Mad about Science: Tyrannosaurs, Redux

By Brenden Bobby
Reader Columnist

Last week, we learned about Sue, the largest and most complete Tyrannosaurus rex skeleton that has ever been found, as well as the dramatic events surrounding its discovery and eventual sale of the fossilized remains to the Field Museum in Chicago. This week, we’re going to jostle the keys of the wayback machine and backtrack some things that I may or may not have written in the past about these giant colossal extinct creatures.

The journey of science is an ever-evolving process — nothing is absolute and everything is subject to change as our insight grows with expanding technology and new observations. This is especially true of dinosaurs, whose archaeological history has largely been cobbled together based on human assumptions about the available data.

‘Don’t move. He can’t see us if we don’t move’

A classic line and moment of extreme tension during Steven Spielberg’s 1993 classic, Jurassic Park. This was likely debunked thanks to Sue. These dinosaurs had eyes that would be considered small in relation to their massive heads, which is particularly noticeable in the elongated and unusually shaped eye sockets in the skull. It’s believed that the small eyes may have minimized the potential for damage during hunts and particularly during attacks on prey. Smaller eyes meant less chance for rogue branches to gouge out eyes, but it also meant more muscles protecting the frail structure of this vital body part when the dinosaur would slam its 600-pound head into something tasty, like a triceratops. 

Another thing we learned from Sue is that T. rex eyes were forward-facing, which supports the data that T. rex was a predatory animal — as though the massive, scimitar-like teeth weren’t proof enough. It’s projected that T. rex could spot moving objects as far as six kilometers away, putting the beast at over four times the effectiveness of even the most eagle-eyed human being. Sorry, Dr. Grant, but that dino can see you standing there.

Hear me roar?

Even if you’ve never watched Spielberg’s masterpiece, you know what a T. rex sounds like — or do you?

The T. rex of Jurassic Park made a deafening roar that was the product of three different animal sounds meshed together: a baby elephant, a tiger and the sound designer’s Jack Russell terrier. This bellowing noise struck fear into the hearts of countless kids, pushing the film’s climactic tension to 11 and giving a voice to a being that had been silent for 65 million years. This sound was great for the film, but it wasn’t at all accurate to what the most famous dinosaur in the world actually sounded like.

Scientists have scanned Sue’s skull, as well as the skulls of other T. rexes that have been excavated, and discovered indentations inside of the structure that seem to have been left by the vocalization organs the dinosaur used to communicate. These constructs were far more reminiscent of those within the skulls of birds than mammals, which makes sense as birds are the evolutionary descendants of dinosaurs. 

Based on the size and shape of these organs, along with the T. rex’s body layout, it’s believed that it never actually roared, but instead created a low and resonant vibration that trailed off in pitch at the end of an exhalation. This pitch is believed to reach levels below that of human hearing, yet if you were lounging amid the palm fronds of the late Cretaceous, you would feel it through your whole body, like the bass from a subwoofer at a music festival.

Roaring is a mechanism reserved for creatures with natural predators, of which the T. rex had none. Though they may have lived solitary lives, they very likely vocalized over great distances while hunting to ward off potential competition without startling their prey.

More to love

Spielberg took fewer liberties with the T. rex than the velociraptors of the film, though we’ve come to learn that the lean form of the T. rex may not have been accurate. More skeletal discoveries since 1993 have given scientists a glimpse into what the king of tyrants may have really looked like, and boy, was it chonky!

It’s now believed that the T. rex, rather than having a slim and muscular form that gripped its ribcage, may have had a large and rounded undercarriage, much like a chicken or a goose. This is reflected in a set of small bones running along the base of the dinosaur called gastralia. These bones did not articulate with the vertebrate during movement, and acted exclusively as support for the creature’s weighty organs. This has been corrected in a number of professional castings of T. rexes, including a model of Sue to which skin and eyes were added.

As well as being heftier than initially thought, Sue’s skeleton revealed that T. rex’s comically small arms were actually much lower on the body than initially believed. The evolutionary purpose of the animal’s arms remains a mystery.

Five-ton turkey?

Feathered dinosaurs have always been a hotly debated topic. The most famous example of a feathered dinosaur is archaeopteryx, a small dinosaur that may have closely resembled the birds we see today. Archaeopteryx may have flown short distances, similar to turkeys. 

The feathered status of T. rex has been debated for some time, despite fairly clear evidence that points to the king of tyrants being primarily scaled. Indentations were left in the substrate where T. rex remains were fossilized, and the indentations are very clearly scales. However, we lack a completely preserved body, so it’s impossible to say whether or not the T. rex had some feathers.

A relative of the T. rex — Yutyrannus huali — has been excavated in China and was believed to be almost entirely feathered. Yutyrannus lived about 125 million years ago, separated from the T. rex by a gulf of time that is about equal to the amount of time humans were separated from T. rexes, so the likelihood of these two creatures closely sharing many physical traits is extremely minimal. However, there is a hypothesis that juvenile T. rexes may have had a form of proto-feather, similar to juvenile chickens. 

Scientists have actually altered the genes of embryonic broiler chickens to convert the scales on their feet into feathers, something breeders have done through selective breeding for hundreds of years with varieties such as brahmas, sultans, faverolles, and everyone’s favorite dinosaur bird: the silkie chicken.

Stay curious, 7B.