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Crocodilia

Crocodilia    (“small lizard”) arose with a distinct lineage by the middle Triassic; extant species include alligators, crocodiles, and caimans. Crocodilians ( [link] ) live throughout the tropics and subtropics of Africa, South America, Southern Florida, Asia, and Australia. They are found in freshwater, saltwater, and brackish habitats, such as rivers and lakes, and spend most of their time in water. Some species are able to move on land due to their semi-erect posture.

The photo shows a crocodile sitting in the mud.
Crocodilians, such as this Siamese crocodile ( Crocodylus siamensis ), provide parental care for their offspring. (credit: Keshav Mukund Kandhadai)

Sphenodontia

Sphenodontia    (“wedge tooth”) arose in the Mesozoic era and includes only one living genus, Tuatara , comprising two species that are found in New Zealand ( [link] ). 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.

This photo shows a green lizard with short spines on its back.
This tuatara from New Zealand may resemble a lizard but belongs to a distinct lineage, the Sphenodontidae family. (credit: Sid Mosdell)

Squamata

Squamata    (“scaly”) arose in the late Permian, and extant species include lizards and snakes. Both are found on all continents except Antarctica. Lizards and snakes are most closely related to tuataras, both groups having evolved from a lepidosaurian ancestor. Squamata is the largest extant clade of reptiles ( [link] ). Most lizards differ from snakes by having four limbs, although these have been variously lost or significantly reduced in at least 60 lineages. Snakes lack eyelids and external ears, which are present in lizards. Lizard species range in size from chameleons and geckos, which are a few centimeters in length, to the Komodo dragon, which is about 3 meters in length. Most lizards are carnivorous, but some large species, such as iguanas, are herbivores.

The photo shows a green lizard with its tail curled like a snail shell. The lizard has two horns and matches the leaves of the plant on which it sits.
This Jackson’s chameleon ( Trioceros jacksonii ) blends in with its surroundings.

Snakes are thought to have descended from either burrowing lizards or aquatic lizards over 100 million years ago ( [link] ). Snakes comprise about 3,000 species and are found on every continent except Antarctica. They range in size from 10 centimeter-long thread snakes to 10 meter-long pythons and anacondas. All snakes are carnivorous and eat small animals, birds, eggs, fish, and insects. The snake body form is so specialized that, in its general morphology, a “snake is a snake.” Their specializations all point to snakes having evolved to feed on relatively large prey (even though some current species have reversed this trend). Although variations exist, most snakes have a skull that is very flexible, involving eight rotational joints. They also differ from other squamates by having mandibles (lower jaws) without either bony or ligamentous attachment anteriorly. Having this connection via skin and muscle allows for great expansion of the gape and independent motion of the two sides—both advantages in swallowing big items.

The photo shows a snake with orange and black bands and white stripes.
The garter snake belongs to the genus Thamnophis , the most widely distributed reptile genus in North America. (credit: Steve Jurvetson)

Testudines

Turtles are members of the clade Testudines    (“having a shell”) ( [link] ). Turtles are characterized by a bony or cartilaginous shell. The shell consists of the ventral surface called the plastron and the dorsal surface called the carapace, which develops from the ribs. The plastron is made of scutes or plates; the scutes can be used to differentiate species of turtles. The two clades of turtles are most easily recognized by how they retract their necks. The dominant group, which includes all North American species, retracts its neck in a vertical S-curve. Turtles in the less speciose clade retract the neck with a horizontal curve.

Turtles arose approximately 200 million years ago, predating crocodiles, lizards, and snakes. Similar to other reptiles, turtles are ectotherms. They lay eggs on land, although many species live in or near water. None exhibit parental care. Turtles range in size from the speckled padloper tortoise at 8 centimeters (3.1 inches) to the leatherback sea turtle at 200 centimeters (over 6 feet). The term “turtle” is sometimes used to describe only those species of Testudines that live in the sea, with the terms “tortoise” and “terrapin” used to refer to species that live on land and in fresh water, respectively.

