Bone-Headed Dinosaur Pictures and Profiles

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Meet the Bone-Headed Dinosaurs

stegoceras
Stegoceras. Dmitry Bogdanov

Pachycephalosaurs--"bone-headed dinosaurs"--were equipped with unusually thick skulls, with which males head-butted each other for the right to mate with females. On the following slides, you'll find pictures and detailed profiles of over a dozen bone-headed dinosaurs, ranging from Acrotholus to Wannanosaurus.

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Acrotholus

acrotholus
Acrotholus. Julius Csotonyi

Name:

Acrotholus (Greek for "high dome"); pronounced ACK-roe-THO-luss

Habitat:

Woodlands of North America

Historical Period:

Late Cretaceous (about 85 million years ago)

Size and Weight:

About four feet long and 75 pounds

Diet:

Plants

Distinguishing Characteristics:

Moderate size; unusually thick skull

 

Sometime during the middle Cretaceous period, about 100 million years ago, a population of ornithopods--small, bipedal, plant-eating dinosaurs--evolved into the first pachycephalosaurs. The recently announced Acrotholus is the earliest bone-headed dinosaur to be discovered in North America, predating the previous record-holder by five million years, and it's one of the earliest pachycephalosaurs yet identified-- possibly only recently evolved from its ornithopod ancestors.

Aside from its place at the base of the pachycephalosaur family tree, Acrotholus is also important because it points to a previously unappreciated diversity among small, herbivorous, Cretaceous dinosaurs. Even at this early date, bone-headed dinosaurs seem to have been widely diverse, albeit sharing one important characteristic: their unusually thick and rounded skulls, which presumably permitted males to butt heads at high speed for the right to mate with females.

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Alaskacephale

alaskacephale
Alaskacephale. Eduardo Camarga

Name:

Alaskacephale (Greek for "Alaskan head"); pronounced ah-LASS-kah-SEFF-ah-lee

Habitat:

Woodlands of western U.S.

Historical Period:

Late Cretaceous (80-70 million years ago)

Size and Weight:

About eight feet long and 500 pounds

Diet:

Plants

Distinguishing Characteristics:

Moderate size; thick skull

 

One of the newer pachycephalosaurs (bone-headed dinosaurs) on the block, Alaskacephale was named in 2006 after the state of the U.S. where its incomplete skeleton was discovered. Originally thought be a species (or perhaps a juvenile) of the better-known Pachycephalosaurus, it was later "diagnosed" as belonging to its own genus based on slight variations in its skeletal structure, especially pertaining to its head. Like other pachycephalosaurs, Alaskacephale was equipped with an unusually thick skull, with which (presumably) males butted one another for the right to mate with females.

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Colepiocephale

colepiocephale
Colepiocephale. Paleopedia

Name:

Colepiocephale (Greek for "knucklehead"); pronounced co-LEE-pee-oh-SEF-ah-lee

Habitat:

Woodlands of North America

Historical Period:

Late Cretaceous (75-70 million years ago)

Size and Weight:

About three feet long and 10-15 pounds

Diet:

Plants

Distinguishing Characteristics:

Small size; flat, sloped skull

 

There's one thing you can say about the paleontologist who discovered Colepiocephale: he or she had a good sense of humor. In true Three Stooges style, this tiny herbivore's name is Greek for "knucklehead," as befits your typical pachycephalosaur (or bone-headed dinosaur). Its odd name aside, Colepiocephale is important for being one of the earliest boneheads discovered to date in North America (Asian pachycephalosaurs, such as Goyocephale, appear to have predated their American cousins by a few million years). Colepiocephale also had an unusual skull compared to other dinosaurs of its kind; it wasn't domed or especially thick, but flat, sloped and roughly triangular.

