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The Guide To Prehistoric Animals

Updated on April 15, 2016


This is a page dedicated to all things prehistoric. Spanning from the Precambrian period to the Quaternary period, life has developed from a single cell into highly complex organisms. Some of the body plans evolution produced were outlandish, bizarre, fascinating and intriguing. With this page I hope to shed some light on the lesser known organisms of Earth's past and learn about newly discovered organisms as I do my research. I hope you enjoy reading along!

Prehistoric Sharks

Helicoprion Tooth Whorl
Helicoprion Tooth Whorl
Edestus Jaw Fossil
Edestus Jaw Fossil
Artist's depiction of the Edestus by Ray Troll
Artist's depiction of the Edestus by Ray Troll

And Now, My Favorite! Prehistoric SHARKS!

Of all the weird and wonderful creatures, Sharks are my personal favorite. They have been around for over 400 million years as top predators and have undergone relatively few changes over that span of time. They are and have been, in my opinion, as close to a perfect predator as one can be. Throughout their time there have been some pretty peculiar traits developed and then left behind... Here are some of the strangest!

The "Can-Opener Shark" Helicoprion:

This is an elasmobranch relative of sharks but is more closely related to their cousins the Chimeras. Like all elasmobranchs, its entire skeleton was made up of cartilage, with the exception of the teeth. As a result, the teeth are the only thing left to fossilize. When paleontologists discovered strange spirals of teeth, they didn't know what to make of them. After analysis and close examination it was determined the teeth were very similar to known shark species. For a long time it was unknown weather the specimens represented the top or bottom set of teeth until a fossil of a similar species was discovered with an imprint of the shark's body shape and features. This showed the scientists that the "tooth whorl" was on the bottom jaw of this odd shark species.

Stethacanthus "The Ironing Board" :

While it may look like a fictitious creature from a B movie... This odd ball shark really did have a modified dorsal fin that look like an ironing board! This fin rose above the back and had rough, short spikes all over the flat top. These spikes were modified dermal denticals, the material that makes up the skin of all sharks. It is unknown exactly what purpose this elaborate head piece served, though it most likely was a result of sexual selection. They also possessed elongated, trailing bands of tissue extending from the pectoral and ventral fins that were believed to be a result of evolution attempting to streamline this strange looking shark.

Edestus Gigantus "Scissor Tooth" :

This shark really just doesn't make sense. The strange lower jaw bones have been discovered and have caused more questions than they have answered. This shark had a similar body shape to many present day pelagic sharks, but its jaws were truly bizarre. The jaws sported one row of large serrated teeth on top and bottom that lined up and acted like scissors, hence the name "scissor tooth". This shark grew to around 20 feet, about the size of most modern day great whites. This shark truly had a face only its mother could love!

Prehistoric Oceans Quiz!

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The Dunkleosteus Skull
The Dunkleosteus Skull
Dunkleosteus size comparison
Dunkleosteus size comparison


If you took the quiz above, you probably know what the name Placoderm means: Plate skin! These fish ranged from small buggers like the Cephalaspis, to enormous Dunkleosteus. Placoderms are an extinct class of prehistoric fish that had articulated bony plates covering the entire head and thorax. They were among the first fish to have a jaw, which is believed to have evolved from the first gill slits. This jaw also lead to the development of sharp bony projections from the jaw, the first rudimentary tooth-like structures. The state was then set for the world's first "Super Predator".

The Dunkleosteus was one of the largest fish of all time, growing just short of 40 feet long. It sported some pretty heavy duty headgear that was up to 3 inches thick and solid bone. Every part of its head including the eye orbit was armor plated. The weight of its skull alone is believed to keep this behemoth from moving very quickly, at least for very long. Even so the Dunkleosteus has been classified as a hyper-carnivore. The majority of Dunkleosteus fossils found have had multiple large fish and bone boluses in their stomachs. The Jaw of this predator was a 4 bar linkage mechanism that allowed for more muscle connections resulting in the ability to open its mouth in 20 milliseconds and the power to close its mouth with the force of 1,660 lbf . This bite force was necessary because the prey of this heavy weight had armor as well. While it did not have proper teeth, its razor sharp bony ridges were highly effective. Though it was built tough, sadly the Dunkleosteus died out after only a 40 million year run, a relatively short period of time.

Cephalaspis  Note the armored bony head
Cephalaspis Note the armored bony head

The development of bones and brains


The Cephalaspis was one of the first armored fish. Like all other fish during its time, it was jawless. They evolved a primitive tail and fins as well as an armored head as a defense from predators such as brontoscorpions. While the bony helmet was useful for protection, it was heavy and would not have allowed these fish to swim swiftly for any notable distance without resting. This fish also had evolved specialized sensors in it's head that could sense minute pressure changes in the water, a sense all fish have to this day. This ability is due to a nervous system that was highly advanced for its time. They possessed the first complex brain which allowed them to retain information.

Sea Scorpion

Pterygotus biggest arthropod of all time. At nearly 6 feet long it was a top predator and scavenger. Like most arthropods, it is believed to have been an opportunistic feeder and only hunted when necessary. One theory is that it hunted much like an angel shark does today, by burying its body beneath the sand and only exposing its eyes. This giant could lay in wait for a prey item, perhaps a brontoscorpio ( a smaller sea scorpion species) to walk by before rising up out of the sand and claiming its prey.

Orthocone Squid

This squid would put all modern-day squid to shame. At their smallest they were the size of a man... and their largest they were as long as a semi truck. Their shells were often elongated, rather like a unicorn horn, and were chambered like modern shelled cephalopods are today. These squid had large complex eyes and a rather advanced brain for their time, allowing them to strategize and learn.

