More Micros From The Peace River And Cookiecutter Creek

[doushantuo]

[MarcoSr]

Found another cookie cutter (Isistius trituratus) symphyseal (5mm x 3.5mm) from the Eocene of Virginia.  It is still puzzling to me that I have a number of these symphyseal teeth from the site and only a single posterior tooth and a couple of distal laterals based on the fact that cookie cutters shed all of their lower teeth together because they are all interlocked.

 

 

 

Marco Sr.

[ynot]

11 minutes ago, MarcoSr said:

Found another cookie cutter (Isistius trituratus) symphyseal

Nice tooth there Marco!

[MarcoSr]

12 minutes ago, ynot said:

Nice tooth there Marco!

 

Tony

 

Cookie cutter teeth are one of my favorites.

 

Marco Sr.

[ynot]

1 minute ago, MarcoSr said:

 

Tony

 

Cookie cutter teeth are one of my favorites.

 

Marco Sr.

Mine too! But I particularly like the teeth that have multiple cusps, like cat sharks.

 

Tony

[digit]

57 minutes ago, MarcoSr said:

Found another cookie cutter (Isistius trituratus) symphyseal (5mm x 3.5mm) from the Eocene of Virginia.  It is still puzzling to me that I have a number of these symphyseal teeth from the site and only a single posterior tooth and a couple of distal laterals based on the fact that cookie cutters shed all of their lower teeth together because they are all interlocked.

 

That's a gorgeous symphyseal, Marco! May I inquire as to what you are using to photograph your micros? The photos are stunningly sharp.

 

I've often wondered how the lower teeth replacement process works. As you mentioned all of the lower teeth are interconnected (I'm assuming with some form of cartilage) so that they are shed together like someone removing a full lower denture. I have to assume that there is some delay before the next rank of teeth flip into place to take over. If this is not an immediate process then a Cookiecutter Shark might have a (brief?) period in which it would be incapable of feeding (only being able to give its prey a nasty hickey). Other than timing, the other thing about Isistius lower tooth replacement that fascinates/confuses me is exactly how the next row of teeth rise into active position from the ranks that are folded down flat inside the lower jaw (so as not to interfere with the plugs of flesh that this shark removes while feeding). If you look at this jaw of the extant species (I. brasiliensis) that I lifted from the New Zealand Terra website, you might notice something interesting about the reserve ranks--they are flexed in the opposite direction.

 

 

If you were to cut out a strip of paper representing the attached row of teeth and bend it the way this would be stored in reserve in back of the active row and then picture this row of teeth rising up on some sort of cartilage conveyor belt to rise up over the very narrow rim of the lower jaw to take their position on the outside of this jaw, the curvature needs to reverse itself at some point. If this is unclear, picture being able to magically detach one of the replacement rows of teeth in the photo above and lift it out (with its existing curvature) and place it in front of the jaw. The symphyseal tooth in the center would be touching the lower jaw but the other teeth would be aligned in an arc in the wrong direction to lay snugly along the upper rim of the jaw. Somehow, this entire row of teeth must flex to reverse its curvature as it migrates over the top. I understand that the teeth are likely interconnected with a flexible attachment like cartilage but it would seem that the joints between the teeth would have to undergo some major torsion and compression in order to accomplish this reversal to the outside of the jaw in working position. I've spent more time than I'd like to admit playing with receipts and other strips of paper trying to image the warping process involved in moving these teeth into the functional position. Extant Cookiecutter Sharks are so rarely captured that I suspect none have been recovered during the awkward stage of tooth replacement. I've read some interesting papers on the method of the tooth ontogeny that allows the "even and odd rows" to be lost in a particular way (more from the lateral and posterior teeth initially) so that the adult rows of teeth all overlay each other at the edges with the symphyseal tooth in front of all in the center. A very interesting (and slightly technical) paper that I can dig up if anybody wishes to read about it.

 

This highly engineered tooth replacement to allow a fresh set of lower teeth to all be replaced at once is really much more sophisticated than the average system that works so well for other sharks (replace single teeth as needed) and is one of the reasons--besides the fact that it is bioluminescent, and the only family of parasitic sharks--that I've loved Cookiecutter Sharks since I was a wee tot.

 

 

Cheers.

 

-Ken

 

[MarcoSr]

4 hours ago, digit said:

 

May I inquire as to what you are using to photograph your micros? The photos are stunningly sharp.

 

I've often wondered how the lower teeth replacement process works. As you mentioned all of the lower teeth are interconnected (I'm assuming with some form of cartilage) so that they are shed together like someone removing a full lower denture.

 

-Ken

 

 

Ken

 

I use a Dino-Lite AM4815ZT digital microscope to take my pictures.

