What are some common features, of newborn dinosaurs? Think about a human baby, and compare how they look to an adult. How might an infant dinosaur, be different from an adult dinosaur? A) They have less prominent facial extrusions. B) Larger eyes. C) Smaller size. D) Shorter relative limb length. Or E) A larger head. Select all the answers you think might be correct. in fact all these things, are features that are different between infants and adults. Babies most often have a relatively different set of physical characteristics. When compared to their adult forms. One of the most obvious differences is that, babies are much smaller than adults. But, after compensating for their size, things like the size of the eyes and length of the limbs, relative to the body, are things that change through time. As well, most babies have less permanent features. Such as smaller noses, and less prominent brows. As we'll see, this holds true for many dinosaurs species we know about. So, all of the answers are correct. When babies of any kind of vertebrate are born, they often have many distinctive and different features compared to their parents. Think about those baby puppies, with their huge eyes. Newborn eyes in all vertebrate species, are relatively large compared to adult facial proportions. As well, most vertebrates have relatively short limbs when they are born, and as they grow into adulthood, their limbs grow much faster, than the rest of their bodies. These changes in characteristics of an organism, as they grow, are called Ontogenetic Changes. Ontogenetic Changes, can lead to incredibly large differences between a newborn and an adult. Take a look at the skull of a relatively young triceratops. You'll notice that its frill and horns are rather small, and not at all enormous, heavy things like we see in the adults. The horns and frill have grown much faster, than the rest of the body as they age. Most ceratopsians probably started off life with small horns and frills. And then took on many of their exaggerated and distinctive features, as they grew into adulthood. >> In order to understand how significant Ontogenetic Changes are within a dinosaur species, we need to have fairly complete skeletal remains of both adults and the infants of the same species. As you can imagine, acquiring both. Skeletons of young and old specimens of the same species, can be quite challenging. Sometimes, though, we get lucky. Hiking through the badlands of Alberta, I made many, exciting, wonderful discoveries over the years. But this one is one of my favorites. In the summer of 2010, I was going up. Cliff side, and I saw the edge of the frill, coming out of the cliff. And when I looked at it I thought, you know, that kind of looks like a ceratopsian skull, but I realized that my chances of finding a skull that small were not very good. And I rationalized to myself, this was probably a turtle rather than a skull at all. But I kept at it, and by the end of the day had uncovered most of the skull, and there was no question this was one of the most exciting discoveries we've made in recent years. Baby dinosaurs are a rare. All the time, but baby ceretopsus dinosaurs, are incredibly rare, we have never found one this small. And the specimen just kept getting better, because we worked on it, realized that the protiba column was there, we started to find ribs, followed the protiba column right back to the end of the tail. And we found the hind legs. One is right here, the left one. The right leg is tucked underneath. What was a bit of a surprise though, is we didn't find the front limbs. And eventually we realized though, it's because the sediment here, had been replaced by more recent sediments. Apparently what had happened, was many years ago, a sink hole cut through the badlands and this particular level. And a sink hole is a like a cave that transmits water, and the water of course, erodes all the sediments around and the sink hole is like a well that goes deep into the cliff, well down below. The sink hole had cut away, or eroded, the front limbs. In fact, it had cut right to the edge of the skull, and if it had continued cutting, before it got filled in, that sink hole would have eroded the skull away too. When I found the skull, this was the edge of the cliff. And so, in a few more years, this skull would've been destroyed by erosion from this side. So, there were two chances this skull was going to be destroyed, but we were very lucky in that this skull was sitting exactly between the sink hole, and the edge of the hill. The skeleton stretched between the sink hole and the edge of the hill and went back into the hill side, but we wouldn't have found that either if, in fact, that skull had not been eroding out slightly. So we were very, very lucky to get what we, we did. We took the specimen back to the laboratory at the university, and as we turned it over we realized that there were many other things to be discovered in this specimen. So, for example, this region here has not been prepared of completely because at this level. We have very subtle indications that this is the skin, of the dinosaur that's been preserved as impressions. When we use low light on this, we can see the scales high lit much better and we can there are large scales surrounded by rosettes of small scales. And it's a fairly common way to find skin. Plant eating dinosaurs in Dinosaur Park, but in particular with Chasmosaurus. So this baby, has the same kind of skin as the adult's. It's just that the scales are different sized. This specimen tells us a lot about how ceratopsian dinosaurs developed. For instance, it tells us that by comparison to the adults, the babies were really cute. The proportions of the face strongly influence, how cute we perceive it to be. As Betsy has explained, babies animals tend to have eyes proportionately larger, in comparison to the entire of the skull than the adults do. And this baby ceratopsian was no exception. It's large orbits indicate it had large eyes. And big eyes, make the face look cute. You can also see that, there's not much of a horn developed above the eyes. And it's basically just a little nub in the bone, to show that the horn will be there in the adult. That raises the question. If it doesn't have a horn, how did this cute, sheep-sized