TURTLES AND TORTOISES
Turtles and tortoises are reptiles with shells. Turtles live mostly in the water and tortoises live mostly on land. According to the official Red List by the World Conservation Union almost half the turtles and tortoises are threatened.
Turtles are common sites in ponds, lakes, rivers and streams. They are commonly seen sunning themselves on rocks and logs. During the winter in temperate areas turtles hibernate by spending months in the mud without taking a breath.
Turtles are reptiles. They are cold blooded and lay eggs. There are 250 species of turtles. They live on land and in salt water and fresh water. Seven species live in the sea. Males can be distinguished from females by their longer tails. Some can live to be over a 100 years old.
The males and females of many turtles species bob their heads up and own, sometimes for hours, before mating. The males of some species bite the females head and suck on her feet to get her in the mood. During copulation the male often bites into the shell of the female to steady himself. Some males have to prop themselves up in an almost vertical position on the female to achieve penetration.
See Separate Article REPTILES factsanddetails.com ; SEA TURTLES: CHARACTERISTICS, BEHAVIOR, REPRODUCTION ioa.factsanddetails.com ; SEA TURTLE SPECIES ioa.factsanddetails.com
Origin of Turtles
Archelon, an extinct marine turtle from the Late Cretaceous (100.5 million years ago to 66 million years ago) is the largest known turtle, with the biggest specimen measuring 4.6 meters from head to tail and weighed 2.2–3.2 tonnes
Oliver Rieppel, curator of fossil reptiles at the Field Museum in Chicago, told the Chicago Tribune, “The origin of the turtle shell has been a big debate in paleontology for a long time. The turtle shell is such a specialized, unique feature. No other vertebrate animal group has this kind of body plan that has always been a big mystery.”
It appears that turtles first had shells only on their bellies. In an article in Nature in November 2008, Rieppel described a fossil — found in what used to be a shallow sea in Guizhou Province of southwestern China — of a turtle that lived 220 million years ago, a time when dinosaurs first appeared. The toothy aquatic creature — named "Odontochelys semitestacea" Latin for — half-shelled turtle with teeth — was about 40 centimeters long and had a shell on its belly (a plastron) but lacked one on its back (the carapace). Its ribs and backbones were beginning to expand and grow together in such a way that millions of year larger would yield a carapace.
Some scientist dispute the conclusion. Robert Reisz, an evolutionary biologist at the University of Toronto, said he thinks Odontochelys once had a carapace and lost as an adaption to its environment the same ways some modern sea turtles have. The oldest previously known turtle fossil has a full shell, beaked mouth and no teeth like modern turtles. It was would found in Germany and dated to about 206 million years ago.
How Turtle Shells Evolved
Elise Poore wrote in Live Science: According to a report published in the journal Current Biology, paleontologists once believed that the shell was formed through the fusion of osteoderms — bony deposits that make up the protective scales on crocodiles and armadillos. But developmental biologists disagreed with this theory, given how the embryos of modern day turtles develop. Instead, they believed the ribs underneath turtle ancestors' bodies fused and gradually united over the body to form the shell. [Source: Elise Poore, Live Science, January 6, 2024]
The debate wasn't settled until 2008, when Chinese scientists discovered the fossil of Odontochelys semitestacea, described above, whose name means "half shelled turtle with teeth." Although the fossilized animal's shell was incomplete, it had no osteoderms and showed widening of the ribs, confirming the developmental biologists' theory. Scientists say it represents an intermediate step in the evolution of the turtle shell. The later stages of evolution are shown in fossils of the genus Proganochelys.
Turtle Characteristics
Turtles don't have teeth. They chew and grasp things with horny jaws that contain sharp, almost knifelike cutting edges. Some turtles are completely vegetarian. Others are completely carnivorous. Many are omnivorous, eating whatever they can find. Turtles can not breath like human by expanding and contracting the rid cage. Instead they rely on muscles around their lungs to do the job.
Turtle shells consist of two parts: 1) the carapace, the upper, arched part; and 2) the plastron, the flat lower part. The carapace is attached to the backbone and ribs. The palstron is fused to the breastbone. In hard shelled turtles the bone is covered by a shield made of a horn-like material. Soft shelled turtles have a covering of tough skin over the bony shell.
The carapace consists of two layers: an inner core of bony plates that are fused together, and an outer layers of shields made of hornlike keratin, called scutes. The shape and patterns of the scutes is a useful clue in identifying different species.
A turtle's shell grows along with the animal and, unlike the skin of lizards and snakes, is not periodically shed. Most turtles when flipped on their back can turn themselves back over.
Soft-Shell and Two-Headed Turtles
Soft shelled turtles like snapping turtles lack the keratin shields of other turtles. Their carapaces instead are covered with a layer of leathery skin. They are generally more aggressive than hard-shell turtles and can deliver a nasty bites with the sharp edges of their jaws.
