Turtle/Tortoise Carapace Fragment

[GPayton]

Found on the Brazos River just southwest of Houston. The title says it all, as that's about all I know about this one! Any help on narrowing it down beyond that to something like a basic genus or even a species would be welcome.

[caterpillar]

Yes, turtle

[caterpillar]

Hypoplastron

[Shellseeker]

Bite marks?

 

It is HARD to ID Turtle... this is some of the better threads:

and

 

[ClearLake]

I'd be surprised if you can get much more definitive than "turtle" on a fragment like this.  But maybe someone can see some sort of distinguishing feature.  

[GPayton]

I didn't know that this particular piece was a hypoplastron (thanks caterpillar!), so for that alone I'm happy. Thanks for the help guys! 

(As an afterthought, does anyone familiar with Texas geologic formations know where these fossils are originating? I'm finding them all on the portion of the Brazos River just southwest of Houston, and I would love to maybe take a trip someday further north to pull some complete pieces out of the ground.)

[Harry Pristis]

There are probably several plastral elements represented.  Here's what we're talking about:

 

[GPayton]

Thanks, Harry! So based off that diagram of the different plastron scutes, it seems like my piece is a mix of fragments from the pectoral, abdominal, and femoral scutes then, correct?

[ClearLake]

20 minutes ago, Wendigo1014 said:

So based off that diagram of the different plastron scutes, it seems like my piece is a mix of fragments from the pectoral, abdominal, and femoral scutes then, correct

Whoa!  Scutes (especially on something like a Slider/Painted turtle that Harry posted a diagram of) are thin horny coverings that are often the first thing to fall off in decomposition.  I'm pretty sure what you have is a fragment of the bony shell material.  And Harry was nice enough to post a diagram of one type of turtle, but a box turtle would look very different as would a snapping turtle, etc etc.  I'm just suggesting to not get too far out on an ID unless someone can show you a comparison piece.  Hypolastron was suggested, and it could be, but again that would only match for a given type of turtle.  Not all hypoplastrons are created equal.  

 

Given where you found it, the age is another big unknown.  The Brazos drains a lot of area and since the piece is a nice chocolate brown, I'm going to assume it did not die yesterday, but it may not be much older than the Pleistocene.  It could have from from 100 yards upstream or 100 miles, who knows.  

[Harry Pristis]

ClearLake is correct, not all hypoplastrons are created equal.

 

[turtlesteve]

I vote hyoplastron and most likely trachemys or pseudemys.

[Harry Pristis]

3 hours ago, turtlesteve said:

I vote hyoplastron and most likely trachemys or pseudemys.

 

Okay, Steve, your opinion is noted.  Now, how about giving us your evidence.

 

 

[caterpillar]

In red what I think about your turtle scute

[GPayton]

Thanks for all the help guys. I've got a modern 12-inch long Red Eared Slider shell at my house and when the fossil bone is oriented on the opposite side of the plastron that caterpillar suggested, it's almost a perfect match. Also, I know that this piece is bone, but the grooves on the shell in the first picture look exactly like plastron scutes when I compare it side by side with the modern shell I have. How is that possible? According to what clearlake said, they're usually some of the first parts of the shell to decompose after the animal dies. 

On a side note, do the small depressions on the outer face of the bone look like tooth marks? I can't really tell myself, but I've seen some pictures on the forum of other shell fossils that look similar. Maybe alligator? Thanks again for all this discussion over such a tiny fossil! 

[caterpillar]

I think these marks are a disease

[turtlesteve]

7 hours ago, Harry Pristis said:

 

Okay, Steve, your opinion is noted.  Now, how about giving us your evidence.

 

 

OK here goes:

 

First, why hyoplastron and not hypoplastron.  See below:

 

 

Mirrored the drawing to match the top & bottom photos.  The scute pattern of the hypoplastron does not match, but the hyoplastron does.  If it were hypoplastron as suggested by others, there would only be one scute boundary visible on the piece (between the femoral and abdominal).  Also, note that the humeral/pectoral, pectoral/abdominal, and femoral/abdominal boundaries have curvature that differentiates between anterior/posterior.  

