[ kot-l-uh-sawr ]
/ ˈkɒt l əˌsɔr /


any member of the extinct order Cotylosauria, comprising heavy-bodied, splay-limbed, plant-eating reptiles that arose during the Carboniferous Period and that are considered to include the ancestors of all other reptiles.

Origin of cotylosaur

1900–05; < New Latin Cotylosauria, equivalent to cotyl(lus) a hollow space in the bones forming the distinctive articulation of skull and vertebrae, which orig. defined the order (masculine noun < Greek kotýlē socket, cup, anything hollow) + -o- -o- + -sauria; see -saur, -ia
Also called root reptile, stem reptile.


cot·y·lo·sau·ri·an, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Science definitions for stem reptile (1 of 2)

stem reptile

See cotylosaur.

Science definitions for stem reptile (2 of 2)

[ kŏtl-ə-sôr′ ]

Any of a number of extinct reptiles of the group Cotylosauria or Captorhinida of the Carboniferous and Permian Periods that include the ancestors of all terrestrial vertebrates except for amphibians. Cotylosaurs evolved from early amphibians, had four sprawling legs and a long tail, and a skull without temporal openings. Also called stem reptile
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.