Trilobite Rarity

[Top Trilo]

Elrathia trilobites are very common, they're small, have no spines, and have a lot of preserved molts. On the other hand you have rare trilobites with spines covering its whole body or trilobites that exceed half a meter. These are not as common, but spines and size seem to be an evolutionary advantage. Why are the trilobites that seem to have the best chance of survival the rarest ones? Or is it just a marketing play?

[Kane]

It may be much more complicated than simply morphology. Trilobite rarity may also be contingent upon the faunal community at the time, local deposition, preservation, and available outcrops. It is not always the case that large or spiny trilobites are more rare than simpler body plans; there are species of proetids that are exceptionally rare. In other cases, larger trilobites may be harder to find complete on account of the effects of disarticulation from environmental factors. It can also be the case that a species which appears in one formation as common may be quite rare in another formation of the same age. 

 

I should also say that large size is not always an advantage, nor is it always the case that having an elaborate exoskeleton is either. Keep in mind that larger creatures need more energy from their environment through available food sources, and that moulting requires sufficient energy to regrow those elaborate spines, horns, etc., which might be less efficient than some of the smaller, simpler types that can survive lean times better. Usually it is the case that there are fewer larger creatures than smaller ones on account of available food sources and fluctuations thereof (but not always). 

[FossilDAWG]

Overall, complete trilobites are infrequent in the fossil record and require particular circumstances to be preserved.  In particular, they must be buried quickly to protect them from disarticulation by environmental forces (such as rolling around in the waves) and scavengers.  Studies with modern crab carcasses indicate that they are completely broken up within as little as a day if not protected, and the same was likely true of trilobites.  Some deposits with relatively large numbers of complete trilobites were formed in deep water, far below the point where the sediment is disturbed by waves or storms, and with few scavengers to break up the carcasses.  This is the case with the Wheeler Shale where the abundant Elrathis kingi are found.  In the Cincinnatti area, the Ordovician formations consist in some part of stacked turbidite deposits, where hurricanes or maybe earthquakes cause unstable mud deposited on slopes to break loose and form a mud avalanche that catches animals on the sea floor and buries them below the reach of scavengers.  Often these trilobites would enroll as they were carried along in the sediment flow, but once deeply buried they were not able to un-enroll and dig their way out.  Being enrolled also helped to protect them from disarticulation by scavengers or animals that burrowed through the mud in search of food.  A similar scenario accounts for many of the crab fossils found in concretions in Oregon/Washington/British Columbia.  Smooth (effaced) trilobites such as Isotelus and Bumastus are thought to have burrowed into sediment on the sea floor, with just their eyes showing, which may help explain the relative frequency of these trilobites as complete specimens.  (Note that "relative" does not mean that such fossils are common even where they occur, most individuals still ended up as broken up sclerites).

 

On the other hand, spinyness can be assumed to have had a fitness cost (more exoskeleton area = more nutrients needed to make the exoskeleton for example), so evolving spines must have been a response to some selection pressure.  It's a fair assumption that one such selection pressure would have been protection from predators, which suggests these trilobites would have lived in an environment where predators such as fish or cephalopods were abundant.  These predators will also feed readily on fresh carcasses with lots of "meat" still attached.  Some odontopleurids are thought to have used their spines to "grasp" bryozoan colonies, perhaps to keep from being washed away in water currents.  In general, spiny trilobites were likely associated with environments with more predators and scavengers, or higher energy (water currents and waves/storm surges).  These factors may have been associated with shallower water depths.  To be preserved intact, such trilobites would have had to be carried to deep water and buried quickly.

 

Don

[Top Trilo]

Thanks guys, this was very informative

 

[jpc]

Ever since I got into fossils nealry 40 years ago, I have wondered the same question about mammal fossils.  Why is the White River Fm so full of complete skulls and even skeletons, but anything more than jaw pieces are exceedingly rare in most fossil mammal deposits.  It is a question of preservation, as has been suggested above.  

[erose]

6 hours ago, Top Trilo said:

 Why are the trilobites that seem to have the best chance of survival the rarest ones? Or is it just a marketing play?

 

now on these two points.....  spines and size have nothing to do with survival.   Evolution is much more complex.

 

"Marketing play?" well yes, 'ol ma nature made that decision. figured if folks were going to profit off her handiwork she was going to make them work for the good stuff.

