Animal Crossing Fish - Explained #133
Brought to you by a marine biologist who is the big dumb…
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I am so dumb. I said the trilobite was the last fossil because I evidently forgot we didn’t actually cover this dude yet. Now everything is ruined. Oh well. So, today we will be the last fossil we are covering for real- Eusthenopteron.
It’s a long name, I know, but you can do it. -> yoos-then-OP-tare-on.
At the beginning of this series, when we spoke about the Coelacanth, we talked about tetrapod evolution, which is a wild ride. Chordata, the Phylum we as humans belong, is pretty awesome. We had such humble beginnings, and by now we have consistently been most of the largest organisms to ever grace this planet, right after the plants. Between dinosaurs, whales, and some sizeable fish, chordates, and more specifically, vertebrates, have dominated in size. We also have dominated ecosystems ever since we evolved jaws and began preying really efficiently on everything else, including each other. Although we have almost never been the first at anything major - we weren’t the first predators and we certainly weren’t the first on land - we have done it really well anyway.
We talked about how tetrapods - four-legged vertebrates - came to be via evolution from the fish body plan. Eusthenopteron is just one species within that transition. It, as well as Acanthostega and the Coelacanth, are lobe-finned fish, fish that actually have supporting bone in their fins, which eventually evolved into the sturdy arms and legs of tetrapods we see today. The fossil in ACNH is most likely based off this one of Eusthenopteron foordi, a really great fossil that preserved the whole fish since the Devonian (some 385 million years ago).
By Haplochromis, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6532784
Here’s what it might have looked like in life.
By Dr. Günter Bechly - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17059501
Is now a good time to talk about how all tetrapods, including you and me, are just really weird fish? Cladistically-speaking, we are all just fish. These days, it’s easy to separate fish from other vertebrates - they have gills and live their lives restricted to the water. If you look back to the Devonian, however, the line between fish and other tetrapods is blurred. The animals we collectively call “fish” are VERY DISTANTLY related to each other as a whole. You and your cat are so much more closely related than a goldfish is to a shark. Likewise, you and the goldfish are also more closely related to each other than either is to the shark. See where it gets weird?
In phylogeny, we try very hard to keep groups of animals monophyletic - this is a big word that means a group of organisms includes their common ancestor and every one of its descendent species. For instance, the group “Mammalia” is monophyletic, because the term encompasses all mammals, no matter how derived, like the whales. In contrast, a paraphyletic group is one in which an ancestor is grouped with only some of its descendants, typically with one very derived group simply left out. “Reptilia” aka the reptiles, are a great example of a paraphyletic group, because the term includes all reptiles (crocodiles, lizards, snakes, dinosaurs) except for the birds, who are still dinosaurs, but because they do the flying and feather thing, we’ve set them apart specially. “Fish” as a group, include all fish, except for the very special lobe-finned fish group, the tetrapods. ‘Fish” is, therefore paraphyletic, as a term. Obviously, we can decide that we are fine with the term “fish” meaning only vertebrates that have gills and live in water, for every-day means…but it’s fascinating to just delve into this clusterfuck of terms we made before we knew just how connected life on Earth really is.
And there you have it. Fascinating stuff, no?