Honestly, icthyosaur fins are incredibly unsettling. What do I mean by that? Well, let’s look at the fin of a dolphin and compare.
It has a hand in there. Good. Homologous structures and all that. This is a good creature.
Now what the hell is this ungodly thing?
The entire fin, it’s just full of bones. A solid bone paddle. What is going on here?
Well, some Icthyosaurs actually exhibit a phenomenon known as polydactyly. What this means is that they had extra fingers. While not entirely uncommon for a single individual of a species to have extra digits, it’s extremely uncommon among tetrapods to gain extras across an entire species. We see it among some early tetrapods, but we also see it here, with Icthyosaurs. In some species, the number of fingers on one limb reaches ten.
Icthyosaurs also exhibit something known as hyperphalangy. While less unique (it’s also present in whales, mosasaurs and plesiosaurs according to Wikipedia), hyperphalangy means that the limbs have extra phalanx bones. What this means in Icthyosaurs is an almost corncob-like grid of bones.
In fact, when I was researching this, google thought that a picture of icthyosaur fins was in fact of corn domestication.
In conclusion, Icthyosaurs have clearly commited some sin in finger theivery, and their extinction was deserved.
I’m just trying to figure out why Secret Fingers Hidden in the Flesh freak you out less than flipperbones being shaped like flippers
It’s because finger fins are the norm! You see them in whales, manatees, turtles, mosasaurs, seals, nothosaurs, and pretty much every other aquatic tetrapod! Seeing homologous structures similarly appear in convergently evolved species is what you expect. Seeing corn-filled fins is not!
