Help identifying turtle species

[Psmith8547]

I found this turtle in Hell Creek formation outside Glendive MT last summer, well below KT junction (image 2670).  I can't find textbooks or images similar.  43 cm x21 cm (2677). Carapace relatively good markings (image 3127) though lots of cracks.  What I can't find is a group of turtles having a carapace without the pygal/supracaudal scutes ( image 3126- i.e. it's indented, definitely not fractured. It is quite fragmented and I'd love to find an anatomy book to aid in gluing it back together right.

[turtlesteve]

So I saw this when you first posted but didn't have time to respond.  This is a really fantastic turtle.  I am interpreting photo 3126 as the FRONT of the carapace showing the nuchal bone which is likely critical for getting an ID.  But, I don't have a clue what species this is.

The best GUESS I can make is that it's a basal species in Trionychidae just based off the bone texture.  My first attempt at interpretation is attached.  Red for bone sutures and yellow for possible location of scute boundaries.  More prep and photos might help confirm.

 

 

[Plax]

Basilemys? there's another genus with similar shell pattern but don't remember it.

[turtlesteve]

OK, I was wrong on what type of turtle this was.   Compare this to Araripemys barretoi which is an early side necked turtle from Brazil.  Not exactly the same but pretty close; same general suture and scute pattern. 

D4B6BC20-BA97-48C7-B167-225C6DBB585E.webp

[turtlesteve]

Here’s another species that’s even more similar in suture pattern.  So Araripemydidae definitely looks like best candidate so far but haven’t stumbled across a species documented from North America yet.

 

https://www.semanticscholar.org/paper/A-New-Long-Necked-Turtle%2C-Laganemys-tenerensis-from-Sereno-Elshafie/af8a60868474697fc463d850b5319047cb2c3164#extracted

[rfarrar]

I am reasonably sure this is a baenid turtle. Baenids are fairly common in the Hell Creek Formation.

[Psmith8547]

Hi all Thank you so much for the time and help you have already put into this.  I fill I did a poor job following instructions on how to post pictures.  My apologies. These are better and on cm. paper, I looked up each of the three genii listed and there are certainly some common features, especially the soft shells.  The texture of the "skin" on those photos match some of what I am seeing.  My problem with all of them is they all have the pygal or caudal bones. I can't find turtles missing this piece. I've included another picture (3159). This is definitely the caudal end (nuchal pic below).   The upper part of the pic is what I is perceive as the missing bone (cup shaped, sandy looking). The edges are very smooth, slightly heaped up and don't look like injury.  At bottom of pic is the lowest nuchal bump (about 5 o'clock).  The nuchal end still as a vertebral body (pointed object pic 3161) and I found the skull (pics 3152 - two eye sockets and beak - out of focus; also included pic Right side with eye socket 3128.  The top was missing.  Any input appreciated. Again thank you.