Eclipse

The scientist in me will discard the notion that the stars, planets or infinitesimal planetoids have anything to do with guiding my life, beyond the "butterfly effect".  However, as a human I can't help but notice how celestial events help us to solidify memory and stir reflection.  I can feel the cold and hear the gasp of my 4-year old son when he first sighted Comet Hale-Bopp with his binoculars.  We mark our lives by the return of the Earth to the same position it was on significant days: birthdays; wedding anniversaries; death anniversaries; work anniversaries; commemoration of other significant events; and holidays.  Our nearest star, the Sun, is the ultimate source of energy for life on Earth and a threat to our existence (for example cosmic rays; coronal mass ejections; gamma ray bursts).  We tend to wake with the Sun and sleep in the dark.  Inability to perceive light or working odd hours throws our body clocks into a frenzies such as non-24 sleep-wake disorder.

Beginning of partial solar eclipse 23 October 2014. Photographed
at Park University.The last three solar eclipses have been obscured
by clouds in NW MO

An eclipse occurs when one celestial body casts its shadow onto another.  A lunar eclipse occurs when the Moon passes through the shadow of the Earth.  A solar eclipse occurs when the shadow of the Moon passes over the face of the Earth, apparently obscuring the disc of the Sun.  Eclipses are actually fairly common occurrences as viewed from SOMEPLACE on Earth, but rare in any ONE location on Earth.  You can expect to experience a solar eclipse in any one place on earth every 360ish years, on average.  Most of these events come and go with very little attention from the general populace.

Every now and again, one catches the public imagination.  These are usually total solar eclipses, since it is possible to look at the Sun without risking injury only during totality.  In the center of the path of totality, the sky will darken enough to see the atmosphere of the Sun (corona), planets and stars.  Diurnal animals will seek nighttime refuge and nocturnal animals will start to come out.  As the solar output dims, shadows change accompanied by a palpable cooling.  It is something that is totally out of the ordinary, and novelty sells.

Filtered view of the Sun

This is the experience being sold across the United States since at least 2015.  An eclipse with totality lasting about two and a half minutes.  The width of the total eclipse path in 2017 is about 70 miles and passes across the United States in a southeastward direction from the Pacific Coast of Oregon to the Atlantic Coast of South Carolina.  Some degree of partial eclipse is visible for thousands of miles on either side of the line of totality.  People from all parts of the world descended on little towns all across the United States.  Populations of areas along the path of totality typically doubled overnight.  Sales of all kinds of memorabilia were through the roof: branded eclipse glasses, t-shirts, posters, festivals...etc.

Take time to experience the world now, for you are a long-time dead

Setting up the camera to photograph the eclipse

One thing is for certain about almost any event that strikes a chord with a broad audience: that event will be over-hyped.  Especially if there is a dollar to be made.  While many experienced amusement at the hype, some individuals (even in the popular media) were openly disdainful of anyone that thought this was an interesting event.  There are always the contrarians, those who will go against popular sentiment just because.  There are those that are contrarians because it sells or is fashionable.  If you are not fascinated with eclipses, there is nothing that I can say to you to change your mind, and I won't try.  You have no sense of wonder about the natural world.

I don't have to convince my friend Ed, from Red Wing, Minnesota.  We have both recently lost close friends who were way too young to die.  Knowing that life is fleeting and wanting to experience the spectacle of a total solar eclipse, Ed hopped on a motorcycle with his daughter Marley and staged overnight looking for a break in the weather.  He ended up at the American Legion in Amazonia, Missouri.  Even though the clouds hid totality, he gave the eclipse a thumbs up.  I have some amazing friends.

Darkness falls on Park University as totality nears

There is a stark beauty to a rapidly changing natural canvas - a fantastic out-of-placeness.  More than that, I revel in the accomplishment of thinkers that can record and eke out complex patterns from data 2,500 years before the computer was a thing.  The Babylonians could predict within about 4 hours, when an eclipse would happen, somewhere on Earth.  Edmund Halley would further refine the ability to predict when AND where eclipses would happen.  The ability to predict the occurrence and extent of an eclipse to within a second of precision is a gigantic accomplishment.  Without understanding celestial mechanics and without computers, Babylonian astronomers could pull an astonishingly convoluted pattern out of a big data pile recorded in cuneiform on clay tablets.  It's all Greek to me.

