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Tracking Titanosaurs in Argentina

For the first time a titanosaur track has been matched to an actual fossil hind foot of one of the world's last and largest dinosaurs.

Dinosaurs aren't just tracked down in movies like "Jurassic World." Scientists in Argentina are tracking titanosaurs -- the largest sauropod dinosaurs and among the last to walk the Earth.

Researchers uncovered at least one footprint so clear it can be matched for the first time to skeletal remains of a new species of titanosaur that's found in the same region of Argentina.

The hundreds of new titanosaur tracks found at the Agua del Choique site, in the Mendoza Province, are revealing secrets about how titanosaurs walked. The tracks also provide clues about other dinos, which strolled along muddy paths near the shores of a small, new sea that grew to become the Atlantic Ocean.

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The most telling titanosaur track discovered at the site belonged to an animal estimated to have been a mid-sized titanosaur: some 7 1/2 feet (2.29 meters) high at the hip and 40 to 45 feet (12 to 14 meters) long. The largest-known titanosaurs, Argentinosaurus, are thought to have ranged from 100 to 130 feet (30-40 meters) long and up to 24 feet (7.3 meters) high.

"Most sauropod tracks simply look like post holes," said paleontologist Spencer Lucas, curator at the New Mexico Museum of Natural History and Science in Albuquerque who was not involved in the discovery. "Tracks in which you can see digit imprints are rather rare, so (it's) a remarkable tracksite for sauropod tracks."

"Although other studies have documented impressions of digits or claws in titanosaurs, they are poorly defined" and don't reveal much useful information that can be compared to fossil bones, explained Bernardo Javier González Riga of Argentina's National University of Cuyo.

Riga and his colleagues are publishing their discovery of the matching track and fossil in the August 2015 issue of the Journal of South American Earth Sciences.

The fossil bones the remarkable track matched were found just 150 miles (250 kilometers) away, in the same red rocks.

"Anatomically, the record of (intact) and complete (hind feet) is really scarce in titanosaurs," Riga reported. In fact, of the 65 species of titanosaurs known worldwide, only three have intact fossils of their feet, he writes.

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That's not to say that the bones belonged to the same individual that made the tracks -- they're not only far apart in space, but also in time. But they do belong to a similar titanosaur.

"Not all tracks can be matched to specific skeletons because foot structures do not vary that much in some dinosaur groups," Lucas said. "Relatively few dinosaur tracks have been matched with certainty to a dinosaur (type). Sometimes, the bones from one rock formation are claimed to represent the trackmaker of tracks in the same formation, but even this is not often a certain link."

Among the other things revealed by the trackways are just how fast some of the titanosaurs walked across the muddy ground they encountered in the late Cretaceous.

By looking at fine details in the fossilized mud, Riga and his team calculated the titanosaurs strolled at about 3 miles per hour (4.8 kph).

The tracks of three different types of small, three-toed theropods dinosaurs were also found in the same mud. The two-legged, usually carnivorous, dinosaurs were relatively small, Riga reports.

But unlike the titanosaur tracks, the researchers could not glean enough information from these tracks to narrow down to which group of theropods they belonged.

The largest of the titanosaurs was the Argentinosaurus, which towered more than two stories high. At, right, the almost completely intact fossilized hind foot bones of a titanosaur from the Mendoza Province of Argentina.

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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