Prehistoric Pokemon: Kabuto and Kabutops/Order Xiphosura
Kabuto, Omanyte’s counterpart fossil, has two different fossil bases. It’s most frequently compared to a trilobite, and its body shape certainly does suggest one. However, it also takes some inspiration from the Xiphosura.
(The xiphosuran Mesolimulus. Image from Wikimedia Commons.)
Xiphosura is an order within the subphylum Chelicerata, which also includes arachnids and sea spiders. They are distinguished by their solid, smooth, dome-like carapaces, which bore a secondary pair of primitive eyes capable of detecting changes in light. This is reflected on Kabuto, which appears to have a different face depending on whether you look at it from the front or above!
Unlike Ammonoidea, Xiphosura is not completely extinct. It is represented today by horseshoe crabs (above - image from the Tybee Island Marine Science Center), which inhabit coastal waters in Southeast Asia and the American Atlantic coast. Modern horseshoe crabs are essentially unchanged from the oldest members of Xiphosura, which originated at some point during the Silurian period, some 450 million years ago.
Despite their unassuming appearance, horseshoe crabs are invaluable to the medical industry; their unique blood is used to synthesize a substance called Limulus amebocyte lysate, which is used to detect gram-negative bacteria.
Just as Omastar evolves into Omanyte, Kabuto eventually evolves into Kabutops. However, while Omastar remains fairly accurate to the realities of ammonite biology (discounting its ability to launch its spikes and attack with jets of water), Kabutops takes a xiphosuran and gives it the rangy, bipedal body of a land-dwelling predator, complete with massive scythe-like claws for killing its prey. While I’m not opposed to Pokemon diverging from biological reality (and while I actually like Kabutops more than Omanyte, from a pure character-design perspective), it’s a bit strange in comparison to Omanyte’s more naturalistic transition.
Also, Kabutops has an internal skeleton? I’m not even going to touch that one.
Kabutops’ segmented anatomy seems more trilobite-like than Kabuto’s, and its head even bears the distinctive shape of the trilobite head segment. However, there’s another extinct animal I find that it resembles...
The eurypterids - such as Eurypterus, pictured above; image by Obsidian Soul - were relatives of the xiphosurans that lived from the Ordovician to the Permian periods. (They’re also known as “sea scorpions”, despite not being true scorpions.) Their ranks included the largest arthropods in Earth’s history, many of which were powerful predators. To me, Kabutops resembles what would happen if a eurypterid grew legs and became a running land predator. It’s even got the spike-shaped eurypterid tail!