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The Trilobite is probably one of the most successful created which evolved in the cambrian explosion.

Though many sources stated the Opabinia has been hunting for Trilobites, this has yet been proven wrong.

Due to my research I haven't found much more animals in the Cambrian age that grow larger than Trilobites or Opabinias - so I do wonder why did Trilobites evolve such a powerful full-body armor when they're have been no clear natural enemies.

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  • $\begingroup$ predators don't have to be larger than their prey. More importantly Opabinia could not eat them with the armor, but they could easily eat them without the armor, that would be the point of evolving armor. $\endgroup$
    – John
    Dec 29 '18 at 5:13
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Your link that says "proven wrong" includes a hypothesis that Opabinia could have eaten trilobites during their molt, simply that it would not be able to eat through their armor (all the better reason to have armor).

The best evidence we are likely to have that trilobites had predators is that they have defenses; the fossil record is incomplete, and just because trilobites are well-preserved does not mean their predators must be. Unless other evidence surfaces for an alternative explanation, the simplest reason for why trilobites evolved armor is that trilobites with armor were protected from something and therefore selected for.

Injuries seen in fossil trilobites are similar to injuries from failed predation of modern related species (see for example Bicknell et al., 2018) and seem to be widely reported (Bicknell et al. 2018 cite a variety of other sources).

Bicknell, R. D., Pates, S., & Botton, M. L. (2018). Abnormal xiphosurids, with possible application to Cambrian trilobites. Palaeontologia Electronica, 21(2), 1-17.

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  • $\begingroup$ I agree with the hypothesis at first sight. Additionally I must confess I did link an older article because I couldn't find the one I was actually pointing to in time (it was also from wired.com stating that these researchers had actually proven it wasn't possible due to further research). The fact that there is such a high amount of Trilobite species which can be found all around the world, yet so few predators makes me wonder how an animal evolves a protection. We can agree they had a better success rate, but why would they evolve such a thing if (let's say) there is no predator yet? $\endgroup$
    – polarlighthouse
    Dec 28 '18 at 20:07
  • $\begingroup$ Also Opibinia appeared in the middle Cambrian age, while Trilobites had evolved in the early Cambrian already. $\endgroup$
    – polarlighthouse
    Dec 28 '18 at 20:12
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    $\begingroup$ @polarlighthouse I'm not an expert in the field, but I thought that the high number of trilobite fossils is simply because they fossilize so well and have been around so long, rather than them being the only animal around. Predators are typically outnumbered quite a bit by the species they prey on. Not having identified a definitive predator does not mean they have none. $\endgroup$
    – Bryan Krause ♦
    Dec 28 '18 at 20:12
  • $\begingroup$ I'm neither an expert, but since the Paelozoic age was actually the longest the earth's existence with animal life it's hard to believe there is no evidence of Trilobite predators when we have so many evidences about the amount of Trilobite species. Of course, predators are naturally less amount of their prey. I'm just wondering and it makes no sense to me to evolve something before there is a predator. But thtat's probably what we wonder about the cambrian explosion at all. $\endgroup$
    – polarlighthouse
    Dec 28 '18 at 21:12
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    $\begingroup$ There are very few animals that can eat a turtle would you argue a turtles shell is not for protection? If he protection was not effective there would be no reason to have it. $\endgroup$
    – John
    Dec 28 '18 at 21:18

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