Lateral flexibility in trilobites

[ScottBlooded]

So I was wondering how one goes about determining if a species of trilobite had lateral flexibility. That is, could wiggle side to side. I’m aware this is a rare quality that you get in like those Olenellus boys, but can’t find how it’s determined to be a trait of the animal as opposed to geological warping. Is there a part of the morphology that gives it away? Or is it just from finding enough intact specimens that were frozen mid wiggle?

[LabRatKing]

16 minutes ago, ScottBlooded said:

So I was wondering how one goes about determining if a species of trilobite had lateral flexibility. That is, could wiggle side to side. I’m aware this is a rare quality that you get in like those Olenellus boys, but can’t find how it’s determined to be a trait of the animal as opposed to geological warping. Is there a part of the morphology that gives it away? Or is it just from finding enough intact specimens that were frozen mid wiggle?

I would guess that in many specimens, they are able to see clearly how each pleural lobe interconnects plus by comparing said morphology to extent species such as various isopods and other Arthropoda with similar morphology.

[Thecosmilia Trichitoma]

From the limited knowledge I have of woodlice (which might be the closest think we have to trilobites nowadays, although they are terrestrial), non rolling woodlice (think Porcellio) have more lateral flexibility than Rolling woodlice (think Armadillidium.)  Note that this is not knowledge I have from any publications, but rather from observation of arthropods in my local area. 

[LabRatKing]

10 minutes ago, Thecosmilia Trichitoma said:

From the limited knowledge I have of woodlice (which might be the closest think we have to trilobites nowadays, although they are terrestrial), non rolling woodlice (think Porcellio) have more lateral flexibility than Rolling woodlice (think Armadillidium.)  Note that this is not knowledge I have from any publications, but rather from observation of arthropods in my local area. 

You are in the right frame of mind!

However, there are thousands of extant species of aquatic isopods, both fresh and saltwater that are likely even more like trilobites for comparison. They currently fill the ecological niche that many biologists think the trilobites used to fill.

 

Just like trilobites, they are both shallow and deep water, some bigger than a housecat! Also some are benthic (bottom dwellers) while others are pelagic (near surface and/or free swimming). Some are predators or even parasites, others are detritovores, the category in which most trilos are believed to fill. Some solitary, others in great swarms or schools!

 

 

I see you are out in San Diego. If you hop the orange or green line out to La Mesa and head to Lake Murray, there are about 15 different species that hang out on the shoreline and on/under rocks in the shallow areas you can check out for yourself! You can also find at least three different saltwater species to observe at the Tide Pools just north of La Jolla Shores beach.

 

[ScottBlooded]

Do these closest modern examples also have lateral flexibility as well as horizontal flexibility (enrolling, or close to it)? It seemed to me like you’d need that axial lobe to achieve that side to side wiggle but again I’m ignorant to the mechanics of the anatomy

[FossilNerd]

18 hours ago, ScottBlooded said:

Do these closest modern examples also have lateral flexibility as well as horizontal flexibility (enrolling, or close to it)? It seemed to me like you’d need that axial lobe to achieve that side to side wiggle but again I’m ignorant to the mechanics of the anatomy

Although I don’t have an answer to your original question, I am intrigued...

I wonder if @piranha might know of a paper focused on trilobite movement or anatomical mechanics?

 

Maybe we can dig around in his posted open access papers and find something. I’m off to look!

 

 

[Kane]

Treatise O: Arthropoda has substantial sections concerning dorsal exoskeleton morphology (as well as the other features, naturally!). Due to how the tergites and sclerites are positioned, one could reasonably infer that any twisting range of motion (ROM) would be somewhat limited. In other words, I would not pilot a trilobite to navigate a hairpin road.  

 

A very good clue to trilobite movement would be in examining Cruziana -- the tracks left by trilobites. You'll notice that there are more gentle curves to their locomotion as opposed to very sharp angles. That movement may be attributed strongly to their legs, of course. Coordinating so many legs would certainly allow for some gentle pivoting of direction. 

[LabRatKing]

19 hours ago, ScottBlooded said:

Do these closest modern examples also have lateral flexibility as well as horizontal flexibility (enrolling, or close to it)? It seemed to me like you’d need that axial lobe to achieve that side to side wiggle but again I’m ignorant to the mechanics of the anatomy

Enrollment is well documented and common both in the terrestrial and aquatic species. Lateral movement varies, just like in trilobites. Some are flexible  on all planes, others rely strictly on their legs as their bodies barely flex.

[Kane]

16 minutes ago, LabRatKing said:

Enrollment is well documented and common both in the terrestrial and aquatic species. Lateral movement varies, just like in trilobites. Some are flexible  on all planes, others rely strictly on their legs as their bodies barely flex.

And hence why trilobites never skipped leg day.

[ScottBlooded]

1 hour ago, FossilNerd said:

Although I don’t have an answer to your original question, I am intrigued...

I wonder if @piranha might know of a paper focused on trilobite movement or anatomical mechanics?

 

Maybe we can dig around in his posted open access papers and find something. I’m off to look!

 

 

Thank you for pointing me towards that post, my god that’s a lot of open access info. Even if this specific issue isn’t covered somewhere in all that, this is a lot of great reading. Piranha continues to be a font of useful info.

 

1 hour ago, Kane said:

Treatise O: Arthropoda has substantial sections concerning dorsal exoskeleton morphology (as well as the other features, naturally!). Due to how the tergites and sclerites are positioned, one could reasonably infer that any twisting range of motion (ROM) would be somewhat limited. In other words, I would not pilot a trilobite to navigate a hairpin road.  

 

A very good clue to trilobite movement would be in examining Cruziana -- the tracks left by trilobites. You'll notice that there are more gentle curves to their locomotion as opposed to very sharp angles. That movement may be attributed strongly to their legs, of course. Coordinating so many legs would certainly allow for some gentle pivoting of direction. 

I imagine cruziana appear in only specific conditions? As in, not every formation in which you find trilobites would have them? If that’s the case, I wonder how you determine if a given formation would even be worth looking through for cruziana in the first place? I imagine they’re hard to spot. And then, even if spotted, I imagine it’s difficult to pin a track to a specific species, unless you have a smoking gun (like the trilobite frozen at the end of a line of tracks, as I’ve seen in some of the most famous examples)

[Top Trilo]

25 minutes ago, ScottBlooded said:

I imagine cruziana appear in only specific conditions? As in, not every formation in which you find trilobites would have them?

Just like not every dinosaur bearing formation has footprints and to your other question I would imagine it would have to be an area with calm waters to preserve cruziana so that limits your trilobite areas that have the potential to contain trilo tracks and as far as identification I can't think of anything else to go off of than width and formation.

[LabRatKing]

Well, that is the fossil conundrum isn’t it?

all we can do is compare to extant species and make guesses based on the available if incomplete evidence.

 

personally, I like to think that the benthic trilobites moved like isopods and other benthic decapods. I also like to think that the pelagic species behaved similar to critters like artemia and triops.

then again, I spend a lot of time with the freshwater critters- marine life is not a strong point for me.

[erose]

Being arthropods I would imagine they could have behaved like a modern crawfish to make quick moves. They basically pop up off the substrate and then twist around to a new direction. I realize that is a rather sketchy SWAG. I've never been clear on how much they could use their "gill" legs to swim...