Trilobites in the modern IDU

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Bears Armed
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Trilobites in the modern IDU

Post by Bears Armed » Wed Mar 11, 2020 7:35 pm

I have added this group of animals to the fauna of the regional map, following a poll in which a clear majority of the voters supported this (even if we don’t count the four voting nations that aren’t [yet] actually on the map, or the one puppet that voted after its player’s main nation had already also done so, that’s still 12-to-1 in favour …) See: https://www.nationstates.net/page=poll/p=153911

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Do we still have Trilobites in the IDU's world?

The Free Bears of Bears Armed wrote: In RL the Trilobites (https://en.wikipedia.org/wiki/Trilobite) became extinct shortly before the rise of the Dinosaurs, but the Horseshoe Crab [of comparable antiquity] still survives. Might we still have living Trilobites in our world, somewhere in the almost-unexplored deeps or even in the shallows alongside -- or replacing -- the Horseshoe Crab?

No: Legionas.
Yes, only in the deeps: Laeral, Ruskayn, Res Publica Melitensis, Gladysynthia, North Cross, Lauchenoiria, and Comhar.
Yes, deeps and shallows (alongside Horseshoe Crab): Zamastan, Libertas Omnium Maximus, Christos, Gardavasque, Agury, Sunemia, Rio Palito, Birnir, and Ponoxien.
Yes, deeps and shallows (replaces Horsehoe Crab): ---
Yes, shallows only (alongside Horseshoe Crab): ---
Yes, shallows only (replaces Horseshoe Crab): Arcadia Dazeber.

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Obviously it’s still up to each nation’s own player to decide whether Trilobites are present in that nation’s own territorial waters, but it seems reasonable to presume that (at the least) those who voted in favour of there being trilobites in the “shallows” will have them present.
Looking at the pattern of votes cast, this suggests so far that our surviving Trilobites’ collective range centres on the Olympic Ocean (although not along the western coasts of Hesperia?), with outlying populations around both Libertas Omnium Maximus and Arcadia-Dazeber, but that they might be absent from most of the Tenebric Ocean’s shores. Decisions by additional players might change this, of course. I am working on IC explanations for this distribution.

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Post by Bears Armed » Wed Mar 11, 2020 7:35 pm

Relationships

Trilobites have a body-plan which places them clearly in the Phylum Arthropoda: A segmented body with jointed limbs, a chitinous exoskeleton, and compound eyes. Thus they are related to the Horseshoe Crabs, Crustaceans, Arachnids (Spiders, Scorpions, Mites & Ticks, etc.), Insects, Centipedes & Millipedes, and several other groups that you are less likely to have heard of. They might even be Crustaceans, although apparently the current consensus among palaeontologists says not. If they branched off from the Arthropods’ basal stocks before the ancestors of the various groups that survive in RL diverged from each other then some taxonomists (favouring a ‘crown group’ model of classification) would place them outside (but as a ‘sister-group’ to) the Arthropoda proper, in a wider assemblage labelled ‘Panarthropoda’: Here in the IDU, however, their own survival into modern times would simply extend the scope of the ‘crown group’ and thus of the Arthropoda proper.
The distinctive three-lobed body-plan that all Trilobites share is no more “unusual” than the body-plans of various Crustacean groups, but there is one feature in which they differ from all other animals! This is the fact that the lenses in their eyes are composed not of organic materials, as in all of those others, but of Calcite crystals — one per individual segment in each compound eye — instead.

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Post by Bears Armed » Wed Mar 11, 2020 7:37 pm

RL history

The earliest fossils of Trilobites that have been discovered so far date from the Cambrian Period (c. 540—485 million years ago), which is the earliest stage in history from which many fossils that can clearly be assigned to surviving phylums have been found. They did not appear right at the beginning of this time, which is known mostly for its “small shelly fauna”, but were present and diversifying well before its mid-point. However, the earliest known forms were already clearly recognisable as fully-complete Trilobites in body-plan, diversified, and geographically widespread, which obviously suggests an earlier evolutionary history for which direct evidence has not yet been found: Maybe the earlier stages simply took place within a limited geographical range from which no fossiliferous rocks have yet been found (Maybe, even, IC they originated in the IDU’s world and then spread to RL Earth? ;) ); maybe those proto-Trilobites, like some other Arthropods, had only relatively “soft” exoskeletons rather than the mineral-reinforced ones of the later forms (and of some Crustaceans), so that remains surviving to be fossilised was much rarer; maybe, perhaps because of that softer casing, those proto-Trilobites were much smaller than the later “true” ones and so any fossils that did manage to form would be harder to spot…

