ornithoscelida

from The Collaborative International Dictionary of English v.0.48

Ornithoscelida \Or*ni`tho*scel"i*da\, n. pl. [NL., fr. Gr.
   'o`rnis, 'o`rniqos, a bird + ? a leg.] (Zool.)
   A group of extinct Reptilia, intermediate in structure
   (especially with regard to the pelvis) between reptiles and
   birds. -- {Or`ni*tho*scel"i*dan}, a.
   [1913 Webster]