Bus-Sized Reptile Terrorized Prehistoric Sealife
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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Mosasaurs, prehistoric marine reptiles that could grow to the size of an 84-seat bus, were much speedier and shark-like than previously thought, an exceptionally well-preserved fossil specimen reveals.
The specimen is in such great shape that it includes soft tissue, according to a paper in the latest Nature Communications. That might open up the possibility of retrieving DNA and cloning the dinosaur-era animal.
For now, scientists are focusing on how surprisingly similar mosasaurs were to sharks both then and now.
“Since both groups occupied similar ecological niches, being top-level carnivores, and lived in similar environments -- i.e., the open sea -- they gradually came to look like each other, so-called convergent evolution,” lead author Johan Lindgren of Lund University’s Department of Geology told Discovery News.
Sharks have existed for hundreds of millions of years, Lindgren said, while mosasaurs lived about 98 to 66 million years ago.
Lindgren and colleagues Hani Kaddumi and Michael Polcyn conducted a detailed analysis of the mosasaur individual, found in what is now central Jordan. The remains include the animal’s crescent-shaped tail and flippers.
These features, plus the mosasaur’s sleek overall body plan, reveal that the toothy predator was built for speed. Until this discovery, researchers thought the animals were not nearly as fast.
“Given that mosasaurs are lizards, they have traditionally been assumed to be lizard-like animals with long, serpentine bodies and paddle-shaped tails, which were capable only of short bursts of speed during brief ambush pursuits,” Lindgren said.
“However, our results clearly demonstrate that mosasaurs underwent the same kind of evolution as did the earlier ichthyosaurs and later whales -- that is, they gradually attained a streamlined body powered by a semiluminate tail fluke. This, in turn, suggests that at least the derived forms were pursuit predators and capable of high-speed swimming over long distances.”
Textbook illustrations of mosasaurs will likely change as a result of this latest research, since earlier drawings made them look more like eels or underwater snakes.
Students might also pay more attention to them in future, since researchers now have such a good fossil record for mosasaur evolution, with nearly every step documented. It’s a bit like looking at a hefty 1920s touring car and then seeing it gradually evolve into a streamlined speed machine.
Being at the top of the food chain, large mosasaurs “were capable of handling virtually anything that came in their way.”
Whales emerged later, so they weren’t a threat. Evidence suggests mosasaurs did battle with sharks, however.
Frank O’Keefe, a Marshall University biologist, has also studied prehistoric marine life.
O’Keefe told Discovery News that the mosasaur ecosystem, aside from sharks, included plesiosaurs (another large now-extinct marine reptile), fish, squid, ammonites and other invertebrates. Mosasaurs might have also encountered toothed birds and pterodactyls, which often hung out near water, hoping for vulnerable prey.
O’Keefe said both plesiosaurs and mosasaurs went extinct about 66 million years ago, when dinosaurs also died out.
It is possible that mosasaurs dined on dinosaurs, but the meal likely would not have been tasty, or fresh.
“Dinosaurs lived on land," Lindgren said, "so the only chance of a mosasaur ever getting a bite out of one of those reptiles would have been a bloated and floating carcass that somehow ended up at sea.”