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Here are two links to posts dealing with how to post pictures on Black River Fossils forums.
1. How to Post Pictures on Black River Fossils Forums by ditchweezil
2. How to Post Pictures on Black River Fossils Forums by Daryl
One of the rarer type of teeth we find in Maryland along Calvert Cliffs is something that many folks refer to as Alopias grandis, aka Giant Thresher. This tooth form seems to come in two varieties up here, serrated and un-serrated. By far, the serrated version is much rarer than the un-serrated type. What's always bothered me about these teeth though is the possibility that they are Alopias. The first time I ever saw one I thought it was an odd looking mako of some sort, not pathological, but maybe a tooth position I hadn't seen before. When I learned that these teeth were being called Alopias, I immediately looked to a modern Thresher shark jaw and several fossil thresher shark teeth (Alopias latidens). I do see some obvious similarities, but the crowns and roots on the Maryland Giant threshers that I have (6 altogether) are thinner and broader than the Alopiid teeth.
Along this same theme though I thought to look at several paratodus teeth (http://www.ecphora.net/mgs/images/parotodus_lc.jpg) and noticed that among Paratodus there is obviously an anterior jaw position where the crown points straight out and not recurved towards one shoulder. Matter of fact, the paratodus teeth seem to be somewhat similar to the Alopiid tooth positions/characteristics, so why didn't Paratodus teeth wind up being called some form of Alopias as well?
None of my Giant thresher teeth have crowns that point straight out, like the anterior tooth I described earlier. They all curve to some degree towards one of the shoulders - what does this mean? Now, I haven't discussed the serrated version of this tooth yet. I only have two specimens of these, and both are very worn. Are these also suppose to be a type of serrated Thresher? I have a hard time with that thought for some reason. I've even seen a couple serrated specimens mistaken for posterior juvenile Megs - or was it mistaken? As with the other unserrated teeth, I've never seen an anterior version of the serrated tooth form. What kind of shark (of this size) has teeth where none of them have crowns that point straight out? Tigers?
I think these teeth are either from some form of mako, or maybe it's just a tooth position that belongs to something else like the mako Isurus Hastalis?
Does anyone have any thoughts/ideas/opinions on these teeth?
vr,
Daryl.
I believe the teeth you are talking about are more properly refered to as Trigonotodus. There appears to be a name change in progress. The earliest examples that I am aware of are heavily cusped teeth from the Eocene. They show up in the Oligocene of Summerville, South Carolina and many, if not most, have small cusps. Toward the end of the Oligocene they loose the cusps and become quite large. The main change in the middle Miocene was the development of serrations. There seems to have been some overlap in the serrated and non-serrated forms when both forms existed at the same time, and I have seen teeth that grade from smooth through coarsly serrated so it is possible that they were not separate species but rather a variable population in which variations in tooth morphology were the norm. The same thing can be seen during the time when makos, transitionals, and great whites were swimming around fin to fin on their way to a new species. Years ago I found both types along the Westmoreland County side of the Potomac.The flip side of the coin is that I have seen teeth of the serrated form at and above two inches in slant length, which is much larger than any of the non-serrated teeth I have seen. (Pause) I just took a half hour break to find and upload pics of some of the serrated Trigonotodus teeth I found a few years back. Unfortunately the quality of my camera in the old days was poor compared to today's models so the pics aren't very good. Look under Shark Teeth and then under Alopias Sp. So why would I get rid of something as rare as one of there? Simple, I found five or six of these over the course of a dozen trips and had no idea they were rare. I haven't found one since.
Here's a link to Trigonotodus sp. shark (serrated giant thresher) teeth on blackriverfossils. Of course, three of them are from BigRedMeg. Thanks for uploading these excellent specimens! Mine has been on the site for a while, but it was lost in the quagmire that was the old version of this site. I only have one of these teeth and it is from the late Oligocene of the ACE Basin in South Carolina. The serrations are coarse near the root, but the become smaller near the tip. I have seen about 5 of these teeth in person, the largest being 2 1/8 inches long and fully serrated. I have seen many more non-serrated Alopias grandis, including some gigantic ones. One was 2 1/4 inches long! One thing I have noticed is the consistency of the tooth shape and thickness between the two types. I've seen more parotodus than the sum of all the giant threshers I've ever seen, and the root thickness makes them obviously different. If you lay a benedeni on the flat side and look at it from the edge, the root towers above the blade on every specimen I've ever seen, even small ones. Not so with a giant thresher - their roots are nearly the same thickness as the thickest part of their blades whether serrated or not.
The serrated variety of giant thresher is exceedingly rare in South Carolina, while we tend to find a reasonable number of non serrated giant threshers. It is well known that SC has a rich oligocene fossil history, while our Miocene deposits are pretty much non-existant except in isolated river locations. What I'm getting at is that I believe the serrated variety to be a progression of the species just like carcharias swimming forth from isurus. Based on distribution, it seems plausible that the serrations developed sometime during the extremely late oligocene and became a more prevalent in the miocene. The flip side is also believable, the non serrated variety losing its foothold in the miocene.
Maybe its just late and the PVA is getting to me.
Thanks BRM and DW for the pics and info on these Trigonotodus/Alopias/? teeth. My point about comparing the teeth to parotodus teeth was not to say that I think these teeth should be called parotodus, but rather, why scientists chose to erect the name Parotodus for teeth that in my opinion have similar characteristics to Alopiid teeth. I personally don't think Parotudus are Alopiid, but for the reasons I've heard calling these teeth "Giant" threshers, then why did they not think that Parotodus was also some form of giant thresher?
In modern Alopias jaws, there exists a few teeth near the midline of the jaw whose crowns are fairly erect and point straight up/out (this is exhibited in mako's as well). If these teeth we have are just "Giant" forms of thresher teeth, then I would think that someone would have one/more specimens with a similar anterior tooth/crown characteristic. I haven't seen any myself. Every example I've ever seen has a crown that bends to some degree towards one of the shoulders. What does this tell us? There must be some other diagnostic characteristics about these teeth (ie. nutrient pore number/location, crown and root lobe thickness/length/angle, etc.) that can help correctly assign/classify what type of shark they came from.
A few years ago my friend took a beautiful/perfect specimen from Calvert Cliffs down to the Smithsonian for their expert to look at. He ID'd the tooth as an upper lateral from an Isurus hastalis (mako), so go figure. This might be the reason why this tooth form didn't show up in the Smithsonian's Lee Creek vol III book.
Either way, these are some pretty rare teeth and quite exciting when you find one. When I get a chance I'll post some pics of my specimens.
If I had to guess who gave the mako ID my money would be on Bob Purdy. Years ago he said the first serrated Trig I found, which was heavily curved, was a type of modern great white. As far as the Paratodus goes, the shape is Alopid like but there is a clear lineage for Paratodus that goes back to Otodus. The Paratodus/Otodus line diverged in the early Eocene and mildly cusped Paratodus show up in Summerville.
BRM, you guessed right!
Below is a picture of a couple of "Giant Thresher" shark teeth found several years ago along Calvert Cliffs, MD. As mentioned in the earlier thread, these teeth are supremely rare in this location, and to find one as large and pristine condition as the larger tooth in the picture is like hitting the Powerball jackpot! The tooth on the left belongs to a friend of mine; the tooth on the right is mine - it's 1.75" along the longer slant and has some deep blue coloring on one side.