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Encyclopedia > Amniote
iAmniotes
Fossil range: Carboniferous (Middle Mississippian) to Recent
A baby tortoise emerges from an amniotic egg.
A baby tortoise emerges from an amniotic egg.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclass: Tetrapoda
(unranked) Amniota
Haeckel, 1866
Living subgroups

Class Synapsida
   Class Mammalia (mammals)
Class Sauropsida
   Anapsida
       Testudines (turtles)
   Diapsida
       Lepidosauria
          Squamata (lizards & snakes)
          Sphenodontida (tuatara)
       Archosauria
          Crocodilia (crocodiles)
          Class Aves (birds) The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ... This article is about the geologic period; for the North American culture, see Mississippian culture. ... Image File history File links Download high resolution version (1204x1204, 318 KB) A baby tortoise hatchling emerges from its shell. ... For other uses, see Scientific classification (disambiguation). ... Phyla Subregnum Parazoa Porifera Subregnum Eumetazoa Placozoa Orthonectida Rhombozoa Radiata (unranked) Ctenophora Cnidaria Bilateria (unranked) Acoelomorpha Myxozoa Superphylum Deuterostomia Chordata Hemichordata Echinodermata Chaetognatha Xenoturbellida Superphylum Ecdysozoa Kinorhyncha Loricifera Priapulida Nematoda Nematomorpha Onychophora Tardigrada Arthropoda Superphylum Platyzoa Platyhelminthes Gastrotricha Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora Superphylum Lophotrochozoa Sipuncula Nemertea Phoronida Ectoprocta Bryozoa... {{{subdivision_ranks}}} See below Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. ... Classes and Clades See below Vertebrates are members of the subphylum Vertebrata (within the phylum Chordata), specifically, those chordates with backbones or spinal columns. ... Classes Placodermi Chondrichthyes Acanthodii Osteichthyes Gnathostomata is the group of vertebrates with jaws. ... Classes Synapsida Sauropsida Amphibia A tetrapod (Greek tetrapoda, four-legged) is a vertebrate animal having four feet, legs or leglike appendages. ... Ernst Haeckel. ... Orders & Suborders Order Pelycosauria * Suborder Caseasauria Suborder Eupelycosauria * Order Therapsida * Suborder Biarmosuchia Suborder Dinocephalia Suborder Anomodontia Suborder Gorgonopsia Suborder Therocephalia Suborder Cynodontia * For complete phylogeny, see text. ... Orders Multituberculata (extinct) Volaticotheria (extinct) Palaeoryctoides (extinct) Triconodonta (extinct) Subclass Australosphenida Ausktribosphenida Monotremata Subclass Eutheria (excludes extinct ancestors) Afrosoricida Anagaloidea (extinct) Arctostylopida (extinct) Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Cingulata Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Dinocerata (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Leptictida (extinct) Litopterna (extinct) Macroscelidea Mesonychia... Clades Subclass Anapsida Subclass Diapsida Infraclass Lepidosauromorpha Infraclass Archosauromorpha Sauropsids are a diverse group of mostly egg-laying vertebrate animals. ... Orders Testudines (Turtles) Millerettid - extinct Nyctiphruret - extinct Pareiasaur - extinct Procolophonoid - extinct The anapsids are a group of amniotes, characterized by skulls without openings near the temples. ... Suborders Cryptodira Pleurodira See text for families. ... Groups See Text Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. ... Orders Sphenodontia Squamata Eosuchia Conservation status: Fossil The Lepidosauria are a subclass of reptiles comprising the orders : Squamata Sphenodontia or Rhynchocephalia Eosuchia Conservation status: Fossil Lepidosaurians are the most successful of modern reptiles. ... Suborders Lacertilia- Lizards Serpentes - Snakes Amphisbaenia - Worm lizards This article is about the Squamata order of reptiles. ... Families Many, see text. ... For other uses, see Snake (disambiguation). ... Species Sphenodon punctatus (Gray, 1842) Sphenodon guntheri Buller, 1877 Sphenodon diversum (extinct) The tuatara is a reptile of the family Sphenodontidae, endemic to New Zealand. ... -1... Suborders Eusuchia Protosuchia † Mesosuchia † Sebecosuchia † Thalattosuchia † Crocodilia is an order of large reptiles that appeared about 220 million years ago. ... Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ... Aves redirects here. ...

