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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 nutrition
Joseph Reply
the process of providing or obtaining the food necessary for health and growth.
fatimah
what are micro-organism
Bukiwe Reply
what is immunity
Moriba Reply
What is cross pollination
Moriba
what is pollution
Georgiana Reply
what is pollution
Georgiana
list four type of biological association
Georgiana
Pollution is the release of harmful substances in the atmosphere.
Immanuel
Four biological associations are 1) commensalism 2)symbiosis 3)mutualism 4) parasitism
Immanuel
What is the function of the hormones
Immanuel Reply
What is the other name of filament of a flower
Immanuel
oxygen
Georgiana
list three bone disorders and explain them
Blessings Reply
oxygen
Georgiana
what is self pollination?
Kelvin Reply
well, self-pollination occurs in a single flower which has the organs of both genders. the pollen grains from the anther shall be captured by the stigma of the flower, when released. and the pollen grain shall start grow pollen tube which grows down in the style, to the ovary, ovules and the
Izzati
insides of the ovules. so pretty much the pollen grains being pollinated from the anther to the stigma of the same flower
Izzati
I think
Izzati
the pollen grains being pollinated from the anther to the stigma of the same flower
Izzati
what is animal science
Rose Reply
Animal science is described as "studying the biology of animals that are under the control of humankind".
AMIIRA
don't you guys have Google
Izzati
what is self pollinating
JOSHUA Reply
what is cleistogamy
JOSHUA
Self pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another flower on the same plant.
Franklina
Cleistogamy is a type of automatic self pollination of certain plants that can propagate by using non opening, self pollinating flowers
Franklina
Self pollination is the transfer of pollen grain from the anther to the stigma
Immanuel
who is the father of biology
Sean Reply
Aristotle
Lubera
Aristotle
estella
yes Aristotle looking at classification
John
Aristotle
JOSHUA
Aristotle
Grace
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Sean
Aristotle
Rose
Aristotle
Immanuel
what are prokaryotic cells
Kusubira Reply
having cell that lack membrane - bound nuclei.
Lubera
Pronkayotic cells are cells that lacks nuclear membrane
Immanuel
Please each person should suggest ur answers
Franklina Reply
differentiate between autelogical and synecology
Christiana Reply
differentiate between autelogical and synecology
Christiana Reply
answer please
Edmond
Autecology is the study of individual organism or individual species. It is also known as population ecology. Synecology is the study of group of organisms of different species which are associated together as a unit in form of a community.
Daniel
Autecology is the study of the environment in relation to only one species in contrast while synecology is the study of the environment affecting groups of species coexisting in an area.
Franklina
Describe the factors affecting homotasis
Grace Reply
Fluids and electrolytes Energy and nutrition Immune response mediators
Franklina

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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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