Bill Sellers, University of Manchester
Argentinosaurus, the world's biggest known terrestrial animal, lumbered along at around 5 miles per hour.
Artwork by Julius Csotonyi
Jurassic Dino Nesting Site
Jan. 23, 2012
-- The oldest known dinosaur nesting site, dating to 190 million years ago, has been unearthed in Golden Gate Highlands National Park, South Africa. The extraordinary site, described in the latest Proceedings of the National Academy of Sciences, includes multiple dinosaur nests, eggs, hatchlings and the remains of adults for this species, Massospondylus. Project leader Robert Reisz, a professor of biology at the University of Toronto Mississauga, told Discovery News that the dinosaur was herbivorous. Like its sauropod relatives, it had a very small head and an extremely long neck. The hatchlings walked on all fours, but adults were bipedal. "The transition from four legs to two during an individual's lifetime is a very unusual growth pattern that we rarely see in animals, but we do see it in humans," Reisz said. "The largest articulated skeleton of this animal was about 6 meters (19.7 feet) in length, but they probably grew even larger."
Dinosaur Nest The discovery provides evidence for "nesting site fidelity," according to Reisz, "as it looks like these dinosaurs liked this place and returned to it repeatedly to lay their eggs." It's also the oldest evidence in the fossil record for a highly organized nest, with eggs carefully laid in a single layer. Reisz and co-author David Evans, an associate curator of vertebrate paleontology at the Royal Ontario Museum, are shown here standing next to a nest in plaster at the site. Plaster protects the excavated nest, just like the broken bone in a human. The plaster cover is later removed in the lab for research. Reisz said clues about the nest are difficult to interpret, but what's known so far is that "the nests seem to be fairly shallow because all the eggs are in one layer," he said. "We do not know if the nests were covered by vegetation or if they were buried because the nature of the sediments preclude the preservation of plant fossil remains. It is quite possible that the mother guarded the nests." Nest guarding today is fairly common among living reptiles, such as crocodiles. It's also now known "that the hatchlings stayed around the nesting area long enough to at least grow to double in size."
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Adult Massospondylus Skull, Complete Embryo This photo compares the size of the skull of an adult next to the skeleton of an entire tiny embryo. The researchers believe each Massospondylus mother laid a lot of small eggs, at least 35, which was a probable survival strategy. "There were large and small meat-eating theropod dinosaurs around at the time Massospondylus lived,” Evans told Discovery News. "The smaller, more agile predator called Coelophysis, was much smaller than adult Massospondylus, but would have been a threat to the hatchlings and juveniles." So far, the researchers have found 10 dinosaur nests at the site, but they suspect many more are still embedded within the South African cliff. They predict many other nests will be eroded out in time, as the natural weathering process continues.
Dinosaur Embryo Close-Up This close-up of a Massospondylus embryonic skeleton reveals that the head was pushed out of the egg after death. The scientists suspect gases produced by decay caused this to happen. They also think the site was so well preserved because the dinosaur moms chose to lay their eggs in what was then, back in the Early Jurassic Period, a wet spot at the edge of a river. Reisz explained, "Periodically there was an unusually wet season and this area was flooded, drowning the unhatched eggs and embryos, and covering the nests with very fine sediment. Yet this turned out not to be such a horrible disaster for paleontologists." South Africa appears to have been a hotspot for Massospondylus, with other possible nesting sites for this dinosaur probably in existence. So far, however, the one at Golden Gate Highlands National Park is the only nursery to yield complete clutches, with eggs containing embryos, Evans said. He added that similar evidence for large-scale nesting among dinosaurs exists, for dinos such as duck bills and sauropods, but that evidence is about 100 million years younger than this South African site.
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Baby Dinosaur Handprint The discovery provides the world's oldest clear evidence for baby dinosaur footprints at a nesting site. The handprint seen here, as well as the other excavated baby prints, indicates that the infants stayed near the nest site after hatching and walked on all four limbs at first. Reisz said, "The overall body shape of the hatchlings with a large, toothless head, relatively long neck, and general look of helplessness suggests that parental care was very likely in Massospondylus. We think that the mother may have guarded the nest and the hatchlings, but may have also fed the babies with plant material." The paleontologists are now in the process of testing this hypothesis by preparing more embryos from different nests, to see if any of them have teeth. This ongoing research would be the first study of different embryological stages in a dinosaur.
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A digital reconstruction of the world’s largest known land animal, the Cretaceous dinosaur Argentinosaurus, has allowed it to take its first steps -- albeit virtually -- in over 94 million years.
The recreation, outlined in PLoS ONE, is the most anatomically detailed walking simulation so far for a dinosaur, according to the researchers. The study also provides the first ever virtual trackway for Argentinosaurus.
The skeleton used in the study shows that the plant-eating dinosaur measured at least 131 feet long. The reconstruction reveals that it lumbered along at around 5 miles per hour.
“The simulation shows a slow walking gait, which is to be expected, given that the animal weighs 80 tonnes,” lead researcher Bill Sellers from the University of Manchester’s Faculty of Life Sciences, told Discovery News. “What is interesting is how well the simulated footfall pattern matches up with typical sauropod trackways.”
For the study, Sellers and his colleagues laser scanned the huge dinosaur’s skeleton. They then used an advanced computer modeling system (Sellers has his own software called Gaitsym) that involves the equivalent of 30,000 desktop computers. It virtually recreated the dinosaur, including the sauropod’s movements.
The discovery that Argentinosaurus could walk counters prior speculation that the animal could not have done so, based on previous estimations of its size.
This latest research concludes not only that Argentinosaurus could walk, but that it was also at the top of its food chain.
“Once you hit 80 tonnes, you don’t have to worry about being eaten by predators,” Sellers explained. “We don’t know whether this animal used its long neck to graze over wide areas of low-laying vegetation or for reaching the tops of trees, but from its locomotion we know that it was a slow, steady mover.”
Argentinosaurus, the world's biggest known terrestrial animal, lumbered along at around 5 miles per hour. Bill Sellers, University of Manchester
Argentinosaurus eggs, however, were no bigger than those of many dinosaurs and large birds. It's therefore likely that Argentinosaurus young were fairly small and would have been easy prey for other carnivorous species that lived along the Cretaceous planes of what is now Patagonia, South America.
Understanding how such past animals moved may help us to better understand modern day musculoskeletal systems.
“If you are trying to understand any body system that is shared by a range of different animals then it is often extremely useful to compare this system across different species,” Sellers explained. “Vertebrate muscles, skeletons and joints work exactly the same way in everything from fish to humans.”
He continued, “The really interesting aspect of dinosaur locomotion is that you are looking at animals that test the limits of the musculoskeletal system simply by virtue of being so big. They have to make compromises and come up with ways of coping that help us to understand the limits and compromises in the human musculoskeletal system.”
Phillip Manning is head of the Paleontology Research Group at the University of Manchester and is a research associate at the American Museum of Natural History.
Manning told Discovery News that paleontology is now undergoing a renaissance, with more interdisciplinary approaches, such as this, helping to solve long-standing questions.
“To carefully break down the key components of the locomotion of such vast animals as Argentinosaurus is allowing us greater insight to the biology and physiology of such vast organisms,” Manning said. “The diverse plethora of techniques and technology available to paleontology today is changing the way we study and interpret the fossil record.”
In the future, the researchers plan to digitally recreate other dinosaurs, such as Triceratops, Brachiosaurus and Tyrannosaurus rex, in order to better understand their movements. Prior simulations of duck-billed hadrosaurs uncovered novel gaits, so Sellers joked that “running, skipping and jumping may well turn up.”