T. rex's brain is long gone, but the braincase reveals how large and complicated that brain must have been. The braincase, together with the size and position of the openings for the eyes, ears, and nose, tells us much about how developed the animal's senses were.
When you consider the size of the animal that went with that brain, the brain doesn't seem quite so imposing. Elephants and rhinoceroses have much bigger brains, and these animals weigh less than T. rex did. But T. rex's brain was larger than that of almost all reptiles and other dinosaurs; proportionately, it was nearly as big as that of some birds. To be a bird-brain is no compliment by our standards, but for most members of the animal kingdom the comparison is flattering. Some dinosaurs, especially T. rex's small carnivorous cousins, approach the relative brain size of ostriches. Ostriches are far from the smartest birds, but they are among the smartest animals nonetheless. That suggests a lot about the intelligence of those dinosaurs. T. rex wasn't as smart as the litde carnivores, pound for pound, but it was still bigger brained than the plant eaters of its day.
Relative brain size does seem to correlate to intelligence, though just how smart T. rex was we'll never know. Uncertainty hasn't stopped many paleontologists from speculating on its brain power, its nervous system, and what both mean for how T. rex sensed its world. It's likely that T. rex had superior eyesight for a dinosaur. When you look at the skull, you see right away that its eyes both pointed forward, though not as much as our own. This eye alignment could mean that T. rex had depth perception like ours. That's unusual among dinosaurs. If you look at the skull of a Triceratops, you'll see its eyes poke out to the side like a cow's. The same with duckbilled dinosaurs.
But you can't tell from afossil how far the eye stuck out of the orbit. Most birds' eyes are set to the side, but they also stick out far enough to see forward. And just because your eyes point forward doesn't mean they have to work together to give you depth perception. Oilbirds, which do have forward-pointing eyes and overlapping visual fields, don't have stereo vision. T. rex also had a deep snout that might have limited the overlap in vision in its eyes. Without other clues to vision that would be found only in soft-tissue parts that don't fossilize, we can't say for sure if T. rex could see in three dimensions.
It's even more difficult to say anything about other senses—hearing, taste, smell—until we understand more about the braincase itself. All those holes in T. rex's skull would have been good resonating chambers for transmitting or amplifying sounds. Phil Currie thinks that was their prime function. In birds the holes are associated with the middle ear. Big air chambers behind the eardrum help them hear lower sounds better. T. rex hadrosaurs had large nasal passages, like this kritosaurus notabilis.
could have used good ears to hear bellowing duckbills from far away.
Bob Bakker has spent a lot of time digging around, literally, in the skull of T. rex. He's even taken a coat hanger to probe the pathway of a nerve that runs sideways alongside two other nerves from the braincase to the upper jaw. In humans that nerve gives more sensitivity to touch. In a T. rex at the Royal Tyrrell Museum, Bob found that the nerve channel ran straight out of the skull all by itself. Among backboned animals, only birds have the same pattern for that nerve.
Russian paleontologist Leonid Tatarinov suggested the holes in T. rex's snout were nerve openings in what might have been a very sensitive snout. Bob Bakker thinks T. rex had a neat row of nerves in the front of the snout that suggest it had lips. Since I know of no counterpart for T. rex's nasal bone structure on any living animal, I won't guess about its function.
Bob with his coat hanger and Phil Currie with needle probes both found that the entire cranial architecture of hadrosaurs with crests (lambeosauri nes) may have tootled by blowing air through them. those without crests, h adros au ri n es, like this anatosaurus may also have produced sounds by inflating air sacs in their snouts.
t. rex's neck had an even more exaggerated s-curve than other dinosaurs. perhaps that gave it more room for the attachment of muscles to power ripping flesh.
large carnivorous dinosaurs had a lot in common with small carnivores, and with birds. Bob thinks the oval-shaped holes on each side of the nose of T. rex were nerve centers for great sniffing power. A keen sense of smell would be useful for T. rex., whether it was a predator or a scavenger, but there's no proving those holes ever had anything in them because cartilage is rarely preserved. But Bob says he's seen the imprint of cartilage on the inside of the snout and compares it to that of modern alligators, which are good smellers. Bob's is a plausible speculation, but those sinuses, and Bob's theory, could just as easily be filled with hot air.
Sometimes Bob isn't going against the facts, just ahead of them. And once in a while the facts catch up and prove Bob's speculation was right after all. That was the case with the nose of that pygmy tyrannosaur,
Nanotyrannus. The delicate, slightiy spiraling turbinal bone within the nostril had never been seen before in a predatory dinosaur. We know turbinals from some keen-smelling mammals like deer. The spiral increases the surface area for better smelling.
Holes and chambers in the skull can also be useful for resonating sounds. What kind of noises could T. rex have produced? Dave Weishampel, a paleontologist at Johns Hopkins University I often work with, has shown how the complicated hollow crests of some duckbilled dinosaurs could have trumpeted low-frequency tunes for great distances. Duckbills were herding animals.
Calling to each other would have been a big help in keeping a herd together and safe from dangers like T. rex. It's possible T. rex bellowed too, when it had sex or territory on its mind.
Dinosaurs, including T. rex,, could hear very well, through a special anatomical innovation. But I can't tell you what that is. I'm not being coy. It's just that a graduate student of mine discovered this feature, and until she publishes her research I shouldn't borrow from it.
It's likely that T. rex had not only superior senses to most animals of its time, but superior speed. Carnivores usually do, whether scavengers or predators. It does seem T. rex was built to move considerably faster than the horned dinosaurs that could have been its prey.
t. rex's posture was like a teeter-totter, head and tail balanced on either end of sturdy legs.
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