Softshell Turtle Fossils

The two softshell turtle fossils from my collection (shown above) are broken-off pieces from the animal’s carapace (shell covering). The fossils were unearthed with other Miocene-Pliocene Epoch (23 – 2.6 mya) fossils from the rich fossiliferous east coast of the USA. Below is an excellent softshell fossil specimen from Florida!

Brief Origin of Softshell Turtles

The earliest known turtles date to the Late Permian Epoch around 260 million-years-ago. Whereas living turtles are toothless, many ancestral forms possessed teeth. Many of the oldest and most primitive forms lacked a shell, however, they possessed precursors to the shell structures.

Researchers led by members at the University of Pennsylvania’s Department of Earth and Environmental Sciences describe one of the earliest known species of softshell turtle. The animal lived 66.5 million-years-ago in what is today North Dakota and was unearthed back in 1975. Hutchemys walkerorum, softshell turtle lived at the same time as some very large and well-known species of dinosaurs, including Tyrannosaurus rex and Triceratops. A phylogenetic analysis suggests that the roots of softshell turtles formed in Asia, from where the animals migrated into today’s North America sometime in the Late Cretaceous (105 mya).

Photo Courtesy of Harry Pristis The Fossil Forum

Turtle Shell Structures

Turtle shells have a top (carapace) and a bottom (plastron). The carapace and plastron are bony structures that usually join one another along each side of the body, creating a rigid skeletal box. While most turtles have hard shells composed of scutes or scales, softshell turtles have a cartilaginous carapace covered in leathery skin. The central part of the carapace in softshell turtles has a layer of solid bone beneath the leathery skin, but the bone is absent at the outer edges.

The light and flexible shells of the these turtles allow them to move more easily in open water or in muddy lake bottoms. Having a soft shell also allows them to move much faster on land than most turtles.

Softshell Turtle Description

Softshell turtles are especially recognizable by their flattened, leathery shells with flexible edges and lack of bony scutes (scales) as with hard shell turtles, and also, by a snorkel-like neck and protruding snout. Softshell turtle snouts possess a ridge around the margin of each nostril, which allows the turtle to remain beneath the water surface with just the snout exposed. Their feet are webbed with three claws giving to the family name, Trionychid, which literally means “three-clawed”. 

Male Spiny Softshell Turtle (Apalone spinifera) Rendering

Three Extant Softshell Turtle Species

The three softshell turtle species described below show a wide U.S. distribution within the Central to South Central regions, and Florida, except the Florida Smooth Softshell turtle is restricted to Florida and lower Georgia. Due to their fossil record age and location, these are possible matches to my fossils.

The Spiny Softshell turtle, Apalone spinifera, is distinguished with tubercles or “spines” along the front edge of the carapace above the neck. Largest of the three, the Spiny Softshell turtle adult female carapace measures from 7 to 20 inches (18 to 50 cm) in length and the turtle can weigh up to 25 pounds, while the male carapace is much smaller from 5 to 10 inches (13 to 25 cm) in length.

The two other species are called smooth softshell turtles, the Florida Smooth Softshell turtle, Apalone ferox (fossil sample above) and the Smooth Softshell turtle, Apalone mutica. Both turtle species are medium to large size. Females are bigger with shells measuring approximately 6.5 to 14 inches (16.5 to 35.6 cm) in length, whereas the male shells measure 4.5 to 10.5 inches (11.5 to 26.6 cm) in length.

The Smooth Softshell turtle, Apalone mutica, is the most aquatic of the softshell turtles and is often referred to as a “swimmer”.

The Florida Smooth Softshell turtle, Apalone ferox, colors range from olive green to dark brown, it has the darkest coloration of the three softshell species.

Florida Softshell Turtle Apalone ferox Photo by Johnskate17 on Wikipedia

More Interesting Softshell Turtle Facts

Male and female softshell turtles carapace can differ slightly in color and patterns, but these features also often differ at various stages of development.

Softshell turtles spend most of their lives in the water. They lead a solitary life and are active during the day. They spend their days foraging or basking in the sun on river banks or logs, as they are obviously cold-blooded creatures.

Softshell turtles hibernate in mud for about half of the year from October to March depending on their range.

Trioncychids (softshell turtles) are strict carnivores feeding mainly on fish, amphibians, shrimp, snails, insects and even birds. Adults have few natural predators, just humans. Young softshell turtles are eaten by raccoons, herons, and large fish.

Extinct Giant Softshell turtle (Axestemys byssinus) fossil from the famous Green River Formation in Wyoming, USA spans 6 feet (1.8 m) long and is the largest specimen of its type discovered in this important locality. It was undoubtedly one of the apex predators of Fossil Lake. Age: Early Eocene – 52 million-years-old.

You can find softshell turtles in or near various types of freshwater sources, from small rivers, lakes and swamps to tiny waterholes or bogs.