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What Is the Spinosaurus Related To? The Surprising Fossil Evidence

We are all aware of the Tyrannosaurus Rex, a gigantic theropod dinosaur from the Cretaceous period. However, millions of years ago, there were far larger, potentially more frightening monsters roaming the earth. One of them was the Spinosaurus, a type of dinosaur species that has confused many paleontologists throughout the years.

Was Spinosaurus more closely related to birds or reptiles? Recent evidence has shown that the Spinosaurus shared more characteristics to modern-day reptiles by staying underwater in waiting for its prey like the crocodiles. Its meat-based diet is similar to crocodiles and its tail shape for locomotion in water. 

If you want to learn even more about the Spinosaurus and its fascinating background, this is the article for you. Ahead, we’ll discuss both the reptile and bird-like origins of this Spinosauridae dinosaur. We’ll also examine its anatomy to decide whether the Spinosaurus is more reptile or bird. 

How Is the Spinosaurus Related to Reptiles?

To dive into whether the Spinosaurus is related to reptiles, we need to open up the two schools of thought scientists claim – whether the Spinosaurus is closer to reptiles or birds. 

The Spinosaurus or spine lizard in the Spinosauridae family lived during the Late Cretaceous Period, specifically the Cenomanian and Upper Turonian Stages. We know very little about the Spinosaurus because of World War II, in which some of its fossil remains were destroyed. The fossils of this species were first discovered in Egypt in 1912 and most recently in 2020, which has provided new fossil material for scientists. 

The Spinosaurus was not only one of the biggest predator dinosaurs, scientists believe it lived on land as well as in water and with new fossil discoveries we are gaining more proof and insight to its water lifestyle – AdventureDinosaurs

The lack of Spinosaurus fossils (due to destruction during the war) and new fossil materials have given rise to two schools of thought: the Spinosaurus was more like a reptile–specifically a crocodile­–or as a bird. 

The Spinosaurus, according to a 2020 report published in the journal Nature, is believed to have “lived in aquatic environments” due to its neural spines and chevrons, not to mention its tail shape. The report says that its tail would have made the Spinosaurus an adept swimmer with “greater thrust and efficiency in the water than the tail shapes of terrestrial dinosaurs.” 

A 2021 article from The New York Times on the Spinosaurus postulated that this dinosaur could have spent some of its time swimming, which would have very much made it crocodilian in Nature like the dinosaur species it shares a clade with. 

However, the article also states “that Spinosaurus had a relatively small number of tail muscles…even fewer than crocodiles, which also tend to have trouble with drag and aren’t particularly effective at pursuing prey underwater. With its tall sail and bulky limbs, Spinosaurus would have produced tremendous drag in anything but the deepest water, making swift subaquatic chases extremely difficult.” 

So, let’s look first at how close the Spinosaurus is to reptiles (crocodiles).

Spinosaurus was at Home in the Water Most Of The Time

In the water, the freshly recreated Spinosaurus looked well at home. Spinosaurus possessed a large fin attached to its backside instead of a tapered whip-like tail. The tail would have been a formidable form of underwater propulsion, as evidenced by the fact that some of the fossil bones were 12-inches thick.

YouTube Video About Spinosaurus With New Updated Information

YouTube Video by E.D.G.E. which details out new fossil discoveries and scientific paper about the Spinosaurus. It focuses a lot on the water habitat which the new discoveries indicate – AdventureDinosaurs

Spinosaurus may have spent the majority of its life in the water, according to the researchers. The researchers used a computer model to compare Spinosaurus’ tail capabilities to extant land-dwelling dinosaurs and semi-aquatic species like crocodiles. The Spinosaurus tail fin was 2.6 times more efficient in the water than the tails of other theropods, which is unsurprising. (Source)

Did Spinosaurus Live Underwater? Looking For New Clues from Fossils

Recent digs have discovered that the Spinosaurus might have spent a lot of its time living underwater, as supported by some new fossils discovered by paleontologists. These discoveries might outdate the current observations we have about Spinosaurus. (Source)

Several years ago, researchers hypothesized that Spinosaurus was predominantly an underwater predator, but the scientific community was skeptical. According to Donald Henderson, a paleontologist at Canada’s Royal Tyrrell Museum, Spinosaurus was undoubtedly top-heavy with its unique back sail and would not have been able to dive underwater.

The study’s lead author, Nazir Ibrahim, believed the answer could be found in fossils. Previous digs had only yielded a few Spinosaurus tail parts, but between 2017 and 2018, the researchers discovered an almost complete set of tail bones at a fossil site in Morocco.

Clues From Related Spinosauridae Subfamilies

The dinosaur family Spinosauridae is named after Spinosaurus, and it includes two subfamilies: Baryonychinae and Spinosaurinae.

Baryonyx from southern England and Suchomimus from Niger, central Africa, are members of the Baryonychinae family. Spinosaurus, Sigilmassasaurus, Oxalaia, Siamosaurus, Ichthyovenator, Irritator from Brazil, and Angaturama, which may be synonymous with Irritator, from Brazil are all members of the Spinosaurinae family.

