Euryapsida are a group of tetrapod animals that are distinguished by a single opening behind the orbit (temporal fenestra). They are different from Synapsida by the precise placement of the opening below. It is now commonly believed that euryapsids are in fact diapsids (having two fenestrae) that lost the upper temporal fenestra. In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. ... Groups Caseasauria Eupelycosauria    Sphenacodontia       Therapsida          (...mammals) Synapsids (fused arch), formerly known as mammal-like reptiles, are a group of amniotes (reptiles and all their ancestors) that developed one hole in their skull (temporal fenestra) behind each eye, about 320 million years ago (Ma) during the late Carboniferous. ... 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. ...

Ichthyosaur

Examples are: Drawing of an Ichthyosaur skeleton, scanned from a copyright free source. ... Drawing of an Ichthyosaur skeleton, scanned from a copyright free source. ... Taxonomy See text Ichthyosaurs (Greek for fish lizard - ιχθυς meaning fish and σαυρος meaning lizard) were giant marine reptiles that resembled fish and dolphins. ...

• Plesiosaurs
• Ichthyosaurs
• Placodonts