Reptile
In the 13th century, a European writer named Beauvais recorded reptiles as a miscellany of egg-laying creatures. His Mirror of Nature listed snakes, lizards, amphibians, and even worms under one category. This broad grouping persisted until the 18th century when Carl Linnaeus published Systema Naturæ. Working from species-poor Sweden, Linnaeus grouped all reptiles and amphibians together in class Amphibia. The terms reptile and amphibian were largely interchangeable at that time. J.N. Laurenti later used Reptilia for an expanded selection similar to Linnaeus's work.
The British anatomist T.H. Huxley made Latreille's definition popular during the early 19th century. He and Richard Owen expanded Reptilia to include fossil antediluvian monsters like dinosaurs. In 1863, Huxley delivered Hunterian lectures at the Royal College of Surgeons where he proposed new groupings. He divided vertebrates into mammals, sauroids, and ichthyoids. Later, E.S. Goodrich used Sauropsida to distinguish lizards and birds from mammals in 1916. Modern cladistic systems now regard traditional reptiles as paraphyletic because birds are nested among them.
The earliest known members of the reptile lineage appeared during the late Carboniferous period about 310 million years ago. These animals evolved from advanced reptiliomorph tetrapods adapted to life on dry land. A series of footprints from Nova Scotia dated to roughly 315 million years ago show typical reptilian toes and imprints of scales. These tracks are attributed to Hylonomus, historically regarded as the oldest known reptile. It was a small lizard-like animal about 20 centimeters long with numerous sharp teeth indicating an insectivorous diet.
Primitive tetrapods were particularly devastated by the Carboniferous Rainforest Collapse while stem-reptiles fared better. They acquired new niches at a faster rate than before the collapse. The close of the Permian saw the greatest mass extinction known as the Permian-Triassic event. Most earlier parareptile and synapsid megafauna disappeared being replaced by true reptiles. Archosaurs became the dominant group during the Triassic period though it took 30 million years for their diversity to match Permian levels. The Cretaceous-Paleogene extinction event wiped out pterosaurs, plesiosaurs, and all non-avian dinosaurs alongside many species of crocodyliforms.
Modern non-avian reptiles exhibit cold-bloodedness relying on external sources of heat to maintain body temperature. For many lizards the optimum body temperature falls in the range of 25 to 30 degrees Celsius. Extreme heat-adapted species like the American desert iguana can have optimal physiological temperatures between 35 and 40 degrees Celsius. A crocodile needs from one-tenth to one-fifth of the food necessary for a lion of the same weight. It can live half a year without eating due to its low basal metabolism.
All lepidosaurs and turtles possess three-chambered hearts with two atria and one variably partitioned ventricle. Some squamate species like pythons and monitor lizards develop functionally four-chambered hearts during contraction. Crocodilians have anatomically four-chambered hearts similar to birds but also carry two systemic aortas. They are capable of bypassing pulmonary circulation through specialized mechanisms. Respiratory systems vary significantly across groups with some turtles using muscles attached to their shells to push viscera up and down for effective breathing.
Reptilian skin is covered in a horny epidermis making it watertight and enabling life on dry land. Exposed parts are protected by scales or scutes sometimes with bony bases called osteoderms forming armor. In lepidosaurs such as lizards and snakes the whole skin is covered in overlapping epidermal scales. The scales found in turtles and crocodiles are of dermal rather than epidermal origin and properly termed scutes. Snakes shed from head to tail while lizards shed in patchy patterns over time.
Many snakes lack external ears but possess inner ear structures connected directly to their jawbone. They feel vibrations generated from sound waves in their jaw as they move on the ground. Pit vipers possess heat-sensitive pits particularly well developed allowing them to sense body heat of birds and mammals. These pits enable hunting rodents in darkness during night hours. Most reptiles have excellent vision adapted to daylight conditions with color vision and advanced depth perception compared to amphibians.
Most reptiles lay amniotic eggs covered with leathery or calcareous shells requiring internal fertilization when mating. Viviparity has evolved in squamates and many extinct clades of marine reptiles like mosasaurs and ichthyosaurs. Temperature-dependent sex determination occurs most commonly in turtles and crocodiles though it also appears in lizards and tuatara. No confirmation exists yet whether this mechanism operates within snake populations today. Giant tortoises represent among the longest-lived vertebrate animals exceeding 100 years by some estimates.
