Some Giant Dinos Had Cute Little Babies: Photos

A recently discovered baby dinosaur was about the size of a golden retriever upon hatching, yet its parents grew to be the largest animals ever to walk the Earth.

Remains of a baby titanosaur, just weeks old when it died, have been found in Madagascar -- and it was surprisingly small. Titanosaurs were the largest animals ever known to walk the Earth, reaching lengths of 49 feet as adults, yet at least some of their young were about the size of a dog, the newly found baby dino reveals. Paleontologists can also tell that the baby

Rapetosaurus krausei

-- one species of titanosaur -- was precocious and therefore required no parental care at birth. "This tiny titanosaur lived around 67 million years ago, at the very end of the age of dinosaurs in the Latest Cretaceous," lead author Kristina Curry Rogers, a vertebrate paleontologist at Macalester College, told Discovery News. "At the time it died it was just a few weeks old, and was about the size of a golden retriever, though with a long, thin neck and a tiny skull, and a long slender tail."

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An adult Rapetosaurus would have towered over a human, had it lived into the modern era. Its youngsters stood only knee-high, however. All were plant eaters known as sauropods that spent much of their days munching on leaves and additional such edibles. "Based on what we know about other sauropods, Rapetosaurus probably took somewhere between 20 and 30 years to reach its full size," Curry Rogers said. She added that as the babies grew, they probably gained around 2 pounds per day. Although this might seem a lot, the growth rate is actually comparable to that of baby elephants, which gain a similar amount of weight per day before reaching adulthood. The plant-eating dinosaurs "grew at rates similar to those of living mammals, not as fast as those of birds, but quite a bit faster than living reptiles."

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The baby dino was found at The Maevarano Formation, which is an Upper Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. Just about 1.5 million years after the little dinosaur's lifetime, all dinosaurs that did not evolve into birds became extinct following a massive asteroid hit. As for what killed the young titanosaur, the scientists believe that it died of starvation between the ages of 39 and 77 days old in what was then a very drought-stressed environment.

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Fossils for the baby dino allowed the researchers to determine its parental care, or lack thereof, and level of independence upon hatching. "The limb bones are the same shape in very tiny babies, in giant adult Rapetosaurus, and in all the growth stages that we know of for this dinosaur so far," Curry Rogers said. She said such similar bone proportions, known as isometry, are "more common in animals that are capable of locomotion early in life, and are also common in animals that don't rely on significant parental care." "The clues for a lack of parental care get even more interesting when you look deep inside the bones, at how bones are organized at a microscopic level," she said.

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Given that the baby dino was about the size of a pet dog, the researchers and artists had fun imagining what our interactions with the young dinosaurs might have been like, had this species lived into present times. Since this species of dinosaur was not a carnivore, there probably would have been little threat of the baby dino biting us. That said, Curry Rogers added "there is no reason to imagine that it was especially cute." Researchers believe that human babies, young chimps and more look cute to attract adult attention, helping them to gain adult care. Since this dinosaur did not need such help, it might not have evolved features at this young age that were specifically meant to attract favorable attention. Nevertheless, the paleontologists believe that the little dinosaur had relatively big eyes, which we associate with human babies, puppies, kittens and other young animals.

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The paleontologists were able to reconstruct the baby dinosaur's size by analyzing its limb bone proportions and other features. Femora, or thighbones, have been found for baby, juvenile and adult

Rapetosaurus krausei

, providing information for each life stage. It should be noted that not all baby dinosaurs were precocious, requiring no parental care. Curry Rogers said "there is good evidence for parental care in duck-billed dinosaurs (like Maiasaura), in ceratopsians (like Psittacosaurus) and in theropods like Oviraptor." Depending on the species, there is much variety in how living birds take care of their young, mirroring to some extent what probably occurred in dinosaurs. Some modern mammals are born requiring no parental care as well. Wildebeest, for example, can stand up just six minutes after birth, walk within 30 minutes and outrun a hyena within a day after birth.

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Scientists can gain an incredible amount of information just by looking at a long-gone animal's fossils. By sampling thin sections of certain bones, Curry Rogers and her team gained important clues about patterns of blood supply and growth rates. "In addition," she said, "we can observe preserved calcified cartilages at the ends of bones, in the areas where bones lengthen as animals age. They are very thin in baby Rapetosaurus, just as they are than in modern animals that don't rely on significant parental care, and contrast with the thicker, more irregular calcified zones of cartilage in altricial animals that require parental care after hatching." Luis Chiappe, director of the California-based Dinosaur Institute, previously found titanosaur embryos from Patagonia that support the new findings. "All evidence seems to indicate that titanosaurs were highly precocial animals that needed minimal parental attendance," he said. "The conclusions about the death of this particular specimen (starvation) are also quite interesting," he added. "It is also in agreement with the argument that these dinosaurs endured significant rates of mass mortality when young, which helps to explain their colonial nesting behavior, minimal parental investment, and r-type of selection strategy (i.e., quantity of offspring over quality)." Regarding that last point, prior research has determined that each titanosaur nest could contain anywhere from 15 to 40 eggs. When the baby dino that Curry Rogers and her team found perished, it's likely that many other of the dinosaur's siblings managed to survive. Chiappe likened that "quantity of offspring over quality" strategy to that of modern day sea turtles. Sea turtle moms lay an average of 110 eggs in a nest, but only a fraction of the hatchlings reach adulthood.

While the baby dinosaur died young, its memory is now living on thanks to the recent discovery of its remains. Matthew Lamanna, assistant curator of Vertebrate Paleontology at the Carnegie Museum of Natural History told Discovery News that the new paper makes "a compelling case that baby sauropods, or at least baby Rapetosaurus, emerged from their eggs ready to rock and roll, as opposed to being nest-bound for a time as is the case in many modern birds." He hinted that the baby dino remains might not yet have given up all of their secrets. "How titanosaurs got so huge has remained a mystery," Lamanna said. "Ironically, this tiniest of titanosaurs may provide clues, in that it shows that these dinosaurs grew extremely rapidly and were ready to begin seeking food right after they left the nest."

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