More Fossils

Getting back to the fossils found in the creek —

These are pieces of a fossil sponge called a finger-like sponge.  They were irregularly knobby shaped masses with finger-like projections.

You can see impressions of other sea life embedded in some of them before they hardened.

One of the largest types of fossils was this stout shell of some type of clam (I believe).  I found several of them and they were always closed like this one.  Most were four to five inches long.

Here, you can see an exceptionally rich section of hardened mud embedded with a great variety of life forms. 

Tip: Click on a photo to see a larger version of the image.

Sea Lamprey

A species that might be mistaken for an American eel is the sea lamprey.  They generally look similar.  The mouth of the sea lamprey, however, is a sucker disk on the inferior side.  It is used to attach itself to a fish and cut into the body, sucking out it's blood.  The fish usually dies from blood loss or infection.  Compare the mouth of this creature with that of the eel in yesterday's post.

I had no idea they were indigenous to the Chesapeake Bay until I saw a great blue heron catch one.  I mistook it for an eel until I looked at the photograph closer and saw the sucker disk on the underside of the lamprey.  It wasn't long after the first incident that I saw the same heron catch a second lamprey.  I'm not sure how common they are in the watershed, but since the Bay is open to the sea, it shouldn't be surprising that they are present.

American Eel

Rockfish and herring are examples of anadromous fish - fish that live in the oceans, but must return to fresh water to spawn.  Eels are an example of just the opposite.  They are a catadromous species which spawn in the oceans and live most of their life in fresh water.  The elvers pictured in this photograph were not born there but have actually travelled thousands of miles to reach this stream! 

In one of the amazing stories of the natural world, adult eels from all over the east coast of North America migrate to the Sargasso Sea, an area in the middle of the Atlantic Ocean east of the Bahamas and north of the West Indies where they spawn and then die.  Newly hatched eels start out as something called a leptocephali.  Carried by ocean currents, they drift toward the coast for about a year as they slowly transform into elvers.  They enter the estuaries along the coast where they mature and live for as many as twenty years before adults make the migration back to the Sargasso Sea.

My brother was fishing in the Patuxent last summer when he hooked a two foot adult eel.  I would have cut the line and my losses, but he had never hooked one before and didn't know how slimy they are.  He got some of the slime on his shoe which was still there months later despite several attempts to clean it off.  Next time, I'm pretty sure he will just cut his line.

While American eels have long been used as bait, they are edible and are considered a gourmet item in Europe where they are shipped by some commercial fisherman in the Chesapeake.  Their numbers have been in slow decline and catching them at maturity when they close to reproducing may be part of the reason.

River Otter

I would never have associated a woodland creek with a river otter.  While exploring the creek that contained the fossils, I began noticing animal tracks along the creek.  Some were raccoon but others I didn't recognize.  I sent an inquiry and photo to the Department of Natural Resources and was surprised to learn the tracks were made by a river otter.  The person at DNR said otters will take day trips up creeks searching for food.  This creek does connect to a larger creek which, in turn, flows into the Patuxent River.

I wondered it it wasn't more than a day trip because every time I would visit the creek, I would see plenty of fresh tracks, even directly following heavy rain.  It meant either the otter was visiting very frequently or it was living nearby even if temporarily.

I saw some evidence of what I would guess an otter's den would look like on a high bank and the opening seemed to be a just about the right size.  When I consider the usual variety of animals known to inhabit these woods, otter den seems like a pretty good guess.  Especially when you consider how it is situated.

As far as food in the creek, there didn't seem to be much to eat.  I never saw any fish.  There may have been some crayfish present, but I never saw any - despite turning over quite a few stones. On a couple of occasions, though, I did see small elvers, the young of the American eel.  I'm pretty sure they would be on a river otter's menu.  More about them tomorrow.

Fossil Creek III

There was a point in the stream where the flood layer became much thicker.  Most of this series was taken in that area.  You can see a leaf in the first image which gives you something of known size to compare to.  Some were reminiscent of petroglyphs.

You can also see where veins of different color mud run through.

The most interesting impression in this area was this image of a an outline of something that was fairly large.  Again, the leaf gives you a standard of comparison.  The impression itself was about two feet long and looked like it could possibly have been a shell, but if it was, it would have been far larger than most any shelled creature living today.  Clearly seen are some spiral indentations much like those seen on a turret snail, but turret snails are often only an inch long.

I also happened across one rock with the impressions of what looked like a group of barnacles in that area.

Fossil Creek II

In this image, you can see a zone of mud that constituted the flood layer where the sea life was deposited.  Once the flood waters receded, the mud dried and hardened.  All of the shelled creatures would have died when the water receded and their soft tissues decayed, leaving only the remnants of the shells themselves. 

Over time, the stream cut through the flood layer, loosening the rock by natural forces.  In cold winters, ice crystals form in cracks and crevices and, since ice expands, it forces the rocks apart.  In this image, you can see the ice crystals that had formed during a cold snap.

Here, you can see how a decaying bank frees up the rocks and gravity takes over.  Tree roots are another force accelerating the breakdown.

In parts of the stream, the water hasn't cut completely through the flood layer.  It creates a hardened sluice where almost nothing sticks, but gets rolled further downstream.

Fossil Creek

I have walked the length of most of the creek where I found the shell fossils and at some places, the
creek banks are simply sand or clay while at other places, the creek runs through harder rock layers. Here are a few photos where you see fossils in the stream bottom

Over time, the erosive action of freeze/thaws and heavy rains break up the rock layers and heavier
rains begin to carry the smaller rocks down stream.

The fossil rocks are easy to spot although if they are face down, the back side is usually just plain rock in appearance.