Origin and Early Evolution of Arthropods
I read a pre-print of a paper, The origin and early evolution of arthropods,
Looks like I cite it thusly:
Aria, C (2021). The origin and early evolution of arthropods.
PaleorXiv, 4zmey,
ver.4,peer-reviewedbyPCIPaleo.DOI:
10.31233/osf.io/4zmey
The paper is 30 pages, including a 189-item bibliography.
I read it because I had hoped to understand what kind of animals arthropods had evolved from, maybe find out the arthropod equivalent of the dinosaur → bird evolutionary relationship. Reading the paper about Arthropod Terrestrialization and Richard Fortey’s Trilobite also gave me a little background that made me aware of how little I know about this topic.
This was a difficult paper. Aria wrote some of the most jargon-heavy technical prose I’ve ever ground through. Despite a 29-item glossary, I still had to look up words like “plesiomorphy”, “tagma”, “apomorphy” and “sclerotized”. Be aware of the definition of “arthrodized” if you attempt this paper.
Aria uses a German word, “Anlage” or “Anlagen” (plural) a lot. In another case of information camouflage, I wasn’t able to use DuckDuckGo to find what this word means in a paleontology or developmental biology context. From context, Aria uses it to mean something like a primitive feature that evolves into something more elaborate. Because this paper deals in arthropods, Aria uses “Anlage” to apparently mean the stubby little primitive legs of worm-like arthropod progenitors.
Aria including some great diagrams, including this information-heavy phylogeny:
It has so much on it, that it appears like the product of a conspiracy theorist. A further amusing facet is that it’s not a pure binary tree as most cladograms are. Aria has multiple lineages of Artiopodans, for example.
Insects, a really important arthropod group today, are just parts of “pancrustacea” on this tree.
Another diagram deals with the famed arthropod biramous limb.
There’s a leg segment that joins with the body, then it splits into two. Various arthropod taxa have lost one or the other of the splits, or used one split as a gill or other weird things.
Did the biramous legs evolve by splitting a single leg, or joining two independent legs? Turns out there’s fossil evidence for both!
And then there’s the place of trilobites in the phylogenetic tree. Were they chelicerates or mandibulates or Something Else?
Aria seems to come down on “closer to chelicerates”.
I did not really get my “ancestors of arthropods” clarity. I do have some arthropod-specific vocabulary now.