temminckii (Alligator Snapping Turtle)

        3 Species under the Genus Chelydra

        The Chelydra genus encompasses species that are highly capable predators within their aquatic environments, equipped with powerful jaws and a belligerent defense mechanism.

        They are a critical part of their ecosystems, acting as both predator and scavenger, which helps control populations of other species and maintain healthy waterways.

        Chelydra serpentina (Common Snapping Turtle)

        • Habitat: Widely found across much of North America, from southeastern Canada through the US and into parts of Mexico.
        • Description: This species is noted for its robust size, aggressive nature when out of water, and powerful bite. It has a rough shell with a saw-toothed back and a long tail.

        Chelydra rossignonii (Central American Snapping Turtle)

        • Habitat: Found in the waterways of Central America.
        • Description: Similar in appearance to the common snapping turtle but generally found in a different geographical region, which is central to its distinct classification.

        Chelydra acutirostris (South American Snapping Turtle)

        • Habitat: Native to parts of South America.
        • Description: It features a slightly sharper snout compared to C. serpentina and adapts to the warmer climates of South America.

        3 Species under the Genus Macrochelys


        The genus Macrochelys, known for containing some of the largest freshwater turtles, specifically the alligator snapping turtles, includes three recognized species.

        These three species within the Macrochelys genus exemplify significant evolutionary adaptations to specific river ecosystems in the southeastern United States.

        Alligator snapping turtles are critical components of their habitats, acting as apex predators.

        Their considerable size and unique method of predation (using a lingual luring technique) make them fascinating subjects of ecological and conservation interest.

        Macrochelys temminckii (Alligator Snapping Turtle)

        • Habitat: Native to river systems draining into the Gulf of Mexico, from the Florida Panhandle to East Texas.
        • Description: Known for its spiked shell and formidable appearance, it is the largest species in this genus. It uses a worm-like appendage on its tongue to lure fish within reach.

        Macrochelys suwanniensis (Suwannee Alligator Snapping Turtle)

        • Habitat: Restricted to the Suwannee River watershed in Florida and Georgia.
        • Description: Similar in appearance to M. temminckii but adapted to the unique river environment of the Suwannee River. It was recognized as a separate species relatively recently, highlighting the biodiversity within these river systems.

        Macrochelys apalachicolae (Apalachicola Alligator Snapping Turtle)

        • Habitat: Found in the Apalachicola River system in Florida.
        • Description: Another species distinct mainly due to its geographical range; like M. suwanniensis, it was only recently classified as a separate species due to its localized habitat and some morphological nuances.

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                About Author

                Muntaseer Rahman started keeping pet turtles back in 2013. He also owns the largest Turtle & Tortoise Facebook community in Bangladesh. These days he is mostly active on Facebook.

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