By CRISTINA JANNEY
Attendees at the monthly FHSU Science Cafe learned Monday night how an egg that could fit in a easter basket could grow into a gigantic dinosaur.
Cat Sartin, FHSU instructor of biological sciences, presented “The Bare Bones About Dinosaur Growth.”
Sartin’s research has focused on the growth patterns found in fossilized dinosaur bones. Sartin studied hadrosaurs, which were a family of dinosaurs that are commonly known as duck-billed dinosaurs. They were herbivores, which meant they ate plants, and among the most common dinosaurs living during the late Cretaceous Period.
Sartin choose the hadrosaurs in part because they lived in herds with individuals of varying ages.
The eggs of a hadrosaurs were about the size of a potato, but the adults grew to up to 20 feet long.
Even the titanosaurs that grew to be 120 feet long started out from an egg that is only about 18 inches long.
“If dinosaurs were up and running around today, we could go out and measure them. We could look at what they were eating. We could put trackers on them. It would be great, but they’re not around,” she said.
Although researches can look to modern birds and reptiles for clues to how dinosaurs may have lived and grown, these animals don’t grow to near the sizes the dinosaurs did.
“We can’t go out and study them because all we have are the bones, and they are not even really bones. They are fossils, which means the bone material has been largely replaced by rock, so it is just a snapshot in time for each individual animal,” Sartin said. “Fossils don’t grow. They don’t exhibit behavior.”
Sartin analyzed thin sections of hadrosaurs bones under a microscope to evaluate their texture. Young individuals have an open or lacy texture to their bones to allow for more blood vessels to feed the rapid growth of the bones. As an individual ages to equivalent of elementary school child, its bone structure has more order. The collagen fibers in the bone lay down in layers almost like plywood.
Skeletally mature individuals bones are the most organized. These individuals have osteons, which are bone canals. These structures are good at stopping stress fractures in older creatures.
“When you are young, you do a lot of stupid things. We all do. It’s OK. Across the animal kingdom, animals do a lot of stupid things and take a lot of risks. They need really strong bones for all the stupid things they do,” Sartin said.
“As you get older, you get into a routine. You are doing the same things over and over again whether you are a human or a dinosaur. That means you are more likely to have stress fractures from that repetitive motion. That is what this is helping to stop.”
The texture, however, will not tell the age of the animal.
Dinosaurs lay down lines in their bones called lines of arrested growth. These lines can be counted like tree rings to determine age. The amount the animal grew each year can also be estimated by the amount of bone between each line.
Researchers used captive populations of animals, such as alligators and king penguins, to determine what triggered the animals to lay down the rings. They suspected the rings were laid down annually.
They turned to a small primate, commonly called a mouse lemur, that they housed in a lab. They changed the mouse lemur’s light cycles to 18-hour days instead of 24-hour days. After 365 of these 18-hour light cycles, the mammal laid down a bone ring.
Specifically of the hadrosaurs, Sartin choose to focus on a group of eolambia fossil that were found in Utah at the site where a river likely flooded.
The curators who held the eolambia fossils were not all that excited to have Sartin slice up their specimens, so she found isolated bone shafts that weren’t likely to be used for display in museums. She ended up with 20 some specimens to study.
By measuring the lines of arrested growth, Sartin determined these dinosaurs grew quickly for 10 to 12 years, and then their growth slowed.
“It makes good sense, because there are things out there that might want to eat you,” Sartin said, “and it might be helpful to grow a little quicker.”
From analyzing the texture of the bones, she also determined the group of individuals found in the Utah deposit were not skeletally mature. Sartin theorized that some of the teenage dinosaurs might be sexually mature and reproducing.
She also determined the first growth ring in the bones was fairly large, which meant they went from an egg the size of a baked potato to a middle schooler in one year.
Sartin again looked to modern animals to help her with her research. Ostriches go from an egg to a full-grown adult in 18 months.
“It is completely reasonable to think a little eolambia could go from a baked potato to yeah high in a year,” she said.
Eolambia did not have spikes or armor or plates for defenses, so growing quickly and living in herds were their defenses against predators.
Other herding herbivores have also shown similar rapid growth patterns.
Apatosaurus, which we used to know as brontosaurus, grew to adult size in 10 years. They had an average length of about 75 feet and weight of 16 to 22 tons. Most of the plant-eaters’ growth came in three years. Researchers are trying to determine how the animals could consume enough food to support that type of growth.
Theropods (meat-eating dinosaurs) also had quick growth spurts, but they were delaying their spurts to a little later in their youth.
“Theropods hang out as small little guys for the first three to five years of their lives. It is kind of cool and groovy to be little, and then they decide to go gangbusters and get really big, really quickly,” Sartin said.
Researches believe the meat eaters did not have to grow quickly for protection. This allowed them to learn hunting techniques from the adults in their family groups. They also may have been learning social cues from the others in their family groups or packs, Sartin said.
Based on these growth patterns and the family groups in which the meat-eaters’ fossils have been found, researchers believe the meat-eating dinosaurs parented their young, she said.