A picture of my friend Ed and his daughter riding from MN to see the
eclipse in MO, taken by Marley and  thieved by me from Facebook

It is only during eclipse that we can really image the corona of the sun - which is key to predicting phenomena such as coronal mass ejections.  An eruption of mass from the Sun aimed at the Earth could bombard us with charged particles and x-rays that would fry our satellites, brick our electronics and destroy the electrical grid.  We got a very little taste of that on 13 March 1989, when a mass ejection hit Earth, causing a widespread blackout in Quebec, Canada.  Understanding space weather is paramount to maintaining our creature comforts, if not our very survival.

Observation of lunar eclipses made by Aristotle allowed him to conclusively state that the Earth is spherical.  He knew from projections of shadows from various geometric figures that a shadow with a rounded edge (such as that of the Earth onto the Moon) could only be produced by a sphere (suck it, Flat-Earthers).  Observations of solar eclipses revealing Bailey's Beads gave us our first indication that the Moon had mountains and valleys.  Eclipses are important because of what we can learn about Earth and its neighbors right here in the comfort of Spaceship Earth.

All That is Now

The eclipse begins

The much ballyhooed Great American Total Solar Eclipse of 2017 arrived to partially cloudy skies at 11:41:06 AM on 21 August in front of Mackay Hall of Park University in Parkville, MO.  The initial obscuration of the Sun's disc by the Moon occurred at about one-o'clock (30 degrees right of straight up).  Lunch was served on the Chapel Lawn, eclipse glasses were passed out and people dispersed over campus to view at various places.  I set up in front of the first building erected on the current campus on a solid, level surface.

Our last glimpse of the Sun in eclipse 21 August 2017

Good views of the eclipse were had all of the way up to the verge of totality.  As more of the Sun's light was blocked out, the shadows got longer, much like a winter's day.  Nadienne noticed that the butterflies had left the flower planters and I noticed that the mosquitoes were biting.  We all noticed that the cicadas started buzzing. About 10 minutes from totality the clouds became heavier, making it almost impossible to see the sun while wearing eclipse glasses or using solar filters, at times.  The clouds totally obscured any view of the sun at about 90 seconds before totality.  In the end, we were about 10 miles too far west.  The clouds held off for a long while to the east.  When totality occurred at about 1:07 PM, we were unable to see anything excepting clouds, but the skies darkened to twilight conditions and lights came on. 

After about a minute of darkness, it lightened up briefly.  Then it started lightning and thundering and the skies opened up, pouring down rain.  The deluge caused flash floods, water overtopped bridges and roads, and Mirror Lake reappeared at the National golf course.  In a time lacking technological savvy, this event would have been recorded with wonder as a Wrath of God event.

Sometimes you use Plan 9

Clouds over St. Joseph, MO on eclipse day

You can predict eclipses and they will come and go on time.  You can predict the weather, but can't do anything about it.  The weather leading up to the eclipse was beautiful.  Nadienne and I enjoyed a nice drive along the path of the eclipse through northeast Kansas and southeast Nebraska on Saturday.  Nearly every community had some kind of viewing area set up or even a festival of some kind taking place.  I had scoped out the yard, figuring where the sun was going to be and making sure I knew how to use the solar filter with my camera.  I bought a 12-pack of Leinenkugel Summer Shandy to enjoy while I took pictures in my backyard - right down the center of the path of totality.

When morning broke, the view outside was dismal.  Hardly a hint of blue in the sky.  The eclipse weather was definitely going to suck.  After checking around for weather, we decided to head to Parkville, which was just at the edge of the path of totality.  We'd get about 60 seconds, but it was better than seeing nothing.

Here comes the Sun!  You can't see a thing with
eclipse glasses on!

