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From the beginning... There were turtles everywhere! Yet, even though some fossils suggest their evolution began in water, the turtle lineage continued and resulted in marine turtles, freshwater turtles (semi-aquatic), as well as the terrestrial form (e.g. tortoises) in more recent years.
This segment contains some basic information about the turtles that live in water, including rivers and ponds, with extra details about their current conservation status.
It's fair to call them ancient because the most significant progression into modern freshwater turtles occurred during the Triassic period.
Despite being difficult to imagine, this geologic period occurred more than 200 million years ago.
Here's the thing:
With sound justification, this era is more commonly known as the "Age of Reptiles"!
This is because some of the dominant and most ferocious land-dwelling vertebrate animals at the time were large dinosaurs - and reptiles.
Nowadays, even though they spend a lot of time basking on dry land, the best places to find freshwater turtles are rivers, ponds, lakes, marshes, and some swamplands (wetlands).
Because the vast majority are omnivores, they eat aquatic plants (including algal material), insects, small fish, and the decaying flesh of dead animals (called carrion).
When they are not eating or sleeping, freshwater turtles like to bask in warm sunshine to help regulate their body temperature. They also need to absorb some ultraviolet rays to metabolise calcium and to improve shell health.
The average lifespan for many freshwater turtles is generally between twenty (20) and forty (40) years. Still, with optimum conditions, it's not uncommon for some species to live even longer, such as tiny map turtles (Graptemys) and slider turtles (Trachemys).
There are some notable differences between sea turtle anatomy and the body parts of the semi-aquatic species.
The shell still has a hard top (carapace) and the plastron (bottom part) is made of bone and keratin. It is part of a skeletal structure that cannot be shed.
Like their ocean based counterparts, they also breathe air with their lungs. They can also hold their breath for long periods of time even while they're submerged in nonsaline water.
But wait - there's more:
During brumation, and even in the time of total hibernation, many of the softshell turtle species are able to absorb oxygen from water through their skin or through the blood vessels in the opening at the base of the tail (called the cloaca).
In a nutshell, some sea turtle characteristics remain unchanged with their fresh water counterparts, such as during reproduction.
The females also lay their eggs in soft soil or sand near to a body of water. Similarly, the temperature of the nest is usually the determining factor for the sex of the baby hatchlings.
The Yangtze giant softshell turtle is a prime example of the freshwater turtle species. At one time, many softshell turtles (family Trionychidae) were found in the Yangtze River (the main river in China) as well as some parts of northern Vietnam, where it's known as the "Hoàn Kiếm turtle".
Even though they're almost extinct, Yangtze giant softshell turtles currently remain as one of the largest freshwater turtles in the world.
Key points:
Matured adults can reach around one (1) metre (more than 3 feet) in shell length and weigh more than one hundred (100) kilograms (220 pounds).
Their shell is relatively flat for a cold-blooded reptile, and their carapace has a leathery appearance with no bony scutes.
They prefer to live in lake and river habitats, and being an omnivore means they tend to eat crustaceans, fish, snails, and some aquatic plants.
With only three (3) living specimens remaining (kept in captivity), this giant softshell is considered as being the rarest turtle on Earth.
Here's why...
Conservation efforts, mostly in the form of captive breeding programs and artificial insemination attempts, have been unsuccessful at producing viable hatchlings.
Pro Tip: In March of 2018, the IUCN Red List of Threatened Species evaluated the Yangtze giant softshell turtle (Rafetus swinhoei) and cited them as being "Critically Endangered" with the current population trend still "Decreasing".
Interesting Fact: Many of the freshwater turtle species are facing severe threats of vulnerability and even outright extinction, such as from habitat destruction, road mortality, pollution, and the illegal pet trade. But another section explains how conservation efforts are finding ways to save turtles, including those focusing on protecting their nesting areas and inshore wetlands.