A Canadian-led team of scientists that probed the tiny, petrified skeletons inside a pair of 190-million-year-old dinosaur eggs has shed new light on the evolutionary origins of such later reptilian giants as diplodocus.
The “remarkably well-preserved” remains of the two unborn members of the species Massospondylus, unearthed in South Africa in 1976, are being described as the oldest embryos ever found from a land-dwelling vertebrate.
The study’s lead author, University of Toronto at Mississauga paleontologist Robert Reisz, said the successful reconstruction of the fossilized babies’ anatomy “opens an exciting window into the early history and evolution of dinosaurs.”
The study, published in the latest issue of the Journal of Vertebrate Paleontology, was co-authored by two of Reisz’s colleagues at the university — David Evans and Diane Scott — and U.S. scientist Hans-Dieter Sues of the Washington-based National Museum of Natural History.
The 20-centimetre-long fossil embryos had been in storage for nearly the entire time since their discovery. But modern imaging techniques and other high-tech tools unavailable in past decades allowed the team to interpret the dinosaurs’ folded remains to gain a clearer picture of their traits and to project how they would have developed toward adulthood.
The diminutive specimens represent an ancestral form of the massive, four-footed sauropod dinosaurs that, later in the Jurassic era, would grow to become the largest land animals that have existed on Earth.
They include the 50-metre-long, 120-tonne giant of all dinosaurs, Amphicoelias fragillimus, known only from a single and subsequently lost bone from a Colorado fossil bed.
“Prosauropods are the first dinosaurs to diversify extensively,” Reisz said in a summary of the study released by the Society of Vertebrate Paleontology.
“And they quickly became the most widely spread group, so their biology is particularly interesting as they represent in many ways the dawn of the age of dinosaurs.”
While the embryos had “relatively long front limbs and disproportionately large heads,” the summary states, the five-metre-long adults they would have become in maturity “had relatively tiny heads and long necks” typical of diplodocus and its sauropod cousins.
Last month, Reisz and Sues co-authored a paper with University of Texas researcher Tim Rowe, announcing the discovery of a “pivotal” new ancestor of the sauropod family of dinosaurs, a species dubbed sarahsaurus.
The sarahsaurus discovery combined with other finds of related dinosaur remains to show that those animals moved from their original southerly habitats into the future North America in “several separate dispersal events” rather than in the “sweepstake” style rush of an unstoppable competitor, Reisz told Postmedia News last month.
The new embryo study appears to highlight connections between the development of dinosaur infants and that of other animals, including our own mammalian species.
“In at least one way, Massospondylus development resembles that of humans; infancy is awkward, and a more erect stance and evenly proportioned body only come later,” the summary of the team’s findings stated.
“There may be another way that Massospondylus infancy was similar to that of humans,” it added. “The embryos lack teeth and this, combined with the awkward body proportions, suggests that the hatchlings may have required parental care. If true, these fossils also document the oldest record of parental care.”
Author: Randy Boswell | Source: The Vancouver Sun [November 14, 2010]