baby manage to avoid being eaten by the not-so-cute predators, like tyrannosaurs and dromeosaurs? Although this particular baby was found by itself. More fragmentary skeletons of other young ceratopsians, have been found mixed in amongst the bones of adult ceratopsian dinosaurs. And this indicates that ceratopsians lived in groups. So it seems that horned dinosaurs, did not grow their weapons until they were big enough to use them. And while they were small, the youngsters were protected by their full grown and offensively adapted parents. The changes in the relative size of the orbits, and the lengths of the horns of ceratopsians as they age, are examples of what we call non-isometric autogenetic changes. Similarly, in dinosaurs like tyrannosaurs, the tibia was much longer than the femur in the juveniles. So when we look at a tyrannosaur hind leg, this bone the tibia would be longer than this bone the femur. However, in ceratopsians the proportions change isometrically, meaning they grew larger in absolute terms but maintained the same proportions. Unlike tyrannosaurs, the length of the ceratopsian hind leg don't change as much. That is, the tibia, which is about the same length as the femur in this baby, is also about the same length, as the femur in the adults. And this is something that's very different than what we see, in the carnivorous dinosaurs. >> How did dinosaurs care for their young, if at all? Where they caring, doting parents showing a high degree of parental care, or did they drop their eggs and leave the infants to their fate? Select the answer, or answers you think are correct. Is it A) A high degree of parental care. And or B) a low degree of parental care. The answer is probably both. Some groups of dinosaurs, probably devoted a lot of time to care for their young, like theropods and hadrosaurs. However, some groups may have laid their eggs, and left the young to their own devices. Like sauropods. So both A and B are correct, but it depends on which dinosaur group we're talking about. Dinosaur parental care, is one aspect of paleontology that is very poorly understood. However, we can take some cues from birds and crocodiles. Birds, as most people know, often show a high degree of parental care. However, what many people may not realize is the crocodile mothers, also show a great deal of care for their young. Baby crocodiles will often stay with their mothers for several months, sometimes riding in the mom's jaws. Because and both crocodiles, and birds provide so much care for their young, we can infer that some dinosaurs likely exhibited the same behavior. As well as looking at living animals, there are incredible examples in the fossil record that demonstrate dinosaur parental care. For example, there are several specimens of oviraptor found sitting on top of the egg nest. We can infer that these specimens were incubating their eggs, just as modern birds do. However, there are some fossil finds that seem to imply a lay 'em and leave 'em strategy. In Argentina, dozens of nests from a species of giant sauropod have been found together. These nests are so close together, that it would have been impossible for a mothering dinosaur to stay near her nest, without trampling the surrounding nests. This seems to suggest that sauropod dinosaurs, may have developed the same nesting strategy seen in modern day sea turtles. Turtles lay their eggs in a concentrated areas on specific beaches, and all of the eggs hatch at once. When these babies emerge from the sand, there are so many of them, that the predators cannot eat them all. Inevitably some baby turtles survive the rush of predators, and the species live on. Sauropods were very large. And because they were so big, they are able to lay many eggs at one time. Like turtles, when baby sauropods hatched, inevitable some would survive even without their mothers watching over them. Though this is not great parenting, it is an excellent evolutionary strategy. Now lets take a look, at how these tiny babies could grow up to be such gigantic parents. How many years do you think it took, for a dinosaur to reach adulthood? Do you think a baby Tyrannosaurus Rex grew up to be a seven ton adult in 20 years? 50 years? or 100 years? Large theropods like Tyrannosaurus Rex had very high growth rates and may have reached maturity by the age of 20. So A is the correct answer. Dinosaurs are unquestionably the largest land animals ever. However, we just talked about how small dinosaur eggs are, relative to their parents. So, how do you go from a tiny baby that weighs about as much as a gallon of milk, to something that weighs as much as a herd of cows? As always, the place to start looking is the bones. It's in an histology lab where we take dinosaur bones, and cut them up into pieces. Though we may be destroying some bones, we are actually releasing knowledge, that is otherwise trapped inside them. If you remember from the previous lesson, we talked about the micro-structure of bones and how they are made of small cells called osteons. As the dinosaur grows, it adds more osteons to the outside of the bone. During harder parts of the year, possibly during cold or drought conditions, the dinosaur may not have enough food, and so its growth would slow down. This creates rings inside the bones, annalogus to those you'd find in a tree. These rings are called Lines of Arrested Growth, or LAGs for short. Here you can see a sample cross-section of bone. We count the LAGs to determine the age of the dinosaur, this bone came from. By slicing up bones of animals at different growth stages, we can calculate how big an animal was, at a certain age. And from there determine, how quickly the dinosaur was growing. Usually we use long bones, like the arm and leg bones, as they are usually the most reliable source of lag. Dinosaurs grew quickly. Large theropods like tyrannosaurs, could have reached adult size in 20 years. Giant sauropods may have taken a bit longer, but were still sexually mature at 30 years of age. This would mean these sauropods were gaining weight, at a rate of two kilograms every day. So happened when these animals grew up? What happened when they reached sexual maturity? And what do we know, about the differences between males and females? The answers are coming up.
