Proboscidean Partial Pelvis needs ID

[dbrake40]

Proboscidean from Southern MN gravel pit on Minnesota river. Mammoth or Mastodon? The acetabulum (socket) is approximately 7" in diameter. Sorry for lack of scale

Edited November 9, 2023 by dbrake40

[ClearLake]

I’m not an expert, but a quick search if the internet indicates that yours is from a mastodon.   First picture is a mastodon, second is a mammoth. See how the acetabulum with its articulation surface widely separated  into two looks like the mastodon and not the mammoths more complete bowl. That’s my take on it. 
 

 

[ClearLake]

Just to add a bit more info to this.  After doing more reading ad looking, I am less certain, but still lean towards mastodon.  The reason being, there is not a lot of material readily available out there that describes the differences between the two pelvises, beyond "mastodon is bigger".  But there is a book (cover page below) which has a page showing the two pelvises (see below).  Unfortunately, Olsen's verbiage for the pelvis is lacking in useful discriminators in the case of the OP's specimen; 

 

PELVIS
The iliac crest (fig. 24) in proboscideans is
greatly expanded. The entire element is fanshaped.
The pubis and ischium are relatively
short and stout. The acetabulum in both the
mastodon and mammoth are of nearly equal
size, but the overall dimensions of the pelvis
are somewhat greater in the mastodon.

 

What is often noted is the pelvic difference between males and females (not an uncommon feature of mammals) but that is usually related to length width ratios and overall shape.  Whether any sexual dimorphism is reflected in the acetabulum or not, I can not say for sure. 

 

In short, I have seen several pictures or diagrams that seem to indicate that the divide at the base of the acetabulum (acetabular notch) is wider and more mushroom shaped in the mastodon than the mammoth, I have not seen this description of the feature in any published material.  So, it is an observation, but I'm not 100% sure it is an discriminating feature between mastodon and mammoth.

 

 

 

[dbrake40]

As you indicated I have also read and heard from a curator that the acetabular notch is wider and larger (you mentioned more mushroom shaped) in the mastodon than the mammoth. So based on this know mammoth partial pelvis I thin the mastodon assesment is correct!