Look, a big meat-eater! Is that a Tyrannosaurus rex?
A simple guide to telling the difference in large carnivorous theropod dinosaurs.
by: crownedrose.

I’ve been in situations where I’ve witnessed, or have had someone ask me the question to whether that big theropod over there is a T. rex. Seeing as the Tyrannosaurus is one of the most well known dinosaurs on Earth, many people mistake other large meat-eating dinosaurs as the T. rex as well. The photos above showcase nine different large sized theropod dinosaurs, including Tyrannosaurus rex in the middle photo.

What is a theropod, you ask? To put it simply, theropoda is the suborder for the bipedal saurischian dinosaurs, which consists of the world’s favourite, T. rex, and is also the suborder which helps us link to the evolution of birds. Many people can’t tell straight away if the big skeleton they see on display is a T. rex or not until they look at the identification panel. If it looks to have a similar skull or a large skeletal body like T. rex, some people will pin it as such. This post is meant to help you see the differences in these guys for the next time you’re at the museum. Each photo above is the skull profile of a large theropod, and the descriptions will also include quick identification traits for the rest of the skeleton. How many can you identify?

1. Albertosaurus sarcophagus (photo source): Albertosaurus is commonly mistaken for a Tyrannosaurus because they are both in the same family: Tyrannosauridae. Albertosaurus was smaller than Tyrannosaurus, but shares the similar features of a large skull, heterodont teeth, and two digits on short forelimbs. On the top of the skull (above and slightly in front the eyes) are bony crests. As well, Albertosaurus is more slender than Tyrannosaurus, especially when you look at the lower legs. (full skeleton)

2. Allosaurus fragilis (photo source): Allosaurus may be one of the more common theropods mistaken for a T. rex that I’ve witnessed. Though smaller than the T. rex, the shape of an Allosaurus skull is flatter at the top, and also is decorated with horns above the eyes, along with a pair of ridges that went along the top of the nasal bones, meeting to the horns. Allosaurus as well had three digits on its forelimbs instead of two like Tyrannosaurus rex. (full skeleton)

3. Carcharodontosaurus saharicus (photo source): In Jurassic Park III, we witness a fight between T. rex and Spinosaurus. Though, do you want to know who who the true rival is? You guessed it: Carcharodontosaurus! (Both reining from what is now Northern Africa). Carcharodontosaurus is larger than T. rex, with three digits on it’s forelimbs (of decent length), a longer skull, and long serrated teeth. (full skeleton)

4. Carnotaurus sastrei (photo source): I’ve done a lot of research work on Carnotaurus the past few months, and when it comes to pathetic forelimbs, Carnotaurus definitely wins out compared to T. rex! Meaning “meat-eating bull”, Carnotaurus has two thick horns decorating its skull right above the eyes; definitely an appropriate name. The skull itself is bulky (and short in length) looking, until you look at the lower jaw that tends to be slender. It’s a very distinctive skull, but those two bull-like horns on the top of the skull and very short arms (don’t let Terra Nova’s bad rendition of the “Carno” fool you!) will help you quickly identify it. (full skeleton)

5. Tyrannosaurus rex (photo source): In centre is the skull of my favourite T. rex: Sue! Most people can recognise them by their iconic skeletons and thick/massive teeth and jaws, but you’d be surprised as well. With such a massive head and body, these dinosaurs were machines when it came to ripping apart carcasses. Then there’s those small forelimbs with two finger digits which are not as pathetic as the public thinks; they’re actually quite powerful! In the Tyrannosauridae family, T. rex is the largest. Most people know a Tyrannosaurus when they see one, but the skull is featured in the centre to show the differences in all nine animals listed here. They have long hind legs (especially compared to the skeleton proportion as a whole), and their skull is quite wide near the back, whereas the tip of the front part of the skull is more narrow; overall, the skull of T. rex is very robust. This structure helped T. rex to have great binocular vision (unlike how T. rex is depicted in Jurassic Park to have movement-based vision was just a fabrication). Like other theropods (and sharks), T. rex constantly replaced their teeth, which were also heterodont (meaning their teeth took on different shapes depending where they lay inside the jaws). (full skeleton)

6. Spinosaurus aegyptiacus (photo source): Believe it or not, I’ve seen people mistake Spinosaurus as a T. rex multiple times. I’ve been surrounded by dinosaurs my entire life, so I’m not sure how you can confuse two very different (and distinct) specimens. Spinosaurus has a large sail on its back, which are extensions of the vertebrae, and a long crocidillian-like snout. If you’ve ever watched Jurassic Park III, you’ll remember this guy being the main antagonist. (full skeleton)

7. Daspletosaurus torosus (photo source): Daspletosaurus is another good example of being mistaken for a T. rex. Daspletosaurus - just like Albertosaurus - is actually in the same family as Tyrannosaurus rex: Tyrannosauridae. Just like T. rex, Daspletosaurus is equipped with two finger digits ending with claws, short forelimbs (though not as short compared to T. rex), but was smaller compared to its North American cousin. Daspletosaurus also walked what is today western North America, but lived about 10 million years before Tyrannosaurus rex came onto the scene. The skull itself had crests near the eyes, and the ‘holes’ in the skull (aka orbit/eye socket, for example) were a bit different in shape compared to T. rex. Sometimes for closely related dinosaurs such as Daspletosaurus and T. rex, you must look closer and closer at detail, and one good way is by look at the shapes of those “holes”. Random note: this guy is the blurry dinosaur in my layout background. (full skeleton)

8. Giganotosaurus carolinii (photo source): This dinosaur is usually confused with Carcharodontosaurus as they are closely related, both belonging to the family Carcharodontosauridae. Giganotosaurus has a long skull (some have described it to me as almost “stretched”), is estimated to be the largest skull of any known theropod, and its teeth are different than Tyrannosaurus: shorter and more narrow. Many though do confuse this to be a T. rex, which is why it’s on the list! (full skeleton)

9. Ceratosaurus nasicornis (photo source): Ceratosaurus is one of my favourite theropods. Decorated with horns/crests above the eyes and a blade-like nasal horn (which is where its name comes from: “horned lizard), these dinosaurs lived in the Late Jurassic. The horns help easily identify these dinosaurs, along with its distinctively long and serrated teeth. Ceratosaurus was much smaller than the T. rex, had shorter forelimbs for its body (possessing three digits on each hand), and one of the more flexible theropods on this list. (full skeleton)

As I was entering the dinosaur names in google and flickr to get photos, I can’t tell you how many of these nine specimens came up in the search when I was not looking for them at that time! There are more theropods out there who get mistaken as a Tyrannosaurus, but the eight above are the ones I see this happen to the most. In the end, you can’t just look at the skull or just the rest of the body to clearly identify a dinosaur; you must take everything into account. Luckily, museums have those nice identification plates for the public to read, but hey, next time you may not need to read them!

If you’d like to know more detailed information about the theropods mentioned here, I am currently writing a series of posts (for Tumblr) called “Theropod Of The Day”. Daily posts (depending on my schedule) will give you quick and easy information on the dinosaurs listed above, and others that are not mentioned here! I’m hoping to get the series started next week, so keep a lookout for the posts, and track the tag “theropod of the day” on Tumblr!