Dinosaurs 101: Theropods and t-rex

Continuing the temporary non-rocketry theme from my last post –

I signed up for two classes beginning in early January: chemistry, which is an accelerated course that crams three months’ worth of material into four dense weeks, and a geology course all about dinosaurs, which takes place at a more reasonable pace. They’re both virtual classes, given the ongoing pandemic. Both have been really fascinating, and everyone loves dinosaurs, so I figured I’d post something about tyrannosaurus rex or a colossal, lumbering brontosaurus (or apatosaurus – more on that later).

Just as background, dinosaurs are generally divided into two major groups: saurischia and ornithischia. Within the saurischia group, it’s broken down even further into theropods and sauropods.

Theropods are a fascinating and really diverse group of dinosaurs, and at the risk of overgeneralizing a bit, theropods are meat-eating predators with very large and very sharp teeth. They had big heads and jaws, and they evolved to run at fast speeds on two legs, something that is obviously quite unusual among any animals, either back then or today. Their arms and hands were notoriously tiny (think t-rex arms), just because they weren’t that useful. Chasing down prey and catching it in your jaws requires powerful leg and jaw muscles, but not hands or arms, necessarily.

Speaking of tyrannosaurs, there have been some interesting recent discoveries about a baby t-rex.

baby t-rex, appears fluffy like baby chick
fluffy


The background on the recent discoveries is that a tiny jaw fossil was found in Montana in 1983, and decades later, another tiny foot claw fossil was discovered in 2018 in Alberta, Canada. Both were roughly 71-75 million years old. Researchers didn’t know what they were looking at right away, but eventually realized that both fossils belonged to a baby t-rex. The jaw was extremely small, but it closely resembles other known t-rex jaws. 

What these fossils meant – for the rest of us non-paleontologists – is that a baby t-rex was extremely small compared to an adult t-rex. Babies, when they hatched, were about 3 feet long, compared to the adult that was up to 40 feet in length! 

What makes these discoveries so unusual is that there aren’t very many fossilized baby or young dinosaur skeletons in general, partly because the bones are so tiny and fragile. And while things like feathers don’t fossilize (as skeletal bones do), there’s indirect evidence that the baby t-rex would have hatched with feathers, looking kind of like a fluffy baby chicken – but much bigger and with a long tail, and presumably more menacing. 

The babies also had a different set of teeth, and it seems that they went through several sets as their diets changed as they grew older and larger. Dinosaurs are nothing if not chock full of interesting facts, and so I will leave you with one final impressive fact: once the babies grew into adults with their final set of teeth (and massive heads, jaws, and corresponding muscles), they could bite through anything, including bone, causing their prey to explode! This is very different from how a modern lion or tiger bites and kills its prey, which is more of a fatal bite that causes the prey to bleed out. Impressive for a creature that starts off life so small and looking like a fluffy chick.

Further reading:

American Museum of Natural History: What Did a Baby T. rex Look Like?

https://www.amnh.org/explore/videos/exhibits/growing-up-tyrannosaurus-rex


Baby tyrannosaurs dinosaurs were the ‘size of a Border Collie’

https://www.bbc.com/news/uk-scotland-edinburgh-east-fife-55796799


First tyrannosaur embryo fossils revealed

https://www.nationalgeographic.com/science/2020/10/first-tyrannosaur-embryo-fossils-revealed/