Indiana, Another Unknown Along With Trilobite Isotelus Pygidium

[Jed '06]

Hi, heres another one I can't identify. Referring to the dark lines at top of photos #1 & #2

I didn't know that there was an Isotelus pygidium (near the bottom of photo #3), only about an 1/8 inch of it was visible when I picked it up. Cleaned it up and found something good!

Many thanks!

Size of unknown fossil is 2cm x 7mm

#1 #2 #3

Edited September 30, 2013 by Jed '06

[howard_l]

I think it is a Glabella which is part of the Cephalon of a trilobite. I do not think it is from an Isotelus.

[squalicorax]

Cool piece. agreed on the cephalon.

Edited September 30, 2013 by squalicorax

[Jed '06]

I think it is a Glabella which is part of the Cephalon of a trilobite. I do not think it is from an Isotelus.

Cool piece. agreed on the cephalon.

Hi Howard & squali,

I don't think I worded my post clearly on the location in the photo of what I thought was the Isotelus pygidium.It is at the bottom of the photo #3 , against the edge of the brachiopod/ bivalve(?). Were you guys referring to this one or the one at the top of the photo #1 (with the dark lines)?

Thanks for the help!

Edited September 30, 2013 by Jed '06

[piranha]

The mystery item appears to be an exfoliated Amphilichas pygidium. The attached example is illustrative for the basic morphology of the genus.

[Jed '06]

The mystery item appears to be an exfoliated Amphilichas pygidium. The attached example is illustrative for the basic morphology of the genus.

Amphilichas.jpg

Thanks again piranha!

This is so much fun, learning from you & all the good people on Fossil Forum! I've already filled up my small notebook full of names and terms to investigate! I was so uneducated about fossils that I didn't even know that trilobites were in Indiana. LOTS TO LEARN:)

I hope all of you who take the time and have the patience to answer all of our newbie questions realize how much you are appreciated! The knowledge that the people on F.F. possess is amazing. When when we say "thank you", we really mean "THANK YOU"!

[Caleb]

It's definitely an Amphilichas sp. pygididium, however it's not exfoliated, but in the ventral position/upside-down. Amphilichas and many other trilobites have a pygidial doublure/"lip" that folds under the pygidium. I'm guessing it helped with movement in some way. Very nice specimen and find!

Here's an Amphilichas pygidium(different species) in the ventral position that also displays the pygidial doublure/"lip".

Edited September 30, 2013 by Caleb

[piranha]

It's definitely an Amphilichas sp. pygididium, however it's not exfoliated, but in the ventral position/upside-down. Amphilichas and many other trilobites have a pygidial doublure/"lip" that folds under the pygidium. I'm guessing it helped with movement in some way. Very nice specimen and find!

Here's an Amphilichas pygidium(different species) in the ventral position that also displays the pygidial doublure/"lip".

Mifflin Pygidium 2-1.JPG

I don't think the term exfoliated is restricted to the dorsal cuticle. By definition exfoliation occurred irrespective of a ventral aspect as part of the doublure is absent. Following up on the doublure and movement, the terrace lines played a key role. Here are a few previously posted fun facts on trilobite terrace lines:

The functional morphology of ventral terrace lines provides a few clues to life habit. It is theorized that trilobites with strong terrace lines interacted more directly with the sediment. As an example, for purpose of feeding, the terrace lines ratcheted outward would have kept the sediment from slumping into the filter chamber. The lack of ventral terracing in other genera suggests active surface feeding in contrast to a burrowing habit. The burrowing habit (e.g., Cruziana, Rusophycus), are supported in part by the frictional resistance of terrace ridges interacting with or facilitating the transport and increasing the efficiency of burrowing in loose or sandy substrates.

[PennyT.]

Jed, you are so right. We really appreciate the education we receive from these fine Forum folks!!!

[Malcolmt]

Piranha, am I wrong in thinking that terrace lines are more prominent in trilobites that could enroll and they assisted in forming the closure.

[piranha]

Piranha, am I wrong in thinking that terrace lines are more prominent in trilobites that could enroll and they assisted in forming the closure.

Great question! The following paper discusses the possible functional morphology of terrace lines as a coaptative device assisting with enrollment. It seems logical that terrace lines occurring on articulating trilobite elements would take good advantage of the available frictional resistance. Along with vincular furrows, notches and a number of other clever mechanisms, trilobites were enrolling engineers! The Open-Access PDF is available at the academia.edu website of Rudy Lerosey-Aubril: LINK

Feist, R., Lerosey-Aubril, R., & Johnson, R. (2010)

Coaptative devices, enrollment, and life habits in Paralejurus, a particular case in scutelluid trilobites.

Palaeobiodiversity and Palaeoenvironments 90(2):125-137

[Jed '06]

Hi all,

I' m saying "Thank You" a lot this week!

Hope my old brain doesn't go into overload, learning quite a bit about trilobites from all of you!

Thank you to all!

[Malcolmt]

Interesting paper, had not seen it but had read about the concept. Almost makes one think of intelligent design. How could such minute intricacies (adaptaions) have evolved as early as the Cambrian.

[Auspex]

...How could such minute intricacies (adaptaions) have evolved as early as the Cambrian.

What can persist, will; what cannot, will not. The incremental effect over a million generations can be profound!

[squali]

What can persist, will; what cannot, will not. The incremental effect over a million generations can be profound!

or even as little as +- 222,222.22 generations for humans

( 4 million years at 18 years/generation)

This is a great thread Thanks for the post and fantastic replies.