An Ultimate Guide to Anomalocaris: The Unusual Shrimp

Leave a comment / / Updated on: 24th September 2023

Name MeaningAbnormal ShrimpHeightN/A
PronunciationA-nom-ah-lo-ca-risLength50 cm (1.6 ft.) 
EraPaleozoicCambrian PeriodWeight9kgs. (20 lbs.)
ClassificationDinocaridida, Radiodonta, & AnomalocaridaLocationNorth America, Australia, Greenland, China (Ocean)

Anomalocaris Pictures

3D illustration of an Anomalocaris
3D illustration of an Anomalocaris | CoreyFord via iStock

The Anomalocaris

Gage Beasley's Anomalocaris Stuffed Plush Toy
Gage Beasley’s Anomalocaris Stuffed Plush Toy

Anomalocaris is a genus of arthropod that lived during the Cambrian period, and was one of the largest animals of its time.

This genus belonged to the Radiodont order, which were a successful group of marine animals, and early arthropods.

The first fossils collected of Anomalocaris were found in 1886 in the Burgess Shale of Canada.

Fossils from the Burgess Shale, including Anomalocaris have confused paleontologists for decades, and even today there are studies revising the mistakes of the past.

Gage Beasley's Prehistoric Shirt Collection
Gage Beasley’s Prehistoric Shirt Collection
Gage Beasley's Prehistoric Plush Collection
Gage Beasley’s Prehistoric Plush Collection

Anomalocaris name translates to “unlike other shrimp”, or “abnormal shrimp”, due to their odd appearance.

Many animals from the Cambrian period represent early forms of the species that we see today.

Anomalocaris existed around 515 to 472 million years ago, and their fossils have allowed paleontologists to gain insight on how the earth looked in a time period before even the dinosaurs. 

From the time of their first discoveries, how Anomalocaris have looked, and what they ate has caused much confusion to those that studied them. 

Here we will go over Anomalocaris, and what fascinating information has been discovered about these animals like their appearance, diet, and how they fit into their environment. 

Anomalocaris' strange appearance is a mishmash of different sea creatures of today
Anomalocaris’ strange appearance is a mishmash of different sea creatures of today | CoreyFord via iStock

Physical Characteristics

In the Cambrian period Anomalocaris was one of the largest animals in their environment, along with other radiodonts.

Like their name suggests Anomalocaris had shrimp-like features, such as their body shape, prongs,and tail fan.

Previous estimations of Anomalocaris had them reaching up to 1 meter (3.3 ft.) in length, but today this is seen as inaccurate, and too large.

The body length of Anomalocaris is currently estimated at 37.8 cm (1.24 ft.) without including their tail fans, and appendages. 

Gage Beasley Prehistoric's Anomalocaris Size Comparison Chart
Gage Beasley Prehistoric’s Anomalocaris Size Comparison Chart

The body of Anomalocaris was made up of several segments that connected with a spine that overlapped.

Each of their body segments overlapped, and got smaller towards their rear.

Their body had flaps on their sides, which aided them in moving through the water using an undulating motion.

At the front of their mouths Anomalocaris had frontal appendages that had spines, and were made up of around 14 segments. 

The tail of this animal was shaped like a fan, which helped propel themselves through the water. 

The eyes of Anomalocaris were advanced, and located on the dorsolateral sides of their head. 

Each of their eyes were around 3 cm (1.2 in.) wide, and one specimen fossilized showed they had more than 24,000 lenses, giving them very advanced eyesight.

Anomalocaris' possessed advanced eyesight for its time
Anomalocaris’ possessed advanced eyesight for its time | CoreyFord via iStock

The mouths of Anomalocaris were shaped like a cut pineapple slice, and known as an oral cone it was made up of several plates.

While the appearance of Anomalocaris is subject to change in the future, studies over the years have allowed these animals appearance to become more accurate. 

Habitat and Distribution

Anomalocaris lived in the ocean during the Cambrian period, and like much other life on earth during this period was primarily a marine animal. 

The first fossils found of Anomalocaris were found in the Burgess Shale of Canada, but have also been found in other formations around the globe in places like Greenland, Australia, Utah, and China. 

In the Cambrian period it is estimated earth was made around 85% ocean, compared to around 70% of earth being ocean today. 

The oceans that Anomalocaris lived in were ice free, and scientists have attempted to measure the temperature of the water using isotopic evidence

Temperature in the water during the Cambrian period have been proposed at being up to  60 °C (140 °F), but these temperatures are considered too warm for life to live in.

