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."
NEWS: Nest Full of Baby Dinosaurs Found
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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An extinct marsupial hunter only the size of a fox may have hunted prey larger than itself, researchers say.
This predatory ability makes the ancient creature different from its most recent living relative, the also-extinct thylacine, or "Tasmanian tiger." The last known wild thylacine was shot in 1930, and the last captive member of the species died in a zoo in 1936.
Hunting apparently helped drive the species to extinction. People targeted the dog-like Tasmanian tigers because they believed that the animals killed sheep; in fact, a 2011 study published in the Journal of Zoology found that the creatures' jaws were too weak to take down large prey, and that they would have only killed animals smaller than themselves.
The new study analyzed an exceptionally well-preserved whole skeleton of an extinct relative of these last thylacines, known as Nimbacinus dicksoni; the specimen dates to about 11.6 million to 16 million years old.
"The discovery of an entire skeleton of Nimbacinus was a truly amazing finding, particularly as it is was in such good condition," said study author Stephen Wroe, a zoologist and paleontologist at the University of New England in Australia.
Tiny lions and carnivorous kangaroos
The marsupial carnivore was about the size of a very large housecat or a small fox, weighing about 11 pounds (5 kilograms). "Its face looked like a cross between a cat and an opossum," said study lead author Marie Attard, a zoologist at the University of New England in Australia. [Marsupial Gallery: A Pouchful of Cute]
The modern thylacine (Thylacinus cynocephalus)was larger, comparable in size to a medium-sized or large dog. Modern thylacines weighed in at between 40 and 70 lbs. (20 to 30 kg).
Paleontologists discovered the fossil in the mid-1990s in the Riversleigh World Heritage Area in Australia. In ancient times, warm, humid, lowland rainforests covered this region — then, about 10 million to 15 million years ago, it became progressively cooler and drier, transforming into dry open woodlands and grasslands.
Nimbacinus belonged to an extinct family of marsupial carnivores known as the thylacinids, consisting of at least 12 known species. Nimbacinus may have lived in ancient Riversleigh with several other thylacinid species, along with marsupial lions smaller than a housecat and small carnivorous kangaroos, potentially competing with them all for prey.
"As a medium-sized carnivore, Nimbacinus was likely hunted by larger meat-eaters, including snakes, ground-dwelling crocodiles and larger species of marsupial lions," Wroe told Live Science.
Aside from studies of the recently extinct thylacine, most knowledge about thylacinids comes from skull fragments, limiting what scientists could deduce about the animals. The newly unearthed Nimbacinus skull, however, helped Attard and her colleagues reconstruct how this creature may have lived.
The skull of an ancient thylacinid from the Riversleigh World Heritage Area in Australia.Anna Gillespie, University of New South Wales
Modeling a marsupial
The researchers created a 3D computer model of the Nimbacinus skull to realistically simulate how the skull may have behaved. Digitally reconstructing the whole skull posed a challenge, as the top of its cranium had been slightly crushed and only half of its lower jaw, or mandible, was intact. "It was like opening a jigsaw puzzle box, only to find crucial missing pieces," Attard told Live Science.
The scientists then compared the mechanical performance of the Nimbacinus skull with that of the extinct thylacine. They also compared its performance to that of living marsupial carnivores such as the Tasmanian devil, spotted-tailed quoll and northern quoll. These belong to a different and diverse family of marsupial carnivores, the dasyurids.
In a surprise, the researchers discovered the mechanical performance of the Nimbacinus skull was far more similar to the spotted-tailed quoll, a member of a different family of marsupial carnivores, than to the Nimbacinus' closer relative, the thylacine.
These findings suggest Nimbacinus had a powerful bite for its size, was mostly carnivorous and was probably capable of hunting prey larger than itself.
"Our biomechanical analysis of the skull of Nimbacinusrevealed that it was likely an opportunistic hunter of the rainforest and had a broadly similar way of life to that of larger living dasyurids such as the spotted-tailed quoll," Attard said. "It likely preyed upon small- to medium-sized birds, frogs, lizards and snakes, as well as a wide range of marsupials, including possums, bandicoots, dasyurids, ancient ancestors of koalas, small wallabies, thingodontans [extinct marsupials with boomerang-shaped molars], marsupial moles and wombats. This suggests possible convergent evolution between Nimbacinus and the spotted-tailed quoll, meaning that these two species independently evolved similar adaptations to similar environments." [6 Extinct Animals That Could Come Back]
In contrast, the recently extinct Tasmanian tiger was considerably more specialized in what it could eat than Nimbacinus and large living dasyurids. This likely made the Tasmanian tiger more restricted in the range of prey it could hunt, "and more vulnerable to extinction," Attard said.
Reconstructing past communities and the ecologies of the species that contribute to them "is pivotal if we are to map out and understand change over time," Wroe told Live Science in an email. "Trying to understand how these animals lived and what they ate is also fun!"
Future analysis of the Nimbacinus skeleton could reveal if it was partially tree dwelling like the spotted-tailed quoll, which could help explain the similarities the researchers have noted so far between the two marsupial species.
The scientists detailed their findings online April 9 in the journal PLOS ONE.
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