[FossilNerd]

On 12/22/2020 at 9:58 AM, Top Trilo said:

On the other hand you have rare trilobites with spines covering its whole body or trilobites that exceed half a meter.

The larger bugs may not always be particularly rare, what is rare is finding them whole or even in recognizable pieces. 

For example... The mighty Isotelus is found here in our Ordovician deposits. In certain exposures one can find fragments of the giants in great number. The caramel brown pieces litter the ground, but finding anything that is diagnostically recognizable is usually rare. I can imagine the smaller trilobites fair better during the fossilization process.

 

So marketing for some of the big bugs may be based upon finding a whole one, or somewhat whole (and therefore diagnostically recognizable) piece.

[FossilDAWG]

Caution: completely off tangent comment coming up.

FossilNerd writes " The caramel brown pieces litter the floor ...".  As I learned the word and have used it all my life, "floor" refers to an artificial surface within a structure such as a house.  The natural surface of the planet is, as I learned it, the "ground" (Excepting of course water covered areas).  If I am hiking outdoors and I spy a fossil at my feet and pick it up, I have picked it up from the ground, not the floor, it seems to me.  If I read about trilobite pieces littering the floor, it makes me think someone dropped a trilobite in their house (or garage) and it shattered.  However I have noticed more and more frequently people using "floor" as a synonym with "ground".  Every time, it jumps out at me.  Am I alone in this? 

 

Don

[FossilNerd]

6 minutes ago, FossilDAWG said:

Caution: completely off tangent comment coming up.

FossilNerd writes " The caramel brown pieces litter the floor ...".  As I learned the word and have used it all my life, "floor" refers to an artificial surface within a structure such as a house.  The natural surface of the planet is, as I learned it, the "ground" (Excepting of course water covered areas).  If I am hiking outdoors and I spy a fossil at my feet and pick it up, I have picked it up from the ground, not the floor, it seems to me.  If I read about trilobite pieces littering the floor, it makes me think someone dropped a trilobite in their house (or garage) and it shattered.  However I have noticed more and more frequently people using "floor" as a synonym with "ground".  Every time, it jumps out at me.  Am I alone in this? 

 

Don

Please pardon my bad use of the English language...

 

To clear up confusion, I have edited my original text from using the word floor to ground.  

[Kane]

I read it as a figure of speech, an idiomatic expression, such as the classic “forest floor.”  

[Fossildude19]

I notice it quite a bit coming from British authors.  

[FossilDAWG]

I didn't mean to suggest that your English was "bad".  Language changes over time.  I'm simply curious if the culture is changing to where "floor" and "ground" mean the same thing and can be used interchangeably.  Of course, if two words mean exactly the same thing eventually one will go extinct.  I admit to being a bit of a language nerd, and something I pay attention to is the nuanced meaning of words, subtle differences that add meaning.  For example, the way I use the words, if you say "I dropped my sandwich on the floor" I have a picture that you are inside a building.  If "floor" and "ground" are exactly the same, some information about context is lost.  I have noticed this happening to a number of words.  Another example off the top of my head is "injured" vs "wounded".  I always thought of "wounded" as being deliberately injured by someone, such as being shot.  If I am unlucky and step on an unstable rock and twist my ankle, I would describe that as being injured but not wounded.  Still, I have seen "wounded" being used in contexts where I think "injured" is more appropriate, even in news reports where I (naively) would think journalists would have a decent command of English.  All in all, I feel that English is losing some of its nuance and ability to convey subtle information.

 

Anyway, rant over.

 

Don

[DPS Ammonite]

30 minutes ago, FossilDAWG said:

Another example off the top of my head is "injured" vs "wounded".

Continuation of the aside. I think of a wound as not always from a deliberate act, the same with wounded. When I get stabbed while hiking by a cactus or agave, I get a wound. Thus I am wounded, not quite a fully deliberate act by the plant. 
 

In geology, I would describe a volcanic crater as having a floor, as in the one in Hawaii that just filled with lava. Same with a cave. 

Edited December 27, 2020 by DPS Ammonite

[FossilDAWG]

Clearly there is overlap, and it's not always obvious what word (if any) is best in a particular situation.  Still, there must be some nuanced distinction between "wounded" and "injured".  Otherwise one of them is superfluous and should be discarded.

 

Anyway we have wandered a long way from trilobite rarity.

