 sauropsida ("lizard faces") is a group of amniotes that includes all existing reptiles and birds and their fossil ancestors. sauropsida is distinguished from synapsida, which includes mammals and their fossil ancestors. ==history of classification== ===huxley and the fossil gaps===  the term sauropsida ("lizard faces") has a long history, and hails back to thomas henry huxley, and his opinion that birds had risen from the dinosaurs. he based this chiefly on the fossils of hesperornis and archaeopteryx, that were starting to become known at the time.huxley, t.h. (1876): lectures on evolution. new york tribune. extra. no 36. in collected essays iv: pp 46-138 original text w/ figures in the hunterian lectures delivered at the royal college of surgeons in 1863, huxley grouped the vertebrate classes informally into mammals, sauroids, and ichthyoids (the latter containing the anamniotes), based on the gaps in physiological traits and lack of transitional fossils that seem to exist between the three groups. he subsequently proposed the names of sauropsida and ichthyopsida for the two latter.huxley, t.h. (1863): the structure and classification of the mammalia. hunterian lectures, presented in medical times and gazette, 1863. original text huxley did however include groups on the mammalian line (synapsids) like dicynodon among the sauropsids. thus, under the original definition, sauropsida contained not only the groups usually associated with it today, but also several groups that today are known to be in the mammalian side of the tree. ===sauropsids redefined=== by the early 20th century, the fossils of permian synapsids from south africa had become well known, allowing palaeontologists to trace synapsid evolution in much greater detail. the term sauropsida was taken up by e.s. goodrich in 1916 much like huxley's, to include lizards, birds and their relatives. he distinguished t
Tetrapods