Most soft-shelled turtles are carnivorous while hard-shelled varieties are most vegetarians. Soft-shelled turtles spend much of their time lying motionless on the floor of a pond, lake or swamp, waiting for passing fish, crayfish, and aquatic insects which they snap up with surprising speed.
Many soft-shelled turtles have greatly elongated nasal cartilages that serve as snorkels when the turtle is under water. With these devises the turtles can stay submerged for long periods of time, occasionally projecting their nose above the water to breath.
Occasionally two-headed turtles or tortoises are born. The owner of a two-headed Mediterranean. Spur-thighed tortoise told National Geographic that his pet had a slightly misshapen shell and back legs stuck out he side of the shell more than with one-head turtles. He said the right head was dominant and it sometimes moved the body while the other head was eating.
Turtle’s Life
In 1953, E. B. White, of “Stuart Little” and “Charlotte’s Web” fame, wrote in The New Yorker: We strolled up to Hunter College the other evening for a meeting of the New York Zoological Society. Saw movies of grizzly cubs, learned the four methods of locomotion of snakes, and were told that the Society has established a turtle blood bank. Medical men, it seems, are interested in turtle blood, because turtles don’t suffer from arteriosclerosis in old age. [Source: E. B. White, The New Yorker, January 23, 1953]
The doctors are wondering whether there is some special property of turtle blood that prevents the arteries from hardening. It could be, of course. But there is also the possibility that a turtle’s blood vessels stay in nice shape because of the way turtles conduct their lives. Turtles rarely pass up a chance to relax in the sun on a partly submerged log.
No two turtles ever lunched together with the idea of promoting anything. No turtle ever went around complaining that there is no profit in book publishing except from the subsidiary rights. Turtles do not work day and night to perfect explosive devices that wipe out Pacific islands and eventually render turtles sterile. Turtles never use the word “implementation” or the phrases “hard core” and “in the last analysis.” No turtle ever rang another turtle back on the phone. In the last analysis, a turtle, although lacking know-how, knows how to live. A turtle, by its admirable habits, gets to the hard core of life. That may be why its arteries are so soft.
DNA Remnants Found in Fossil of 6 Million Year Old Turtle
In September 2023, scientists announced that they had discovered the remnants of DNA in fossilized remains dating to 6 million years ago of a sea turtle closely related to today's Kemp's ridley and olive ridley turtles, marking one of the rare times genetic material has been identified in such ancient fossils of a vertebrate. Reuters reported: The researchers said some bone cells, called osteocytes, were exquisitely preserved in the fossil, which was excavated along Panama's Caribbean coast in 2015. The fossil is partial, with a relatively complete carapace - the turtle's shell - but not the rest of the skeleton. The turtle would have been about a foot (30 centimeters) long when alive, they said. [Source Reuters, September 29, 2023]
In some of the osteocytes, the cell nuclei were preserved and reacted to a chemical solution that allowed the researchers to recognize the presence of remnants of DNA, the molecule that carries genetic information for an organism's development and functioning, said paleontologist Edwin Cadena, lead author of the study published in the Journal of Vertebrate Paleontology. "I want to point out that we did not extract DNA, we only were able to recognize the presence of DNA traces in the nuclei," added Cadena, of Universidad del Rosario in Bogota and the Smithsonian Tropical Research Institute.
DNA is quite perishable, though in the right conditions it has been preserved in some ancient remains. Researchers last year reported the discovery of DNA from animals, plants and microbes dating to about 2 million years ago from sediment at Greenland's remote northernmost point. Cadena said the only older vertebrate fossils than the newly described turtle to have been found with similar DNA remnants were of two dinosaurs - Tyrannosaurus, which lived about 66 million years ago, and Brachylophosaurus, which lived about 78 million years ago. Cadena said DNA remnants also have been reported in insects dating to tens of millions of years ago.
The turtle is from the same genus - Lepidochelys - as two of the world's seven living species of sea turtles - the Kemp's ridley, the world's smallest sea turtle, and the olive ridley, Cadena said. Kemp's ridley, with a triangular-shaped head and a slightly hooked beak, is primarily found in the Gulf of Mexico. The olive ridley, which closely resembles the Kemp's ridley, has a larger distribution, primarily found in the tropical regions of the Pacific, Indian and Atlantic oceans.
The fossil represents the oldest-known member of Lepidochelys and helps to shed light on the poorly understood evolutionary history of this genus, the researchers said. They did not identify it by species because the remains were too incomplete, Cadena said."Each fossil, each fossil site has specific conditions of preservation that in some cases could have favored preservation of original biomolecular remains such as proteins and DNA," Cadena said. "Maybe in the future and with more studies of this kind, we could be able at some point to sequence very small pieces of DNA and to infer things about their close relatives or involve that information in a broader molecular evolutionary study," Cadena added.
Image Sources: Wikimedia Commons
Text Sources: Mostly National Geographic articles. Also David Attenborough books; Live Science, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
Last updated November 2024