Acrotholus: Highest Dome Dinosaur of Late Cretaceous

Welcome, fellow dinosaur enthusiasts! Today, we’re embarking on a journey back in time, to the Late Cretaceous period, to meet a fascinating creature–the Acrotholus. This dinosaur, whose name intriguingly means ‘highest dome’, is a captivating subject of study for paleontologists and dinosaur lovers alike. Its unique features and the era it lived in offer a wealth of insights into the world of dinosaurs.

Acrotholus Key Facts

Acrotholus pronunciationack-row-tho-lus
Meaning of nameHighest Dome
Type SpeciesAcrotholus audeti
Period & TimeLate Cretaceous
EpochLate/Upper Santonian
Time it Lived85.8 to 83.5 MYA
Length6.0 ft
Height6.0 ft
Weight0.04 tons
MobilityMoved on two legs
First Discovery2008 by David Evans and Ryan Schott
Location of first findMilk River Formation, Alberta, Canada
First Described2013 by David Evans, Ryan Schott, Derek Larson, Caleb Brown, Michael Ryan
HolotypeRTMP 2008.045.0001

Acrotholus Origins: Taxonomy, Timeline, and Discovery

Let’s start our journey by understanding the name of our dinosaur. The name is derived from the Greek words ‘akros’, meaning highest, and ‘tholos’, meaning dome. Therefore, this name perfectly encapsulates the most distinctive feature of this dinosaur–its dome-shaped head.

The Acrotholus belongs to the Ornithopod group, specifically the Pachycephalosaurid family. Acrotholus audeti is the type species of this genus, and is named in honor of Roy Audet. He originally granted access to his ranch, leading to the discovery of this species.

Illustration of Acrotholus, a small, bipedal dinosaur with a thick, dome-shaped skull, shown in a side profile. The dinosaur has a robust body, short arms, and a long tail, with a textured skin appearance, featuring a mix of blue and green coloration.
image by Nobu Tamura is license under CC BY-SA 4.0

Our journey takes us back to the Late Cretaceous period, specifically the Late Santonian epoch. This time frame places the Acrotholus between 85.8 and 83.5 million years ago in a time when dinosaurs were the dominant terrestrial vertebrates.

The first discovery of this dinosaur was made in 2008, by David Evans and Ryan Schott in the Milk River Formation in Alberta, Canada. They later went on to describe it in 2013. This discovery has significantly contributed to our understanding of the diversity and evolution of small-bodied dinosaurs.

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Fossil Evidence

The first fossil evidence of it was found in the Deadhorse Coulee Member of the Milk River Formation in Southern Alberta, Canada. This formation is known for exposing organisms from the Late Santonian. 

The fossil consists of a nearly complete frontoparietal dome along with the anterior half of the frontoparietal dome. Pachycephalosaurs, in general, are unique in dinosaur fossil records due to their relatively small size in relation to most dinosaurs in their time period–40 kilograms (90 pounds) or less. 

Pachycephalosaurs are unique in this regard due to their recognizable head dome which is resistant towards pre-depositional destruction. Approximately 66% fossil specimens are known from only cranial material. This dinosaur is no exception to this, with the majority of its fossils being cranial.

Acrotholus Size and Description

The Acrotholus is a fascinating dinosaur, known even among Pachycephalosaurids for its unique physical characteristics. Let’s delve into a detailed description of this dinosaur.

Short description of Acrotholus

This is a small dinosaur, known for its distinctive dome-shaped head, formed by the frontoparietal bones, which is the highest among all pachycephalosaurs. Its body is bipedal with a slender neck supporting the heavy head. The limbs are proportionate to the body with the hind limbs being longer and stronger, suggesting a bipedal locomotion. The tail is long and slender to provide balance while moving.

Size and Weight of Type Species

Because of a lack of more fossil evidence, the exact size and weight are not known . However, based on the size of the skull and comparison with other pachycephalosaurs, it is estimated that the Acrotholus was a small dinosaur, possibly around 2 meters (6 feet) in length.

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The Dinosaur in Detail

The most distinctive feature of this dinosaur that sets it apart from its relatives and contemporaries is its dome-shaped head, which is the highest among all pachycephalosaurs. It was formed by the frontoparietal bones of the skull and is speculated to have been used for head-butting during territorial disputes or mating rituals.

The Acrotholus also exhibits a bipedal locomotion, with its hind limbs being longer and stronger than its forelimbs. These proportions suggest that the dinosaur was a fast runner capable of escaping predators.

The discovery of this particular dinosaur has significantly contributed to our understanding of the diversity and evolution of small-bodied dinosaurs. Its unique features and the era it lived in offer a wealth of insights into the world of dinosaurs.

The Acrotholus in its Natural Habitat and Environment

This herbivore lived in what is now Alberta, Canada. This region during the Late Cretaceous period was a diverse ecosystem teeming with a variety of flora and fauna on a paleocontinent known as Laramidia. The climate was warm and humid, with lush vegetation providing ample food for herbivores like the Acrotholus. As an herbivore, the Acrotholus would have fed on the abundant plant life in its environment. 

Its distinctive dome-shaped head made it a unique presence in its environment. Its head is speculated to have been used for head-butting during territorial disputes or mating rituals. It would also have made it a formidable opponent for the predators of the time.

Interesting Points about Acrotholus

  • It is known for having the thickest dome of any Pachycephalosaur.
  • The name means “high dome”, referring to its distinctive dome-shaped head.
  • Despite its small size, it was an herbivore that lived alongside larger carnivorous dinosaurs like the Tyrannosaurus.
  • The discovery has significantly contributed to our understanding of the diversity and evolution of small-bodied dinosaurs.

Contemporary Dinosaurs

In this snapshot of prehistoric time, the Acrotholus shared its world with a captivating array of contemporaries. Gryphoceratops, Tyrannosaurus, and Edmontosaurus each helped to contribute to the intricate dynamics of Laramidian dinosaurs and their shared ecosystem.

The Gryphoceratops, smaller in comparison, presents an interesting contrast. Despite its diminutive size, this dinosaur was a resilient survivor that navigated the same landscape and possibly competed for similar resources. The interaction between these two species–one larger, the other smaller–paints a vivid picture of the diverse life forms that coexisted during this period.

The Edmontosaurus was considerably larger than the Acrotholus. Despite their size difference, these two herbivorous dinosaurs might have had a peaceful coexistence, each occupying a different niche in the ecosystem. 

The Tyrannosaurus, a creature of immense size and formidable reputation, introduces a different dynamic. As a potential predator, its presence would have significantly influenced the behavior and survival strategies of the Acrotholus. This relationship is a classic example of the predator-prey dynamic and adds a layer of complexity to our understanding of not only the Acrotholus but also the herbivores with which it shared an environment.

Featured Image Credit: Nobu Tamura, CC BY-SA 4.0, via Wikimedia Commons


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“Please note that the information in this article is based on various sources, drawing on scientific research, fossil evidence, and expert analysis. The aim is to provide a comprehensive and accurate overview of the Afrovenator. Please be aware however, that our understanding of dinosaurs and their world is constantly evolving as new discoveries are made.”

Article last fact checked: Joey Arboleda, 06-09-2023