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Paleocene Fossil Identification Guide for the Potomac River


Thumbnails of Types of Paleocene Fossils


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Sharks

Shark teeth are by far the most common Paleocene fossils found along the Potomac River. A careful searching the gravel bars will produce at least a few teeth.
To learn all about Sharks, go to the Shark Gallery .



Anomotodon novus (Winkler 1874b)
Extinct Goblin Shark

These fossil Goblin sharks are a smaller genera than the living goblin sharks.

The teeth rarely exceed 1 inch,are very slender and have smooth enamel. They look very similar to Sand Tiger Teeth (Carcharias sp.).

One way to distinguish these fossil shark teeth from Sand Tiger teeth is they are very slender and do not have the large cusps that sand tigers do/ The laterals instead, have an enamel shoulder, while the anteriors have a very reduced cusp. If the tooth is very worn, it is nearly impossible to distinguish it from a small fossil sand tiger shark tooth.

For information about Goblin sharks including pictures and vidoes, go to the Goblin Shark Gallery


These are a type of Goblin shark. They are smaller than the extant Goblin shark. These fossil shark teeth are fairly common along the shores of the Potomac, however, if worn, they are difficult to identify.
Aquia Formation, Piscataway Member
Paleocene, ~56-59 m.y.
Potomac river, Charles Co., MD




Carcharias hopei (Agassiz, 1843b)Extinct Sand Tiger Shark

Sand tiger teeth are very hard to identify, the key to identifying this species from the other sand tigers in the aquia formation is their smooth enamel; they have no striations.


These fossil sand tiger shark teeth are abundant.

The left most tooth is a profile view. All teeth are anteriors except the rightmost one, which is a lateral. The top tooth is a lingual view, all others are labial views.
Aquia Formation, Piscataway Member
Paleocene, ~56-59 m.y.
Potomac river, Charles Co., MD




Cretolamna sp. (appendiculata?)
Extinct Mackerel-type shark

Cretolamna is a small type of mackerel shark. They are common along the Aquia Formation.


Cretolamna appendiculata fossil shark teeth from the Potomac River - Aquia formation




Otodus obliquus (Agassiz, 1843b)
Extinct Megatooth Shark

These self evident teeth are the second most sought after teeth in the Aquia formation (the first is the rare Palaeocarcharodon orientalis). O. obliquus teeth can reach slant heights of up to 4", however anything over 2.5" is rare for this location. Small teeth around an inch in size are fairly common.
This shark is probably the ancestor of the Giant Megatooth shark, C. megalodon.

Read about the Megalodon Shark to see how Otodus fits into this lineage.


The Otodus fossil shark teeth found along the Potomac River are smaller than their Moroccan counterparts. They are usually around an inch in size. Sometimes shark teeth over 2 inches can be found.
Aquia Formation, Piscataway Member
Paleocene, ~56-59 m.y.
Potomac river, Charles Co., MD




Paleocarcharodon orientalis (Casier, 1960a)
Extinct Pygmy White Shark

These enigmatic teeth are the most sought after teeth in the Aquia formation, and probably some of the more sought after fossil shark teeth in general. This is because these sharks only existed for a very brief geologic time period in the Paleocene. This means they also have a very limited geologic range.
In North America they are mainly found in a unit of the Aquia formation. They are also found in parts of Morrocco and Russia.

Identification: These teeth look similar to a small great white shark tooth. However, Paleocarcharodon sharks are not related to Great whites. They were most likely a dead end lineage. Paleocarcharodon teeth have irregular and coarsly serrated blades, and often have coarsly serrated cusps. The average size of these teeth in the Aquia formation is around an inch (2.54 cm).


This is a rare tooth, and the only one I have found. It was found underwater while walking back up river from a collecting trip
This specimen has worn serrations, and probably had cusps that are worn off.
Aquia Formation
Paleocene, ~56-59 m.y.
Potomac river, Charles Co., MD






Striatolamia striata (Winkler, 1874b)
Extinct Sand tiger Shark

Identification: The key to identifying Striatolamia sp. from Carcharias hopei is that Striatolamia sp. have striations on their enamel, where Carcharias


These fossil shark teeth are abundant, especially small ones of less than 1".
In this image, the box shows what the striations look like. They are tiny grooves that run up the enamel of the teeth. if you run your fingernail over them it feels like grooves in a record (if you know what a record is!). The striations may be worn off on very worn striatolamna teeth.

