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Most mammals use all four limbs to move and so are called quadrupedal. Animals that spend most of their time walking are called ambulatory, and are generally plantigrade, which means that they walk on the soles of their hands and feet. Animals that do a lot of running are called cursorial, and are either digitigrade or unguligrade. Digitigrade mammals are mostly carnivores, and are called digitigrade because they run on their toes. Hoofed animals have unguligrade foot posture, which means that they have extended limbs with reduced digits, and elongated and fused tarsal bones. Another form of locomotion is saltatory locomotion, which includes jumping and ricocheting. Jumping is saltatory locomotion that uses all four feet, whereas ricocheting primarily only uses the two hind limbs, and most animals that use it are bipedal. Other types of locomotion include swimming, flying and gliding, and digging and burrowing.

Ichthyostega lived at the end of the Late Devonian Period and was was one of the first four-limbed vertebrates in the fossil record. It is an early genus of tetrapodmorph, and although its possession of both limbs and fingers has lead to it often being labeled as a tetrapod, it was more primitive than crown tetrapods and could therefore be more accurately described as a stem tetrapod, or stegocephalian. Whereas crown tetrapods are the group identified as the most recent common ancestor of all living amphibians, the term “stem tetrapods” (tetrapodmorphs) is used for any animal that is more closely related to living amphibians, reptiles, birds, and mammals than to living lungfishes.  Until other finds of early stegocephalians,  Ichthyostega was alone as a transitional fossil between fish and tetrapods. Ichthyostega may have used its tail for swimming, and its forelimbs to move on land. Its forelimbs seem to have been strong enough to pull its body out of the water, and were larger than its hindlimbs. It had a large ribcage with overlapping ribs, which would have limited its ability to make side-to-side motions, and probably moved by dragging itself as its forelimbs did not have the range of rotational motion needed to move in typical quadrupedal gaits.

The Gorgonopsia (“Gorgon faces”) are an extinct suborder of a group of therapsids called theriodonts, which are a group of therapsids. The gorgonopsians evolved from a reptile-like therapsid in the Middle Permian, and although early gorgonopsids were no larger than a dog, later gorgonopsids were some of the largest carnivores of the Late Permian period. They have mammalian specializations that include having teeth of different shapes (heterodonty), having a fully developed temporal fenestra, a vaulted palate, and early ear bones. They possibly had a combination of scales and bristles, and they are assumed to have been terrestrial. The Gorgonopsia were the only theriodont line that went extinct during the Permian-Triassic mass extinction event.

Tiktaalik is a monospecific genus of extinct lobe-finned fish. It is monospecific because Tiktaalik roseae is the only species classified under the genus. It lived during the Late Devonian Period about 375 million years ago, and although it generally had the characteristics of a lobe-finned fish, it also had traits similar to tetrapods. Not only did Tiktaalik have gills, scales and fins, like a fish, it also had rib bones, lungs and a mobile neck. It also had intermediate features, such as radiating, fish-like fins coupled with a functional wrist joint, and a half-fish, half-tetrapod ear region. Because of its amalgamation of features, Tiktaalik is referred to as a "transitional fossil": while not an ancestor to any living animal, it is evidence of the intermediate forms that bridged the evolutionary gap between fish with fins and animals with arms and legs.

On my mother’s side my grandfather was Palestinian and my grandmother was American-born to parents of German descent who likely had Danish origins further down the line. Going back about 500 years or more, the Palestinian side has some possible connections to Syria and/or Yemen. There is some speculation that there may also be some Russian or Greek heritage, based on some Greek Orthodox backgrounds and the fact that my mother’s grandmother had a Greek name. A significant portion of my genetic ancestry is Mediterranean/ Middle Eastern, and I think my phenotypes reflect this. I inherited my father’s dark brown eyes, thick eyebrows, and light olive skin that rarely burns and tans easily; all very common traits in that region of the world. From my mother’s side I got my round face and my wavy/curly hair. My hair color is an medium/dark brown, an intermediate between my father’s black hair and my mother’s light brown hair. 

My genetic ancestry is a mixed bag: my father's side, as far as I know, is Cypriot through and through, although the island’s long history of being invaded and conquered by anyone and everyone means that “Cypriot” has little genetic meaning. Cyprus history dates back to first being settled in around 10 000 BC. During the Bronze Age there were two waves of Greek settlement before the island was ruled first by Assyria, then briefly by Egypt, and then by Persia. It was then part of the Byzantine Empire until the Crusades, when it was captured and sold to the Republic of Venice before being conquered by the Ottoman Empire in 1571. In 1878 Cyprus was leased to the British Empire, and then invaded by Turkey in 1974. Because of the island’s history, the genetic origins of its population are complex and varied, so although I am Cypriot I do not the exact genetic origins of that side of my family. On my mother’s side my grandfather was Palestinian and my grandmother was American-born to parents of German descent who had Dutch origins further down the line.

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Mammal and reptile are morphologically different in a few ways. Mammal skulls are synapsid: they have a single, large opening called a temporal fenestra behind each eye that allows for more attachment of jaw muscles. This muscle attachment gives mammals a larger range of motion in their jaws, which allows them to have stronger bites. Reptiles such as alligators are diapsid, which means they have two temporal fenestrae on each side of their heads, while other reptiles such as turtles do not have any of these openings and are thus referred to as anapsid. Another difference between mammal and reptile skulls is the mammalian middle ear is made up of three bones, the malleus, the incus, and the stapes, whereas the reptilian middle ear is made up of only the stapes. Reptiles have articulate and quadrate bones in their mandibles and skulls respectively, and in mammals these bones have migrated up towards the middle ear and formed the malleus and incus. Mammal skulls also differ from reptile skulls in that they have two occipital condolytes at the articulation between the skull and the cervical vertebrae. This allows mammals to move their heads up and down through, which is beneficial to them because this gives them the ability to further manipulate their food. Reptiles on the other hand only have a single occipital condolyte, which limits their head movements, most of which involve moving the entire body.

Skull morphology differs between mammal and reptile skulls. Mammal skulls are synapsid: they have a single, large opening called a temporal fenestra behind each eye that allows for more attachment of jaw muscles. This muscle attachment gives mammals a larger range of motion in their jaws, while also allowing them to have stronger bites. Reptiles such as alligators are diapsid which means they have not one, but two temporal fenestrae on each side of their heads, while other reptiles—including turtles— do not have any of these openings, and are thus referred to as anapsid. Another difference between mammal and reptile skulls is the mammalian middle ear is made up of three bones, the malleus, the incus, and the stapes, whereas the reptilian middle ear is made up of only the stapes. The malleus and incus however are the result of the migration of the articulate and quadrate bones found in the reptilian mandible and skull respectively.

It is not correct to use the term "ancestral" to describe platypuses relative to mammals that bear live young because although they share a common ancestor platypuses diverged into a separate group before the mammals that bear live young evolved to acquire the trait. Platypuses can however be described as being "more primitive", because they have gone through far fewer evolutionary changes than the mammals that bear live young have.