What are Turtles?
Physical Description
Within the class Reptilia, the class of reptiles, the order Testudines includes all turtle species. This group is distinct by their shells that develop primarily from their ribs and are made mostly of bone. The order Testudines includes land-dwelling tortoises, freshwater terrapins, softshell turtles, sea turtles, and snapping turtles. The distinctive physiological trait of a turtle is its shell, which is unique amongst vertebrates. The turtle shell provides protection and shelter to the animal and is comprised of between 50-60 bones in two parts: the dorsal carapace (the dome on the back) and the ventral plastron (the belly plate). Softshell turtle species retain these bony components, but their carapace lacks the hard, horny projections, called scutes, that adorn hard-shell turtles. Living turtles are classified into one of two groups based on their neck physiology: side- and hidden-neck turtles. Side-neck turtles belong to the suborder Pleurodira and can be differentiated from the other suborder, Cryptodira, because they retract their head in front of their legs by bending their neck in the horizontal plane. Cryptodirans, hidden-neck turtles, retract their heads and tuck them and their necks between their forelimbs within the shell.
Geographical Distribution and Habitats
Turtles have a wide distribution around the globe. Some species are terrestrial, semi-aquatic, or fully aquatic and they are therefore able to inhabit a number of different environmental niches. Most turtles are tropical or subtropical, but some leatherback species inhabit the colder waters of the Atlantic and Pacific Oceans. All side-neck turtles live in fresh bodies of water in the Southern Hemisphere, whereas hidden-neck turtles include terrestrial, freshwater, and saltwater species that live in more variable environments.
Types of Turtles Alive Today
There is considerable diversity in turtle species that are alive today; however, many turtle species face a number of threats to their survival. Of modern turtle species, 60% are considered threatened or extinct. Notable living species are the Galapagos giant tortoise, the common snapping turtle, the red-eared terrapin, the leatherback sea turtle, and the painted turtle, which is the most widespread turtle native to North America. So, what are some turtle species that are no longer alive today?
How Are Animals Classified by Conservation Status?
The conservation statuses of various animal and plant species are assessed by the International Union for the Conservation of Nature (IUCN) and added to their “Red List”. The IUCN evaluates different species and assigns them to one of the following categories on the IUCN Red List: data deficient, least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild, and extinct. These categories are distinguished by a set of criteria that grade the level of endangerment of a species. Animals and plants at the lowest risk for extinction are “least concern” and those at high risk are “critically endangered”. The IUCN also tracks if certain populations are trending upwards or downwards in total size.
Archelon ischyros
One cool species of extinct turtle is Archelon ischyros, the largest turtle to ever live on earth. Archelon was a marine turtle that lived during the Late Cretaceous epoch between 80.2 and 74.2 million years ago. The largest fossil specimen ever was 15 feet long from head to tail, with weight predictions between 4,800 and 7,000 pounds! That is just around the length and weight of an average minivan! Archelon had a leathery back, rather than the hard, horny shell characteristic of many sea turtles. Originally, it was thought to be a close relative to the living leatherback sea turtle. It is now in its own taxonomic family separate from any living sea turtles. The holotype Archelon specimen, the original specimen that led to the description of the new species, was found in South Dakota along the Cheyenne River by an American paleontologist in 1895. The largest specimen ever found was discovered later and was nicknamed ‘Brigetta’. Although its discovery was in South Dakota, it is now on display in the Natural History Museum Vienna in Austria. There are only five specimens of the genus Archelon in the known archeological fossil record.
Stupendemys geographica
Another extinct species of turtle is Stupendemys geographica, the largest ever freshwater turtle. This turtle’s shell had a diameter of up to 6 feet! Due to carapace size and other body dimensions gleaned from fossil remains, the largest Stupendemys specimen is suspected to have weighed approximately 2,525 pounds. Stupendemys lived during the Middle Miocene and inhabited a large network of interconnected lakes in what is now South America. This giant freshwater turtle survived in this area until becoming extinct in the Early Pliocene. It survived on a diverse omnivorous diet of fish, mollusks, snakes, small crocodilians, fruit, and palm seeds. Current hypotheses suggest there was some degree of sexual dimorphism in the species, with the male turtles growing to be much larger than the females.
Eunotosaurus africanus
Arguably the first ever species of turtle, another cool type of extinct turtle is Eunotosaurus africanus. Eunotosaurus africanus is an extinct reptile species that was alive between 265.8 and 259 million years ago! Many scientists argue this species represents the first ever turtle species or a transitional fossil between turtles and their prehistoric ancestors. This is because the Eunotosaurus had flat and wide ribs that formed plates resembling the carapace of a turtle. They also had similar vertebrae to turtles with regards to number, size, and shape. Some features of their skulls, however, were more similar to other primitive reptiles than turtles. Eunotosaurus‘ first description by scientists was in 1892. By 1914, the prevailing theory was that Eunotosaurus was the ancestral turtle species. It was recognized as such until 1956, when the hypothesis was challenged by American paleontologist Alfred Sherwood Romer. He claimed that there was insufficient evidence to classify Eunotosaurus as the ancestor of turtles, and the discussion remains inconclusive to this day.
Yangtze giant softshell turtle (Rafetus swinhoei)
An interesting species of extinct turtle is the Yangtze giant softshell turtle, Rafetus swinhoei. The IUCN classifies this species as critically endangered, but this is based on an outdated assessment from 2018. Currently, there are only two individuals potentially alive in the wild, but they live in separate, isolated lakes, rendering this species effectively extinct. Recent artificial insemination attempts have been unsuccessful as well. The Yangtze giant softshell turtle’s push towards extinction has been due largely to habitat destruction, subsistence hunting, and use in traditional medicines. The Yangtze giant softshell turtle used to inhabit freshwater lakes and rivers in Southeast Asia, including the Yangtze River, Lake Tai, and Hoan Kim Lake. They’re omnivores that primarily fed on water hyacinth, rice leaves, fish, frogs, crabs, and snails. These massive turtles could grow up to 39 inches long and 28 inches wide, easily weighing up to 220 pounds. In fact, the largest specimens reported from Vietnam weighed 546 pounds! The Yangtze giant softshell turtle had a deep-set head with eyes positioned on the top surface, and a pig-like snout. Males were typically smaller than females but had longer and thicker tails.
Additional Fun Turtle Facts!
The largest snapping turtle ever weighed 249 pounds!The largest leatherback seat turtle ever weighed 2,120 pounds!The oldest tortoise ever is 190 years old (and counting)!
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