Eilenodon is an extinct genus of rhynchocephalian reptile from the Late Jurassic Morrison Formation of western North America,[1] present in stratigraphic zone 4.

It and other eilenodonts had very wide and strongly packed teeth as well as a deep jaw for chewing and shredding plant material.

If the jaws were complete, they would have been about 10 centimeters (4 inches) long, signifying that Eilenodon robustus was among the largest species of rhynchocephalians known, surpassed only by its fellow eilenodont Priosphenodon avelasi.

This creates two wear facets (worn away areas) in all but the most posterior teeth, converging in a 90-degree angle to form a blade-like ridge.

The labial wear facet (worn-away area on the side facing the lips) was originally believed to have been positioned practically vertically while the apical (upward-facing) wear facet would have been positioned nearly horizontally, making the tooth row rectangular in cross-section.

Towards the front of the jaw the wear facets shift inwards to a more diagonal position, making the tooth row triangular in cross-section.

[5] Eilenodon's dentary teeth differ from those of Toxolophosaurus by being more closely packed and somewhat simpler, only slightly concave from the front and having only two dental ridges per tooth.

[3] Referred maxilla fragments are low and thick, covered in grooves, and curve sharply inwards above the tooth row.

[5] The holotype specimen of Eilenodon robustus was collected in 1976 near Fruita in western Colorado, an area known for its Morrison Formation outcrops.

The teeth would have been able to withstand 2.3 to 3.1 times as much resistance to fracturing and would have had a cumulative maximum bite force of 625 to 843 Newtons, compared to 275 N in Sphenodon.

This would have allowed wear facets to have been acquired early in life, to facilitate slicing and grinding plant matter.

The study suggested that Eilenodon and other opisthodonts may have fed on horsetails of the genus Equisetum, which were nutritious and common in the Morrison Formation, but also high in silica, necessitating sharp and fracture-resistant teeth to process the plants.