Ankylosphenodon is an extinct genus of sphenodontian known from multiple specimens recovered from the Early Cretaceous deposits of the Tlayúa Formation, near Tepexi de Rodriguez, Mexico.
[1] It is likely part of a sphenodontid lineage that also includes Eilenodon and Toxolophosaurus, though has similarities to the sapheosaur clade.
Ankylosphenodon is known from multiple specimens recovered from the Tlayúa Formation, a vertebrate-rich Lagerstätte near Tepexi de Rodriguez, in Central Mexico.
The holotype (IGM 7441) is a partial skeleton, consisting of a skull, the left forelimb, and the front half of the presacral vertebral column.
[3] On collection, the specimens were transported to the Geological Institute of the National Autonomous University of Mexico.
[1] The strict consensus tree in Reynoso's paper on Ankylosphenodon recovers it as part of a small, unnamed clade within Sphenodontidae, one that also includes Eilenodon and Toxolophosaurus.
[1] Among sphenodonts, Ankylosphenodon is distinct in having pachyostotic (thickened) vertebrae and ribs, which were massive compared to those of related genera.