Precambrian Life: The Beginning

The Precambrian period was 570 million years ago. The planet was completely unrecognizable. There was one land mass that was relatively small. The rest of the planet was covered in ocean, two actually, the Panthalasic and the Panafrican oceans. While the little dry land there was completely barren of any and all life, the oceans began teaming with a vast variety of life forms all descended from a single celled organism that was the first to be "alive". Life is believed to have first began in the Eoarchean Era, around 4.5 Billion years ago. By the Precambrian period, life had diversified into an amazing variety of simple and complex organisms.

In biology we are taught that there are requirements that need to be met to be considered a life form:

  • Have a Metabolism
  • Strive for Homeostasis ( internal balance chemically, temp etc.)
  • Can Grow
  • Responds to Stimuli
  • Can Reproduce
  • Can adapt to their environment through successive generations.

The precambrian world was hostile and rapidly changing. There was an unprecedented rate of diversification across hundreds of thousands of years. What had started as a single cell exploded into hundreds then thousands of different organisms. The rate of evolution is mind blowing. In the fossil record we see what was a barren empty world, and in the next layer of the strata, hundreds of thousands of organisms. Now at this point, all of the organisms were restricted to the ocean, life on land had not developed yet. The dry land was arid, empty of all life and had high volcanic activity.

Trilobite Fossil

Trilobite Fossil
Trilobite Fossil | Source


The fossil originally deemed to be a tail, but was actually a feeding arm of the Anomalocaris
The fossil originally deemed to be a tail, but was actually a feeding arm of the Anomalocaris
The Anomalocaris
The Anomalocaris

Sea Pen

Modern Day Sea Pen
Modern Day Sea Pen

The Devonian Period

The devonian period saw the first "significant adaptive radiation of terrestrial life". Adaptive radiation refers to the process by which animals and plants rapidly diversify into new forms due to changes in their environment such as the introduction of a new resource. Sporing plants began evolving specialized traits such as roots and leaves. These allowed for larger, more stable plants and an increased ability to absorb sunlight. The devonian period is known as the "Age of Fish" due to the high number of diverse species alive at the time. Ray and lobe finned fish came into play while placoderms were busy taking over the world's oceans. Certain fish began evolving muscled pectoral and pelvic fins that would evolve further to be legs. Sharks became more diverse, and the sizes of the majority of predators continued to increase resulting in killer giants roaming every aquatic environment on earth.

Cambrian Critters

The majority of all the phyla that exist today came into being during the Cambrian period. That is not to say that the creatures then would be at all recognizable to us now... but they were the beginning, the ancestors of every animal alive and extinct.


'Trilobite' literally means "Three-Lobed". It is the name for a group of extinct marine arthropods that roamed the seas for nearly 270 million years. There were hundreds of species that sported all sorts of different armor including some pretty elaborate helmets! Their closest and perhaps only living relative is thought to be the horseshoe crab.


The story behind the discovery of Anomalocaris is quite funny. A very strange fossil was found by a young paleontologist sifting through shale rock. It looked rather like a shrimp ( see images on right)... but there was no discernible head... which, as you can imagine, was puzzling to the scientists that examined it. It was then deemed to be the tail of another prehistoric arthropod. Another fossil was found with the mouth , feeding appendages, and tail of an unknown creature. Many years later the dots were connected between the first odd fossil and the feeding appendages of the newer fossil found. Finally a full skeleton was discovered and the pieces finally all fell in to place. Anomalocaris is a bizarre arthropod that is believed to have been the top predator of its time. In the picture to the right you will see the shrimp-looking feeding appendages and large eyes. These were some of the first complex eyes to evolve. They greatly improved the Anomalocaris' effectiveness as a predator. It is believed to have fed primarily on hard bodied arthropods including trilobites. It could grow to up to 7 feet long.

Sea Pens

Sea Pens are a colonial marine cnidarian, a soft coral, that were very wide spread and numerous in the Cambrian Period. These creatures have remained virtually unchanged to this day. They are found in both shallow and deep environments and in many sizes and colors. As a colonial species, every 'pen' is a group of individual organisms acting in concert to survive.


The Haikouichthys is , or rather, was, the earliest known fish and one of the first craniates ( possesses a backbone and a distinct head). It was narrow and only grew to about an inch long. It was fist discovered in a formation near Haikou, Yunnan, China. This fish was an important step. Before craniates, complex organisms had extremely primitive nervous system... and if they were a bit more advanced, they possessed what is called a notochord. The notochord is a hollow dorsal nerve chord, the predecessor of the spinal chords in vertebrates today. The development of a head , a cranial space, allowed for the development of a specialized cluster of nerves that made up their rudimentary brains and primitive light receptors (early eyes).


Depiction of Haikouichthys
Depiction of Haikouichthys

The Precambrian World

Precambrian life was restricted to the ocean.
Precambrian life was restricted to the ocean. | Source
Epocs and Eras
Epocs and Eras
The Precambrian Earth
The Precambrian Earth

Leading up to the Cambrian

It all started with microscopic bacteria. These bacteria went forth and multiplied until they had just about depleted the ocean of their food source until a handy adaptation came into play: using the sun to produce food. Photosynthesis. This process resulted in the oxygenation of the oceans. "About 800 million years ago, oxygen levels reached about 21 percent and began to breathe life into more complex organisms. The oxygen-rich ozone layer was also established, shielding the Earth's surface from harmful solar radiation." 1

The stage was then set for an explosion of diversity, in a 'relatively' short period of time. This is known as the Cambrian Explosion.



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