Macrocnemus is an extinct genus of archosauromorph reptile known from the Middle Triassic (Late Anisian to Ladinian) of Europe and China.

Macrocnemus bassanii, the first species to be named and described, is known from the Besano Formation and adjacent paleontological sites in the Italian and Swiss Alps.

[7] Numerous complete or partial specimens of M. bassanni housed at PIMUZ (Paläontologisches Institut und Museum der Universität Zürich) include A III/208, T 1534, T 2470, T 2472, T 2474 through T 2477, T 2809, T 2812 through T 2816, T 4822, and T 4355.

According to Olivier Riepple et al, “a large, plate-like lacrimal is located in front of the tall, columnar prefrontal that defines the anterior margin of the orbit.

[7] Macrocnemus obristi was discovered by Christian Obrist during an excavation from the Upper Prosanto Formation, which is dated to the middle Triassic.

It is noticeably characterized by its gracile limb elements (including slender metatarsals) and a tibia which is 20% longer than the femur.

[3] Some features of the limbs imply that Macrocnemus lived in terrestrial habitats and was capable of rapid bipedal movement.

The presence of both Macrocnemus and Tanystropheus in both Switzerland and southwestern China suggest that the fauna of the western and eastern Tethyan realms was similar during the Middle and early Late Triassic.

[2] In 1970 Romer classified Macrocnemus as a lepidosaur related to modern lizards and tuataras, but in 1988 Carroll reclassified it as a member of Protorosauria.