 In 2018, Kenneth Carpenter renamed "Amphicoelias fragillimus" as the new genus "Maraapunisaurus", and reclassified it from Diplodocidae to Rebbachisauridae.Henry Fairfield Osborn and Charles Craig Mook noted the overall close similarity between "Amphicoelias" and "Diplodocus", as well as a few key differences, such as proportionally longer forelimbs in "Amphicoelias" than in "Diplodocus".The femur of "Amphicoelias" is unusually long, slender, and round in cross section; while this roundness was once thought to be another distinguishing characteristic of "Amphicoelias", it has since been found in some specimens of "Diplodocus" as well.