Sauropods were the biggest dinosaurs – and the greatest land animals – never to step on the planet. Their long-necked group included apatosaurus, brontosaurus, camarasaurus, and even more massive titansosaurs, whose leg bones were longer than a tall person
. But their first steps on Earth were teensy. These great beasts came from small packets, which came out of eggs no bigger than grapefruit or soccer balls. They must have had "a ridiculous growth rate," said D. Cary Woodruff, director of paleontology at the Museum of the Great Plains Dinosaurs of Montana.
Woodruff knows how small these animals were born – along with a team of dinosaur experts, describes Woodruff the smallest diplodocus skull ever found in a new study in the journal Scientific Reports.
Sauropod skulls are rare. The skull, from a diplodocus that scientists have nicknamed Andrew, could be adapted to Woodruff's shell-shaped palms. The immature, small and fragile skulls are even rarer. Paleontologists can collect a lot of information from the skulls: the orientation of the ear canals tells researchers how the animal held its head. The fossilized teeth are indicators of what he ate. This skull was about nine inches long. Andrew had huge eyes, a short snout and unusual teeth.
The skulls are particularly valuable for experts studying the growth of sauropods, because other developmental characteristics are relatively rare, Woodruff said. Dinos like triceratops had frills and horns, which scientists can track down through various epochs of animal life. Not so for a sauropod.
The skull just described filled critical gaps in understanding the size and development of sauropods, Woodruff said. The diplodocus for adults had teeth like wooden pegs. They were herbivores, like cattle, with their soft ferns and long snouts. Other sauropods, like the camarasaurus, had spoon-shaped teeth, better for munching on tougher vegetation.
Andrew, surprisingly, had both types of teeth: pegs in the front, spoons in the back. This, according to Woodruff, would have allowed Andrew to hatch all sorts of food, to cut soft ferns but also to munch more fibrous things.
"It would be difficult to imagine that sauropods would eat the same things throughout their lives as dimensional disparity with their age," said Macalester College paleontologist Kristina Curry Rogers, who was not involved in this research, but has studied sauropods of children from fossils found in Madagascar. "There is certainly no way that juvenile sauropods can feed at the same navigational heights as adults."
The skull and the two vertebrae were collected from a quarry in Montana. Woodruff estimated that the animal should have been 2 to 4 years old, about 20 feet in length and about the height of the thorax. It is very small for an animal that, if it survived, would grow to about 90 feet in length and 13 tons in the space of two decades.
Andrew's nickname came from the industrialist Andrew Carnegie, who financed excavations to excavate dinosaur fossils and has a sauropod namesake – Diplodocus carnegii . The authors of the study are not exactly sure what the species is, but they know it is a diplodocide, which means a member of the same family of diplodocus. (Paleontologists have no idea if the animal was male or female.)
Andrew was found in a confusion of other young sauropods, Woodruff said. He said that this probably represented a "segregated herd of age", young animals within a similar age group who found food and shelter in a dense forest. In this perspective, diplodocus were the opposite of helicopter parents. He suspects that the animals were like sea turtles: the duty of a mother ends with the laying of the eggs, leaving the little ones to look after themselves.
The teeth of the Swiss army, said Woodruff, are a sign that young sauropods do not rely on adults to feed them ferns "If so, why do they have different types of teeth?" He said .
Curry Rogers was not sure if the teeth were so revealing. "I do not see such an obvious topic when it comes to the link between different feeding strategies and the lack of parental care," he said. He said the hypothesis needs more data, including anatomical features beyond a skull and some vertebrae.
There is still a lot to study. "I want to find Andrew's younger sauropods," Woodruff said. "There's still a lot more to learn."
Younger younger sauropods could also shape the idea of how they lived. "As adults, sauropods are so gigantic that they seem almost impossible biological – it's really hard to understand how something so strange can work so well in an evolutionary sense," said Curry Rogers. "Sometimes, studying sauropods is like studying aliens."
The audience will be able to study Andrew's bones closely from November 11, Woodruff said when the skull is unveiled at the Cincinnati Museum.
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