 

The teeth themselves are interconnected and locked together with joints kind of like half-lap joints in woodworking held together by the cartilage.  I can visualize the active interlocked teeth falling out together.  However, it isn't as clear how the replacement teeth flip up when they are all interconnected.  They may all move together at the same time.

 

Marco Sr.

 

[ynot]

In My imagination, I see an accordion like movement of the teeth as they move into position.

[digit]

Ah, nice "handheld microscope" the Dino-Lite seems to be. Somehow, this expensive model did not show up when I was looking for such things (possibly luckily as this thing costs darn near a boat payment). I ended up with a much cheaper Celestron scope that is really little more than a glorified webcam. The biggest complaints I have about the Celestron are the lack of depth-of-field (DOF) contol as there is no way to adjust the aperture (if it even has one). Scanning through the Dino-Lite's product info, it seems that it can take several photos on different focus planes and automatically stack the images--pretty slick. Also seems to come with some EDR (Extended Dynamic Range) functionality that I can see would be quite useful. With it's high magnification (to 220x) I can well see how you are getting those spectacular Isistius images. Since you have been focusing on micro-fossils lately, I can see how this would be a wise investment. I saw the Dino-Lite booth at the GSA conference last month though I didn't stop by for the sales pitch--maybe I should have?

 

Regarding the full set replacement of the lower Isistius teeth, I can imagine the cartilage connecting the teeth where they overlap to be flexible yet sturdy enough to hold the teeth together as a set. I still can't wrap my head around the geometry of the flexation as the teeth migrate from the inside of the mandible to the outer.

 

Additionally, since the stunningly sharp image of Marco's Cookiecutter Shark tooth is from the Eocene of Virginia, we are lead to believe that this makes it the extinct species Isistius trituratus which is known from that period. The Cookiecutters we find in Cookiecutter Creek are likely Pliocene in age and thus come from the Miocene-Pliocene species Isistius triangulus. After a bit of research I am able to distinguish the two extinct species from the two (some say three) modern species based on tooth aspect ratio (the modern are more elongate and narrow). Has anybody come across a reference to allow an out-of-context fossil tooth to be discerned as being I. trituratus or I. triangulus (without knowing the age of the deposit)? Other than I. trituratus coming from older formations, I fail to see obvious distinguishing features between it and the younger I. triangulus. We are left with precious little to distinguish fossil species of sharks and in the case of the Cookiecutters virtually all we have are lower teeth to work with. Is it possible that the there are two species described solely on the basis of separate time periods? Is it not possible that the same species might not have spanned the Eocene through Pliocene?

 

I understand how different parts of fossil plants are described with separate binomial names (I first encountered this with Mazon Creek fossils). At some later point in time if the two parts (bark, fronds, seeds) are found convincingly together then one binomial may be dropped in favor of the one with precedence. Imagine finding a new species of (living) plant and associating separate binomial names to various parts of it--a shocking thought to those who are used to modern botany. Obviously, with limited fragmented specimens in the fossil record, it makes sense to give each a binomial name for identification till the puzzle may someday be reconstructed--(but it still seems weird). I wonder if we have two species of extinct Cookiecutter Shark simply because they were separately described from different age formations--and for no other reason?

 

 

Cheers.

 

-Ken

[MarcoSr]

23 minutes ago, ynot said:

In My imagination, I see an accordion like movement of the teeth as they move into position.

 

Tony

 

I hadn't thought of that possibility.  It would work!  Makes more sense than the crazy ways I was thinking of like the shark straightening and stretching its lower jaw intentionally somehow so the active row popped out of the cartilage and the replacement teeth flipped up. The replacement teeth flipping up may push the current active teeth out of the jaw.

 

Marco Sr.

[MarcoSr]

20 minutes ago, digit said:

Has anybody come across a reference to allow an out-of-context fossil tooth to be discerned as being I. trituratus or I. triangulus (without knowing the age of the deposit)?

 

-Ken

 

Ken

 

From Cappetta 2012:

 

 

This seems pretty general to help a lot.

 

 

Marco Sr.

[digit]

Ah, I've read through Cappetta 2012 a number of times but the dropping (or drooping) button-hole as a distinction between species seems not to have stuck firmly in my gray matter. As you have spectacular images of the Eocene species and I have several of the intermediate, I'll have to do some comparisons to see if I can see what they are seeing.

 

Thanks for the highlighted text in the reference.

 

 

Cheers.

 

-Ken

[Coco]

Hi,

 

Your conversations on the lifting of teeth in wait is very interesting. I have two recent jaws (Centrophorus squamosus and Centroscymnus coelolepis) which present the lifting of the lower teeth a little as a wave, it begins at a corner to recover gradually towards the other corner of the mouth. I have to make photos but I do not think of having time before the next week. If ever I forget, don't hesitate to remind it to me ! I took out them of my drawers and they are on my table...

