Two dinosaur embryos discovered in the Free State in the 1970s have been identified as the world’s oldest ”rotten eggs”.
Dr Michael Raath, a palaeontologist at the University of the Witwatersrand who was involved in the study, said the two embryos are the oldest known embryos for any terrestrial vertebrate from anywhere in the world.
”These are the oldest known dinosaur eggs and are about 190-million years old,” Raath said.
”The embryos are also the oldest known for any terrestrial vertebrate and thus the oldest embryos in an amniote egg known from anywhere in the world.”
Most of the other known dinosaur embryos are from the Cretaceous period and are at least 100-million years younger.
Two embryos were exposed in the group of seven eggs. They belong to the early sauropodomorph dinosaur Massospondylus.
”This identification allowed the team to reconstruct in detail the growth trajectory in Massospondylus, from pre-hatchling to full adult — a first for a dinosaur,” Raath said.
One of the embryos is almost complete and curled up inside its egg. It appears to be trapped in the act of hatching.
The team that studied the eggs was led by Professor Robert Reisz of the University of Toronto, and had its findings published in the scientific journal Science on Friday.
The eggs were discovered by Professor James Kitching in spoil rock from a road cutting through the Golden Gate Highlands National Park in the late 1970s.
The eggs remained on the shelves of the fossil store at Wits University until January 2000, when Kitching found someone skilled and patient enough to remove the rock around the embryos.
”Finding eggs like these is not like finding eggs on the supermarket shelf. These are very difficult to find,” Raath said.
Reisz suggested to Kitching that a woman who worked in his laboratory, Diane Scott, had the skills and patience to do the job.
”So, off went the rotten eggs to Canada,” Raath said.
Scott started chipping away rock around the embryos in 2000 and came up with ”an almost complete beautiful embryo in its egg”.
The eggs are still in Canada, but it is hoped they will be brought to South Africa later this year to be displayed.
Raath said the reason it took so long to make the findings of the study known was because of a lack of manpower, training and skills in the field.
”This is very different from normal palaeontological preparation. It needs a very skilled and patient person to do this. The rock around these fossils is damned hard to get off.”
Raath said prosauropods were the first dinosaurs to diversify extensively and they quickly became the most widely spread group.
”They represent in many ways the dawn of the age of dinosaurs, the group that was to become so dominant on earth for so long [more than 100-million years] in later geological times.”
Massospondylus skeletons are quite common in South Africa and range in size from small juveniles to full adults up to about 5m in length.
Raath said the growth trajectory of Massospondylus shows it started out as an ”awkward-looking little creature”.
”It 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.”
He said the dinosaur changed from a tiny quadruped into a weird-looking large animal that had a very long neck; a thick, massive tail; a very small head; short forelimbs; and long hind limbs.
It was assumed that sauropods probably evolved through a phenomenon called paedomorphosis, the retention of embryonic and juvenile features in the adult. Humans are thought to have evolved through this process.
The absence of well-developed teeth in the two preserved embryos, which were clearly on the point of hatching, and the awkward body proportions suggest that the hatchlings required parental care after emerging from the egg.
”If this interpretation is correct, we have here the oldest known indication of parental care in the fossil record,” Raath said. — Sapa