Macelognathus is an extinct genus of sphenosuchian crocodylomorph from the Late Jurassic.

[1][2] The type species, Macelognathus vagans, was described by Othniel Charles Marsh in 1884 as a turtle based on a partial jaw from the Late Jurassic Morrison Formation at Como Bluff, Wyoming.

[3] After being referred to the Dinosauria by Moodie in 1908,[1] it was later reclassified by Ostrom in 1971 as a crocodilian relative.

[4] Based on new material from the Morrison Formation at Fruita, Colorado, in 2005 Göhlich et al. identified it as a basal crocodylomorph ("sphenosuchian").

[5] It is considered an example of convergent evolution, due to the similarities to caenagnathid dinosaurs, with which it was not closely related.