| Named By: | Richard Owen in 1854 |
| Time Period: | Early Jurassic, 200-183 Ma |
| Location: | Lesotho - Upper Elliot Formation, South Africa - Clarens Formation, Upper Elliot Formation, and Zimbabwe - Forest Sandstone Formation, Mpandi Formation, Upper Karroo Sandstone Formation |
| Size: | Between 4 and 6 meters long |
| Diet: | Herbivore |
| Fossil(s): | Many individuals |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Sauropodomorpha | Plateosauria | Massopoda | Massospondylidae | |
| Also known as: | | Aetonyx | Aristosaurus | Dromicosaurus | Gyposaurus | Hortalotarsus | Ignavusaurus | Leptospondylus | Pachyspondylus | |
Massospondylus ( mas-oh-SPON-di-las; from Greek, masson (masson, "longer") and spondulos (spondylos, "vertebra")) is a genus of sauropodomorph dinosaur from the Early Jurassic Period (Hettangian to Pliensbachian ages, ca. 200-183 million years ago). It was described by Sir Richard Owen in 1854 from remains discovered in South Africa, and is thus one of the first dinosaurs to have been named. Fossils have since been found at other locations in South Africa, Lesotho, and Zimbabwe. Material from Arizona's Kayenta Formation, India, and Argentina has been assigned to this genus at various times, but the Arizonan and Argentinian material are now assigned to other genera.
The type species is M. carinatus; seven other species have been named during the past 150 years, but only M. kaalae among these is still considered valid. Early sauropodomorphs systematics have undergone numerous revisions during the last several years, and many scientists disagree where exactly Massospondylus lies on the dinosaur evolutionary tree. The family name Massospondylidae was once coined for the genus, but because knowledge of early sauropodomorph relationships is in a state of flux, it is unclear which other dinosaurs--if any--belong in a natural grouping of massospondylids; several 2007 papers support the family's validity.
Although Massospondylus was long depicted as quadrupedal, a 2007 study found it to be bipedal. It was probably a plant eater (herbivore), although it is speculated that the early sauropodomorphs may have been omnivorous. This animal, which was 4-6 metres (13-20 ft) long, had a long neck and tail, with a small head and slender body. On each of its forefeet, it bore a sharp thumb claw that was used in defense or feeding. Recent studies indicate that Massospondylus grew steadily throughout its lifespan, possessed air sacs similar to those of birds, and may have cared for its young.