Giant Tortoise Peripheral?

[GPayton]

Found this huge chunk of tortoise shell yesterday while scouting a new gravel bar on the Brazos River near Houston. I've found many fragments before, but never anything this large. What got me even more excited was how it seems that it's a mostly complete bone (except for some wear on one of the flat edges that would have been an area where the bone joined another piece of the shell). I tentatively identified it as a peripheral from the edge of the shell from a Hesperotestudo sp., since they seem to be the only species of giant tortoise that lived in Texas during the Pleistocene. Can anyone with better references than me confirm or deny this? Thanks for looking!  

 

[digit]

Sure looks like the ones we occasionally find in the Peace River. The profile is a dead giveaway.

 

 

Cheers.

 

-Ken

[Lorne Ledger]

yep, I agree it is shell from giant tortoise.  Nice find, it looks like a relatively complete piece too, bonus

[darrow]

agreed Hesperotestudo sp.  There's a good reference in the thread below. 

I found this eplilastron on the Brazos in the same local...

 

 

[darrow]

Your fragment appears to be the gular scute front part of the epiplastron.(the bone marked ep on the right.)  May be the right side or opposite of my left fragment.

[digit]

Keep in mind that the scutes shown in the left side of the above drawing are indicating the thin horny (keratin) scutes that overlay the bones of the carapace and plastron. The bones themselves are listed in the left of the drawing above. The item found is definitely one of the shell bones as the scutes themselves don't really fossilize.

 

I'm much better at recognizing the carapace and plastron bones of the Trachemys slider turtle that is commonly found at the Montbrook site. We also have a large snapping turtle, a softshell (Apalone sp.) turtle and a very small musk turtle at this site but I have not heard of any of the larger tortoises at this site. It is likely too old for this type of find. The only Hesperotestudo shell fragments I've found are from the Peace River. I occasionally find think chunks of plastron and carapace that are so large they could only come from this Galapagos size tortoise. The pointed tip in the profile photo seems like a peripheral bone from the carapace as it is most similar to the peripherals from the big snapping turtle I see regularly. These peripherals are connected to the costals with a bit of cartilage and in older individuals the cartilage is lost as the bones fuse together along a suture line. The smooth edge on the right side seems to match this inner edge of a peripheral that would adjoin the cartilage before suturing (indicating a younger individual). This is just my read of this bone based on my limited (but growing) knowledge of turtle shell bones from volunteering at the FLMNH.

 

6 hours ago, GPayton said:

 

Cheers.

 

-Ken

[darrow]

Thanks for clarifying Ken!

[GPayton]

Thanks for the help everyone. I had actually seen your epiplastron post before @darrow, but for some reason didn't realize it was the same as my piece. Definitely happy with this find! 

[digit]

10 hours ago, darrow said:

Thanks for clarifying Ken!

I don't have as wide or deep a knowledge of fossils as many here on the forum but when I see something that is in my wheelhouse (things I'm picking up from recent volunteering with the FLMNH) I do like to contribute and pass it along. Knowledge is really only useful when shared.

 

         

 

This is a snapping turtle peripheral I reassembled from pieces collected at the Montbrook site. Sadly, I neglected to take a profile photo which would have been useful for seeing that it had not only a wedge-shaped outer edge but also a smooth (unsutured) inner edge. You can just barely make out that the left and right edges have the ragged suture surfaces to knit with the adjoining peripheral bones. On the underside of this peripheral you can see the depression into which the end of the rib bone fits. When I first reassembled this bone I was clueless as to what it was. The much more common Trachemys slider turtles found at the Montbrook site produce many carapace and plastron pieces. In these carapaces the only smooth (non-sutured) edges on the bones are the outer edges of the peripherals (and the special nuchal and pygal bones which are specially named peripherals on the midline behind the head and above the tail respectively). When I saw a bone that had the cross-section shape of a peripheral but a smooth (unsutured) inner edge I was greatly confused (easier than it sounds) and I asked Richard Hulbert what it was I was looking at. He very generously took the time to walk to the back of the vertebrate paleontology warehouse where we were and open a cabinet and find the drawer with the modern snapping turtle skeleton that is used for comparative material. He showed my how in younger individuals that the peripheral bones form a separate ring that is attached to the costal bones with cartilage. Bone slowly replaces the cartilage in older adults fusing the peripherals to the costals. Here's how it looks before it is fused (from a modern snapper).

 

 

Softshell turtles (Apalone sp.) are even weirder as they don't have peripherals just a ring of cartilage around the costals. There's a good discussion (and photos) here.

 

http://www.thefossilforum.com/index.php?/topic/92494-need-help-with-this-one/&do=findComment&comment=1017544

 

The size of the fossil that started this discussion seems to be right for the giant "Galapagos-size" tortoise that once roamed the south. The wedge shape seems like it should be on the shell periphery. Beyond that I'm just making informed choices (aka guesses) as to the specific element in question. I'll try to drop the photos to Richard and see if he can provide any more elucidation.

 

 

Cheers.

 

-Ken

[Tidgy's Dad]

Yes, nice bit of epiplastron. 

[digit]

As our forum "tortoise whisperer" this matches your concept of a tortoise epiplastron? The epiplastron bone for those who don't speak Testudines is the bone at the front of the plastron directly underneath the tortoise's head.

 

 

Cheers.

 

-Ken

[digit]

Yup. Confirmation from Richard that @Tidgy's Dad was (as expected) right on the mark. A partial tortoise epiplastron.

 

 

Cheers.

 

-Ken

[GPayton]

Thank you very much for both sharing your incredible wealth of knowledge on this subject @digit, and for passing along the pictures of my find to Dr. Hulbert. I can't tell you how many times I've used his book to help ID my finds since I bought it four months ago. 

[digit]

Happy to share the information and leave a record of it here for future viewers. Great to have a forum populated with knowledgeable members like @Tidgy's Dad and others with connections in high places.

 

 

Cheers.

 

-Ken

[Tidgy's Dad]

3 minutes ago, digit said:

Happy to share the information and leave a record of it here for future viewers. Great to have a forum populated with knowledgeable members like @Tidgy's Dad and others with connections in high places.

 

 

Cheers.

 

-Ken

Don't be so modest, Ken, you're a positive and most excellent  contributor yourself. Someone who knows what they are talking about. 

Merry Christmas to you and yours.

[grandpa]

20 minutes ago, Tidgy's Dad said:

27 minutes ago, digit said:

 

Don't be so modest, Ken, you're a positive and most excellent  contributor yourself. Someone who knows what they are talking about. 

Oh, Heck yeah!  One of the BEST!

[digit]

Don'tcha all go makin' me blush--I look terrible in red.

 

It may take a bit of maneuvering to get around to the correct answer but we have a pretty good track record here on the forum.

 

I'm grateful that this forum is a font of knowledge that we can dip into on a continual basis.

 

 

Cheers.

 

-Ken