Then the clouds rolled in while we waited for the eclipse.  The kick in the teeth came as it started to rain.  Dejected, I nearly got in the car and rolled back home to St. Joseph, halted only by the memory of the parking lot that was traffic from Platte City to St. Joseph.  Not really seeing anything good on the cloud map, we decided to stay put and watch a live stream using on the projectors in a lecture room.  Less than a half hour before things got interesting, a break in the clouds appeared and held off long enough for us to see about 49% of the eclipse. Right before totality, thick clouds blocked our view: eclipsis interruptus.  We were clock (and cloud) blocked.  This just proved my theory of life: Always expect the worst - that way you are never disappointed.  If things go badly, you expected it - no disappointment.  If things go well - it's a bonus - no disappointment.  We didn't get to see totality, but we didn't expect to see anything at all - WIN!


And All That is Gone

Start of lunar eclipse 27 September 2015 viewed in St. Joseph, MO

I saw my first eclipse on the 9th-10th of February 1971 in Honolulu, Hawaii.  My Mom woke me up at night, which was weird.  Even stranger was that she wanted me to go outside and look at the Moon.  As we watched, a rounded edge of darkness crept across the face of the Moon.  What the heck was that?  Then Mom told me it was an eclipse.  We watched to totality, when the moon brightened up to a coppery color.  As the Moon began to reappear, I went back in the house to bed.  A local TV station was broadcasting the event - something that is difficult to find unless you stream it over the Internet.

On the night of 25 May 1975, I was sitting at a picnic table outside of our camper in Minnesota waiting for the moon to go into eclipse.  I had found the dates of the eclipses that would be visible to me for the next few years, and was waiting for this one. This time it was my Dad that came outside and watched with me as the Moon was blotted out by the Earth's shadow and then became an intense, angry red as it passed through totality.

I cut class for the first time on 26 February 1979.  The nefarious reason?  To see the solar eclipse that was occurring that day.  While St. Joseph, MO was not in the path of totality, we would be able to see the Sun eclipsed about 85%.  The event did not generate a lot of buzz and our school administration held no viewing parties.   I made my pinhole projector, asked to be excused to the library (which had windows facing the Sun) to do research for a paper, and sat through a few classes to watch as the light dimmed perceptively and then brightened up as the Moon slid over and past our view of the sun.  I did research for a paper all right, just not the one that was currently assigned to me.

Crescent Sun peeking through the clouds

On 10 May 1994, an annular eclipse sorely tested a marriage.  An annular eclipse occurs when the Moon is just far enough away from the Earth in its elliptical orbit that it can't quite obscure the disc of the Sun, resulting in a dark center with a light edge.  The day was very cloudy in Keego Harbor, MI that day.  Just as the eclipse hit annularity, a break in the clouds occurred and through the haze came a filtered image of this ring of sunlight around the Moon.  I asked Nadienne to get my camera, and between us we managed to drop it, shattering it into several pieces and exposing all of the film that had been in it.  The perfect picture...shot to hell.

I have observed close to 20 lunar eclipses and 6 solar eclipses.  Each one is locked away in memory.  I can close my eyes and see, hear and smell what that day or night was like.  What I was looking forward to, what the last and next disappointment would be.  This was my first real chance to see a total eclipse of the Sun, but the weather nicked me by 90 seconds and 10 miles.  Better luck next time.


And All That's to Come

The next lunar eclipse will come soon - a total lunar eclipse will occur the morning of 21 January 2018 and the setting moon will be in total eclipse as viewed from northwest Missouri.  The next North American solar eclipse will be an annular eclipse on 14 October 2023.  The next Great North American Total Solar Eclipse will be on 08 April 2024.  You will find me somewhere on the path from Dallas to Little Rock to Carbondale to Indianapolis to Cleveland to Niagara Falls (Niagara Falls?  Slowly I turned....).  Book your seats now, seven years is sooner than you think.

Great American Eclipse figure for 2024

Solar eclipses are due to a string of coincidences.  We have a moon, the orbital path of which crosses a path directly between us and the Sun from time to time during the new moon, throwing the Moon's shadow onto Earth.  The disc of the Sun is 400 times as large as that of the Moon, but the Moon is almost exactly 400 times closer to Earth than is the Sun.  This geometry makes it possible for the disc of the Moon to totally block out the disc of the Sun, especially if eclipse happens close to perigee (when the Moon is closest to Earth).  If the eclipse happens close to apogee, the increased distance between Earth and Moon decreases the apparent size of the Moon's disc just enough that the Moon cannot totally cover the Sun's disc, resulting in an annular eclipse. 
  

