What type of fertilization do reptiles have

Cloacal probing is the most common technique performed in snakes. All chelonians turtles and tortoises , pythons, most colubrids, monitors, and most iguanas lay eggs. Eggs can often be detected during visual examination in many species of snakes, although larger species like pythons require palpation. Viviparous or live bearing reptiles include many skinks, chameleons, boas, all rattlesnakes, and most vipers.

Egg production The process of egg production in reptiles is very similar to that described in birds. Depending on the species, the egg can normally remain within the oviduct anywhere from 9 days to 6 months, however most reptiles retain eggs for 1 to 2 months. Many females can lay eggs in the absence of a male Many lizard species, including iguanas, geckos, and some snakes such as the corn snake can begin folliculogenesis and even lay eggs without the presence of a mate.

Although these eggs are frequently infertile, this is not always the case since some species can store sperm for extended periods of time. Thinly shelled eggs The thinly shelled eggs produced by many normal reptiles may surprise anyone familiar with the hard, strong avian eggshell. All snakes, most lizards, and some turtles produce thinly shelled eggs that are normally pliant.

The eggs of tortoises, many geckos, and crocodilians are more rigid. Phallus or hemipenes The chelonian phallus sits in a groove on the cloacal floor.

When engorged, the phallus extends cranioventrally Fig 3. Figure 3. Normal extended phallus in a box turtle Genus Terrapene.

Photo credit: Dr. Ed Ramsay. Male snakes and lizards posses paired copulatory organs called hemipenes that normally range in color from pink to black. Hemipenes sit within pouches at the base of the tail just caudal to the cloaca Fig 4, Fig 5. They are connected to the testes by the ductus deferens, and each hemipenis is functionally complete.

Sperm travels along a groove on the outside of the everted organ. Figure 4. Hemipenes of a Western diamondback rattlesnake Crotalus atrox. Photo credit: Tess Thornton via Wikimedia Commons. One of the oldest-known amniotes is Casineria , which had both amphibian and reptilian characteristics. One of the earliest undisputed reptiles was Hylonomus.

Soon after the first amniotes appeared, they diverged into three groups synapsids, anapsids, and diapsids during the Permian period. The Permian period also saw a second major divergence of diapsid reptiles into archosaurs predecessors of crocodilians and dinosaurs and lepidosaurs predecessors of snakes and lizards.

These groups remained inconspicuous until the Triassic period when the archosaurs became the dominant terrestrial group due to the extinction of large-bodied anapsids and synapsids during the Permian-Triassic extinction. About million years ago, archosaurs radiated into the dinosaurs and the pterosaurs. Although they are sometimes mistakenly called dinosaurs, the pterosaurs were distinct from true dinosaurs. Pterosaurs had a number of adaptations that allowed for flight, including hollow bones birds also exhibit hollow bones, a case of convergent evolution.

Their wings were formed by membranes of skin that attached to the long, fourth finger of each arm and extended along the body to the legs. Pterosaurs : Pterosaurs, which existed from the late Triassic to the Cretaceous period to Instead, they may have been able to soar after launching from cliffs. The dinosaurs were a diverse group of terrestrial reptiles with more than 1, species identified to date.

Paleontologists continue to discover new species of dinosaurs. Some dinosaurs were quadrupeds; others were bipeds. Some were carnivorous, whereas others were herbivorous. Dinosaurs laid eggs; a number of nests containing fossilized eggs have been found. It is not known whether dinosaurs were endotherms or ectotherms.

However, given that modern birds are endothermic, the dinosaurs that served as ancestors to birds were probably endothermic as well. Some fossil evidence exists for dinosaurian parental care. Comparative biology supports this hypothesis since the archosaur birds and crocodilians display parental care. Quadruped dinosaurs : Edmontonia, an example of an extinct quadruped reptile, was an armored dinosaur that lived in the late Cretaceous period, The Cretaceous-Tertiary extinction resulted in the loss of most of the large-bodied animals of the Mesozoic Era.

Birds are the only living descendants of one of the major clades of dinosaurs. Class Reptilia, amniotes that are neither mammals nor birds, has four living clades: Crocodilia, Sphenodontia, Squamata, and Testudine. Class Reptilia includes many diverse species that are classified into four living clades. These are the 25 species of Crocodilia, 2 species of Sphenodontia, approximately 9, Squamata species, and the Testudines, with about species.

