NCE WE'VE FOUND AS much hard data as we can from our T. rex skeleton and all the others, and from T. rex's environment, we're back to speculating about T. rex in the flesh, this time with some more reasonable inferences. We're left with an awful lot of pure guesswork, however, since we still don't have a T. rex nest, eggs, or much of a young T. rex.
It's a reasonable guess to say female T. rexes laid eggs, since we have eggs from many other dinosaurs, including carnivores like the man-sized Troodon. The eggs probably weren't huge, since even the eggs of huge sauropod dinosaurs like the fifty-foot-long titanosaurs aren't any bigger than cannonbails. And T. rex probably laid eggs in clusters, whether in two straight lines like the sauropods, spirals like the hypsilophodontids, or concentric circles like Protoceratops.
Mom and Dad T. rex might have been good parents. The Maiasaura duckbills I found in western Montana apparently kept fermenting vegetation on their nests to warm the eggs. And once their young hatched, the parents brought food to their nestlings and chewed it up before feeding them. Their young were born helpless. We know that from the soft and pitted ends of their bones. And from the trampled eggshell we can tell the young were nest-bound for at least one month (judging by comparative growth rates of fast-growing large modern animals) after they were born. So Maiasaura had to be a good parent for its young to survive.
On the other hand, T. rex parents could have been uncaring. In the same environment where I found
this is a view of maiasaura dinosaurs nesting, based on my discoveries in montana.
Maiasaura eggs, I also found the bones of the young of a far smaller plant-eater, Orodromeus tnakeli. These litde "mountain runners" had smooth, finished bone surfaces even before birth. That means they were probably born up-and-running. Their parents didn't have to give them much care. Maybe baby T. rexes were pretty self-sufficient.
But if you asked me to guess, I'd say baby T. rexes hung around the nest for a while after they hatched. Maybe the kids even picked up some feeding behaviors tagging along with their parents.
We don't know how long T. rex could have lived, nor how big it could have grown, since it continued growing all its life. We can't even say for sure the eleven reasonably well-preserved T. rexes we have, all within 10 percent of each other in size, were adults, though chances are they were mature animals. For one, it's difficult to define just what an adult animal is—is it a certain size, or sexually mature? How do we know with a fossil animal?
Perhaps T. rex lived more than a hundred years. The this is a view of maiasaura dinosaurs nesting, based on my discoveries in montana.
biggest animals tend to be the longest lived today. But few animals make it past a century. From better-known members of T. rex's family we can guess that as a T. rex grew, it became sturdier. Its skull became taller and its snout relatively shorter. The eye socket changed from round or oval to keyhole shaped. A big bar grew partway across the middle of the eye socket under the eye, and the horns over the eyebrows and bones behind the eye became tighdy sutured, just as ours do when we are children. But in T. rex this didn't seem to happen until it was older.
Do these changes mean T. rex became less "cute" as it grew up? That's not as dumb a question as it sounds. One of the great animal behavior scientists, Konrad Lorenz, observed that many animals, including ourselves, exhibit parental behavior in response to certain widely shared anatomical and behavioral features of our young. Human babies and many other young animals have round heads, high foreheads, big eyes, small chins, and uncoordinated movements. These are qualities most of us find "cute."
baby maiasaurs were helpless and couldn't leave the nest. I discovered this when i examined nestling bones and saw they were unfinished.
Baby dinosaurs, at least those of Maiasaura, had the same cute features, which may have helped them elicit parental care. Baby tyrannosaurs' round eyes were cute, but not their long snouts. Still, young tyrannosaurs might have been different enough from grown-ups that maybe their parents found them cute and worth caring for.
Whether adult T. rexes were compatible with one another is another matter. Pete Larson of the Black Hills Institute asserts that "Sue" has broken and healed-over bones from combat with another T. rex. Big animals can be pretty nasty to their own kind. Us, for instance. Or crocodiles, which fight each other viciously, even biting a rival's snout clean off, with fatal results. And Bob Bakker suggests T. rexes used their skull bumps to butt each other. Of course, Sue could have gotten its wounds after death, and its other injuries from disease, or just from being brittle and clumsy. Or from sex. Perhaps T. rexes fought over access to mates.
How did T. rex reproduce? That's not a very scientific baby maiasaurs were helpless and couldn't leave the nest. I discovered this when i examined nestling bones and saw they were unfinished.
question, but only because we don't know how to answer it. But one scientist, Beverly Halstead of Britain, did spend a lot of time trying to figure out dinosaur sex. Dr. Halstead did some serious research in vertebrate paleontology, but I'm not sure I'd put his theories on dinosaur mating among his most distinguished work. Halstead died in 1991 in a car accident, but he will not be forgotten by those who saw him simulate dinosaur mating on stage with his companion, Helen Haste (they kept their clothes on, to the audience's relief, I think).
Halstead believed that dinosaurs had the same reproductive anatomy as reptiles and birds have today. These animals' sex organs are hidden inside vents, called cloacas, beneath their tails. The dinosaurs mated, Halstead thought, by positioning their tails so their cloacas lined up. The male cloaca, scarcely a foot long, would engorge with blood and fill the female's cavity and pass sperm into it.
Halstead thought a male T. rexwould have mounted a female from the rear, with his front limbs on her shoulders and one hind leg across her back while twisting his tail beneath hers to line up their cloacas. All the while, according to Halstead, the male dinosaur would keep one foot on the ground. Otherwise he might have crushed the female. "Their mating had to be done with great delicacy and great decorum," Halstead told Omni magazine for an odd article called" Tyranno-saurus Sex." Certainly the dinosaurs with plates and spines on their backs, like Stegosaurus, would have had to have been very careful.
There is, however, no evidence to support the idea of such delicate sexual acrobatics by any dinosaur. But there is some evidence to suggest we may be able to discriminate one T. rex sex from the other.
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