The photo shows a very large tortoise.
The African spurred tortoise ( Geochelone sulcata ) lives at the southern edge of the Sahara Desert. It is the third largest tortoise in the world. (credit: Jim Bowen)

Section summary

The amniotes are distinguished from amphibians by the presence of a terrestrially adapted egg protected by amniotic membranes. The amniotes include reptiles, birds, and mammals. The early amniotes diverged into two main lines soon after the first amniotes arose. The initial split was into synapsids (mammals) and sauropsids. Sauropsids can be further divided into anapsids (turtles) and diapsids (birds and reptiles). Reptiles are tetrapods either having four limbs or descending from such. Limbless reptiles (snakes) are classified as tetrapods, as they are descended from four-limbed organisms. One of the key adaptations that permitted reptiles to live on land was the development of scaly skin containing the protein keratin, which prevented water loss from the skin. Reptilia includes four living clades: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles).

Art connections

[link] Which of the following statements about the parts of an egg are false?

  1. The allantois stores nitrogenous waste and facilitates respiration.
  2. The chorion facilitates gas exchange.
  3. The yolk provides food for the growing embryo.
  4. The amniotic cavity is filled with albumen.

[link] D

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[link] Members of the order Testudines have an anapsid-like skull with one opening. However, molecular studies indicate that turtles descended from a diapsid ancestor. Why might this be the case?

[link] The ancestor of modern Testudines may at one time have had a second opening in the skull, but over time this might have been lost.

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Questions & Answers

what is reproduction
mana Reply
reproduction is the process by which living organisms give rise to young ones of their own kind
Miriam
What is evolution
Wengelawit
the production of new forms of life over time as documented in the fossil record.
mana
hmm
Marvin
give two parasites where secondary host is water snail?
Kevin Reply
what is treats
Raih Reply
what are the organelles in cell that involves in protein sythenis
Rita Reply
what is a melanin?
Judith Reply
what is telophase
Elphas
melanin in that black color we posse in our skins
Marvin
Why do parasites take on a parasitic life?
Asadullah Reply
what is cell
Ousman Reply
A cell is the basic structure unit of an organ
Yaa
what is respiration
Igwe
what is organisms?
Bashir
Organisms are living things that can function on their own
EZEA
A cell is a functional basic unit of an organisms.
Evelyn
Organisms is a entity which consists of one or more cells and are able to undergo all life processes
Evelyn
A respiration is the physical and chemical break down of complex food substance into absorbable or simple form.
Evelyn
What will to a cell if the nucleus is removed..?
Goodrick Reply
When a cell nucleus removed then the cell will not be able to function properly, it will not be able to grow .All the metabolic functioning of the cell will stop .Without nucleus the cell will lose it's control. It can not carry out cellular reproduction .
Evelyn
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walid
write a short note on how the kidney carry out osmoregulation in man
Rhoda Reply
Kidney play a very large role in human osoregulation by regulating the amount of water reabsorbed from glomerular filtrate in kidney as tubules, which is controlled by hormones such as antrdiuvetic hormone (ADH) , aldosterone and angiotensin.
Evelyn
kidney is capable of osmoregulation in mammal ,
Judith
simple definition for respiratory system
Gift Reply
Respiratory system is a network of organs and tissues that helps you to breathe or help in getting the rids of oxygen and discharge of carbon dioxide in the body.
Ruhiyatu
What are uses of respiratory system
Joster
how it functions
Ousman
what is inresparetion
Fikkabex
Why do parasites take on a parasitic life?
Asadullah
A respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plant
Evelyn
diseases of respiration
walid
when air enters to the body called inresparetion
walid
explain why plants responds to stimuli slowly than animals
Bekoe
how is a aerenchyma tissue adapted to its function
fatuma Reply
Have large air spaces that store air for gaseous exchange... Large air spaces also facilitate bouyancy.
Goodrick
what does DNA mean
innocent Reply
dioxiribo nucleic acid
Lekan
Deoxyribonucleic acid
Goodrick
dioxide nucleic acid
Shadrack
what does RNA mean
Shadrack
Ribonucleic acid
Goodrick
what is DNA and RNA
Miriam
defin work of DNA
walid
what is a zygote
Victor Reply
zygote is developed or fertilized egg cell
Lekan
what is the difference between cell wall and cell membrane
Ruhiyatu Reply
cell wall is found in plant while cell membrane is found in animal cell
Lekan
please this is the main answer to that question okay Cell wall gives shape and support to the cell whiles Cell membrane support the movement of substances into and out of the cell. This question is very tricky that's why I asked.
Ruhiyatu
cell wall makes the cell turgid,in times of flaccidity while cell membrane is a semi permeable tissue
Judith
how cell I form
Elijah Reply

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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