Maurits Cornelis Escher was a Dutch graphic artist who made mathematically inspired woodcuts, lithographs, and mezzotints. Despite wide popular interest, Escher was for most of his life neglected in the art world, even in his native Netherlands. He was 70 before a retrospective exhibition was held. In the late twentieth century, he became more widely appreciated, and in the twenty-first century he has been celebrated in exhibitions across the world.
Turtles are an order of reptiles known as Testudines, characterized by a shell developed mainly from their ribs. Modern turtles are divided into two major groups, the side-necked turtles and hidden neck turtles which differ in the way the head retracts. There are 360 living and recently extinct species of turtles, including tortoises and terrapins. They are found on most continents, some islands and much of the ocean. Like other reptiles, birds, and mammals, they breathe air and do not lay eggs underwater, although many species live in or around water. Genetic evidence typically places them in close relation to crocodilians and birds.
A tessellation or tiling of a flat surface is the covering of a plane using one or more geometric shapes, called tiles, with no overlaps and no gaps. In mathematics, tessellations can be generalized to higher dimensions and a variety of geometries.
House of Stairs is a lithograph print by the Dutch artist M. C. Escher first printed in November 1951. This print measures 47 cm × 24 cm. It depicts the interior of a tall structure crisscrossed with stairs and doorways.
Relativity is a lithograph print by the Dutch artist M. C. Escher, first printed in December 1953. The first version of this work was a woodcut made earlier that same year.
Waterfall is a lithograph by the Dutch artist M. C. Escher, first printed in October 1961. It shows a perpetual motion machine where water from the base of a waterfall appears to run downhill along the water path before reaching the top of the waterfall.
Metamorphosis III is a woodcut print by the Dutch artist M. C. Escher created during 1967 and 1968. Measuring 19 cm × 680 cm, this is Escher's largest print. It was printed on thirty-three blocks on six combined sheets and mounted on canvas. This print was partly coloured by hand.
The spotted turtle, the only species of the genus Clemmys, is a small, semi-aquatic turtle that reaches a carapace length of 8–12 cm (3.1–4.7 in) upon adulthood. Their broad, smooth, low dark-colored upper shell, or carapace, ranges in its exact colour from black to a bluish black with a number of tiny yellow round spots. The spotting patterning extends from the head, to the neck and out onto the limbs. Sexually mature males have a concave plastron and a long, thick tail. By contrast, sexually mature females possess a flat plastron and have a tail notable shorter and thinner than mature males. Mature males also have a dark iris and face; females typically have a yellow or orange iris and a similarly coloured face that is distinctly lighter than males. Juveniles appear female-like in this regard and at maturity males begin to develop darker features.
Drawing Hands is a lithograph by the Dutch artist M. C. Escher first printed in January 1948. It depicts a sheet of paper, out of which two hands rise, in the paradoxical act of drawing one another into existence. This is one of the most obvious examples of Escher's common use of paradox.
The pig-nosed turtle, also known as the pitted-shelled turtle or Fly River turtle, is a species of turtle native to northern Australia and southern New Guinea.
The common box turtle is a species of box turtle with six existing subspecies. It is found throughout the Eastern United States and Mexico. The box turtle has a distinctive hinged lowered shell that allows it to completely enclose itself. Its upper jaw is long and curved.
The Pleurodira are one of the two living suborders of turtles, the other being the Cryptodira. The division between these two suborders represents a very deep evolutionary divide between two very different types of turtles. The physical differences between them, although anatomical and largely internal, are nonetheless significant, and the zoogeographic implications of them are substantial. The Pleurodira are known more commonly as the side-necked turtles and the name Pleurodira quite literally translates to side neck, whereas the Cryptodira are known as hidden-necked turtles. The Pleurodira turtles are currently restricted to freshwater habitats in the Southern Hemisphere, largely to Australia, South America, and Africa. Within the Pleurodira, three living families are represented: Chelidae, also known as the Austro-South American side-necked turtles, the Pelomedusidae, also known as the African mud terrapins, and the Podocnemididae, also known as the American side-neck river turtles. However, they are a cosmopolitan clade across the Cretaceous and Cenozoic, and even occurred in marine environments across the world.
The Roti Island snake-necked turtle, also commonly known as McCord's snakeneck turtle, is a critically endangered turtle species from Rote Island in Indonesia.
The turtle shell is a shield for the ventral and dorsal parts of turtles, completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles. The bone of the shell consists of both skeletal and dermal bone, showing that the complete enclosure of the shell probably evolved by including dermal armor into the rib cage.
The hawksbill sea turtle is a critically endangered sea turtle belonging to the family Cheloniidae. It is the only extant species in the genus Eretmochelys. The species has a worldwide distribution, with Atlantic and Indo-Pacific subspecies—E. i. imbricata and E. i. bissa, respectively.
Eunotosaurus is an extinct genus of reptile, possibly a close relative of turtles, from the late Middle Permian Karoo Supergroup of South Africa. The Eunotosaurus resided in the swamps of southern Africa. It is often considered as a possible "missing link" between turtles and their prehistoric ancestors. Its ribs were wide and flat, forming broad plates similar to a primitive turtle shell, and the vertebrae were nearly identical to those of some turtles. It is possible that these turtle-like features evolved independently of the same features in turtles, though some studies suggest Eunotosaurus is a genuine, primitive turtle relative. Other anatomical studies and phylogenetic analysis suggest that Eunotosaurus is a parareptile and not a basal turtle.
Cyclemys is a genus of freshwater turtles, commonly referred to as Asian leaf turtles, from the family Geoemydidae. The genus occurs throughout Southeast and South Asia, and currently contains seven species.
The serrated tortoise, Psammobates oculifer, German: Kalahari-Strahlenschildkröte, is a species of tortoise that occurs in the Kalahari desert regions of southern Africa. Also known as the Kalahari tent tortoise, it is one of three members of the genus, Psammobates.
Circle Limit III is a woodcut made in 1959 by Dutch artist M. C. Escher, in which "strings of fish shoot up like rockets from infinitely far away" and then "fall back again whence they came".
Chubutemys was an extinct genus of meiolaniform turtle. It lived during the Early Cretaceous of Argentina, around the Albian-Aptian border, within the Puesto La Paloma Member of the Cerro Barcino Formation. It is known from most of the skeleton and carapace, and part of the skull.
