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Dinosaur Skulls: Why Did They Have So Many Holes?

Have you ever gotten to see a dinosaur skull up close before? As you study the details, you’ll realize that the average dino skull was absolutely full of holes. It seems like they had more holes than for eye sockets and nostrils, so why so many?

Dinosaur skulls had as many fenestrae or holes as possible so the species could grow unencumbered in size. The fenestrae would have acted as ventilation of sorts to maintain brain temperature during this growth. A skull with many holes would have weighed less than denser skulls also. 

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There’s plenty to talk about regarding dinosaur fenestrae ahead, including the type of skull an average dinosaur possessed, the reason for so many skull holes, and whether evolutionary ancestors like the chicken or crocodile have similar skulls. Let’s get started! 

What Type of Skull Did Dinosaurs Have? Did All Dinosaurs Have the Same Type of Skull?

Perforations or fenestrae were standard of all dinosaur species. First, let’s explore the types of fenestrae an average dinosaur possessed, then delve into how these fascinating skulls varied by species.  

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The Anatomy of a Dinosaur Skull

Although some of the fenestrae a dinosaur skull possessed made clear sense–such as for the eyes–others are a bit more fascinatingly mysterious. We’ll uncover some of that mystery by revealing the types of fenestrae now.

Eye Sockets

All dinosaurs had eyes, although their size and how effectively their vision assisted them in hunting and surviving varies by species. The eye sockets are the most easily identifiable fenestrae. 

For most dinosaur species, the socket openings are in an area you’d expect, on either side of the dinosaur’s head. 

Antorbital Fenestra

The eye sockets themselves are not the only opening in this area. A gap in front of a dinosaur’s eye socket is not a continuation of the socket but rather a fenestra known as the antorbital fenestra. 

Although it doesn’t look like much when examining an empty dinosaur skull today, the antorbital fenestra attached to an air chamber that was linked to a dinosaur’s respiratory system. 

The respiratory system told the dinosaur to keep its head cool, quite literally, in this case.

Temporal Fenestra

Dinosaurs also had temporal fenestrae for each eye. This opening is behind the dino’s eye socket. Thanks to the presence of a temporal fenestra, a dinosaur’s jaw muscles connected to the rest of its face. 

Behind the eyes is not the only location of temporal fenestra in a dinosaur’s head. Nearer the top of the dinosaur’s skull were dual temporal fenestrae. These were smaller than the ones by the dino’s eyes. Linking the temporal fenestrae were muscles that would extend to the neck. 

Depending on the dinosaur species, the connection points of the secondary temporal fenestrae varied. For example, the Tyrannosaurus’ temporal fenestrae sets were attached to another set of fenestrae much larger. 

The Archosaurus had smaller secondary temporal fenestrae that crossed over the main temporal fenestrae.

Nostrils

Dinosaurs had to breathe, and they could do that through both their nose and their mouth. Nostril openings on either side of the snout or nose made breathing easy. The size and shape of the nostrils differed by dinosaur species

Mandibular Fenestra

The last fenestra was the mandibular fenestrae. It is where the jaw muscles would go beyond the temporal fenestrae. A T. Rex’s mandibular fenestra was larger and more apparent than the Archosaurs. (Source)

Were All Dinosaur Skulls the Same?

The Archosaurus is an interesting example to talk about, as its skull was almost like the blueprint for reptiles. The Archosaurus was an Archosaur, including birds, pterosaurs, and other dinosaurs. It wasn’t a very large dinosaur. 

Although many dinosaur species followed that so-called blueprint for the skull shape and fenestrae, dinosaur skulls are not the same. You only have to compare an Archosaurus to the famed T. Rex to see the differences.

As we mentioned above, the positioning of Tyrannosaurus Rex’s fenestrae and the prominence and size of some of these fenestrae varied from species to species of Archosaurs.

It’s not only fenestrae that differentiated dinosaur skulls. Here are some other factors that were at play.

Size

The smaller the dinosaur, the smaller its skull will be. Otherwise, the dinosaur would have been lopsided and likely wouldn’t have lived very long. 

Shape

Some dinosaur species have a skull shape that we’ve come to expect of dinosaurs, with a broad, sizable head and then a longer snout. Others had flatter heads and smaller snouts, and more still had bird-like heads. The range of dinosaur skulls is truly phenomenal!  