The Spinosaurinae have unserrated, widely spaced straight teeth (e.g., 12 on one side of the maxilla). In contrast, the Baryonychinae have serrated, curved teeth that are numerous (e.g., 30 on one side of the maxilla).

Clues from Classification and Phylogeny

So how do we know whether the Spinosaurus is more bird than reptile or vice-versa? Well, until paleontologists can uncover more fossils from this dinosaur, which may or may not ever happen, then we won’t know for sure. What we can do, though, is look at the anatomy and classification of the Spinosaurus for clues. 

Spinosaurus, meaning “spine lizard,” was a genus of spinosaurid dinosaurs that lived in what is now North Africa between 99 and 93.5 million years ago, during the Cenomanian to upper Turonian stages of the Late Cretaceous period.

This genus was initially discovered in 1912 in Egypt and described in 1915 by German paleontologist Ernst Stromer. S. aegyptiacus is the most well-known species. However, S. maroccanus, a putative second species, has been discovered in Morocco. These are known to frequent the surface of North Africa, composed of what is now Algeria, Morocco, Tunisia, Libya, and parts of Egypt.

Other Observations Based On The New Fossils

Apart from the bigger idea that the Spinosaurus might have lived underwater for most of their existence, there are also other observations that paleontologists have seen. Some paleontologists have believed that the Spinosaurus had tails very much the same as that of a crocodile. That can also be compared in terms of its shape, size, and power.

However, the shape of the hips of the Spinosaurus resembles a mix of a dinosaur and a bird. Again, we must remember that when trying to recreate a full animal from partial remains, the fossil record is incomplete, and we sometimes get things wrong. That happens most of the time.

How Is the Spinosaurus Related to Birds?

Now let’s take a look at an alternative theory, its close relation to birds. There’s a second school of thought that the Spinosaurus isn’t related to crocodilian reptiles at all, but rather, birds. In fact, there’s one bird in particular that experts believe the Spinosaurus is like, and it’s the heron. 

As The New York Times article linked to above mentions, the Spinosaurus has some traits in common with the heron, including nostrils that are further back on its snout than nearer the end of its nose. Considering the size of its snout, this is peculiar. The Spinosaurus’ neck might have also been able to move downward at unique angles, much like herons can do.

The College of Computer, Mathematical, & Natural Sciences published an article about the origins of the Spinosaurus as well. Their article mentions data from London’s Queen Mary University and the University of Maryland. The studies concluded what The New York Times article had reported as well, that the Spinosaurus could swim, but it probably wasn’t the greatest swimmer that some thought it was.  

However, this doesn’t mean the Spinosaurus didn’t pick off prey in the water, as it’s thought to have done just that. Like a heron, the Spinosaurus hunted along the shoreline rather than in the water’s depths.  

Birds Are Avian Dinosaurs: The Real Deal

Birds are avian dinosaurs, non-avian dinosaurs are non-avian dinosaurs, and birds are technically considered reptiles, as strange as that may sound. The evidence strongly suggests that birds are descended from a maniraptoran dinosaur, most likely a small dromaeosaur.

In general, there is a strong link between dinosaurs and birds, which makes birds a modern version of dinosaurs. One of those is the Archaeopteryx. Archaeopteryx, a dinosaur, could be the evolutionary link between dinosaurs and birds. Archaeopteryx was discovered in Germany and was found to be in remarkably good condition. (Source)

Birds Have The Similar Body Features As Spinosaurus

Spinosaurus had a smaller pelvis or hip bone than other gigantic theropods, with the ilium, or the main body of the pelvis, having half the surface area of the rest of the clade. 

The hind limbs were short, accounting for slightly over 25% of total body length, with the tibia (calf bone) being longer than the femur (thigh bone) (thigh bone). The hallux (or fourth toe) of Spinosaurus touched the ground, unlike other theropods, and the phalanges of the toe bones were extremely long and well-built.

Shallow claws with flat bottoms were attached to their ends. This type of foot shape is also seen in shorebirds, implying that Spinosaurus’ feet adapted for walking on uneven ground may have been webbed. The tail’s caudal vertebrae protruded notably enlarged, thin neural spines, similar to the condition seen in other spinosaurids, but to a greater extent.

The Similarities And Differences Between Birds And Spinosaurus

The similarities between birds and Spinosaurus are shown more on their bottoms. Their feet are compared to shorebirds such as storks, flamingoes, and other birds living on the shores with their alleged webbed structure.

However, what sets them apart is that Spinosaurus has no wings, unlike pterodactyls, the closest dinosaur equivalent of birds. Therefore, they cannot fly. They also do not have beaks or any other facial structure similar to that of birds, and they have teeth. Birds do not have teeth, and that is also a good contrast to the Spinosaurus.

Spinosaurus Anatomy, Classification and Phylogeny to Put The Pieces Together 

Let’s go one step further and match the fossil evidence the Spinosaurus skeletons give us. 