The Carcharias teeth found here DO NOT have striations, only Striatolamnia teeth do.
Aquia Formation
Paleocene, ~56-59 m.y.
Potomac river, Charles Co., MD




This is the largest Sand Tiger Shark Tooth I found. It is actually, the largest Striatolamia I have ever seen! It was found in about a foot of water along the Potomac.




Shark Vertebra

Shark vertebra are also found on occasion. They are generally small in this area, since most of the prehistoric sharks were small in size. They look like small disks.


Verteberal Centrum from a shark.




Rays

Rays are related to Sharks and Skates, as they are all in the Chondrichthyes Class. Fish in this class have a skeleton made of cartilage instead of true bone. What this means for the fossil collector is bones from these animals seldom fossilize. Occasionally a vertebra may be found, however mostly the hard shark teeth and ray crushing plates are found.

Myliobatidae family
Eagle Rays

Rays have modified teeth that form flat crushing plates. These crushing plates are adapted for eating mollusks and crustaceans on the sea floor. They suck their prey up like a vacuum and simply crush them between their upper and lower crushing plates.


The first fossil is the central part of a ray dental plate, the second is one broken in half.






Reptiles

Reptile fossils are also common along the Potomac river. Most reptile fossils are from Crocodiles and

Eosuchus, Thoracosaurus, and Hyposaurus
Marine Crocodiles

Crocodile Teeth, Scutes, and bone fragments are often found along the Aquia formation. There has been little research on the crocodilian fauna of the Aquia formation. From the scant research, there appears to be at least three genera of salt water crocodiles present: Eosuchus, Thoracosaurus, and Hyposaurus

Unfortunately, isolated fragments such as teeth, cannot be identified to even a genus level.




Crocodile Teeth

Crocodile teeth come in all shapes and sizes, and are usually black.


Fossil Crocodile teeth are a common find along the beaches of the Potomac river.



Crocodile Skull Fragment - Eosuchus

This is a fragment from the skull of a smaller crocodile, Eosuchus minor, found along the potomac. A nice geologist and website visitor correctly identified this fossil for me. Thanks!


Crocodile fossil skull fragment of eosuchus minor from the Potomac River, Maryland - Paleocene - Aquia Formation





Crocodile Humerus Fragment
(leg bone fragment)

While bone fragments of crocodiles are often found, identifiable ones are less common. This is the distal end of a right humerus from a rather large crocodile.


Crocodile humerus fragment of from the Potomac River, Maryland - Paleocene - Aquia Formation



Crocodile Scute Fragment

Crocodile scutes serve as body armor. They are bone plates just under the skin throughout most of a crocdiles head, neck, back, and upper half of the tail.
Scutes also serve to warm the crocodiles blood (as crocs are cold blooded animals). Blood collects in the little dimples on the scutes, when the crocodile basks in the sun, the blood in the dimples warm up and circulate through the crocodiles body.

Crococile scutes can be differentiated from turtle scutes, as the dimples in crocodile scutes are much deeper than in turtle scutes.


This is a fragment of a larger scute. Notice the large dimple pattern in it.




Turtles: Testudine order

Turtle fragments are common in the aquia formation.




Turtle plastron fragment


This is a scute from of the bottom of a turtle shell (the plastron). There are no patterns on the plastron, so it is very difficult to determine what type of turtle this came from.



Trionychidae family - Softshell Turtles
Trionyx sp.
Freshwater turtle

Scutes from the carapace of Trionyx are readily identifiable by their deep intricate patterns (which can be seen in both images). They are different from crocodile scutes in that the dimples in a crocodile scute are much deeper.


This is a carapace scute from the top of the turtle shell (the carapace). Notice the ligament-like attachment protruding in the side view of the scute from.






Invertebrates

Invertebrates are abundant in most fossil bearing formations in Maryland and Virginia.

Gastropods
Turritella sp.

There is a layer of gastropod internal molds along the Potomac cliffs. In this layer, the matrix is harder than the gastropod shells. So the shells erode, and internal molds are left behind. At times, entire cliffsides collapse and these molds spill out onto the beach.


Internal Molds of the Gastropod: Turritella.




Internal Molds of the Gastropod: Turritella.




Fossil Turritella shells.




Fossil Turritella shells.






Recommended Books Potomac River Shark Teeth:


** PLEASE DESCRIBE THIS IMAGE **

Fossil Shark Teeth of the World
by Joe Cocke, 2002

A great book for identifying all those teeth. This book is laid out "as simple as possible." It's ease of use and small size makes it great to carry during collecting trips. This book shows teeth from around the globe, but all the New Jersey teeth can be found in it.



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