NASA figure of solar eclipse configuration

The force interactions between the Moon and Earth result in the Moon acting like a brake on the Earth.  As the rotation of the Earth slows, the momentum change causes the Moon to slip a little bit further away.  The rate of change in the Earth's daily rotation slows down by about 4 hours every billion years and the distance to the Moon increases by about 3.78 centimeters per year.  In 1.2 billion years (give or take an hour), the Moon will be distant enough from us that its apparent size will always be smaller than that of the Sun - and eclipses will be a thing of the past, replace by transits of the Moon across the Sun's disc.

And Everything Under the Sun is in Tune

I'm being followed by a Moon shadow, Moon shadow, Moon shadow
But the Sun is Eclipsed by the Moon

This time I was armed with a DSLR camera, telephoto lens and eclipse filter, courtesy of Nadienne, Breena and Christian in all.  Thanks to Randy for the film!

Composite view of Sun during eclipse 21 August 2017

And all that is now

And all that is gone

And all that's to come

And everything under the sun is in tune

But the sun is eclipsed by the moon.

Pink Floyd - "Eclipse"

I've got a crush on you...

Sharks are an incredibly diverse group of fish.  Most live in the ocean, some live in freshwater, and some move back a forth between both.  "Jaws" perpetuated the image of the shark as an ambush predator, tearing big pieces out of large prey and chewing it up.  Many sharks do eat like this, but more of them swim up onto a school of fish, open their mouths and swallow whatever goes in whole.  Some strain algae and other plankton out of the water, while others eat hard shelled critters like mussels, clams, lobsters, crabs...etc.

The Cretaceous Western Interior Seaway was inhabited by many different kinds of shark.  One of the most peculiar was the durophagous (eats hard-shelled animals) shark Ptychodus.  These sharks had jaws with robust teeth with low roots and massive crowns that could apply three point forces to hard material to break it.  The crowns have transverse ridges and the margin of the crowns are decorated with a number of ridges and bumps (tubercles).  Their mouths were filled with pavement dentitions composed of hundreds of teeth.  Collections of these teeth is seen at right and below (pictures by Mike Everhart).  Note the flattened surfaces caused by wear of the teeth from grinding hard materials.

Although teeth from these sharks are relatively common in the Cretaceous Greenhorn and Niobrara Formations of Kansas, little is truly known about the shark.  It is estimated some species of this shark were up to 11 meters in length.  Since there was abundant hard-shelled prey and little competition, this is entirely possible.  Included in this diet were likely mollusks such as these small inoceramid clams (left).  Nautiloids (think squid with shells) and small fish would have also been important food sources.  The general body shape has been inferred to be fusiform, since the vertebral centra are round.  The fact that these centra are calcified suggest that these are modern sharks (neoselachians).  The only semi-well known skeletal elements of these sharks are the jaws.  No well articulated skeleton of Ptychodus has ever been found, so all attempts at classification of this fish are based on circumstantial evidence.

While I was examining the enameloid of teeth of a 305 million year old shark that I had collected from the Farley Limestone as Park University, I decided that I should examine the enameloid of a more recent shark to understand the difference between primitive and modern sharks.  I did a couple of quick surface digests of Ptychodus teeth with 10% HCl.  After 30 seconds, I was able to see the single crystallite enameloid (SCE) on the surface (figure at right: Panels 1,3, 5 are before digestion and 2, 4, 6 are of single crystallites).  After 3 minutes, I could easily see parallel-bundled enameloid (PBE) crystals on the surface (figure below).  After a couple of days sectioning a tooth, I could see a triple-layered enameloid.  A pretty good week's work I thought.  Then I made the mistake of searching the literature for what was known about Ptychodus tooth ultrastructure.  Turns out, the answer is very little.  But what is accepted says that these teeth do not exhibit a triple-layered enameloid, but rather an SCE.  Based on this observation and ignoring a lot of other evidence, the experts placed this shark among the hybodonts, an ancestral group of modern sharks.