 

OK, now to species.  The shape and robustness of the hyoplastron limits you basically to emydidae or testudinidae (which are relatively closely related as turtles go).  If we look at testunidinidae, like Gopherus, the curvature/shape of the scute boundaries is not a good match:

 

So we are probably somewhere in emydidae.  The common emydid turtles in Texas would be pseudemys, trachemys, and (possibly) graptemys.  As with the tortoises, graptemys generally has different curvature of the scute boundaries:

 

 

Both pseudemys and trachemys look pretty similar though, so no way to easily differentiate that I can see.  The diagram posted already is trachemys, so here is pseudemys:

 

So, generally, I think it's probably Trachemys or Pseudemys, but it's definitely in either Emydidae or Testudinidae.

 

 

[Shellseeker]

  TFF.  While experts may occasionally disagree, there are members who have significant knowledge on topics where I know little or nothing. and I really enjoy learning new things about my favorite hobby.

[caterpillar]

I am not an expert and I hesitated between hypoplastron and hyoplastron. But I think Steve is right

[ClearLake]

@turtlesteveThanks for the explanations and "models", I see where you are coming from and can buy into the ID.  Always helpful to have a comparative set when trying to ID these fragments.

 

8 hours ago, Wendigo1014 said:

Also, I know that this piece is bone, but the grooves on the shell in the first picture look exactly like plastron scutes when I compare it side by side with the modern shell I have. How is that possible? According to what clearlake said, they're usually some of the first parts of the shell to decompose after the animal dies.

I can help with that.  While my thinking on the scutes is correct (see in the picture below) that they are a thin veneer and probably fall off during decomposition (think of finger/toe nails or the covering on a birds beak, or hoof coverings, etc, etc), what I failed to take into account was the fact that the edges of the scutes are marked by a shallow groove on the underlyng bony material.  So while the actual scute is gone, the outline of it is still visible and this is what you are seeing.  My mistake for not recognizing and pointing this out.

 

[Harry Pristis]

I'm sure that Turtlesteve means well, but he has made a fundamental error.   He has confused the plastron bone sutures with the plastron scute sutures -- they are not the same.  He has mirrored the plastron scute diagram then drew in the outline of the fossil plastron bone to make his match.  Again, the scute sutures are not the same as the bone sutures -- they are NOT CONGRUENT.

 

Further, his illustrations of other species of turtle plastrons show the SCUTE SUTURES which shed no light on the fossil BONE SUTURES.

 

This easy-to-make error is the reason I have in the past resisted the use of the term "scute" for osteoderms and other bits of bone.  A scute in turtles (and some other animals) is a thin, translucent, keratinous scale.

 

So, got any other evidence, @turtlesteve ?

[turtlesteve]

Harry, I am not confused and please look again at what I am posting.  The shell fragment is part of a single bone with no sutures crossing into it - either the hypoplastron or hyoplastron.  I am intentionally using the scute boundary lines, which remain permanently visible on the bone after death and decay of the keratin scutes, to show that this bone is the hyoplastron with the anterior edge being broken.  The strait edges of the fossil (bottom edge and edge facing the ruler) were the suture lines.

 

The images of scute boundaries are absolutely 100% relevant here.  Note that on the pseudemys image the bone sutures are actually visible through the scutes as well.

[Harry Pristis]

That's a disappointing response, Steve.  Sometimes it's better to simply admit a mistake.

[JohnJ]

1 hour ago, Harry Pristis said:

That's a disappointing response, Steve.  Sometimes it's better to simply admit a mistake.

 

Harry, your reasoning is usually sound; could you please explain your rationale as to why this is an error?

[turtlesteve]

Harry, I'm honestly a little perplexed here.  I get that you think I've made an error, but you have not provided specifics as you previously requested of me.  I'll try to clarify exactly what I am seeing.  Anyone is free to annotate where they feel I've made a mistake:

 

[Harry Pristis]

Yes, I think it may be my mistake.  I assumed that the creases on the bone were sutures, and couldn't let go of that idea.  I see now that those creases represent margins of plastral scutes which makes turtlesteve's analysis pertinent.  My bad.