During the remainder of the Cambrian and through most of the following Ordovician (c. 485—434 million years ago) the Trilobites remained a major component of the marine fauna and different forms developed for a wide range of lifestyles: Most walked along or swam close to the sea-bed, as predators, scavengers, ‘deposit feeders’ (which “mined” the seabed for smaller organisms & organic debris), or filter-feeders; some swam higher up, apparently filter-feeding and maybe actively hunting in the plankton; it has been suggested that one family had become parasitic on some types of ‘sessile’ (i.e. fixed-in-place) animals, although this is still disputed; and one family is even thought to have developed a symbiotic relationship with sulphur-using bacteria which supplied them with nutrition. However, the end of the Ordovician featured a ‘mass extinction’ event: There was an Ice Age, which lowered sea-levels (as well as global temperatures) and thus not only drained wide expanses of the continental shelves over which the Trilobites had lived but also — probably — brought oxygen-poor water from the deeps close to the surface. Trilobites were among the [numerous] groups of animals that suffered quite heavy losses during this stage, but survived it although with their phylogenetic and ecological diversities significantly reduced: form then on, it seems that most if not all of them were restricted to primarily-scavenging lifestyles. They declined further during the subsequent Silurian and Devonian Periods (c.434—419 MYA; and c. 419—386 MYA), presumably due to the evolution of more effective competitors and/or predators, and a series of extinction events during the second half of the latter (possibly linked to another Ice Age?) reduced them to just a single Order whose surviving lineages seem to have been restricted to moderately deep water. This remnant stock then managed to persist through the Carboniferous Period (or ’Mississippian’ & ‘Pennsylvanian’ Periods; c. 386—291 MYA, either way…) and Permian Period (c.291—252 MYA)… but the end of the Permian was marked by a ‘mass extinction event — this time apparently linked to a rise in global temperature, rather than to a serious drop — which was so severe that some palaeontologists call it “The Great Dying”! No fossil Trilobites have ever been found for which dates later than this are considered appropriate, and so they are presumed to have been among the numerous groups that it exterminated completely. The overall pattern of changes in faunas (and to some extent in marine ‘floras’, as well, although less so among the land-based plants…) was so extreme that this event is used to mark the transition from a Palaeozoic Era (i.e. “Era of Ancient Life”) to a Mesozoic Era (i.e. “Era of Middle Life”; also popularly called “The Age of Dinosaurs”).

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Post by Bears Armed » Wed Mar 11, 2020 7:38 pm

Survival in the IDU

Our world’s different pattern of continents presumably indicates a different history of ‘plate tectonic’ events going back a long way, quite possibly even back past the beginning of the Cambrian Period. This being the case, our world’s history of ‘mass extinction’ events could plausibly have been different as well, even if external factors such as the ones that might help to start Ice Ages — or major meteoric impacts — were the same here as in RL.
I am not going to suggest that all of our world’s ‘mass extinctions’ were less severe than those of RL Earth, nor to deny that ecosystems here might then also have had to cope with one or two additional such events which RL ecosystems did not. Nevertheless, it seems reasonable to me to presume that these differences also led to some differences in the compositions of the post-extinction ecosystems… although some of those differences would probably later have been evened-out by some extinct groups being replaced — and possibly some surviving groups being out-competed, as well — by members of groups that had survived in one or more RL-like Earths and “leaked” across to here. (I had already mentioned that idea elsewhere in this sub-forum, in the specific context of the mass-extinction at the end of the Mesozoic Era and the subsequent developments of — especially — our Mammal and Bird faunas…).
Unless any of you insist on changing this, I think that our modern-day Trilobites would belong to two or three separate Orders, one or two of which had also existed in RL but one of which would be endemic.

The Proetida were the last order of Trilobites to appear on RL Earth, and were also the order to which the last surviving Trilobites on RL Earth belonged. They seem to have lasted that long because they had become adapted to deeper waters, where there was less competition: As some other groups of animals that followed such a pattern have survived on RL Earth until today, even though all of their close relatives living in shallower water have long been extinct, it doesn’t stretch probability too far to suggest that these could also have done so. Thus, this order would contain our deep-sea species.