The amniotes are a taxon of tetrapod vertebrates that include the Synapsida (mammals) and Sauropsida (reptiles and dinosaurs, including birds). They are defined by embryonic development that includes the formation of several extensive membranes, the amnion, chorion, and allantois. Amniotes develop directly into a (typically) terrestrial form with limbs and a thick stratified epithelium, rather than first entering a feeding larval tadpole stage followed by metamorphosis as in amphibians. In amniotes the transition from a two-layered periderm to cornified epithelium is triggered by thyroid hormone during embryonic development, rather than metamorphosis [1]. The unique embryonic features of amniotes may reflect specializations of eggs to survive drier environments, or the massive size and yolk content of eggs designed for direct development to a larger size. A taxon (plural taxa), or taxonomic unit, is a grouping of organisms (named or unnamed). ... Groups See text. ... Classes and Clades See below Vertebrates are members of the subphylum Vertebrata (within the phylum Chordata), specifically, those chordates with backbones or spinal columns. ... Orders Multituberculata (extinct) Volaticotheria (extinct) Palaeoryctoides (extinct) Triconodonta (extinct) Subclass Australosphenida Ausktribosphenida Monotremata Subclass Eutheria (excludes extinct ancestors) Afrosoricida Anagaloidea (extinct) Arctostylopida (extinct) Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Cingulata Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Dinocerata (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Leptictida (extinct) Litopterna (extinct) Macroscelidea Mesonychia... Subclasses Anapsida Diapsida Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane. ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Aves redirects here. ... Embryogenesis is the process by which the embryo is formed and develops. ... For the alien race in Stephen Donaldsons The Gap Cycle, see Amnion (Gap Cycle). ... For the entertainment company see Chorion (company) The chorion surrounds the embryo and other membranes. ... Allantois is a part of a developing animal embryo. ... Subclasses and Orders Order Temnospondyli - extinct Subclass Lepospondyli - extinct Subclass Lissamphibia   Anura   Caudata   Gymnophiona Amphibians (class Amphibia; from Greek αμφις both and βιος life) are a taxon of animals that include all living tetrapods (four-legged vertebrates) that do not have amniotic eggs, are ectotherms, and generally spend part of their time...

Anatomy of an amniotic egg 1. Eggshell 2. Outer membrane 3. Inner membrane 4. Chalaza 5. Exterior albumen (outer thin albumen) 6. Middle albumen (inner thick albumen) 7. Vitelline membrane 8. Nucleus of Pander 9. Germinal disk (blastoderm)10. Yellow yolk11. White yolk12. Internal albumen13. Chalaza14. Air cell15. Cuticula
Anatomy of an amniotic egg
1. Eggshell
2. Outer membrane
3. Inner membrane
4. Chalaza
5. Exterior albumen (outer thin albumen)
6. Middle albumen (inner thick albumen)
7. Vitelline membrane
8. Nucleus of Pander
9. Germinal disk (blastoderm)
10. Yellow yolk
11. White yolk
12. Internal albumen
13. Chalaza
14. Air cell
15. Cuticula

Features of amniotes designed for survival on land include a sturdy but porous leathery or hard eggshell, and an allantois designed to facilitate respiration while providing a reservoir for disposal of wastes. Their kidneys and large intestines are also well-suited to water retention. Most mammals do not lay eggs, but corresponding structures may be found inside the placenta. Image File history File links Anatomy_of_an_amiotic_egg. ... Image File history File links Anatomy_of_an_amiotic_egg. ... A greek word - from khalaze - meaning hailstone. It is composed of one or two spiral bands of tissue that suspends the yolk in the center of the white. ... Albumen redirects here. ... As soon as the spermatozoön has entered the yolk, the peripheral portion of the latter is transformed into a membrane, the vitelline membrane which prevents the passage of additional spermatozoa. ... A Blastoderm as of 1935 is the layer of cells formed at one pole of the yolky egg of reptiles and birds. ... on leaves: a water-repelling surface that protects plants from uncontrolled transpiration and mechanical damages. ... Allantois is a part of a developing animal embryo. ... The kidneys are bean-shaped excretory organs in vertebrates. ... The large intestine is the last part of digestive system: the final stage of the alimentary canal in vertebrate animals. ... The placenta is an ephemeral (temporary) organ present only in female placental vertebrates during gestation (pregnancy). ...


The first amniotes, such as Casineria kiddi, which lived about 340 million years ago, resembled small lizards. Their eggs were small and covered with a membrane, not a hard shell like most modern amniote eggs. Although some modern amphibians lay eggs on land, with or without significant protection, they all lack advanced traits like an amnion. This kind of egg only became possible with internal fertilization. The outer membrane, a soft shell, evolved as a protection against the harsher environments on land, as species evolved to lay their eggs on land where they were safer than in the water. One can assume the ancestors of the amniotes laid their eggs in moist places, as such modest-sized animals wouldn't have too many difficulties in finding depressions under fallen logs or other suitable places in the ancient forests, and dry conditions were probably not the main reason why the soft shell emerged. Binomial name Casineria kiddi Casineria was a tetrapod which lived 340 million years ago, in the Mississippian period. ...


In fish and amphibians there is only one inner membrane, also called an embryonic membrane. In amniotes the inner anatomy of the egg has evolved further, new structures have developed to take care of the gas exchanges between the embryo and the atmosphere, as well as dealing with the waste problems. To grow a thicker and tougher shell there were no other alternatives than finding new ways to supply the embryo with oxygen, as diffusion alone wouldn't be enough any more. After the egg had gotten these structures, further sophistication of them allowed the amniotes to lay much bigger eggs in much drier habitats. Bigger eggs meant bigger offspring, and bigger adults meant bigger eggs, which meant the amniotes had gotten the opportunity to grow bigger than their ancestors. But real growth was not possible until they stopped relying on small invertebrates as their main food source, and started to eat plants or other vertebrates, or returned to the water. New habits and heavier bodies meant further evolution for the amniotes, both in behavior and anatomy.


