From Tiny Trilobites to the Colossal Megalodon
Life of the Seas
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While dinosaurs and other terrestrial animals tend to garner the most attention, perhaps the most complexity of life can be seen in the water from lakes to oceans. In water, the constraints of such factors as gravity and transportation across land do not pose the same problems. As a result, sea creatures were able to diversify extensively in several events that defined the power of a water environment as a catalyst for evolution.
Check out the Life of the Seas gallery!
Trilobites
While many organisms appeared and perished throughout the fossil record, trilobites are one of the most well known prehistoric creatures for their abundance. This iconic group of extinct sea arthropods diversified into many different shapes and sizes and thrived over the 270 million years that they existed.
The Peanut Trilobite
This trilobite plate contains several specimens of Itagnostus interstrictus, a small genus of trilobites that appears similar to a peanut.
It is part of a group of trilobites called agnostids. They all resemble this peanut shape and are known to be the smallest type of trilobites, appearing like specks.
They existed during the Middle Cambrian, around 513 to 501 million years ago, when most of the Earth was covered with water. This was directly after the pivotal event of the Cambrian explosion. All major animal groups (phyla) appeared during this time, allowing for great diversification that allowed small creatures such as these to appear and survive.
Flip through the gallery to see all the I. interstrictus on this plate and their different sizes.
Here is another I. interstrictus plate. You may have noticed some differences between this plate with the previous. Flip through the gallery to learn more!
What's with the color?
Both of these specimens come from the Wheeler Shale in Utah, which is renowned for the trilobites found there. You can see other specimens from the Wheeler Shale in this exhibit!
The most common color Wheeler Shale specimens are found in is dark gray and black, which is what is seen with the lower I. interstrictus to the right. This color is a result of the trilobite being replaced by cryptocrystalline calcite during fossilization. Cryptocrystalline means a crystal structure that is so small and fine that it cannot even be clearly seen under a microscope.
In some cases, a reddish-brown color can be observed, like the upper I. interstrictus to the right. This color is a result of the trilobite being replaced by iron oxide instead.
This is why color is not always the best way to determine where a fossil could be from. The same location can produce a multitude of different colored specimens!
The Iconic Trilobite
The specimen to the left is an Elrathia kingii trilobite. It is one of the most common trilobite types found in the United States. As such, whenever a person thinks of a trilobite, E. kingii is the one that often comes to mind.
E. kingii is highly concentrated in the Wheeler Shale, along with agnostids like the I. interstrictus above. During the Middle Cambrian, the two lived alongside one another, resulting in plates to be found with both present.
While the most evident specimen to the plate on the left is the complete E. kingii, you may have noticed bits and fragments of other trilobites throughout.
Flip through the gallery to see all that is within this plate!
Where's the cheeks?
Earlier, E. kingii was mentioned to be one of the most iconic trilobites. Yet, with the specimen to the right, why does there seem to be something missing?
If you thought the E. kingii was incomplete, you were right in noticing it is missing its cheeks. The question then is what happened to those cheeks?
E. kingii was a trilobite, meaning it possessed an exoskeleton much like modern arthropods today, such as lobsters and crabs. When arthropods grow, they have to shed their existing exoskeletons in a process called molting, leaving behind an empty "shell" as they develop a new, bigger exoskeleton.
The E. kingii to the right is not the actual trilobite but instead a molt, the left behind exoskeleton. That is why no cheeks are observed.
The Moroccan Trilobites
The Index Trilobite
The specimen to the left is a Flexicalymene trilobite from Morocco. It lived during the Ordovician, the time period directly after the Cambrian, around 485 to 444 million years ago. The Ordovician is well known for its diversity of marine life that included invertebrates like trilobites and brachiopods.
Flexicalymene is known for being an index fossil in the Ordovician. Index fossils are fossils whose age is known to help in dating other specimens found in the same strata, or rock layer, as them. To be an index fossil, it must be easy to identify, widespread, common, and found within a short period of time. Flexicalymene meets these requirements, allowing other specimens found alongside it to be dated to the Ordovician.
While this specimen was found in Morocco, Flexicalymene are often found in North America, especially in the state of Ohio. They are also usually found in an enrolled state, much like a roly-poly. Rolling may have been a defensive tactic to protect their softer exposed ventral side.