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Dracorex Hogwartsia

dracorex hogwartsia
Dracorex hogwartsia. Wikimedia Commons

As bone-headed dinosaurs grew, their head ornamentation became more and more elaborate, so adults looked very different from teenagers--which is why Dracorex hogwartsia is now believed to have been a Pachycephalosaurus juvenile. See an in-depth profile of Dracorex

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Goyocephale

goyocephale
Goyocephale. Joao Boto

Name:

Goyocephale (Greek for "adorned head"); pronounced GOY-oh-SEFF-ah-lee

Habitat:

Woodlands of Asia

Historical Period:

Late Cretaceous (85-70 million years ago)

Size and Weight:

About six feet long and 50-100 pounds

Diet:

Plants

Distinguishing Characteristics:

Slim build; small protrusions on head

 

Like its close cousin, Wannanosaurus, Goyocephale is important because it was ancestral to the more evolved (and thicker-skulled) pachycephalosaurs of the late Cretaceous period, such as Stegoceras and Stygimoloch. This small, nimble plant-eater had only rudimentary ornamentation on its head, and its relatively primitive skull was punctuated by noticeable holes (the skulls of later pachycephalosaurs, by contrast, were solid masses of bone). It's unknown whether Goyocephale males (or females) head-butted each other for dominance in the herd, but in any case, it's unlikely they could have done much damage!

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Homalocephale

homalocephale
Homalocephale. Sergey Krasovskiy

Name:

Homalocephale (Greek for "level-headed"); pronounced HOE-ma-low-SEFF-ah-lee

Habitat:

Woodlands of Asia

Historical Period:

Late Cretaceous (80-70 million years ago)

Size and Weight:

About five feet long and 100 pounds

Diet:

Plants

Distinguishing Characteristics:

Broad, flat skull; bumps on snout

 

The skull of Homalocephale, a type of pachycephalosaur (bone-headed dinosaur), has fueled debate among paleontologists about the behavior of boneheads in general. Homalocephale's broad, flat skull wasn't especially hard or rigid; rather, it was made of porous bone interlaced with blood vessels, meaning two males head-butting each other at top speed would likely have killed one another. So for what other reason would Homalocephale (and other pachycephalosaurs) have evolved such thick skulls? Theory B is that they used their noggins to butt away other members of the herd--not on their heads, but on their softer flanks--or even (a bit less believably) to drive away curious predators.

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Micropachycephalosaurus

micropachycephalosaurus
Micropachycephalosaurus. H. Kyoht Luterman

The size of the bone-headed dinosaur Micropachycephalosaurus was inversely proportional to the length of its name: this tiny pachycephalosaur wouldn't have been much of a match for your average house cat. See an in-depth profile of Micropachycephalosaurus

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Pachycephalosaurus

pachycephalosaurus
Pachycephalosaurus. Wikimedia Commons

Pachycephalosaurus has bestowed its name on an entire breed of boneheaded dinosaurs, the pachycephalosaurs, other famous examples of which are Dracorex hogwartsia and Stygimoloch (the "horned demon from the river of hell"). See an in-depth profile of Pachycephalosaurus

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Prenocephale

prenocephale
Prenocephale. Wikimedia Commons

Name:

Prenocephale (Greek for "sloped head"); pronounced PREE-no-SEFF-ah-lee

Habitat:

Woodlands of Asia

Historical Period:

Late Cretaceous (70-65 million years ago)

Size and Weight:

About six feet long and 200 pounds

Diet:

Plants

Distinguishing Characteristics:

Bipedal posture; thick, round skull

 

You might not be surprised to learn that pachycephalosaurs ("thick-headed lizards") are often represented in the fossil record only by their massive skulls. To date, that has been the case with Prenocephale; the rest of this plant-eater has been reconstructed with reference to closely related boneheads such as Homalocephale and Tylocephale. The abiding mystery about pachycephalosaurs is why they had such thick skulls in the first place. Some paleontologists believe males head-butted each other for the sexual favors of females, but others say boneheads used their thick noggins to butt the flanks of other members of the herd--or even curious predators--since a full-on collision might well have been fatal to both combatants!

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Sphaerotholus

sphaerotholus
The skull of Sphaerotholus. Wikimedia Commons

Name:

Sphaerotholus (Greek for "ball dome"); pronounced SPHERE-oh-THOLE-us

Habitat:

Woodlands of North America

Historical Period:

Late Cretaceous (75-65 million years ago)

Size and Weight:

About six feet long and 100 pounds

Diet:

Plants

Distinguishing Characteristics:

Large, hemispherical, domed skull

 

Sphaerotholus presents a bit of a paradox: when this dinosaur was dug up in New Mexico a few years ago, its skull was one of the most complete ever found of a pachycephalosaur (bone-headed dinosaur). However, not much was located besides the skull, which has led some experts to speculate that Sphaerotholus was actually a species of another pachycephalosaur genus, Prenocephale.