Other estimates of water temperature vary between 27 to 53 °C (80.6 to 127.4 °F).

The eyes of Anomalocaris suggest these animals lived in deep waters up to 1,000 m, (3,281 ft.), which is why they evolved to have better vision in this dark environment. 

Evidence suggests that Anomalocaris may have spent most of its time in the dark depths of the ocean floor
Evidence suggests that Anomalocaris may have spent most of its time in the dark depths of the ocean floor | Scanova via Additional Creatures Wiki

The Burgess Shale is where Anomalocaris was found the most, but their fossils found suggest they had a widespread range. 

Behavior and Diet

Anomalocaris was a carnivore, and active predator, but what this animal ate has been debated just like their appearance. 

The frontal appendages designed for grabbing, and their mid-gut glands suggest these animals had a predator lifestyle. 

Originally Anomalocaris were thought to feed on hard-bodied animals, and they had the ability to penetrate the exoskeleton of trilobites.

Evidence that suggests Anomalocaris fed on hard-bodied animals is fossilized trilobites with bite marks on them that have the same shape as the mouth of Peytoia, which is a similar species to Anomalocaris

Ecological reconstruction of Anomalocaris hunting smaller prey
Ecological reconstruction of Anomalocaris hunting smaller prey | Qohelet12 via Wikipedia CC BY-SA 4.0

Coprolite has also been discovered containing trilobite parts, and it was so large it is believed to have been able to come from the large Anomalocaridids that existed.

Fossils with little wear on the grabbing appendages, and mouth parts of Anomalocaris suggest these animals fed mainly on softer bodied prey. 

Reconstruction of the Anomalocaris mouth suggests these animals did not have a strong bite force, and could not even fully close their mouth. 

Anomalocaris likely preyed more on soft bodied prey that had a size between 2 to 5 cm (0.78 to 1.96 in.) in diameter.

Nektonic, and soft-bodied animals are what these animals likely ate, but more studies may make their diet more clear.

Life Cycle

There is still much mystery of the Anomalocaris, including how these animals reproduced, and how long they lived. 

It is believed that Anomalocaris reproduced by using external fertilizations, and laid eggs like modern arthropods. 

Anomalocaris life span is unknown, and the fossil specimens age are also not known, which is why it has been difficult in learning the true size of these arthropods. 

Image of the first complete anomalocaris fossil found
Image of the first complete anomalocaris fossil found | Keith Schengili-Roberts via Wikipedia CC BY-SA 3.0

The end of the Cambrian period is when these animals went extinct, disappearing around 488 million years ago.

Evidence suggests there was a mass extinction event that is theorized to be caused by volcanic activity. 

A lack of food, and other animals evolving to out-compete them is what also contributed to the extinction of Anomalocaris.

Evolution and History

The first fossils of Anomalocaris were discovered in Burgess Shale in 1886 by Richard G. McConnell.

A largely complete specimen of Anomalocaris canadensis from the Burgess Shale
A largely complete specimen of Anomalocaris canadensis from the Burgess Shale | Cédric Aria et al. via Wikipedia CC BY 4.0

When discovered, Anomalocaris fossils were found with many trilobites, and brachiopod fossils.

Around 50 specimens in the Burgess Shale were described later in 1892, which is when the type species Anomalocaris canadensis was created. 

When first found the front half of Anomalocaris was mistaken as a type of jellyfish, and put into the Peytoia genus by Charles Doolittle Walcott. 

It took several years until the late 1900s for Anomalocaris to become better understood.

Paleontologists Harry B. Whittington working out of Cambridge University reanalyzed the fossils found in Burgess Shale, and while making a few mistakes this study allowed for Anomalocaris mouth piece to be found.

Other discoveries that have furthered the knowledge gained include compound eyes found in 2011, and 2020, found in Emu Bay in Australia. 

There have been several species like A. daleyae in Australia, A. whiteavesi, A. gigantea and A. cranbrookensis that have been described.

Size estimation of Anomalocaris
Size estimation of Anomalocaris | Junnn11 via Wikipedia CC BY-SA 4.0

Some of the species of the past have been reassigned, and are no longer valid.

It is believed that Anomalocaris evolved from flatworms, into trilobites.

There have been many mistakes made in the past about Anomalocaris, and likely more needed to be revised in the future. 

