Alopias (Thresher Shark) Tooth?

[ynot]

While looking through the Elasmo site's Shark tooth hill section I found something that looked like one of the teeth that I found there in February.

They called theirs a Thresher shark, so is this a member of that group?

Scale in photos is in millimeters.

Thanks for any help on this.

Tony

[finderskeepers]

I think what you have is an Isurus retroflexus, a narrow toothed mako. The Thresher (Alopias) have a lower and wider crown. I'm guessing your thinking it was an upper anterior tooth, but you will notice your photo has some what almost look like cusp remnants. Alopias wouldn't have that. Nice tooth, I'm hoping to make it to that site someday.

This is from elasmo.com and I think its much closer and although the root and crown have a slightly different shape there is variety depending on the tooths location in the jaw:

Edited March 18, 2015 by finderskeepers

[siteseer]

Tony,

If you give us a profile view of that tooth, we can settle whether it's I. retroflexus but it doesn't look like one at this point. It's certainly not a thresher as finderskeepers pointed out.

To be retroflexus it would have to have a noticeably flatter crown than oxyrinchus/desori or hastalis. I also don't see good indications of the inflated root sections (called an "elevated platform" by Kent in his 1994 fossil sharks of the Chesapeake Bay book) at the crown-root boundary. It looks more like an Isurus (Carcharodon) hastalis lower or what has been interpreted as an Isurus (Carcharodon) planus lower.

Elasmo says threshers are "relatively rare" but I would say they are very rare - even if you do a lot of screening. It makes sense because it seems that by the Middle Miocene at least, threshers have been more of an open ocean animal seldom entering bays.

Jess

While looking through the Elasmo site's Shark tooth hill section I found something that looked like one of the teeth that I found there in February.

They called theirs a Thresher shark, so is this a member of that group?

Scale in photos is in millimeters.

DSCF2638.JPG

Thanks for any help on this.

Tony

[Auspex]

My knee-jerk is desori.

[Adron]

I agree with siteseer. In my opinion this is an Isurus planus lower (the shape of a lower hastalis is a little bit different).

Up to now I've only seen one retroflexus from Bakersfield.

regards

Aaron

[ynot]

I think what you have is an Isurus retroflexus, a narrow toothed mako. The Thresher (Alopias) have a lower and wider crown. I'm guessing your thinking it was an upper anterior tooth, but you will notice your photo has some what almost look like cusp remnants. Alopias wouldn't have that. Nice tooth, I'm hoping to make it to that site someday.

This is from elasmo.com and I think its much closer and although the root and crown have a slightly different shape there is variety depending on the tooths location in the jaw:

Tony,

If you give us a profile view of that tooth, we can settle whether it's I. retroflexus but it doesn't look like one at this point. It's certainly not a thresher as finderskeepers pointed out.

To be retroflexus it would have to have a noticeably flatter crown than oxyrinchus/desori or hastalis. I also don't see good indications of the inflated root sections (called an "elevated platform" by Kent in his 1994 fossil sharks of the Chesapeake Bay book) at the crown-root boundary. It looks more like an Isurus (Carcharodon) hastalis lower or what has been interpreted as an Isurus (Carcharodon) planus lower.

Elasmo says threshers are "relatively rare" but I would say they are very rare - even if you do a lot of screening. It makes sense because it seems that by the Middle Miocene at least, threshers have been more of an open ocean animal seldom entering bays.

Jess

My knee-jerk is desori.

I agree with siteseer. In my opinion this is an Isurus planus lower (the shape of a lower hastalis is a little bit different).

Up to now I've only seen one retroflexus from Bakersfield.

regards

Aaron

Hey-lo Folks,

Thanks for the replies on this tooth. I will try to get the requested photo up tomorrow. Until then I will reserve My thoughts on the label.

Good luck with the hunt,

Tony

[Vball]

I agree this is a Isurus planus lower.

[ynot]

I agree this is a Isurus planus lower.

Thank You.

[ynot]

Hey Jess et All,

Here is the photo that You asked for.

I added a couple of angles, hope that helps.

Thanks to all for the help, here and on My other posts.

Tony

Tony,

If you give us a profile view of that tooth, we can settle whether it's I. retroflexus but it doesn't look like one at this point.

Jess

[finderskeepers]

I'm not very familiar with Isurus planus and I think now that I'm reading about it online and looking at images, I think my ID was wrong. This is why I love this site. It is a learning opportunity. I did know that it wasn't an Alopias. I found this earlier posting very informative. http://www.thefossilforum.com/index.php?/topic/36189-isurus-hastalis-or-isurus-planus/. The updated angles of the tooth are really great for understanding the tooth, especially the thickness.

Thank you everybody for this info. and thanks for the original post.

[ynot]

On 3/17/2015 at 10:42 PM, siteseer said:

If you give us a profile view of that tooth, we can settle whether it's I. retroflexus but it doesn't look like one at this point.

See 2 post above^.