I puzzled over this for quite a while, because my results had seemed so clear-cut.  I repeated these observations on several teeth and in several planes of section, but kept coming up with the same result:  the enameloid of these teeth had a triple-layered structure.  There was a superficial SCE/SLE, PBE on the crown, especially at the level of the transverse ridge, and tangled-bundled enameloid (TBE) next to the dentine.  More careful examination of the literature revealed a couple of other studies that documented a triple-layered enameloid in Ptychodus.  One of the reports was in an obscure journal and the Ptychodus teeth were a side study and only shown in a couple of pictures.  The other report was a Masters thesis which was unpublished.  What had started as an attempt to gain a proper control for one study turned into the main focus of another.  I would have to prove that what I was seeing was a real phenomenon.

The figure at the right shows the PBE adjoining the TBE, and the TBE next to the dentine in sectioned teeth.  Getting just the right images with the correct brightness and contrast took about 6 months.  The enameloid of Ptychodus had a lot of similarities to that of Squalicorax curvatus, including having a TBE that became single crystallite in structure at the enameloid-dentine junction.  Dentinal tubules rise high into the crown, penetrating into the enameloid, much like those seen earlier in my post on the hybodontiform shark.  Preservation of the teeth is amazing and casts of the odontoblasts (tooth-building cells) can be seen below.

The figure at right is my recreation of the one experiment that is cited the most often.  A whole Ptychodus tooth (1, 2, 3 below) was soaked in 10% HCl for 23 minutes, 35 seconds (4, 5, 6) it is easy to see the great degree of erosion in the surface decoration of the tooth.  In 7 and 8 you can see that the enameloid has been eroded to the level of the dentinal tubules, which show up as divots in the surface of the tooth.  The enameloid in this area (9) is single crystallite enameloid in appearance.  The previous studies are correct in interpretation of the results of the experience.  The problem is in the preparation.  The tooth was soaked in acid way too long, and the bundled enameloid layers were destroyed.

This study solidified (for me, at least) the idea that "If it isn't published, it isn't known.  If it is published, ask if it is truly good science in technique and interpretation."  The work done here shows that Ptychodus is not a hybodont (primitive shark or proto-shark), but rather is a selachimorph neoselachian fish (modern shark).  Reviews of the work have been very positive and the paper is cited in the second edition of "Oceans of Kansas" by Mike Everhart, which should be published this Fall.

Oh, the shark has pretty teeth, dear...

In the last post, I talked about the triple-layer enameloid that is one of the defining characteristics of a modern shark.  That enameloid has an outer single crystallite enameloid/shiny-layered enameloid (SCE/SLE) that resists the spread of cracks in the teeth; a middle parallel-bundled enameloid (PBE) that resists compressional (straight down) force; and an inner tangled-bundled enameloid (TBE) that resists rotational (twisting) forces.  These are tremendous properties for a shark that bites big chunks out of something else and needs to chew them up.  A Cretaceous predator, Squalicorax curvatus from the Western Interior Seaway of Kansas (about 90 million years ago), has teeth that everyone would recognize as shark's teeth.  Squalicorax has a labiolingually compressed (flat) shape, with a strong triangular cusp and a shoulder with serrated edges (like a steak knife).  These teeth are perfect for running up on something even bigger than the shark, slicing out a chunk of prey and chewing it up.

Squalicorax curvatus teeth coated with ammonium chloride to show detail

Squalicorax curvatus would be very recognizable to the casual observer as a shark.  It just LOOKS like a shark.  Mouth behind and below snout, large dorsal fin, fusiform body, mouth full of nasty teeth and big (up to about 10 feet long).  A few extremely well preserved specimens have been found, including a nearly complete skeleton (very rare for cartilage - even calcified cartilage) recently sold by PaleoSearch, Inc. in Hays, KS from the Smoky Hill Chalk of Kansas (about 85 million years ago).

