Massospondylus, meaning “longer vertebrae,” is a genus of prosauropod dinosaur from the Hettangian to Pliensbachian ages of the Early Jurassic Period (200 to 183 million years ago). Massospondylus was discovered in 1853 by J.M. Orpen in the Upper Elliott Formation at Harrismith, South Africa. It was described in 1854 by Sir Richard Owen. It is one of the first dinosaurs to have been named.
The type species is M. carinatus. There have been seven other named species during the past 150 years, of which, only M. kallae is still considered valid. While several papers support the validity of Massospondylus as a unique genus, many scientists disagree where exactly this dinosaur lies on the evolutionary tree.
The first collected specimen from South Africa included vertebrae from the neck, back and tail, a shoulder blade, a humerus, partial pelvis, femur, tibia, and bones of the hand and feet. The original holotype material was part of the Royal College of Surgeons collection in London and was destroyed in World War II; only casts of the specimen remain.
Possible remains of Massospondylus have been found in the Upper Elliot Formation, the Clarens Formation, and the Bushveld Sandstone of South Africa and Lesotho; the Forest Sandstone and the Upper Karroo Sandstone of Zimbabwe; and the Kayenta Formation of Arizona. These remains consist of at least 80 partial skeletons and four skulls, representing both juveniles and adults.
The Massospondylus remains found in Arizona represent a specimen 25 percent larger than the largest skull found in any of the African specimens. The Arizona specimen also possesses four teeth in the premaxilla and sixteen in the maxilla, distinct of the African specimens.
Based on recent studies of the African Massospondylus remains, the Arizona specimen may not be a true Massospondylus. The Arizona skull and associated postcranial elements has been recently referred to the newly described genus Sarahsaurus.
Although Massospondylus has been long depicted as a quadruped, a 2007 study found it to be a bipedal plant-eater. However, according to some speculation, it is omnivorous, eating both plants and meat.
The adult is 13 to 20 feet long with a long neck and tail, 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 it grew steadily throughout its life. It also possessed air sacs similar to those of birds, and may have cared for its young. The adult weighed about 300 pounds, or more for larger specimens.
In 1977, seven 190-million-year-old eggs were discovered in Golden Gate Highlands National Park in South Africa by James Kitching, who identified them as belonging to Massospondylus. It was nearly 30 years before extraction began. They are the oldest dinosaur embryos ever found. Notably, the near hatchlings had no teeth, and the animal’s body proportions led scientists to speculate that postnatal care might have been necessary.