Dino of the Week: Massospondylus

Type Species: Massospondylus carinatus
Classification: Dinosauria - Saurischia - Sauropodomorpha - Prosauropoda
Time Period: Early Jurassic
Location: Africa & North America
Diet: Herbivore

This Lower Jurassic dinosaur has been found in Africa and North America. Stretching to between 15-20 feet, Massospondylus was smaller than many of the larger prosauropods that preceded it by millions of years. This dinosaur had a body kept long and low, and it stood no higher than five feet tall at the hips. Its body may have been smaller than its predecessors, but its neck was longer, made so by its neck vertebrae being four times long as they were wide (the presence of these elongated vertebrae gives the meaning of Massospondylus’ name: “the Longer Vertebrae”). The extra-long neck and long tail served as bookends for its bulky, low-slung body. Rounded, peg-like teeth designed for stripping leaves off trees lined the jaws of its small head. Massospondylus’ forelegs were half the length of the hind limbs, but they were by no means scrawny: the broad upper end of the humerus implies that these fore-arms had strong muscle attachments and could deliver a fatal punch. Such a “killer punch” would’ve been made that much more lethal by the gruesome thumb claw on each large hand. Though it was long thought that Massospondylus was confined to a quadrupedal stance, recent studies have shown that it could walk on two legs if it so desired.

The presence of a few large holes for blood vessels on the surface of the jaw bones implies that it had, like many prosauropods, cheeks (reptiles without cheeks have numerous small blood vessel holes in the jaws rather than a few large ones); these cheeks helped keep food from falling out of the mouth. Some scientists have speculated that Massospondylus may have had a beak, like the ornithischians, but the evidence for this is dubious at best. On the subject of its dietary apparatuses, it seems Massospondylus employed a gastric mill: a specimen from Zimbabwe was found with gastroliths in its gut area, and these particular stones had their origin nearly twelve miles from the gravesite. This specimen had probably ritualistically swallowed gizzard stones only hours or days before its death. 

Like Plateosaurus, Massospondylus possessed small air cavities in some of its bones. Most saurischian dinosaurs had these hollowed-out cavities (called pneumatic foramina) that served as a rudimentary “flow-through ventilation system” similar to that of present-day birds. The neck vertebrae and ribs are hollowed out by the cervical air sack; the upper back vertebrae, by the presence of the lungs; and the lower back and hip vertebrae by the abdominal air sack. Prosauropods are the only major group of saurischian dinosaurs that lack an extensive system of pneumatic foramina, despite some species—such as Massospondylus—possessing the miniscule “building-blocks” that could, one day, blossom into full-blown pneumatic foramina. The presence of air sacs in Massospondylus doesn’t mean that it had a full-blown pneumatic system like that of birds (or even like that of wider saurischian); it does mean that, at the least, we have glimpses of the plodding evolution of such structures. 

The remains of nearly eighty individuals have been unearthed, indicating that Massospondylus may have engaged in gregarious behavior, traveling in herds throughout both Laurasia and Gondwana. Such gregariousness is attested to by marked differences between the skulls of these prosauropods: such minor variations are often symptomatic of sexual dimorphism. Sexual dimorphism—changes in anatomy between males and females—is most prominent in gregarious animals. Furthermore, gregarious animals have a tendency to care for their young, and this is precisely what we see with Massospondylus. In 1976, a clutch of seven 190 million year old Massospondylus eggs were found in South Africa. They were attributed to Massospondylus from the get-go, but detailed examination of the eggs didn’t start until the turn of the century. Scientists were able to examine the actual embryos, making these embryonic dinosaurs the oldest known. More digging uncovered another ten more egg clutches, and each clutch contained up to 34 eggs. Because these egg clutches were found in at least four different time zones in the rock formation, we can deduce that we’ve stumbled across a nesting colony that was revisited on a cyclical basis. Nesting colonies are common among gregarious animals, and detailed studies of the hatchlings (and the track-ways they left behind) tell us that infant Massospondylus were unable to function well on their own. Not only were they ungainly (not optimal for running from predators), but they lacked teeth! It seems parental care may have been a necessity for the Massospondylus line to continue; without such parental care, the babies would starve to death and the species would go extinct.