So where's the paradox? Well, for one thing, Prenocephale roamed the woodlands of Asia during the late Cretaceous period, whereas the dinosaur known as Sphaerotholus seems to have been confined to North America. If they do turn out to belong to the same genus, Sphaerotholus/Prenocephale would automatically become the most widespread of all the pachycephalosaurs.

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Stegoceras

stegoceras
Stegoceras. Sergey Krasovskiy

Paleontologists believe the adult males of the bone-headed dinosaur Stegoceras held their heads and necks parallel to the ground, build up a head of speed, and rammed each other on the noggins as hard as they could. See an in-depth profile of Stegoceras

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Stygimoloch

stygimoloch
Stygimoloch. Luis Rey

What paleontologists know as Stygimoloch ("horned demon from the river of hell") may in fact have been a juvenile specimen of Pachycephalosaurus; the same reasoning applies to another famous bone-headed dinosaur, Dracorex hogwartsia. See an in-depth profile of Stygimoloch

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Texacephale

texacephale
Texacephale. Jura Park

Name:

Texacephale (Greek for "Texas head"); pronounced TEX-ah-SEFF-ah-lee

Habitat:

Woodlands of North America

Historical Period:

Late Cretaceous (80-70 million years ago)

Size and Weight:

About five feet long and 50 pounds

Diet:

Plants

Distinguishing Characteristics:

Large, thick skull with distinctive grooves

 

Texacephale ("Texas head") is the latest example of the odd breed of dinosaurs known as pachycephalosaurs, or "thick-headed lizards"--males of which head-butted each other for dominance within the herd and the right to mate with females. What set Texacephale apart from other pachycephalosaurs is that, in addition to its three-inch-thick noggin, it had characteristic creases along the sides of its skull, which seem to have evolved for the sole purpose of shock absorption. If confirmed, this would eliminate one objection some paleontologists have had to the "head-butting" theory, which is that two male pachycephalosaurs would be likely to knock each other unconscious when they butted heads at high speeds!

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Tylocephale

tylocephale
Tylocephale. Getty Images

Name:

Tylocephale (Greek for "swollen head"); pronounced TIE-low-SEFF-ah-lee

Habitat:

Woodlands of Asia

Historical Period:

Late Cretaceous (80-70 million years ago)

Size and Weight:

About five feet long and 50-75 pounds

Diet:

Plants

Distinguishing Characteristics:

Tall, thick, heavy skull

 

During the late Cretaceous period, North America and Eurasia were connected by a land bridge (which explains why so many types of dinosaurs, like hadrosaurs and raptors, lived pretty much exclusively on these two continents). Pachycephalosaurs, or bone-headed dinosaurs--of which Tylocephale is an example--are believed to have evolved in either North America or Asia, and then migrated to the opposite side of the globe.

The question is, where did the boneheads first arise? Tylocephale is an object lesson in how complicated this question can be. Based on analysis of this dinosaur's remains, some paleontologists have concluded that pachycephalosaurs evolved in Asia in the middle Cretaceous period and then migrated to North America.The catch is, some of these American boneheads are theorized to have migrated back to Asia a few million years later (via that land bridge), where they evolved into genera like Tylocephale.

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Wannanosaurus

wannanosaurus
Wannanosaurus. Wikimedia Commons

Name:

Wannanosaurus (Greek for "Wannan lizard"); pronounced wah-NON-oh-SORE-us

Habitat:

Woodlands of Asia

Historical Period:

Late Cretaceous (80-70 million years ago)

Size and Weight:

About two feet long and 10 pounds

Diet:

Plants

Distinguishing Characteristics:

Small size; thick skull

 

We may never know for sure, but it seems likely that Wannanosaurus (or a dinosaur very much like it) was the ancestor of all the pachycephalosaurs, or bone-headed dinosaurs. Like most ancestral genera, this herbivore was very small, and probably scurried beneath the feet of the larger hadrosaurs and titanosaurs of the late Cretaceous period. The question, of course, is why Wannanosaurus had such a thick skull: some paleontologists believe pachycephalosaur males head-butted each other for dominance, but for a creature the size of Wannanosaurus, it seems more likely that its bony head would have served as a primitive form of defense.