The Lichida were among the orders that became extinct during the latter half of the Devonian period on RL Earth. Their members were characteristically spiny, which is why they’re distinct enough from all the others for me to consider them worth using. I don’t yet have any particular theory about how & why they would have survived here when so many others do not, so would suggest that if we do use them then it as the stock for an area isolated from the world’s “main” Trilobite populations — perhaps the coastal waters of Libertas Omnium Maximus, as that nation was among those voting for the presence of trilobites “in the shallows” but the only other nations near there who voted at all were against that possibility — with their origin a mystery (and possibly due, although nobody IC would know this, to [fairly recent?] interdimensional “leakage” from a version of Earth that is still in its Ordovician or Devonian period?)

The Neotrilobita — unless I find a better name for them — would then be our endemic order, containing primarily species resident in the shallower waters around [some of the] shores of the Olympic Ocean. As my ideas about the region’s geological history involve that ocean only having formed as a former super-continent (including all four of our present main land-mases) broke up from the mid-Mesozoic onwards, my suggestion for their evolution & survival is that their ancestors had actually managed to spread — unlike any Trilobites known of so far on RL Earth — successfully through the brackish water of estuaries into the fresh waters further inland: This let them survive the sea-level changes of the later Devonian and even the end-Permian mass extinction. During the Mesozoic they then expanded back downstream into the shallow seas (or, at least, salty “lakes”) that existed at times in various places “within” the super-continent, and thence into the Olympic Ocean as that opened up as well. Any last freshwater Trilobites that managed to survive until the end of the Mesozoic were probably wiped out in the ‘K-Pg Event’ (i.e. “Death of the Dinosaurs”), although some limited re-colonisation of that environment might have taken place more recently. I will presume that they and Crustaceans such as those that fill [probably similar] ecological roles today on RL Earth are ecologically balanced enough against each other for both groups to exist here, although in some cases conditions in certain areas may favour one or the other.
Arcadia Dazeber voted in favour of trilobites in shallow waters, but Legionas to their north voted against us having any surviving Trilobites at all: If those views are matched by their decisions now about having Trilobites in their own nations’ coastal waters, and if no linking populations around the southern end of that continent are approved by players there, then possibly the ancestors of Arcadia Dazeber’s stocks “returned to the sea” locally in the late Mesozoic, separately from those that populated the Olympic Ocean, and have been unable to spread further because (? reason still to be determined…).

The basic ecological role filled by these coastal species would be as scavengers & sometimes predators, although the latter would be probably limited to smaller and relatively slow-moving (or even sessile) prey, without heavy armour of its own, as is also the case for many types of Crab or Lobster, but I have some ideas about various more-specialised lifestyles & forms that would also be possible.
Bearing in mind the “origin story” that I now suggest for our main group of Trilobites, and having done some more research into the RL ones, I am dropping my suggestion that some species might — like the Horseshoe Crabs — crawl ashore to lay their eggs in beach sands. However, if we do go with my suggestion of a ‘freshwater’ stage in the evolution of the endemic order Neotrilobita, there might be species whose adults normally live in brackish estuaries or swamps but migrate upriver to reproduce and whose young spend some time developing in freshwater before moving back downstream…

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Post by Bears Armed » Wed Mar 11, 2020 7:39 pm

Reserved for my suggestions about particular types of Trilobites, with differing roles & features, we might have here.

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Post by Bears Armed » Wed Mar 11, 2020 7:39 pm

Reserved for my suggestions about particular types of Trilobites, with differing roles & features, we might have here.

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Post by Bears Armed » Wed Mar 11, 2020 7:40 pm

(Reserved for the summary that I will make of people’s wishes about Trilobites present in their own nations’ waters, or discovered by their explorers in international waters.)

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Post by Bears Armed » Wed Mar 11, 2020 7:40 pm

(Reserved for the summary that I will make of people’s wishes about Trilobites present in their own nations’ waters, or discovered by their explorers in international waters.)

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Post by Bears Armed » Wed Mar 11, 2020 7:41 pm

(Reserved for the summary that I will make of people’s wishes about Trilobites present in their own nations’ waters, or discovered by their explorers in international waters.)

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Post by Bears Armed » Wed Mar 11, 2020 7:41 pm

(Reserved for the summary that I will make of people’s wishes about Trilobites present in their own nations’ waters, or discovered by their explorers in international waters.)

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