Compared to the trilobite specimens earlier, this Flexicalymene is not on top of any rock. This specimen has been removed from its matrix to be just the trilobite itself.
The Bug-Eyed Trilobite
The specimen to the left is a Hollardops trilobite from Morocco. It lived during the Devonian, around 419 to 359 million years ago. The Devonian is well known for being the Age of Fishes with the appearance of some of the earliest sharks, lobe-finned fishes, and placoderms. Placoderms were armored fish that were one of the first fishes to possess jaws.
Hollardops is an example of the diversification of trilobites and the amazing traits they can show. With this Hollardops specimen, the most alluring characteristic is the highly intricate, complex eyes that resemble those of bugs today.
Notice the tiny pustules (bumps) that can be seen on its cephalon, especially on its extending genal spines.
With its current position on the matrix, it appears to be in a lifelike pose, giving an example of how Hollardops might have moved on the ocean floor.
Flip through the gallery to learn more about the exquisite details of this specimen.
The Golden Trilobite
While the trilobite specimen to the right appears it is made of gold, do not let looks deceive you. This is actually a very rare and unique pyritized trilobite. Pyrite is commonly known as fool's gold.
This specimen is a Triarthrus eatoni trilobite from the Lorraine Shale in New York, which contains the famous Beecher's Trilobite Bed site known for its pyritized trilobites. It dates back to the Late Ordovician, around 423 to 428 million years ago.
While all the other trilobites in this exhibit are the fossilized exoskeletons, this specimen is unlike any other. The reason it is so rare and unique is because of soft tissue preservation that can be seen of the legs, antennae, and gills. With such tissues preserved, we are able to really see what a trilobite actually looked like.
This exquisite soft tissue pyritization has allowed paleontologists to learn extensively about trilobite anatomy. In fact, some pyritized trilobites from this area have been discovered with eggs!
You can learn more about pyritized trilobites and this specimen with this video.
Ammonites
Along with trilobites, ammonites serve as an easily recognizable prehistoric animal with its coiled shell and squid-like appearance. While this group of cephalopods first appeared around 450 million years ago (subclass Ammonoidea), true ammonites (order Ammonitida) appeared during the Jurassic Period around 200 million years ago and lasted until the end of the Cretaceous 65 million years ago, perishing with dinosaurs.
The Golden Ammonite
Much like the previous pyritized trilobite, the ammonites in this matrix appear to be made out of gold, but they are examples of pyritized ammonites. However, unlike pyritized trilobites which are extremely rare due to their soft tissue preservation, pyritized ammonites are far more common and are seen with just their shells fossilized.
This specimen is a Pleuroceras ammonite from Germany. It dates back to the lower Jurassic (upper Pliensbachian), which is around 185 million years ago. The Jurassic period is well known for the dinosaurs that flourished, including Allosaurus and Stegosaurus.
To undergo pyritization, low oxygen conditions with rapid burial under sediments is needed along with sulphate reducing bacteria and reactive iron in the water to facilitate the process. The result is this beautiful golden luster given by the pyritized shells.
In this particular matrix, there are several ammonites that show the detailed spiraled shells and the interior of the shell chambers. Flip through the gallery to see the ammonites!
The Leafy Ammonite
This specimen is a Cleoniceras ammonite from Madagascar. It dates back to the Cretaceous (Albian stage), which is around 110 million years ago. The Cretaceous Period is one of the most recognizable time periods in prehistory with some of the most loved dinosaurs, including Tyrannosaurus rex and Triceratops.
After polishing the ammonite, the result is this mesmerizing leaf pattern throughout the shell. These intricate lines are actually suture lines that indicate the locations of the septa, the walls that divide the chambers of the shell. The chambers of an ammonite were usually filled with fluid and gas. Suture patterns are one way ammonites can be distinguished from one another.
Click on the image to see the suture pattern of this Cleoniceras in closer detail!
Shells
While ammonite shells are perhaps the most iconic fossil shell, there are many different prehistoric animals that possessed shells, many of which look similar to animals today. Some of these shells may look familiar or modern, but they actually once belonged to ancient animals millions of years ago.
