HOME

TheInfoList




Diapsids ("two arches") are a group of
amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...
s that developed two holes ( temporal fenestra) in each side of their
skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North A ...

skull
s about 300
million years ago One million (1,000,000), or one thousand thousand, is the natural number In mathematics, the natural numbers are those used for counting (as in "there are ''six'' coins on the table") and total order, ordering (as in "this is the ''third'' l ...
during the late
Carboniferous The Carboniferous ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other ...
period. The diapsids are extremely diverse, and include all
crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...

crocodilia
ns,
lizard Lizards (suborder Lacertilia) are a widespread group of Squamata, squamate reptiles, with over 6,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic as it excludes the s ...

lizard
s,
snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Many species of snakes ...

snake
s,
tuatara Tuatara (''Sphenodon punctatus'') are reptiles Endemism, endemic to New Zealand. Although resembling most lizards, they are part of a distinct lineage, the order Rhynchocephalia. Their name derives from the Māori language, and means "peaks on ...

tuatara
,
turtles Turtles are an Order (biology), order of reptiles known as Testudines, characterized by a turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira, side-necked turtles and Cryptodi ...

turtles
, and
birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

birds
. Although some diapsids have lost either one hole (lizards), or both holes (snakes and turtles), or have a heavily restructured skull (modern birds), they are still
classified
classified
as diapsids based on their ancestry. At least 17,084
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
of diapsid animals are extant: 9,159 birds, and 7,925 snakes, lizards, tuatara, turtles, and crocodiles.


Characteristics

The name Diapsida means "two arches", and diapsids are traditionally classified based on their two ancestral skull openings ( temporal fenestrae) posteriorly above and below the eye. This arrangement allows for the attachment of larger, stronger jaw muscles, and enables the jaw to open more widely. A more obscure ancestral characteristic is a relatively long lower arm bone (the
radius In classical geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . It is concerned with properties of space that are related with distance, shape, size, and relative ...
) compared to the upper arm bone (
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extremity of h ...

humerus
).


Classification

Diapsids were originally classified as one of four subclasses of the class
Reptilia Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids ...

Reptilia
, all of which were based on the number and arrangement of openings in the skull. The other three subclasses were Synapsida (one opening low on the skull, for the "mammal-like reptiles"),
Anapsida An anapsid is an amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; fro ...
(no skull opening, including turtles and their relatives), and Euryapsida (one opening high on the skull, including many prehistoric marine reptiles). With the advent of
phylogenetic nomenclature In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
, this system of classification was heavily modified. Today, the synapsids are often not considered true reptiles, while Euryapsida were found to be an unnatural assemblage of diapsids that had lost one of their skull openings. Genetic studies and the discovery of the Triassic ''
Pappochelys ''Pappochelys'' (''παπποχέλυς'' άππος (grandfather) + χέλυς (turtle)meaning "grandfather turtle" in Ancient Greek, Greek) is an extinct genus of diapsid reptile closely related to turtles. The genus contains only one speci ...
'' have shown that this is also the case in turtles, which are actually heavily modified diapsids. In phylogenetic systems, birds (descendants of traditional diapsid reptiles) are also considered to be members of this group. Some modern studies of reptile relationships have preferred to use the name "diapsid" to refer to the crown group of all modern diapsid reptiles but not their extinct relatives. However, many researchers have also favored a more traditional definition that includes the prehistoric
araeoscelidia Araeoscelidia or Araeoscelida is a clade of extinct diapsid reptiles superficially resembling lizards, extending from the Late Carboniferous to the Early Permian. The group contains the genus, genera ''Araeoscelis'', ''Petrolacosaurus'', the possi ...
ns. In 1991, Laurin defined Diapsida as a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
, "the most recent common ancestor of
araeoscelidia Araeoscelidia or Araeoscelida is a clade of extinct diapsid reptiles superficially resembling lizards, extending from the Late Carboniferous to the Early Permian. The group contains the genus, genera ''Araeoscelis'', ''Petrolacosaurus'', the possi ...
ns, lepidosaurs, and
archosaur Archosauria ("ruling reptiles") is a clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), l ...
s, and all its descendants".Benton, M. J., Donoghue, P. C., Asher, R. J., Friedman, M., Near, T. J., & Vinther, J. (2015). "Constraints on the timescale of animal evolutionary history." ''Palaeontologia Electronica'', 18.1.1FC; 1-106; palaeo-electronica.org/content/fc-1 A cladistic analysis by Laurin and Piñeiro (2017) recovers
Parareptilia Parareptilia ("at the side of reptiles") is a subclass or clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its ...
as part of Diapsida, with pareiasaurs, turtles, millerettids, and procolophinoids recovered as more derived than the basal diapsid '' Younginia''.


Relationships

Below is a
cladogram A cladogram (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

cladogram
showing the relations of the major groups of diapsids.
Cladogram A cladogram (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

Cladogram
after Bickelmann ''et al.'', 2009 and Reisz ''et al.'', 2011:


See also

*
Vertebrate paleontology Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossil A fossil (from Classical Latin: , literally "obtained by digging") is any preserved remains, impression, or trace of any once- l ...
*
Synapsid Synapsids are a group of animals that includes mammal Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome ...

Synapsid
a *
Anapsid
Anapsid
a * Euryapsida


References


External links

*
Diapsida
Michel Laurin and Jacques A. Gauthier. ''Tree of Life Web Project''. June 22, 2000. {{Taxonbar, from=Q134688 01 Reptile taxonomy Reptiles of the United States Extant Pennsylvanian first appearances Taxa named by Henry Fairfield Osborn