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By Ray Jacobs, Part-Time Tutor

February 23, 2023

Ahhh, dinosaurs. The coolest animals we never got to meet. You love them, I love them, an incredibly lucrative film franchise was made about why we shouldn’t be so cool with them…

When it comes to dinosaurs and other prehistoric creatures, theropods are probably what most people think of. One of the most diverse and longest-living classifications of dinos, it includes the Allosaurus, Deinonychus, Velociraptor, and the most famous of all: Tyrannosaurus Rex. The subject of our discussion today, however, is a less-known member of this family, one of my favorites… the Spinosaurus.

It was first discovered in 1915 by German paleontologist Ernst Stromer in the deserts of Northern Africa. He named it for the large spines extending from its back, which in most depictions are interpreted as a sail fin. I truly love the trope of scientists naming a new thing in as obvious a manner as they can. It brings me so much joy.

What the name fails to convey, though, is that this Cretacious cretin was even bigger than the T. Rex! It had “a skull 1.75 metres (roughly 6 feet) long, a body length of 14–18 metres (46–59 feet), and an estimated mass of 12,000–20,000 kg (13–22 tons).” Super cool, right?! This peculiar dino gained most of its notoriety after the release of Jurassic Park 3, where it served as the T. Rex’s adversary. However, the truth of the matter is that we really don’t know much about it!

The partial skeleton Stromer discovered was accidentally destroyed when the Munich museum that housed them was bombed by the British in 1944. For about half a century, all we had to go by were Stromer’s 2D renderings of the bones he recovered. To this day only 7 skeletons - all incomplete - have been found.

So what’s the point of contention here? Why has this weird lizard been throwing the paleontological community into a tizzy for so long? Well the short, dramatically oversimplified version is that people really like to be right. The long version is that we haven’t gotten enough of a representative demographic to be able to get a good read on this lad. There have been a lot of competing pieces of evidence about whether it was aquatic or land-dwelling, which could also give us clues about its mating habits, diet, lifestyle, and why the dang thing needed to be so dang big. We don’t even know what its back sail is for!

Let’s take this point by point, shall we?

First, let’s take a closer look at the Spino’s head. At a whopping 6 feet long, its skull has a distinctly crocodilian appearance - a common adaptation for animals that had a fish-heavy diet, alongside its cone-shaped teeth. These features’ presence in other dinos created a subgroup called spinosauridae. Speaking of its diet, partially-digested fish scales were discovered in the abdominal region of one of the discovered fossils, but scientists have also unearthed spinosaurid teeth in the fossilized wing of a pterosaur. Another aquatic adaptation that’s been discovered is the way its tail is structured, similar to that of an axolotl. The thing about this is that this tail structure is that is moves side-to-side as a crocodilian tail would, but it’s unclear whether this would be the most efficient in terms of underwater propulsion.

Theropod dinosaurs all share the characteristic of having shorter, prehensile forelimbs. The Spinosaurus’s back legs, on the other hand, are a huge point of debate. If Spino had an aquatic or semi-aquatic lifestyle, having big ol’ honkin’ drumsticks like in JP3 would make swimming really difficult. It’s unlikely to have walked with the same posture as other theropods like the T. Rex or Velociraptor, but theories have been proposed that while walking amongst its terrestrial counterparts, Spino’s tail could have helped it balance against its short rear legs like a pangolin instead!

Next, we pivot back up to the midsection to talk about this whole sail fin business…

Again, we don’t know what this thing was for. We don’t even know what shape it was; It’s been depicted as either arched or M-shaped, but no sail bones have ever been found intact, so we can’t say for sure. It could have been for sexual display/dominance, thermal regulation, or to help it corral fish in the water so they couldn’t escape. It could’ve also been the base structure of a hump on its back used for fat and water storage like a camel. (I don’t need to put a picture of a camel, right? We all know how weird-looking camels are? Okay, cool. Camels freak me out.)

Unfortunately, looking to other theropods doesn’t give us a ton of information on this. As previously mentioned, they were an extremely diverse group, unified only by the traits of being flesh-eating and having those little grabby hands. Theropods could have bumpy scaled skin, feathers, or large and protrusive bony scales called osteoderms; They were carnivores, omnivores, piscivores, and insectivores. Lots goin’ on with these guys.

Luckily, there’s one thing we still haven’t touched on - bone density. Similarly to how birds have hollow bones to make themselves lighter, different environments mean their respective species have to be built different. (Fun fact: all birds are descended from small, flight-specialized coelurosaurian theropods!) In order to deal with water pressure at lower depths, both for swimming and diving, you need denser bones. And that’s exactly what scientists have found! They compared the bones of Spinosaurus to almost 300 land- and water-dwelling species, living and extinct, including other spinosaurids, and found that spinosaurids’ bone density was directly related to an aquatic lifestyle. Others in the taxon like the Suchomimus had less bone density, indicating they were wading predators rather than deep swimmers.

Most aquatic prehistoric creatures of Spino’s caliber, like the massive archelon and dunkleosteus, aren’t technically dinosaurs. All of this in conjunction with spinosaurids’ crocodilian features means that this group were likely the only dinosaurs making a habit of splashin’ around.

There’s a lot that’s still up in the air about these guys, even with everything we’ve found. Some people, for example, still hold that Spino’s aquatic adaptations are only representative of its feeding habits, not its entire livelihood. The discoveries about their bone density were only made last year, and the scientists that conducted the study are still thrown by that stupid sail fin, which would’ve made it really hard to swim underwater. Unfortunately, until we find more Spinos, a lot more speculation about these theories will be thrown around - likely for years to come.

“But in the meantime,” you ask, “what should we consider the most accurate representation of these boyos?” Worry not, dear reader, I have the answer! The Hong Kong Science Museum unveiled a scientifically accurate model of our dear Spino in July of 2022… Wait, you can’t get to Hong Kong? Okay, no worries! Here’s a picture!

Before that, however, the title of best portrayal that was held for 2 years came from an unlikely source… A cute little video game called Animal Crossing: New Horizons. Blathers really knows his stuff.