Here is some information about this theropod’s anatomy, phylogeny, and classification. Let’s see what it tell us. 

● Length

The Spinosaurus might have been bigger than even the Tyrannosaurus, like we said before, as it was 49 inches or 15 meters long. 

The Suchomimus is another similarly-sized dinosaur, as are the Trachodon, Saurolophus, Edmontosaurus, Anatotitan, Maisaura, and Hadrosaurus, the latter of which are all Hadrosaurids. 

● Weight

Besides being lengthy, the Spinosaurus was also a heavy dinosaur species. It weighed about 6.6 short tons. Paleontologist Gregory Paul, in 1988, narrowed that weight, saying the Spinosaurus weighed about 4.4 short tons.  

Dal Sasso, in 2005, increased the weight and length limits of the Spinosaurus. He believed the dinosaur might have been between 52 and 58 inches long and weighed somewhere in the ballpark of 7.7 and 9.9 short tons. 

● Skull

The Spinosaurus’ skull featured a long but slim snout, as we talked about earlier. Inside its mouth were about seven teeth per side, all conical with no serrations. The Spinosaurus had one longer tooth per side of its mouth. Studies done on Spinosaurus skulls have found them similar to the Irritator’s skulls in the postorbital section. 

It only takes one look at the massive skull of the Spinosaurus (which is estimated to be around 5.5 feet long), and its head reminds you of one animal. That’s right; it’s the crocodile. 

● Neck

The neck of a Spinosaurus was believed to have been shaped like an S with natural curvature. The neck would have been strong, powerful, and long, which suggests that, yes, the Spinosaurus could have moved its head and neck like a heron. 

● Tail 

Let’s take a look at the Spinosaurus’ tail as well. As we had mentioned, this dino had neural spines, all very tall. The spines together comprised its sail, which is another word for a spinal protrusion. 

It’s not clear if the Spinosaurus’ sail was exactly that or sort of like a hump, as that’s what some experts believe. If that’s the case, then the Spinosaurus would have had a humped back like a modern-day buffalo, which makes matters even more confusing! 

Spinosaurus Phylogeny

Some experts classify the Spinosaurus in a clade or group with only the Irritator, which lived during the Early Cretaceous Period some 110 million years before the Spinosaurus. 

The Irritator genus had anatomy akin to crocodilians, including a secondary palate in its mouth. It is a bone on the roof of the dino’s mouth between its nasal and oral cavities. Theropods–which the Spinosaurus is–generally do not have secondary palates, which is interesting.

If the Spinosaurus is classified into any other clade, it will share that clade with Irritators and Oxalaias. The Oxalaia was believed to have lived during the Late Cretaceous Period about 100 million years ago. That would have put its existence right before or even coexisting with the Spinosaurus. 

Not only did the Oxalaia eat fish like crocodilians, but its caudal vertebrae featured neural spines for swimming just as crocodilians have. (Source)

Spinosaurus Classification 

The Spinosaurus is a member of the Spinosauridae family, which we mentioned before, but within that family are sub-families. 

The first of these is Spinosaurinae. The Spinosaurinae sub-family are the Irritator and Oxalaia and the Angaturama, the Ichthyovenator, the Siamosaurus, and the Sigilmassasaurus.

The Angaturama is a Brazilian dinosaur believed to be very close to the Irritator. Ichthyovenator lived about 113 million years back. Its name translates to “fish hunter.” Siamosaurus only exists today through fossils of its teeth, so it’s hard to say too much about it.

The second sub-family classification of the Spinosauridae family is the Baryonychinae, which had only two dinosaur species: Suchomimus and Baryonyx.

The Suchomimus or “crocodile mimic” lived 112 to 125 million years ago, predating the Spinosaurus. Very similar is the Baryonyx, a theropod that roamed this earth 125 to 130 million years back. 

These classifications tell us that the Spinosaurus leans more towards reptiles than birds. 


The Spinosaurus was a Late Cretaceous dinosaur that’s believed to be even bigger than the Tyrannosaurus. As exciting as that is. Unfortunately, many of the Spinosaurus fossils no longer exist, so we can only guess how this dinosaur used to live.

Spinosaurus has confused paleontologists about its relationship to modern-day animals, whether it has relative similarities to birds or reptiles. The newest findings based on the fossils discovered have uncovered another unique quality of this dinosaur: the ability to live underwater for a long time and a crocodile-like tail that points to Spinosaurus being more related reptiles

Let’s hope that future fossil finds of the Spinosaurus will lead to more definitive evidence of its closeness to reptiles or even birds. 

Recommended Reading:

● I’ve written a whole article about the Spinosaurus as possibly being the first water dinosaur that covers many of the features, especially the tail, that makes a good adaptation for balance and as a propeller in the water.
● If you are interested in which dinosaurs the most terrifying, I’ve written an article that covers a list of 13, including the Spinosaurus. It could hunt on land and sea and qualifies as one of the most terrifying dinosaurs!