 

Coco

[doushantuo]

I can recomend this,for what it's worth: 

(PNAS,so free access.However ,it was too large( 4+ Mb) to post directly)

 

Below: from Marquard's excellent study(in German) on tooth development in sharks(mostly Lamna*:

Histological section,upper dextral 11th row,Cestracion:

* freely available on line ,Rev Suisse de Zool.).

Below:outtakes from Rasch/Martin,Dev.Biol.(free access,couldn't post it directly(11,7 Mb))

 

 

 

 

 

 

 

 

the musings of Reif(and he definitely knew his sharks!!!):

 

 

 

 

[digit]

Thanks for the heads-up on the article. I've saved it for airport reading (heading up to Chicago soon for the big annual synchronized feasting day involving the most un-dinosaur members of the class Aves--the commercially raised turkey).

 

Thanks for highlighting the text in the images above. I definitely understand the connective tissue conveyor that brings teeth forward in each file in "normal" shark tooth replacement. It is the flipping up of an entire interconnected row of teeth that seems more magical to me.

 

14 hours ago, Coco said:

I have two recent jaws (Centrophorus squamosus and Centroscymnus coelolepis) which present the lifting of the lower teeth a little as a wave, it begins at a corner to recover gradually towards the other corner of the mouth.

 

Ah, Coco! You made me thing outside of the small family of Dalatiidae (the Kitefin Sharks) who which the Cookiecutter Shark belongs and consider the larger order of Squaliformes many of which also have overlapping (and I'm assuming interconnected) lower teeth. While doing a search for your two species above I came upon this image apparently of teeth in motion. It comes from a terrific website that I've bumped into from time to time: http://shark-references.com/species/view/Centroscymnus-coelolepis

 

 

This image would seem to show an interconnected row of lower teeth from the Portuguese Dogfish lifting into place. The "flip" seems to originate at the symphysis (center of the jaw) and spread outward toward the back teeth. It would seem that a replacement row rotates around to the working position on the front of the jaw just before the active set of teeth are shed. In effect, the shark would temporarily have a double set of working teeth before the previous set lose their attachment to the connecting tissue and are shed (assumingly as a set). Thus, the shark would never have any "down time" waiting for the new set to work its way into position--a toothless shark would be a hungry shark.

 

Thanks all for the feedback in allowing me to finally picture how entire sets of lower teeth are swapped in species where the entire row (rank) are interconnected. I'll sleep easier tonight.

 

 

Cheers.

 

-Ken

[doushantuo]

[Coco]

Hi,

 

Here are some pics but they aren't good quality, in this period the natural light isnt good to do pics... They are yellow color because of low light.

 

Centrophorus squamosus

 

 

 

 

 

Centroscymnus coelolepis

 

 

 

 

Usually the biggest teeth are on the top of shark jaws. You can observe here that it is the opposite on Centroscymnus coelolepis.

 

Enjoy !

 

Coco

[MarcoSr]

27 minutes ago, Coco said:

Hi,

 

Here are some pics but they aren't good quality, in this period the natural light isnt good to do pics... They are yellow color because of low light.

 

Centrophorus squamosus

 

Centroscymnus coelolepis

 

Usually the biggest teeth are on the top of shark jaws. You can observe here that it is the opposite on Centroscymnus coelolepis.

 

Enjoy !

 

Coco

 

Coco

 

Thank you for posting these jaw pictures.  It is very interesting to see the interlocked replacement teeth flipping up into place.

 

Marco Sr.

[digit]

Nice images despite the the white balance due to natural lighting this time of year--reminds me of French vanilla ice cream that bites back.

 

You can see that these species with interlocked lower teeth rows don't all flip up at once but that the rotation from the reserve position to the active position progresses in a wave along the jaw. Between your images and the one I found online, I think I am finally satisfied that I now understand what seemed to be an impossibility of the entire row flipping into position at once. This is the second insight I've learned about the unusual lower dentition of this group of sharks with the interlocked lower teeth. This paper shows how the symphyseal tooth in the lower jaw ends up in the most anterior position with an obliquely formed row of teeth layered below this central tooth on either side. Extra teeth are lost on the sides from the initial rows during development till the final rows are formed out of an oblique assortment of teeth from a series of rows--quite ingenious!

 

Cheers.

 

-Ken

 

Underwood C, Johanson Z, Smith MM. 2016 Cutting blade dentitions in squaliform sharks form by modification of inherited alternate tooth ordering patterns. R. Soc. open sci. 3: 160385.
http://dx.doi.org/10.1098/rsos.160385