 

Don

[FossilNerd]

40 minutes ago, FossilDAWG said:

 

I didn't mean to suggest that your English was "bad".

No worries!  

 

I also learned that “floor” and “ground” have the meanings that you described. Given that this is an international forum, I can see how using one word over another could cause confusion so I made the correction.  I honestly didn’t even realize that I typed floor versus ground until it was pointed out. I typically do not use the words interchangeably.  

[grandpa]

Another interesting case of "floor" vs. "ground" - "Ocean floor", not "ocean ground". 

[jeannie55]

19 hours ago, FossilDAWG said:

I didn't mean to suggest that your English was "bad".  Language changes over time.  I'm simply curious if the culture is changing to where "floor" and "ground" mean the same thing and can be used interchangeably.  Of course, if two words mean exactly the same thing eventually one will go extinct.  I admit to being a bit of a language nerd, and something I pay attention to is the nuanced meaning of words, subtle differences that add meaning.  For example, the way I use the words, if you say "I dropped my sandwich on the floor" I have a picture that you are inside a building.  If "floor" and "ground" are exactly the same, some information about context is lost.  I have noticed this happening to a number of words.  Another example off the top of my head is "injured" vs "wounded".  I always thought of "wounded" as being deliberately injured by someone, such as being shot.  If I am unlucky and step on an unstable rock and twist my ankle, I would describe that as being injured but not wounded.  Still, I have seen "wounded" being used in contexts where I think "injured" is more appropriate, even in news reports where I (naively) would think journalists would have a decent command of English.  All in all, I feel that English is losing some of its nuance and ability to convey subtle information.

 

Anyway, rant over.

 

Don

When a language ceases to evolve and in some cases devolve, it will become like ancient Hebrew and Latin or a dead language. An example of devolving is using bad for good or good for bad. Recently, we’ve witnessed an evolution in our language by the addition of a couple of COVID portmanteaus like maskhole, Covidiot, maskne, and doomscrolling. But I agree with the incorrect usage of floor vs ground and injured vs wounded. In my day, before cable, portable landlines, and all you can eat buffets, everyone hated gross and groovy. Well the adults. Gross stayed the course and groovy...well it died except in dragnet reruns. Wine?  Yes I need it badly. 

[grandpa]

So, since we've gone down this rabbit hole that totally steals from the OP's purpose of the initial post .  .  .

 

I'd like to give my 2 cents +/- on what I understand the purpose of language to be.  Put simply, the purpose of language is to communicate.

 

Common language = communication within a common group.

 

"Repurposed"/newly invented words (e.g., bad to mean good) are often intentionally used as a type of "code" within a select community.  Whether one understands and uses such communication is a factor of whether one is an accepted/intended participant in said community.  One may understand what is intended but not use that communication style indicating that one is NOT part of that community.

 

Every generation that I've been privy to observe, and some before my time (e.g., roaring 20's) has co-opted new word usage to set that generation uniquely apart from the previous generation.  I see that as generational identity and assign to it no ill will nor ill purpose.  It is meant as a "code" for that identity group to converse with each other and signify the identity of the user as part of the group.  Others outside that generation come to know the meaning of the words, but they would look strange using them.  For example, it would weird for my grandsons to say "Hey Grandpa, that's a groovy hat."  It would be equally out of place for me to say "Kobe is a GOAT, may he rest in peace" even though I would know what I'm saying.  That would make me a perp.

 

So again I say that language is for communicating. 

• Common language is for common communication. 
• But there is also "code" communication that is in a common language but that reforms or re-appropriates words for an "in-group" usage and identity.
• And the third alternative is the evolution of language and/or of specific words such as ground vs. floor.  This naturally occurs over time and, as long as the usage becomes universal, communication among the masses is maintained.  An example would be the prior usage of light globe (early 20th century) for what is today known as a light bulb.

Now back to "floor" vs. ground".  Wayne, @FossilNerd has stated that what he meant to say was ground.  Yet we have seen some good examples of where the term "ground" is replaced by "floor", e.g., forest floor, ocean floor.  So is there an evolution of terms taking place here?  Only time will tell, but for now I'm satisfied with Wayne's explanation that his was a slip and that there are exceptions where "floor" is the accepted term but where "ground" is the general term for terra firma.  Let's make a date to check back in 100 years to see if I was correct. 