Butterfly Shells
These specimens are Mucrospirifer. They date back to the Middle Devonian, around 393 to 383 million years ago. Because of their winged appearance, they also go by the name "butterfly shells."
Mucrospirifer is part of a group of marine animals called brachiopods that have upper and lower shells. If you look closely at the ones to the left, you can see the two shells that have been fossilized together.
Brachiopods are some of the most widely available and found fossils due to their abundance, diversification, and distribution. For example, Mucrospirifer can be found everywhere around the world except Antarctica and Australia.
Brachiopods, including Mucrospirifer, are known to be filter feeders, straining floating food particles in the water.
Check out the detail of the Mucrospirifer shells in the gallery to the left!
Mystery Shell
Unfortunately, some fossils lack any noticeable diagnostic features or important information on their location that it becomes near impossible to assign proper identification.
The shell on the right is of unknown classification or location, which means we are not able to easily tell how old it is.
However, it is interesting to note how this shell bears resemblance to a seashell you might find on the beach, showing how some present day organisms appear the same as those millions of years ago.
Snail Shell
This shell also lacks proper information to identify and date it, like the mystery shell, but its morphology (form or shape) is characteristic of a gastropod.
Gastropods are a group of mollusks that also include snails and slugs. If you look at the spired shape of this shell, it does look similar to what you may see with a modern day sea snail and its turban or cone shell. Thus, we are at least able to identify this fossil as a gastropod shell.
Sometimes, animals today are used as present day counterparts to compare with prehistoric animals as similar structures, like shells, are thought to be used in similar or the same way then and now. As you look at fossils, try to make connections with living animals you know!
Marine Reptiles
Prehistoric marine reptiles are often confused with underwater dinosaurs, but that is a common misconception. Marine reptiles were some of the biggest, fiercest predators of the seas, preying on such animals as ammonites. They first appeared during the Permian Period, around 299 to 252 million years ago, known as the Age of Reptiles.
Killer Reptile
This tooth is from a mosasaur. The mosasaurs were a group of large marine reptiles that roamed the seas as an apex predator. It comes from Morocco and dates back to the Late Cretaceous, around 101 to 66 million years ago, going extinct alongside dinosaurs.
This specimen is an example of a tooth crown, the exposed part of the tooth that would help the mosasaur eat, much like with what you see with your own teeth. The glossiness of the tooth is the enamel, the outer layer that protects the tooth.
The root, which is what anchors the tooth to the jaw, is missing. Why is that? This tooth may have fallen out of the mouth while the mosasaur was still living and fossilized on its own. Finding fossil teeth with roots are rare as it requires the animal to have died with the tooth still anchored to the jaw so that the root can fossilize as well.
Sharks
Sharks today often hold the title as a group of ferocious fish due to their menacing teeth and prowess in the ocean. While the diversity of sharks today are remarkable, prehistoric sharks had even more unusual and deadly features that would strike fear in the ancient seas. The first fossil evidence of sharks, some scales, are from the Late Ordovician around 450 million years ago!
The Ancestor
This tooth is from Cretalamna maroccana, a species of shark part of the genus Cretalamna. It comes from Morocco and dates back to the Late Cretaceous, around 101 to 66 million years ago, with the shark probably roaming around the seas competing against such animals as mosasaurs.
Cretalamna existed for about 60 million years from the Late Cretaceous to the Eocene Epoch. It is known as the ancestor of some of the biggest sharks that ever lived, including the infamous Megalodon and the older Otodus angustidens. Although the ancestor of some megatoothed sharks, the Cretalamna was medium-sized (2.3 to 3 meters in length).
The teeth, as shown to the left, have a large, wide cusp (the main "triangle") with two lateral (side) cusplets (the smaller "triangles"). They can have bilateral symmetry or be asymmetrical. This tooth appears to display a degree of both.
The Descendant
This tooth is from Otodus obliquus, a species of shark part of the genus Otodus. It comes from Morocco and dates back to the Paleocene Epoch (66 to 56 million years ago) to the Eocene Epoch (56 to 34 million years ago).
Otodus is an extinct group of mackerel sharks, the same type of shark as the great white shark. Its name means "ear-shaped tooth." Fossil evidence suggests Otodus was a very large top predator. Fossils have been found across the world, including North America, Europe, Africa, and Asia.
