Euryapsida
Encyclopedia
Euryapsida is a polyphyletic (unnatural, as the various members are not closely related) group of reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s that are distinguished by a single temporal fenestra, an opening behind the orbit
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

, under which the post-orbital and squamosal bones articulate. They are different from Synapsida, which also have a single opening behind the orbit, by the placement of the fenestra. In synapsids, this opening is below the articulation of the post-orbital and squamosal bones. It is now commonly believed that euryapsids are in fact diapsid
Diapsid
Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...

s (which have two fenestrae behind the orbit) that lost the lower temporal fenestra. There are no surviving descendants of the euryapsids.

The term "enaliosauria" was once used for ichthyosaurs and plesiosaurs combined as well.

Examples are:
  • Ichthyosaur
    Ichthyosaur
    Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...

    s
  • Placodont
    Placodont
    Placodonts were a group of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. It is believed that they were part of Sauropterygia, the group that includes Plesiosaurs...

    s
  • Plesiosaur
    Plesiosaur
    Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...

    s
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