[FranzBernhard]

On 27.12.2020 at 5:12 AM, FossilNerd said:

Given that this is an international forum, I can see how using one word over another could cause confusion so I made the correction.

Not really. Within the context, it was totally clear what was meant.

Btw, its nice to see a "forest floor" here! I had difficulties translating "Waldboden" (the surface, not the soil, which is the same word in German...) into English some time ago, but the translator gave indeed "forest floor" (as well as "forest soil"...).

Back to topic: These Isotelus fragments are a nice example of turning a rare fossil into an abundant fossil !

Franz Bernhard

[LabRatKing]

On 12/26/2020 at 9:05 PM, Kane said:

I read it as a figure of speech, an idiomatic expression, such as the classic “forest floor.”  

Aye, and English is full of confusing idioms.

 

but, my money based idiom (2 cents worth) on topic is this:

 

I long supposed that the frequency of trilobite finds and the elaborate exoskeletons of some species were/are linked to life cycle.

 

in other words- I believe bugs like Elrathia reproduced rapidly and in great numbers due to relatively short lifespans. Crazy, spiked specimens like Ceratarges had longer slower life cycles.

 

we see this evolutionary behavior in many extant species...think carpet beetles (Dermestids) vs stag beetles (Lucanidae). Fast, small and numerous vs big, slow, and relatively uncommon.

 

for real fun, try googling a “mortality plate” of extant species...

[grandpa]

6 hours ago, LabRatKing said:

I long supposed that the frequency of trilobite finds and the elaborate exoskeletons of some species were/are linked to life cycle.

 

6 hours ago, LabRatKing said:

we see this evolutionary behavior in many extant species. . . .  Fast, small and numerous vs big, slow, and relatively uncommon.

Biologists talk about this in terms of k-species and r-species.  For those wanting some detail on this see:

https://www.britannica.com/science/K-selected-species

https://www.britannica.com/science/r-selected-species

[LabRatKing]

Yep

 

5 hours ago, grandpa said:

 

Biologists talk about this in terms of k-species and r-species.  For those wanting some detail on this see:

https://www.britannica.com/science/K-selected-species

https://www.britannica.com/science/r-selected-species

Exactly 

[RJB]

Gloor or Fround  

 

RB

[Tidgy's Dad]

KISSING FORMATIONS

 

I've lost count of the Formations

Where my faced has kissed the ground.

At least twenty down in Kem Kem

Boda, Sweden kissed a mud mound

Twenty three in Burgess Shale

Much Wenlock, seventeen

You can see there's lots of places I've been drunk

But, really haven't seen.

 

Kissed forest floors in the Dunlap,

The ground in Payatte, Idaho

Fourteen times in Upper Chalk

And Aguija, Mexico

It's not that I'm a fighter

It isn't that I'm mean

I'm just a drinker with a problem

In the places that I've been

 

It doesn't matter where I am,

I'm not selective, not at all

I drink out of my hipflask

And in a while I fall

I move around the fossil world

Kissing rocks in every state

I'm the alcoholic fossil guy

Kissing rock floors is my fate.

 

I kissed six in the Hell Creek 

Eleven more in the McMillan

Twice, I ended in a bush

So, I counted them as one

Horseshoe Canyon I kissed plenty

I lost count in Georgian Bay, Ontario

Up there the floors are softer

And I landed in the snow

 

The Ocala, I kissed the beach

Seven times, at least I think

One time doesn't count though

I kissed the sand but didn't drink

London Clay, I kissed a lot there

There's a lot of ground to kiss

I hit every site on Isle Of Wight

There's not one I didn't miss.

 

Wheeler's Shale I can't remember

Few bars to top up my flask

But I did once get some moonshine

I kissed the ground then, should you ask.

The Glenshaw and the Fairview

East to  the Laoning too

The Morrison, oh boy, oh boy

I kissed near twenty two

 

In Mazon Creek I kissed nineteen

Connasauga, I kissed nine

I found six teeth where I last fell

And only two of them were mine

There is scarcely one location

Where my face and floor haven't met

I'm an alcoholic travel guide

Who hasn't finished yet

 

It doesn't matter where I am

I'm not selective, not at all

I drink, I get befuddled

My head spins then I fall

I move around the whole wide world

Kissing rocks in every State.

I'm an alcoholic fossil dude.

Kissing Formations is my fate. 

 

 

 

 

 

(I know they're not all actually formations and big apologies to Roger Turner)