Interactions with Other Species

During the Cambrian period life existed solely in the ocean, and this time period began to see an increase of diversification. 

The so called "Cambrian explosion" or "Cambrian radiation" that brought about the diversification of life
The so called “Cambrian explosion” or “Cambrian radiation” that brought about the diversification of life | canbedone via iStock

Anomalocaris was one of the first apex predators on earth, due to their size, and carnivorous diet. 

It is still not known whether Anomalocaris ate soft-bodied animals like worms, or fed on harder bodied trilobites. 

Anomalocaris have been found around the globe, and the number of fossils suggests they were a very abundant animal. 

Some of the other aquatic life that lived in the Cambrian ocean include:

  • Hallucigenia
  • Wiwaxia
  • Opabinia
  • Aysheaia
  • Ottoia
  • Pikaia

There is still plenty to learn about the Cambrian environment, and at the time Anomalocaris was one of the most advanced species.

Anomalocaris was the "top dog" of its time
Anomalocaris was the “top dog” of its time | dottedhippo via iStock

Very few animals at the time could compete with Anomalocaris, and being the apex predator of the time they had very few threats to worry about. 

Cultural Significance

Anomalocaris represents some of the earliest known life on earth, and is the face of the Cambrian period that occurred around 484 to 541 million years ago.

Large theropods such as Spinosaurus, and Ichthyosaurus are known for being the top apex predators of the Mesozoic period, while Anomalocaris fills that role in their time period.

Paleontology is important in learning how to decode fossils, and helps discover what ancient species lurked earth millions of years ago.

The mistakes made on Anomalocaris have been corrected, and was a valuable experience that other paleontologists can learn from as they further their research. 

Frontal appendage of Anomalocaris canadensis
Frontal appendage of Anomalocaris canadensis | James St. John via Wikipedia CC BY 2.0
Mouthpiece of Peytoia nathorsti which was originally assigned to the species above
Mouthpiece of Peytoia nathorsti which was originally assigned to the species above | James St. John via Wikipedia CC BY 2.0

Games, movies, and other types of media about early life on earth often get their inspiration from Anomalocaris, and their fossils. 

Anomalocaris is a species that has been essential in understanding the early forms of life, and how they evolved over time. 


Gage Beasley Prehistoric's Anomalocaris Concept
Gage Beasley Prehistoric’s Anomalocaris Concept

Anomalocaris has been an anomaly in paleontology, and a lot has changed about their consensus since their first discovery.

Not only have these animals’ size, and appearance changed over the years, but by analyzing fossils left behind it has become more clear just what type of animal Anomalocaris was.

At a time when most of the life existed in the ocean Anomalocaris was one of the largest animals, and was one of the first apex predators to exist. 

You can see some traits of Anomalocaris that are similar to animals today like shrimp, and dragonflies, but the Anomalocaris lived in a time when animals did not even exist on land. 

There is still lots to learn about Anomalocaris, but scientists have done their best to correct the mistakes made in the past about these animals. 

It is likely that some of what is known about this ancient marine animal may change in the future as more studies come along.

The Cambrian period experienced one of the greatest diversifications in life, and some of the animals that lived alongside Anomalocaris have ancestors that are similar today. 

Anomalocaris dominated its time period around 500 million years ago, and their presence had an evolutionary effect on the life around them that can be seen even some animals alive today.


How quick did Anomalocaris swim?

Anomalocaris is believed to have a similar swimming speed to modern water bugs, and their estimated movement speed is around 1 to 3 BL/s (body lengths per second).

The undulating movements and flaps on the sides of their body allowed Anomalocaris to swim effectively even without needing a complex brain, and their body acted as a single fin.

What was unique about the Anomalocaris vision?

Anomalocaris at the time had one of the most advanced eyes, and this was likely due to their predatory nature, and the dark ocean environment they lived in. 

These animals had compound eyes that gave them nearly 360 degrees of vision, and extremely advanced eyes for animals of the time. 

Dragonflies and bees are animals today that have similar compound eyes, but Anomalocaris had some of the largest compound eyes, with some estimates having close to 30,000 lenses in each eye. 

Are Anomalocaris and shrimp related?

Not only do Anomalocaris and shrimp look similar, but both animals’ origin date back to the Cambrian period, and belong to the larger phylum of Arthropoda.

While both are arthropods, Anomalocaris is a member of the extinct radiodonta order, while shrimp belong to the Decopoda order. 


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