Due to similar characteristics in tooth morphology with Cretalamna, Otodus is believed to have originated from that genus.
Notice that this tooth is not entirely complete and is missing some of its root in the upper left.
Gnarly Serrations
This tooth is from Hemipristis serra, an extinct type of weasel shark. It comes from the Peace River Formation in Florida and dates back to the Late Miocene, around 12 to 5 million years ago.
H. serra can be compared to the modern-day snaggletooth shark, but H. serra was much bigger with larger teeth. In fact, H. serra is suggested to have actively preyed on manatees (specifically Metaxytherium) based on teeth marks found on their bones.
The most striking feature of its teeth are the large, deadly looking serrations that give them a very unique appearance compared to other shark teeth. These serrations are an example of an evolutionary trait that is not seen with older shark teeth, such as the C. maroccana tooth from earlier.
An Extinct Tiger
This tooth is from Galeocerdo aduncus, an extinct type of requiem shark. It comes from the Pungo River Formation in North Carolina and dates back to the Middle Miocene around 16 to 12 million years ago.
It is part of the genus Galeocerdo that includes the species Galeocerdo cuvier, otherwise known as the modern tiger shark. G. aduncus is a now extinct species of tiger shark but has similarities to its modern-day relative. Compared to modern tiger shark teeth, G. aduncus teeth are less broad and smaller with similar shaped serrations.
Like the modern tiger shark, G. aduncus had a very free diet, eating almost everything in the water from fish and squid to other sharks.
Mystery Shark
This tooth is so worn with no noticeable diagnostic features that it has not been identified yet. With no location, the age of this tooth is also unknown.
Much of its detail is now gone or very damaged, including its root, rounded tip, and a crown that may have had serrated edges. The bourlette, a v-shaped area of thin enamel, is no longer present as well.
More research may eventually yield an identification on this tooth in the future.
Big Tooth
Out of all the ancient creatures of the sea, perhaps the most famous is the mighty megalodon, seen in all areas of pop culture from books to films. With infamously large teeth and jaws, there is no question why megalodon has solidified its standing as one of the fiercest predators that once roamed the ocean.
Megalodon was a type of mackerel shark that existed during the Early Miocene to the Pliocene, around 20 to 3.6 million years ago. Based on the fossil record, it had a cosmopolitan distribution, meaning megalodon was widespread and could be found across the world.
Although you have probably seen a recreation of a megalodon, whether a physical model or drawing, what it actually looked like is unknown. Sharks are known to have cartilaginous skeletons that decompose rapidly and are not able to fossilize as readily as bones. Estimates on megalodon's size and shape are based mainly on teeth. For example, the left megalodon tooth above measures just under a whopping 6 inches! Most teeth are between 3 to 5 inches. The left tooth above most likely came from a megalodon that was at least 40 feet in length!
Fun fact: Megalodon teeth are usually measured on the slant, from the tip to the longest end of the root.
What's the Genus?
Megalodon is actually the species name of the shark. When referring to organisms, a genus name is also usually included, such as Hemipristis serra. In this case, Hemipristis is the genus, and serra is the species. This naming system is called binomial nomenclature.
With megalodon, the classification gets a bit more complicated. Megalodon is at the crossroads between its ancestors and descendants. Due to transitional fossil evidence, it is considered a chronospecies, meaning it displays evolutionary change with features that differ from its ancestor but not quite part of an entirely new group. As a result, you may have seen many genus names paired up with megalodon, such as Carcharodon and Carcharocles. Paleontologists argue which genus megalodon exactly falls under, and there is still much debate as to its proper taxonomic classification. The current consensus is Otodus megalodon.
If you are confused, think about it like this. You have a group of marbles of varying colors and sizes and decide to group them based on color and size. You have a group of large yellow marbles and another group of small red marbles. Suddenly, you discover a marble that is large and red, almost like a transition from the large yellow marbles to the small red ones. Which group do you put it in? Is the size more important or the color? There really is no clear answer.
Scientists have to consider many factors and characteristics when classifying different organisms. If anything, megalodon is a testament to the ever-changing nature of paleontology and how new fossils can yield monumental changes to current understanding.
Stay tuned for new specimens!
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