There are three main lines of amniotes, which may be distinguished by the structure of the skull and in particular the number of temporal fenestrae (openings) behind the eye. In anapsids there are none, in synapsids there is one, and in most diapsids there are two. It has been suggested that temporal fenestra be merged into this article or section. ... Large holes in the side of the skull. ... Orders Testudines (Turtles) Millerettid - extinct Nyctiphruret - extinct Pareiasaur - extinct Procolophonoid - extinct The anapsids are a group of amniotes, characterized by skulls without openings near the temples. ... Orders & Suborders Order Pelycosauria * Suborder Caseasauria Suborder Eupelycosauria * Order Therapsida * Suborder Biarmosuchia Suborder Dinocephalia Suborder Anomodontia Suborder Gorgonopsia Suborder Therocephalia Suborder Cynodontia * For complete phylogeny, see text. ... Groups See Text Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side of their skulls, about 300 million years ago during the late Carboniferous period. ...


The skeletal remains of amniotes can be identified by their having at least two pairs of sacral ribs and an astragalus bone in the ankle. This article or section may be confusing or unclear for some readers, and should be edited to rectify this. ... The human rib cage. ... Grays Fig. ...


Taxonomy

(see sub-pages for in depth classification for each group).

Groups Amniota Anthracosauria Batrachosauria Chroniosuchidae Diadectomorpha Embolomeri Gephyrostegidae Seymouriamorpha Solenodonsauridae Tokosauridae Westlothiana lizziae Reptiliomorpha is a name given either to reptile-like amphibians, or to amniotes and those amphibians related to them. ... Binomial name Casineria kiddi Casineria was a tetrapod which lived 340 million years ago, in the Mississippian period. ... Orders & Suborders Order Pelycosauria * Suborder Caseasauria Suborder Eupelycosauria * Order Therapsida * Suborder Biarmosuchia Suborder Dinocephalia Suborder Anomodontia Suborder Gorgonopsia Suborder Therocephalia Suborder Cynodontia * For complete phylogeny, see text. ... Suborders Biarmosuchia Dinocephalia Eotheriodontia Anomodontia Gorgonopsia Therocephalia Cynodontia Therapsids, previously known as the mammal-like reptiles, are an order of synapsids. ... Orders Multituberculata (extinct) Volaticotheria (extinct) Palaeoryctoides (extinct) Triconodonta (extinct) Subclass Australosphenida Ausktribosphenida Monotremata Subclass Eutheria (excludes extinct ancestors) Afrosoricida Anagaloidea (extinct) Arctostylopida (extinct) Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Cingulata Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Dinocerata (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Leptictida (extinct) Litopterna (extinct) Macroscelidea Mesonychia... Subclasses Anapsida Diapsida Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane. ... Genera Brasileosaurus Stereosternum Mesosaurus Mesosaur (middle lizards) were an order of small marine reptiles that lived during the early Permian period, roughly 320 to 280 million years ago. ... Orders Testudines (Turtles) Millerettid - extinct Nyctiphruret - extinct Pareiasaur - extinct Procolophonoid - extinct The anapsids are a group of amniotes, characterized by skulls without openings near the temples. ... Genera See text Captorhinidae (also known as cotylosaurs, or stem reptiles) were the earliest and most primitive reptiles. ... Protorothyrididae was a clade of small, lizard-like reptiles, possibly the ancestors of turtles and tortoises. ... Hylonomus lyelli was an early reptile. ... Classes Ichthyosauria Sauropterygia Lepidosauria Archosauria Diapsids (two arches) are a group of tetrapod animals that developed two holes (temporal fenestra) in each side their skulls, about 300 million years ago during the late Carboniferous period. ... Aves redirects here. ...

External links


  Results from FactBites:
 
Evolution of the Amniote Brain (3508 words)
The earliest amniotes were the Captorhinida, which eventually gave rise to modern amniotes (reptiles, birds, and mammals).
Dorsal thalamic nuclei in amniotes which receive ascending visual input from the retina receive such input either directly (as in the thalamofugal or lemnothalamic pathway) or indirectly via the tectum (as in the tectofugal or collothalamic pathway).
Common to amniote forebrain organization is that ascending sensory information is relayed through dorsal thalamic nuclei to parts of both the pallium and subpallium.
Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds, and Reptiles | LibraryThing (249 words)
Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds, and Reptiles
Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds, and …
A collaborative effort of twenty-four researchers, Amniote Paleobiology presents thirteen new and important scientific perspectives on the evolution and biology of this familiar group.
  More results at FactBites »

 
 

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