Reconstruction of Squalicorax curvatus  by Dmitry Bogdanov

Exceptional Squalicorax skeleton - absolute once-in-a-lifetime find

Squalicorax skull detail

Squalicorax curvatus SLE and PBE - surface etch.  Size bars: (1,2,6)
1 micron, (3) 100 microns, (4) 50 microns, (5) 5 microns.

There is no argument in the literature that this particular shark is a selachimorph neoselachian (read SHARK).  The external anatomy of Squalicorax curvatus teeth was examined first using teeth that had not been exposed to 10% hydrochloric acid (HCl) (panel 1), treated with HCl for 30 seconds (panel 2) or 3 minutes (panel 3-6).  There is not much relief on the surface of the untreated teeth, but you can easily see randomly oriented enameloid crystallites on the surface of a tooth treated for 30 seconds with 10% HCl.  Longer treatments remove all of this SCE/SLE from the surface and expose the parallel bundled enameloid of the Squalicorax tooth.  Panel three shows the parallel bundles at the level of the serrations in the tooth.  As the parallel bundles approach the serration, they turn direction, so that they point towards the edge of the serration, instead of towards the apex of the tooth.  As you zoom in on the parallel bundles, it is possible to see that there are two populations of bundles; one that runs parallel to the long axis of the tooth, and one that runs perpendicular to the long axis.

Cross section of Squalicorax teeth.  Size bars: (1) 500 microns,
(2,3,6) 50 microns, (4) 20 microns, (5) 5 microns

It is possible to see all three enameloid layers simultaneously in sectioned teeth.  In panel 1, the lighter area is the enameloid and the darker area inside is the dentine of the tooth.  The tooth is embedded in plastic.  In the upper right and lower left of the picture, you can see the serrations (cutting edges) of the teeth.  In panel 2, we are looking at the interface between the enameloid upper right and the dentine (left).  The arrows show where the dentine and enameloid meet.  The TBE (T) is seen next to the dentine (left) in panel 3, and the PBE (P) is to the right.  Panels 4-5 show the interface between the TBE and dentine.  As the dentine is approached, the enameloid becomes more like an SCE/SLE.  The dentine has a structure that looks a lot like bone, with channels for odontoblasts that are surrounded by concentric rings of dentinal material.  Shark teeth have not changed a whole lot in appearance in the past 90 million years.  There are small changes, but those mostly reflect stress introduced onto the tooth what the shark eats.

Almost to the pay-off for the paper.....

Is you is or is you ain't my sharky?

Life was going swell, then work showed up and shot everything to hell.  My writing got in the way of my writing anyway.  So this is what I have been doing instead of writing blog entries.  One line of my research is examining the value of tooth enameloid characteristics in sharks as a way of determining whether they are a "shark ancestor/primitive shark" or a "modern shark".  "Sharks" are generally thought of as fish with a skeleton made out of cartilage (chondrichthyan), a mess of teeth in the mouth that are replaced over time, tooth like scales (denticles) in their skin, and a torpedo- shaped (fusiform) body.  As such, shark remains can be identified from the Devonian Period, over 400 million years ago.

1) Enameloid layers in shark teeth; 2) possible directions of
parallel bundles; 3) sectioning directions of teeth

Shark biologists spend a bit of time arguing about what characteristics make a chondrichthyan a modern shark or a shark ancestor.  The one telling characteristic of the teeth seems to be the structure of the tooth enameloid.  A shark's tooth has a core of dentine, surrounded by fluoroapatite crystals.  Primitive sharks such as the ctenacanths, symmoriids and hybodonts had a single-layered enameloid composed of randomly oriented single crystals of fluroapatite (single crystallite enameloid - SCE).  A modern shark (selachimorph) has a triple-layered enameloid, with an outer layer of SCE (called shiny layered enameloid - SLE) plus two underlying layers of bundled crystals.  The middle layer is composed of bundles arranged in parallel (parallel bundeled enameloid - PBE), while the inner layer next to the dentine is composed of interwoven bundles (tangled-bundled enameloid - TBE).

