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The trilobites vanished from the fossil record many millions of years ago, but they were obviously arthropods of some sort. Do we know which animals are their closest living relatives? I've heard both Armadillidiidae and horseshoe crabs. Can we tell which is right (or if there is a different answer), and how?

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    $\begingroup$ Without their DNA, it's difficult to know the answer to that, from physiology of >250mn year old fossils, perhaps crayfish and scorpions also come from trilobites, also arthropods, they appeared 100 million years afterwards. it's best to content ourselves with a map of genetic distance between shrimps, earwigs, horeshoe crabs, crayfish, and find a map of animals that comes from them. I can't find a genetic distance mapping tool on the web. $\endgroup$
    – DwayneDeSouza
    Apr 16 '19 at 9:32
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There were so many species of trilobites for 300 million years, so perhaps some trilobites species are closer to horseshoe crabs whilst others are closer to woodlice, some trilobites were amphibious and could walk onto the seashore.

If you check this research about horseshoe crabs, there are a dozen fossils that are hybrids between a trilobite and a horseshoe crab, i.e. bellinatus trilobitoides. enter image description here From the family tree you can see some early horseshoe crabs: enter image description here

this is a harpetida trilobite: enter image description here

The morphology of the fossils is mostly saved as dorsal morphology and ventral morphology. from the top the are similar to horseshoe crabs, and the different legs are similar to woodlice and bathynomus and horseshoe crabs in different fossils: enter image description here

There are other living animals that resemble them like Serolina Delaria: enter image description here Tadpole Shrimps: enter image description here That's from this cool page with images of lots of things like trilobites. Silverfish: enter image description here Bathynomus, similar to woodlice: enter image description here The videos of bathynomus are cool: https://www.youtube.com/watch?v=jfnHQPkta-Q

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The Tree of Life Web Project is a good resource for these kinds of questions. It looks like we cannot distinguish trilobites' origin from the origin of arthropoda: link. Also, some references on trilobite evolution and systematics from the same source: link.

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