DNA analysis of Lonesome George the last member of Chelonoidis abingdoni revealed lineage-specific variants affecting DNA repair genes. Aldabra giant tortoise Aldabrachelys gigantea showed similar genetic markers contributing to increased lifespan. Asexual reproduction called parthenogenesis occurs in several species including geckos teiids and lacertids. Komodo dragons have reproduced via parthenogenesis in captivity while chameleons and agamids are suspected to exhibit similar capabilities across their ranges.
Dinosaurs have been widely depicted in culture since English paleontologist Richard Owen coined the name dinosaur in 1842. The Crystal Palace Dinosaurs appeared on public display in south London as early as 1854. Charles Dickens placed a Megalosaurus in the first chapter of his novel Bleak House published in 1852. The snake or serpent has played powerful symbolic roles in different cultures throughout history. In Egyptian history the Nile cobra adorned the crown of pharaohs worshipped as one of the gods.
In Greek mythology snakes are associated with deadly antagonists serving as chthonic symbols roughly translated as earthbound. Medusa was one of three Gorgon sisters defeated by Perseus who gave her head to Athena fixed upon her shield called the Aegis. Hinduism worships snakes as gods with many women pouring milk on snake pits annually during Nag Panchami festivals. Christianity and Judaism feature a serpent appearing in Genesis to tempt Adam and Eve with forbidden fruit from Tree of Knowledge. Turtles symbolize steadfastness and tranquility carrying worlds upon their backs in cosmological myths worldwide.
Deaths from snakebites remain uncommon globally yet still count tens of thousands per year specifically within India. Antivenom production involves injecting mixtures of venoms into horses until immunized then extracting serum for purification. Cytotoxic effects of snake venom are researched as potential treatments for cancers today. Gila monsters produce compounds reducing plasma glucose now used in anti-diabetes drug exenatide marketed under brand name Byetta. Turtle farming remains controversial despite demand for meat and traditional medicine placing pressure on vulnerable wild populations.
Crocodiles are protected in many parts of the world farmed commercially for hides tanned into leather goods like shoes and handbags. Saltwater crocodile population increased in Australia after eggs harvested from wild incentivized habitat conservation. Snake farms primarily located in East and Southeast Asia have intensified production over last decade. Waste protein from poultry and pig industries serves as feed while farms produce meat skin and antivenom simultaneously. Growing demand for turtle meat threatens conservation efforts across Asian regions where commercial breeding may introduce infectious diseases into wild populations.
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Common questions
When did Carl Linnaeus publish Systema Naturæ and how did he classify reptiles?
Carl Linnaeus published Systema Naturæ in the 18th century. He grouped all reptiles and amphibians together under class Amphibia.
What is the earliest known member of the reptile lineage and when did it appear?
The earliest known members of the reptile lineage appeared during the late Carboniferous period about 310 million years ago. Hylonomus is historically regarded as the oldest known reptile with footprints from Nova Scotia dated to roughly 315 million years ago.
How do modern non-avian reptiles regulate their body temperature and what are their optimal ranges?
Modern non-avian reptiles exhibit cold-bloodedness relying on external sources of heat to maintain body temperature. For many lizards the optimum body temperature falls in the range of 25 to 30 degrees Celsius while extreme heat-adapted species like the American desert iguana can have optimal physiological temperatures between 35 and 40 degrees Celsius.
Which reptiles possess four-chambered hearts and how does this compare to other groups?
Crocodilians have anatomically four-chambered hearts similar to birds but also carry two systemic aortas. Some squamate species like pythons and monitor lizards develop functionally four-chambered hearts during contraction while all lepidosaurs and turtles possess three-chambered hearts with two atria and one variably partitioned ventricle.
What cultural roles did snakes play in ancient civilizations such as Egypt and Greece?
In Egyptian history the Nile cobra adorned the crown of pharaohs worshipped as one of the gods. In Greek mythology snakes are associated with deadly antagonists serving as chthonic symbols roughly translated as earthbound where Medusa was one of three Gorgon sisters defeated by Perseus who gave her head to Athena fixed upon her shield called the Aegis.
How is snake venom used in modern medicine and what specific drugs derive from it?
Cytotoxic effects of snake venom are researched as potential treatments for cancers today. Gila monsters produce compounds reducing plasma glucose now used in anti-diabetes drug exenatide marketed under brand name Byetta.