Thickness

Some clades of dinosaurs evolved and adapted by developing thicker skulls. One such example is the large Pachycephalosaurus, a dome-shaped, protruding, thick skull. The dino’s skull might have been 10 inches thick!

Interestingly, the Pachycephalosaurus didn’t have a large brain, so you might wonder why it needed so much extra cushioning. We’re not sure ourselves. 

Horns or Crests

Many dinosaurs feature horns or crests. These growths were part of the dinosaur’s skull, which you can discover for yourself if you ever get a chance to see certain dinosaur exhibits at a museum.

An enormous crest protrudes from the top of the Parasaurolophus’ head and curves at a backward angle over its neck. A bony frill surrounds the back of the Triceratops’ head, along with two horns on the skull and a third horn near its nostrils. 

Why Were There So Many Holes in a Dinosaur’s Skull?

You’re impressed with what you’ve learned about fenestrae so far. What purpose did these perforations offer besides providing us a glimpse into how a dinosaur’s nerves and muscles connected? 

Per the intro, here are three reasons for all the holes in a dinosaur’s skull. 

Brain Ventilation

A 2019 article from Smithsonian Magazine explores what is arguably the top benefit of fenestrae in dinosaur skulls: safeguarding the brain from overheating. 

According to the article, when University of Missouri researchers explored a dinosaur’s fenestrae in more detail, they realized the holes had to do with more than impacting a dino’s biting abilities. The holes might have acted as a form of ventilation.

Why did a dinosaur need ventilation in its brain? To answer that question, the University of Missouri researchers investigated common alligators, watching their behavior at a zoo and taking thermographic images of the animal.

Early in the morning, when the weather was usually cooler, the alligators had a warmer skull opening even though their bodies were cold. 

Then, later in the day, as the weather began to warm up, the alligators’ brain temps cooled down while their body temperatures remained high. 

We don’t know if dinosaurs had similar abilities, but it’s possible!

Growth Potential

Holes in the skull of a dinosaur’s brain, designed to prevent overheating, are what ties directly into the creature’s growth potential. 

We’re sure we don’t have to tell you that very few modern creatures are on par with the size of dinosaurs. The great blue whale is bigger, but you’d be hard-pressed to find many other examples.

As a dinosaur grew, its body would have retained more and more heat. Their brain was at a higher risk of overheating as the dinosaur expanded in size, where the fenestrae came into play. They maintained the dinosaur’s core temperature. (Source)

Weight Reduction

A dinosaur with a thick skull such as the Pachycephalosaurus could use its head as a weapon if it wanted to, but not every dinosaur could afford to be burdened by a heavy head. How would pterosaurs have flown? How would long-necked dinosaurs have been able to keep their neck and head upright?

Fenestrae reduces the weight of a dinosaur skull considerably. 

How Does a Dinosaur Skull Compare to a Crocodile or Chicken Skull?

As the dinosaurs went extinct and the creatures that appeared in modernity kept getting smaller, you would think they need for fenestrae would disappear entirely. Yet that’s not quite the case. 

Let’s take a look at the skulls of two animal species with ties to dinosaurs–the alligator and the chicken–and see if there’s anything familiar. 

Crocodile Skulls

We’ve talked about the skulls of crocodilians several times throughout this article. Taking one look at the skull of a crocodile reveals that it’s got more fenestrae than you might have thought. 

Yes, those include the standard eye sockets and nostril openings, but there’s more. This Smithsonian piece from 2003 reveals that crocodiles have openings throughout their skulls to easily travel for facial nerves and blood vessels, especially those that send olfactory and optical signals. 

The nerves correlate to bumps on a crocodile’s jaw. The researchers in the article conclude that the bumps might have acted as sensors that could transmit data to the crocodile’s brain so the animal could be adept at both water and land survival. 

Of course, the researchers aren’t completely sure yet what the bumps do, especially when you consider that other crocodilians feature the bumps not exclusively on their jaws but also on their bodies. 

Chicken Skulls

An intact chicken skull might not look like it due to the huge gaps on either side of the bird’s head. According to this Nature study from 2014, T. Rex and chicken brains share a lot in common, including a similar number of bones in their heads. 

Conclusion

Dinosaur skulls feature holes or fenestrae to prevent their brains from overheating as the dino grew. Although the need for these openings is largely nonexistent today, some modern animals have holier skulls than most, including chickens and crocodiles!