Biggest Dino Killer: Volcano vs. Asteroid
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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Some 20 years after its conviction in slaying of the dinosaurs, the Chicxulub impact crater is facing a retrial by a growing number of geologists who think the mass extinction event 65 million years ago was caused by something much larger. Not a larger meteorite, but a far bigger disturbance that was happening on the other side of the planet before, during, and after the Chicxulub impact: the massive Deccan Traps volcanic eruption.
The latest debate over the ultimate reason for the mass extinction is occurring this week at the Natural History Museum in London. Researchers from around the world are meeting there for the International Conference of Volcanism, Impacts, and Mass Extinctions -- which includes a lot of new science on the extinction event that wiped out the dinosaurs. This is despite the fact that advocates for the Chicxulub theory published a paper three years ago, with a whopping 41 authors, reviewing the evidence and concluding once and for all that Chicxulub was the dino killer.
“That paper helped the volcanism side because it dismissed volcanism,” said Princeton University paleontologist Gerta Keller, who has long been skeptical of the timing of the Chicxulub impact and has sought answers to the Cretaceous-Tertiary (a.k.a., K-T, or Cretaceous-Paleogene) extinction in India's Deccan Traps, which are arguably the largest volcanic deposit on the planet.
While the timing has long been debatable, more recently, however, radiometric dating of the impact debris suggests the K-T event and the Chicxulub collision happened no more than 33,000 years apart.
Still, Keller's work, and that of others, has unearthed evidence that the Deccan Traps' series of eruptions were not only timed right, but they released an order of magnitude more climate altering greenhouses gases into the atmosphere than the single Chicxulub impact could have. What's more, they have been directly tied to extinctions in the oceans in that part of the world.
The research has revealed that the Deccan Traps had three main periods of eruption spanning some 2.5 million years. Each phase of eruption lasted on the order of 100,000 years or less and had within them powerful pulses that released roughly 10,000 cubic kilometers (2,400 cubic miles) of lava in less than a century and maybe even in just a decade, explained Vincent Courtillot of the University of Paris, who is among those presenting at the meeting.
That's enough lava, just from a single pulse of a larger eruption, to bury the state of Delaware under a mile of rock. And like all eruptions, the Deccan Traps released vast amounts of carbon dioxide and other greenhouse gases that would have rapidly altered Earth's climate.
“An impact alone is not likely to cause a mass extinction," Courtillot told DNews. "But in the K-T case an impact occurred after volcanism had started and added a major blow to the sequence of events.”