A reptile is any amniote a tetrapod whose egg has an additional membrane, originally to allow them to lay eggs on land that is neither a mammal nor a bird. Unlike mammals, birds, and certain extinct reptiles, living reptiles have scales or scutes rather than fur or feathers and are cold-blooded. Modern reptiles inhabit every continent with the exception of Antarctica. Crocodilians are large, solidly built lizard-like reptiles with long flattened snouts and laterally-compressed tails, and eyes, ears, and nostrils at the top of the head.

Their skin is thick and covered in non-overlapping scales. They have conical, peg-like teeth and a powerful bite. As with birds, they have a four-chambered heart and a unidirectional system of air flow around the lungs; however, in contrast to birds, they are ectotherms, as are all other reptiles.

They are found in freshwater, saltwater, and brackish habitats, such as rivers and lakes; they spend most of their time in water. Some species are able to move on land due to their semi-erect posture.

Crocodilians : Crocodilians, such as this Siamese crocodile Crocodylus siamensis , have large flattened snouts and thick skin. Tuataras measure up to 80 centimeters and weigh about 1 kilogram. Although quite lizard-like in gross appearance, several unique features of the skull and jaws clearly define them and distinguish the group from the squamates.

Their dentition, in which two rows of teeth in the upper jaw overlap one row on the lower jaw, is unique among living species. Tuatara : Tuataras may resemble a lizard but belongs to a distinct lineage, the Sphenodontidae family.

They are most closely-related to tuataras; both groups evolved from a lepidosaurian ancestor. Squamata is the largest extant clade of reptiles. Most lizards differ from snakes by having four limbs, although these have been variously lost or significantly reduced in at least 60 lineages. The shell, membranes, and other structures of an amniotic egg protect and nourish the embryo.

They keep the embryo moist and safe while it grows and develops. They also provide it with a rich, fatty food source the yolk. The amniotic egg is an important adaptation in fully terrestrial vertebrates. It first evolved in reptiles. The shells of reptile eggs are either hard or leathery.

Unlike amphibians, reptiles do not have a larval stage. A "lack of transitional forms", as noted elsewhere in this review, is a standard creationist canard, but in this book transitional forms are lacking only because the authors choose to ignore them.

In fact, the living mammals illustrate a clear transition from egg-laying through various transitional stages along the way to live birth as seen in humans. In monotremes, which consist of the platypus and spiny anteaters called echidnas, the reproductive system is, as James Vaughan explains in his textbook Mammalogy , "a mix, including primitive features shared with amniotes and unique specializations.

Monotremes, like reptiles, have a structure called a cloaca, in which the reproductive, urinary and digestive tracts all exit through a single opening, rather than through two, a trait shared with birds, reptiles and marsupials, but not with the rest of the mammals.

It is a small step from laying these sorts of eggs to the marsupial system of briefly holding the developing embryo internally and nursing the partially developed embryo externally, then successively modifying the placental interface between fetus and mother until we see the sort of live birth found in humans, other eutherian mammals, and even a few transitional marsupials. This sequence illustrates several important errors in Explore Evolution.

Clearly, EE badly misrepresents mammalian reproduction. More fundamental, and more widespread, is its tendency to treat a large taxonomic group of species as if they are all practically identical. Species do differ one from another, and in important ways. Those differences are essential to evolutionary processes, and understanding such variation is vital to a student's understanding of evolution.

By teaching students that it is acceptable to treat mammals or reptiles or other groups as if all members of the group were interchangeable does students a disservice and misinforms them about the range of adaptations which exist in the natural world, and how the variation among living things reveals evolutionary processes.

Only by obscuring legitimate science can Explore Evolution create the false impression that there are unbridgeable gaps between major taxonomic groups; gaps which bolster their preconceptions against common descent. These three errors and the original eggs-in-placenta error could have been avoided if the authors consulted a standard college-level introductory textbook, or if they were familiar with basic biological literature, or even if they had used used basic resources like Wikipedia, Google, or even a smart 5th grader.

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