Guest Factoid: Massospondylus

Greetings. I am the Massospondylus. The mass is only in my name–I myself am lean and lithe, perfect for a muy macho dancer, no? But I do not chew upon the roses. They have not been invented yet. Que lastima!

John Michalski is a graduate from the University of Wisconsin, Milwaukee with a bachelor’s degree in geology. Currently he is working on achieving a masters of science degree at Utah State University, aiming for a career in vertebrate paleontology. He has been passionate about dinosaurs since he could walk and talk, and loves to discuss and educate others about paleontology and prehistoric life.

Of all dinosaurs, the sauropods are the physical manifestations of the awe and majesty that percolates through our fascination with these animals and their ancient world. But as with all other famous lineages, their origins were laid down by creatures bearing similar physical features while significantly lacking in grandeur. Originally termed prosauropods, now referred to as basal sauropodomorphs, these early forms were the blueprint for the giants that were to come with their large bodies, long necks, and small heads. Though many species have been described, their similar body plans and complicated fossil record make only a select few all that memorable. Even dinosaur enthusiasts may not immediately recall genera like Riojasaurus, Lessemosaurus, or Lufengosaurus off the top of their heads.

But one member of these early giants has enough fossil material to give us not only a glimpse at what it looked like, but also remarkable clues into its behavior and biology. This was Massospondylus carinatus, an animal whose history within paleontology goes back many years but has only recently revealed to us some of its many secrets.

o Massospondylus was a medium-sized massospondylid sauropodomorph from the early Jurassic of southern Africa. Fossils of this dinosaur were described by Sir Richard Owen in 1854 (Royal College of Surgeons of England 1854) and were first discovered in the Upper Elliot formation in South Africa (Yates and Barrett 2010). Other remains have been found in the Clarens Formation and the Bushveld Sandstone of South Africa and Lesotho, and the Forest Sandstone of Zimbabwe. Material originally assigned to Massospondylus was found in Arizona and Argentina but have since been reassigned to different genera (Sarahsaurus (Rowe et al. 2011) and Adeopapposaurus (Martínez 2009) respectively. Over the years, many species have been named, though few are now considered valid.

o Current estimates place the average Massospondylus around four meters in length, and one thousand kilograms. Some sources suggest the species could reach a length of six meters, however. A slender dinosaur, Massospondylus was not as heavily built as the more famous Plateosaurus from the late Triassic of Europe but shared its relative’s long neck and small head. Although once believed to have been quadrupedal, Massospondylus, Plateosaurus, and other similar sauropodomorphs lacked the forelimb range of motion to walk on all fours and may have been obligate bipeds (Bonnan 2007).

o Massospondylus fossils have been dated between from the Hettangian to the Pliensbachian stages of the early Jurassic period (between 200 and 183 million years ago). Following the end of the Triassic, which saw the extinction of many families of animals that dominated global ecologies, the dinosaurs were quick to take the reins as the ecological heavy-hitters among terrestrial organisms throughout the world. The Upper Elliot formation, the most fossil rich site to include Massospondylus, supported a wide variety of dinosaurs. These included fellow sauropodomorphs Ignavusaurus and Aardonyx as well as possible early sauropods like Antetonitrus. Several genera of basal ornithischians are also known from the formation, like Heterodontosaurus, Abrictosaurus, and Pegomastax. Theropods, and possible hunters of Massospondylus, included Coelophysis (Originally named Syntarsus, then Megapnosaurus. Synonymy with North American species remains controversial), and the fragmentary Dracovenator (sometimes depicted as resembling the more famous Dilophosaurus).

o Though dinosaur nesting sites are known all over the world, Massospondylus holds the title of having the oldest geologically speaking. A clutch of seven eggs belonging to the genus were found in Golden Gate Highlands National Park in South Africa in 1976. Some thirty years later, extraction of the embryos within the eggs began. At around fifteen centimeters long, they were dated to around 190 million years ago, making them the oldest dinosaur embryos discovered thus far. By 2012, at least ten egg clutches had been found with about thirty-four eggs per clutch from four fossiliferous horizons. This would indicate that the site was used continuously by multiple Massospondylus, representing the oldest evidence of colonial nesting in dinosaurs (Reisz et al. 2012).

o The thinness of the eggshells (about 0.1 millimeters) suggests that they were partially buried after being laid to enable some degree of gas exchange. This exchange is crucial in allowing an embryo to breathe during growth while protecting it from outside elements. Though there does not seem to be any evidence that the eggs were laid in nests, their arrangement into tight rows supports the notion that they were actively adjusted into these positions by adults. Further care by adult Massospondylus has been suggested since the embryos, believed to have represented near-hatchlings, had no teeth in their mouths while simultaneously bearing large heads and, like the adults, bearing forelimbs poorly suited for a quadrupedal gait. This would’ve made it impossible for them to feed themselves or move around properly. Some have therefore suggested that Massospondylus, like some of its later relatives, enacted postnatal care to ensure their offspring the best chance of survival early in life (Reisz et al. 2012).

o Sauropodomorphs are one of the few groups of saurischian dinosaurs (meaning lizard-hipped and includes meat-eating and long-necked dinosaurs) that lack the pneumatic foramina cavities present in theropods and sauropods. These cavities are usually found in the ribs and vertebrae and may indicate a lung configuration with air-sacs like modern day birds (O’Connor et al. 2005). A study in 2007 suggested that sauropodomorphs, such as Massospondylus, likely had similar air-sacs (Wedel 2007), but cold hard proof remains unknown. For now, the file remains very open for future discussion.

The snow has left this denizen of Mesozoic South Africa literally frozen with terror!

References:

Bonnan, Matthew F. “Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds?” Evolution and palaeobiology of early sauropodomorph dinosaurs (2007): 139-155.

Martínez, Ricardo N. “Adeopapposaurus mognai, gen. et sp. nov.(Dinosauria: Sauropodomorpha), with comments on adaptations of basal Sauropodomorpha.” Journal of Vertebrate Paleontology 29.1 (2009): 142-164.

O’Connor, Patrick M., and Leon PAM Claessens. “Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs.” Nature 436.7048 (2005): 253-256.

Reisz, Robert R., et al. “Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus.” Proceedings of the National Academy of Sciences 109.7 (2012): 2428-2433.

Rowe, Timothy B., Hans-Dieter Sues, and Robert R. Reisz. “Dispersal and diversity in the earliest North American sauropodomorph dinosaurs, with a description of a new taxon.” Proceedings of the Royal Society B: Biological Sciences 278.1708 (2011): 1044-1053.

Royal College of Surgeons of England. Museum. Descriptive Catalogue of the Fossil Organic Remains of Reptilia and Pisces Contained in the Museum of the Royal College of Surgeons of England. Taylor & Francis, 1854.

Wedel, Mathew J. “What pneumaticity tells us about ‘prosauropods’, and vice versa.” Special Papers in Palaeontology 77 (2007): 207-222.

Yates, Adam M., and Paul M. Barrett. “Massospondylus carinatus Owen 1854 (Dinosauria: Sauropodomorpha) from the Lower Jurassic of South Africa: Proposed conservation of the usage by designation of a neotype.” (2010).