This is a group of animals widely known as the turtles. The order testudines has over 250 known species of turtles. Testudines are a very unique group of animals due to their shells. The shell is a modified ribcage and vertebral column. All testudines are placed in the order chelonia. (Keith p.5). They can be divided into different categories depending on where they live. Sea turtles and terrestrial turtles. Terrestrial turtles are mostly termed as tortoises while aquatic turtles are known as terrapins. Those that live in salty water oceans are referred to as sea turtles. Apart from Antarctica, testudines can be found in all other continents of the world. They are characterized by a shell. The upper side of the shell is known as the carapace while the lower side is known as plastrone. The shell is normally part of the skin.
The first testudines are believed to have lived in the late Triassic periods. This is about two hundred and twenty million years ago. Over two hundred species represented by thirteen group exist today. Since Triassic period, turtles have evolved little by little though it is likely that the modern turtle could resemble the ancient ones with remarkably stable body plan. Testudines are believed to have evolved from body extensions of their back bones and broad ribs that enlarged and grew together to form the protective shell that offered protection at every stage of its evolution even when the components of the bones were not complete( Rieppel 1996 pg453). This is proved by the fossils of freshwater turtles; the odontochelys semitestacea dated back at Triassic period. This species display a complete bony plastrone and an incomplete shell which resembles that of a turtle at embryonic development.
There is no study that shows an exact ancestor for turtles. A molecular analysis of about two hundred and forty eight genes of sixteen vertebrate taxa suggests that testudines could be a sister to birds and crocodiles. (The Achosauria pg35). The separation dates of birds, crocodiles and a turtle is estimated to be two hundred and fifty five million years. The recent common ancestor of the modern turtle is estimated to have occurred about one hundred and fifty seven years ago and corresponds to the separation between cryptodira and preurodira.
Proganochelys is the earliest known fully shelled turtle of the late Triassic period. This genus had so many undisputed traits of the modern turtle. However it lacked the ability to pull its head back into the shell and had a long spiked tail ending in a club. This body form resembles that of ankylosaurs is believed to have resulted from convergent evolution.
Testudines have two extant suborders; pleurodira and cryptodira. Cryptodira is the larger of the two and include all terrestrial turtles, marine turtles and most of the freshwater turtles. Pleurodira is the smaller suborder and consists most of the freshwater species.
Testudines are commonly referred to as tortoises, turtles or terrapins. . There are fourteen extant families of this order. The order has more than three hundred known species though others may have been extinct with time. Ninety seven genera of testudines are also known. These genera are split into two suborders which are cryptodirans and pleurodirans in which the distinguishing factor is how the animals fold their neck to pull their head back into the shell. Pleurodirans have long necks and which they fold sideways while cryptodirans have short ones and they fold them straight back to pull their heads back into the shell. Pelomedusidae and cheidae are the only known extant families of the pleurodires.
The cryptodirans the following known families: carettochelydae, cheloniidae, Testudinae, Dermochelyidae, Chelydridae, kinosternidae, Emydidae and Trionychidae. (Romer 1933 pg 5)
Testudines are placed in a subclass known as Anapsida. Generally, testudines are placed in the following scientific classification.
Kingdom- AnimaliaPhylum- ChordataClass- SauropsidaOrder- Testudines (Linnaeus, 1758 pg 40)
The diet of the testudines varies with the environment as well as the age. Adult turtles’ main diet is aquatic plants, invertebrates such as warms, insects and snails but sometimes they can eat dead marine animals. Some freshwater turtles are carnivals and are reported to feed on small fish and other aquatic small creatures. Young turtles are purely carnivores and feed on crab and snails. This is because proteins are essential for the formation of the carapace and other body features.
Sea turtles feed on sponge, jellyfish and other and other soft bodied sea creatures. Turtles that have stronger jaws have been reported to feed on jellyfish. Some turtles such as green sea turtles are purely herbivores and feed on mainly algae.
Turtles are extant reptiles and therefore are all of their species endotherms. With this they are seen basking in the sun especially in morning either on rocks or bare soil for terrestrial ones or floating on water for sea turtles. Turtles breathe through the lung and lay their egg on dry ground and not in water. A turtle will fold its neck and pull its head in the shell if it notices any form of danger. Turtles have good night vision due to large number of rod cells in their retina therefore most of them prey at night. They have a great color vision with sensitivities ranging from the near ultraviolet to red. Testudines have poor pursuit movement especially the terrestrial ones. However, carnivores ones can move their necks very fast to catch their prey.
All turtles have rigid beaks and use their jaws to catch, cut and chew their food. Testudines are social creatures and sometimes switch between promiscuity and monogamy in their sexual behavior. The rigid carapace of the turtle is dome-shaped which is difficult for any prey to crush and it is also used for camouflaging in case of danger or when preying. (Laurin 1999 pg65)
Turtles live for long and take long before they reach breeding age. They do not have any parental care so ones they lay their eggs, they leave them to hatch on their own and the young ones are left to find their way to their natural habitat.
Testudines resides in different environments ranging from freshwater, salt water, coastline and tropical reefs. They inhabit almost all non-arctic terrestrial region which include deserts, mountains, prairie and mountains. (Alderton, 2012 pg15)
Interactions of turtles with human beings
Some turtles such as red-eared sliders are considered pests where they are not native.
The flesh of turtle’s calipii is used for food in some cultures.
In the Island of Grand Cayman, turtles are a traditional diet.
Fat from turtles is used in cosmetic industry in Mexico and Caribbean.
Chinese use turtle plastrons as traditional medicine.
Small sized Testudines are mostly used as pets in most parts of the world.
Alderton, David, and Susan Barraclough. Amazing snakes and reptiles. New York: Sandy Creek, 2012. Print.Fogel, David. Matamatas: the natural history, captive care, and breeding of Chelus fimbriatus. Ada: Living Art Publishing, 2011. Print.
Wood, Roger Conant. Two new species of Chelus (Testudines: pleurodira): from the late tertiary of Northern South America. Cambridge, Mass.: Museum of Comparative Zoology, 1976. Print.