Convergent Evolution of Cross Continental Trilobites?

[NoahW24]

At work, I study convergent antibody evolution in response to COVID vaccination. When you have a chisel everything around you is shale, so during my internet endeavors in paleontology, I find a lot of questions coming up for me about trilobite convergent evolution, particularly between the Moroccan and North American species with which I am most familiar. This thread will be a few different posts of species which have really stood out to me as similar, and I would be delighted if others shared their own observations! 

 

 For a little background which got me thinking on the topic- I'm in Boston, where the Braintree trilobites once were, (and currently exist as mostly as gravel in the harbor  ). These Olenellus bugs are here because Boston was the little plug blocking up the straight of Gibraltar between Morocco and Spain, where the same species can also be found due to the shared origin, pre-continental drift https://www.jstor.org/stable/4094982 (Fletcher et al 2005, J Paleontology). So anyway below are some photo side-by sides and some very very amateur observations on convergent evolution after earlier speciation, or just half-way there divergent evolution after population separations. I'm interested to hear others thoughts, and if anyone knows of any good literature on this subject and better ways of distinguishing morphologically between Moroccan and North American Trilobites, and what niches these species filled which may help inform shared body structure. I'm holding out hope @piranha might have some insights if they are feeling generous :0 . The following critters are all Devonian in some capacity. Thanks for your input! (ALSO please let me know if this belongs in a different forum)

Edited August 10, 2021 by NoahW24

[NoahW24]

Pair 1: Dolmanites limulurus and Zlichovaspis rugosa

 

So on this pair we see a few distinct differences on the rostrum, a little more rounded on dolmanites, and a little more of a scoop on the zlichovaspis, GRANTED we do see a similar schnoz on Huntonia, closely related to Dolmanites. Almost looks like a middle point between the two, especially considering the larger eyes, schnoz protrusion (scientific term), and rounded posterior resembling more the Moroccan Zlichovaspis. Any thoughts on how feeding strategy/predator avoidance niches may have caused this trait convergence, or if they actually are a related lineage? The nose-spoon makes me think sand foraging, with better eyesight for keeping watch for predators during. I wonder what accounts for the Dolmanites Difference^tm ?

 

http://www.online.com/EDCOPE_Enterprises/trilobites/OKTrilo7/OKTrilo7.htm

http://www.fossilmuseum.net/Fossil_Galleries/USTrilobites/Dalmanites_limulurus/Dalmanites_limulurus.htm

Zlichovaspis rugosa, Ihandar Formation, MaOder Region, Morocco - Houston Museum of Natural Science - DSC01511.JPG

 

 

 

Edited August 10, 2021 by NoahW24

[NoahW24]

Pair 2: Morocops/Austerops/PhacopsETC and Eldredgeops

 

These two share what seems to be a very successful body plan for trilobites, or maybe just the best preserved due to shell thickness. Eye morphology and armor suggests similar lifestyle strategy, too tank-like to chomp perhaps? Any literature recommendations on the subject much appreciated!

Pair 3: Hollardops/Metacanthinia vs Greenops

 

Another case of similarity which ends at eye size, the northern American trilobites (were they even further north at the time) seem to have smaller eyes in general. We also see sharper spines on the Greenops, which Metacanthinia and Coltraneia share, though they are distinctive in other ways. Any insight on the function of posterior spines? Are they racecar trilobite speed spoilers?

[Tidgy's Dad]

Dalmanites and Zlichovaspis are from the same family so naturally share many features but have diverged to show show some differences.

The next lot follow a fairly typical phacopid bodyplan as this is common in the Order Phacopida. 

The last three belong to the family Acastidae, so are similar in many ways. 

I would guess that the posterior spines on the latter bunch are partly to help stop them sinking into soft substrate, but mainly to act as defensive spikes when the animals were enrolled. 

Scott will know more. 

 

[NoahW24]

On 8/9/2021 at 8:49 PM, Tidgy's Dad said:

Dalmanites and Zlichovaspis are from the same family so naturally share many features but have diverged to show show some differences.

The next lot follow a fairly typical phacopid bodyplan as this is common in the Order Phacopida. 

The last three belong to the family Acastidae, so are similar in many ways. 

I would guess that the posterior spines on the latter bunch are partly to help stop them sinking into soft substrate, but mainly to act as defensive spikes when the animals were enrolled. 

Scott will know more. 

 

Thanks for the reply! Studying early wildlife is such an adventure, with current geographic positioning meaning so much less for familial distance than it does for contemporaries. Do you have any recommended reading to get more familiar with trilobite phylogeny? I’m working my way through Sam Gon IIIs website, if you have any other favorites I would be much obliged.

 

best,

 

Noah

[cck]

They may not have been at a distance in the day

[cck]

Is posit these fellows evolved pretty close together... so no mystery

I’d