Losing its maxilla
(Fig. 1) did not stop this taxon from sporting a lot of other teeth in the palatine, ectopterygoid and maybe the vomer, even though only the premaxillary teeth line up with dentary teeth.
Proteus the white olm
(Figs. 1, 2), is a blind cave salamander with a long torso, tiny limbs and external gills (Fig. 2).
(Laurenti 1768) nests with Necturus, the mudpuppy. The lacrimal and maxilla are absent. The postorbital and postfrontal are stretched out. External gills enable Proteus to remain underwater. Apparently the dorsal portion of the vertebral column is very short (about 5 vertebrae), with the majority comprised of lumbar vertebrae (without dorsal ribs).
Laurenti JN 1768. Synopsin Reptilium. J.T. de Trattnern, Viennae, pp. 35–36.