|Massospondylus adult burying a clutch of eggs by Christopher DiPiazza.|
Massospondylus was what we refer to as a basal sauropodomorph. Basal sauropodomorph is the group of dinosaurs that we believe would eventually evolve to give rise to the largest land animals the earth has ever seen, the sauropods, like Apatosaurus and Giraffititan. Plateosaurus, a close relative of Massospondylus, was another example of a basal sauropodomorph, or prosauropod, as they are also sometimes called. Massospondylus was not that big compared to its later relatives but for it's time in the early Jurassic, it was relatively large for a dinosaur.
|Massospondylus skull. You can see all the small, leaf-shaped teeth that could have been useful for slicing tough plant material.|
The oldest fossil dinosaur eggs ever discovered are from Massospondylus. The fossil site where these eggs have been found actually shows layers upon layers of nests that existed years apart from each other. This means that the dinosaurs were returning to the same place to lay eggs over and over again every generation. This sort of thing has actually been discovered a few times with extinct dinosaurs, specifically with sauropodomorphs.
|Massospondylus eggs showing unhatched embryo inside one of them at the Royal Ontario Museum. The eggs were laid in rows rather than just plopped in a pile, suggesting mom took at least some care with regards to her young, unlike many other reptiles.|
Along with some eggs, unhatched Massospondylus embryos and young have also been uncovered. The babies of this dinosaur are actually surprising in that they don't resemble the parents much at all. Adult Massospondylus were pretty typical for basal sauropodomorphs with small heads, long necks and tails, and bipedal posture. The babies, some of which are as small as six inches long, had really big heads, short necks (to support the huge noggins), walked on all fours, and were toothless! Even more interesting, many baby skeletons were in the nest that were too big to have been just hatched. That, combined with the fact that they were still toothless, suggests that the adults were caring for them in some form. This is not consistent with what paleontologists believe about later, larger sauropod parental behavior, which consisted of simply laying the eggs and leaving the clutch and young to fend for themselves. There could be a size limit somewhere in sauropod evolution that has a connection. After all, when a parent is over one hundred feet long, as oppose to Massospondylus' modest fifteen feet, it may be more likely to accidentally step on its hatchlings than protect them! One must ask how much good can a parent with that big of a size difference really be?
Parental care in some form or another is also present in many modern non-avian reptiles. All crocodilians build, guard, and protect young, certain large snakes protect eggs by wrapping their bodies around the clutch and generating heat through muscle friction, even some lizards and testudines (turtles and tortoises) guard their young, as well! Theorizing a primitive sauropodomorph did too isn't so crazy.
That is all for this week! As always feel free to comment below or on our facebook page. Also, special thanks to friend and paleontologist, Dr. Heinrich Mallison, for helping out with this week! Having worked with prosauropods, he lent his expertise for the post and illustrations!
Bonnan, Matthew F.; and Senter, Phil (2007). "Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds?". In Paul M. Barrett & D. J. Batten (eds.). Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs. Special Papers in Palaeontology 77. London: The Palaeontological Association. pp. 139–155.
Reisz, Robert R.; Diane Scott, Hans-Dieter Sues, David C. Evans, and Michael A. Raath (2005). "Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance". Science 309 (5735): 761–764. Bibcode:2005Sci...309..761R. doi:10.1126/science.1114942. PMID 16051793.
Reisz, Robert R.; David C. Evans, Hans-Dieter Sues, Diane Scott (2010-11-01). "Embryonic Skeletal Anatomy of the Sauropodomorph Dinosaur Massospondylus from the Lower Jurassic of South Africa". Journal of Vertebrate Paleontology 30 (6): 1653, 1664. doi:10.1080/02724634.2010.521604. ISSN 0272-4634.
Reisz, Robert R.; David C. Evans, Eric M. Roberts, Hans-Dieter Sues, and Adam M. Yates (2012). "Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus". Proceedings of the National Academy of Sciences of the United States of America 109 (7): 2428–2433. Bibcode:2012PNAS..109.2428R. doi:10.1073/pnas.1109385109. PMC 3289328. PMID 22308330.
Yates, Adam M. (2012). "Basal Sauropodomorpha: The "Prosauropods"". In M. K. Brett-Surman, James O. Farlow, Thomas R. Holtz (eds.). The Complete Dinosaur (2. ed.). Indiana University Press. pp. 430, 435. ISBN 978-0-253-35701-4.