OLDEST KNOWN DINOSAUR EMBYROS IDENTIFIED THROUGH WITS/UTM COLLABORATION

Two 190-million-year-old dinosaur embryos, out of a group of seven eggs, have been identified as the world’s oldest dinosaur embryos found to date. Discovered in South Africa, they are also the oldest known embryos for any terrestrial vertebrate from anywhere in the world.     

Fossilised embryo in its egg

Artist's reconstruction of the embryo in its egg

The embryos are of an Early Jurassic prosauropod dinosaur according to Dr Mike Raath, from the Wits Bernard Price Institute for Palaeontological Research (BPI). Raath is one of five authors who describe the embryos and their evolutionary significance in the leading international journal Science published on July 29, 2005. “The embryos belong to the early sauropodomorph dinosaur Massospondylus carinatus. These skeletons are quite common in South Africa and range in size from small juveniles to full adults, up to about 5m in length. This identification is a major coup, because embryos are often difficult to identify to species,” says Raath.

The late Professor James Kitching from the BPI originally discovered the cluster of eggs containing the embryos nearly thirty years ago in the Golden Gate Highlands National Park in the northeastern Free State, South Africa.They have lain on the shelves of the fossil store in Wits University since then, awaiting someone with the necessary training and skill to prepare the fossil eggs for detailed study because of the extremely delicate nature of the tiny embryonic bones and their intricately curled up position in the eggs. “In January 2000, Professor Robert Reisz from the University of Toronto at Mississauga in Canada was on a research visit to South Africa and borrowed the fossil eggs to take back to Canada, where Diane Scott of his lab carried out the detailed and difficult preparation under high magnification using a special microscope and achieved spectacular results,” explains Raath.

Prof James Kitching who discovered the eggs in 1977

The embryos provide significant insights into the growth and development of this early dinosaur. Raath explains that this discovery allowed the team to reconstruct in detail the growth trajectory of Massospondylus, from pre-hatchling to full adult - a first for any dinosaur. Prof Reisz, the project leader, points out that adults and juveniles of other types of dinosaur are known, but they are usually either recovered from bone beds, where the skeletons are broken up, disarticulated and scattered, or the rare articulated skeletons are not sufficient to reflect a growth series.

The growth trajectory of Massospondylus shows that this dinosaur started out as an awkward-looking little creature that was an obligate quadruped, had a relatively short tail, a horizontally held neck, long forelimbs and a huge head. As the animal grew, the neck grew faster than the rest of the body, but the forelimb and head grew much more slowly than the rest of the body, so the body proportions changed dramatically as the animal grew. This means that Massospondylus changed from a tiny, awkward-looking quadruped into a weird-looking large animal which had a very long neck (still held horizontally) a thick, massive tail, a very small head, short forelimbs, and long hindlimbs.

Skull of adult Massospondylus above and embryo in its egg below.

The result is an adult animal that looked very different from the embryo and was probably at least partly bipedal. In other cases where embryos and adults are known, as in the hadrosaurs or duck-billed dinosaurs, such dramatic changes in body proportions are not shown.

The embryos also provide clues about the origin of the quadrupedal gait of the giant sauropods (the ‘brontosaurs’) of later times, which are descendants of the prosauropods. The embryo of Massospondylus looks like a tiny sauropod with massive limbs and a quadrupedal gait, which the authors believe shows that the quadrupedal gait of sauropods probably evolved through a phenomenon called paedomorphosis - the retention of embryonic and juvenile features in the adult. “Some people think that humans too are products of paedomorphosis,” says Raath.

The absence of well developed teeth in the two preserved embryos, which were clearly on the point of hatching, and the overall awkward body proportions suggest that the hatchlings required parental care of some kind for some time after emerging from the egg. The authors say that if this interpretation is correct, it constitutes the oldest known indication of parental care in the fossil record.
27 July 2005.

For more information, contact:
Dr. Mike Raath
Bernard Price Institute for Palaeontological Research
University of the Witwatersrand, Johannesburg
Phone:   +27 11 717 6683
Mobile:  +27 83 766 1568
Email: raathm@geosciences.wits.ac.za

or to find out answers to more questions on embryos of an early Jurassic prosauropod dinosaur, click here.