Looking at these enameloid crystals takes some doing, since they are held in place with smaller "cement" molecules.  Fortunately the enameloid crystals are more acid resistant than are the cement molecules, so 5 sec to 3 minutes exposure of fossil shark teeth to 10% hydrochloric acid is usually enough to see the enameloid, depending on what layer you want to look at, and how you have prepared the teeth.   With whole teeth, 15-30 seconds is enough to see the randomly oriented crystals of the SCE/SLE; while seeing the PBE may take 1-3 minutes.  You can see all of the layers at once if you cut the tooth open (or embed it in plastic and sand it down) and then treat with acid for about 5 seconds.

Gold coated Ptychodus tooth, about 1 cm across

Enameloid crystals are really small, so you have to use a very powerful microscope to see them.  A regular light microscope will usually allow for a 1000X magnification, but you need to magnify these teeth about 5000X to see the individual crystallites of the SCE/SLE well at all.  This requires the use of an electron microscope, which uses a beam of electrons in a vacuum to image a specimen instead of light.  Most biomaterials are natural insulators, which means that they will absorb electrons and not reflect or re-emit them.  To solve this problem, we coat the specimen with a one atom thick layer of gold.  These sharks are all pimped out.  The gold will allow us to see the shape of the surface they are deposited on by reflecting electrons (backscatter) or by absorbing an electron and emitting one in its place (secondary electrons).

Tooth embedded in plastic, ground sandpaper, and coated in gold.
Copper tape is used as a pointer

The Hybodont Tooth

One group of primitive sharks that are seen as being ancestral to the modern shark are the hybodonts.  The first record of hybodontiform sharks is seen in the Mississippian of the Carboniferous Period, about 340 million years old.  The hybodonts were very successful, surviving late into the Cretaceous Period.  This is an evolutionary life of about 270 million years.  Remember that dinosaurs went extinct only 67 million years ago.  The hybodonts had mouths that were not overhung by their noses (rostrum), large cranial scales, barbed spines in front of their dorsal fins, a variety of different denticle types, and SCE on their teeth.

Reconstruction of Onychoselache

One of the early hybodontiforms was Onychoselache.  They were very small, about 10 inches long with teeth that were about 1 mm in maximum dimension.  Their teeth had low, flat crowns for crushing hard shelled organisms.  They had barbed dorsal fin spines, oval hooked denticles on their pectoral fins, and c-shaped denticles along their lateral line (sensory region on flanks of fish).  I have found very similar remains from the 307 million year old Farley Limestone of the Kansas City Group.

Hybodontiform parts:  scale bars(1-5) 1 mm, (6-9) 0.5 mm,
(10-11) 0.2 mm

The remains at the right are from an indeterminate hybodontiform.  There is not adequate material to describe a fish, and while the remains are associated, they are separate bits and pieces.  This is just not enough material to describe an organism down to the species level.  Views 1-5 are various views of a tooth: 1-top (occlusal) view; 2-front (labial); 3-side (lateral); 4-broken side (medial); 5-back (lingual) views.  View 6 is a piece of dorsal fin spine with hooked denticles on the posterior (back) side.  Views 7-9 are denticles from the pectoral (front) fins and 10-11 are denticles from the lateral line.  I sectioned several pieces of these teeth and looked at the structure to make sure that they were really hybodontifom and had an SCE.

Sectioned hybodontiform teeth:  Scale bars: (1)  200 microns;
(2) 10 microns ; (3,4,6) 1 micron; (5) 50 microns

The tooth crown is composed of dentine, which extends in columns up into the enameloid.  In the electron micrographs at left, the dentine is dark and the enameloid is light colored.  In panel 1 you can see columns of dentine approaching the surface of the tooth.  The enameloid has several channels for conducting odontoblast (tooth-building cells) processes through the enameloid (panel 2).  In panels 3-4, randomly distributed enameloid crystals make up the outer layer of the tooth.  Dentinal tubules are seen in section in panel 5.  The junction (arrows) between the dentine (D) and enameloid (E) is seen in panel 6.  The SCE is clearly visible in this section as well.  A channel carrying an arm of an odontoblast cell can be seen between the left two arrows.

That is about 3 months worth of work to get everything done just right.  Next is the last two years of my research life.




Reconstruction by Kahless28