Dale Allan Russell (1967) considered the form of the teeth, the shape of the frontal and the large suprastapedial process of the quadrate as evidence of a close relation between Ectenosaurus and Platecarpus.

He separated Ectenosaurus from Platecarpus based on the elongated snout, the exclusion of the prefrontals from the narial borders and the fusion of the supra- and infrastepedial processes.

[3] The combination of small and firmly anchored body scales as well as a complex meshwork of alternating crossed-helical and longitudinal fiber bundles suggest that the anterior torso of Ectenosaurus was reasonably stiff.

The type specimen was collected by Charles Hazelius Sternberg or Georg Bauer from Logan County in Kansas and was housed in the Bayerische Staatssammlung für Paläontologie in Munich, where it was likely destroyed in 1944 during the Second World War.

The specimen, formerly catalogued as GFS 109-53, was about 3 metres (9.8 ft) in length and largely articulated, though the tail and rear limbs were missing due to erosion.

[5] In 2023, Caitlín R. Kiernan and Jun A. Ebersole named two new species of the genus: E. tlemonectes from the Niobrara of Kansas and E. shannoni from the Mooreville Chalk of Alabama.