The ocean will seemingly never run out of strange creatures to baffle the mind — especially when you factor in the extinct ones from millions of years ago.
You think the hammerhead shark or the barreleye fish are weirdly built, right? But, then you hear about animals like the ancient Dunkleosteus or the giant sea scorpion, and you're probably like, "Wow I am so glad I didn't live in a time where 8-foot swimming scorpions and fish with blades for teeth existed."
Millions of years ago, the sea was kind of a free-for-all in terms of what nightmare animals lived there. Take, for instance, the Stethacanthus, a shark with spikes on its head and dorsal fin.
And it's the weirdest-looking dorsal fin you'll ever see.
It may have been pretty small and just ate fish, crustaceans and cephalopods, per Melbourne Museum. But that doesn't make this 350-million-year-old fish any less threatening with those head spikes. Technically those spikes are called denticles, per the Journal of Vertebrate Paleontology.
Modern-day shark skin is made up of the same sort of spiny scales, just more tightly woven.
Scientists aren't sure what the purposes of these spikes or dorsal fin were. Or why it's shaped like an ironing board. But they have made some educated guesses:
1. For scaring.
The Stethacanthus was only 2 feet long, per the Melbourne Museum, and BBC reported that some have suggested that the spiny patches may have been to make itself look bigger.
Perhaps the alignment of head and dorsal spikes were able to make the shark look like it had a wide, toothy mouth.
This optical illusion would have made it seem larger or more dangerous to scare off potential predators.
2. For transportation.
The ReefQuest Centre for Shark Research noted that some have theorized the Stethacanthus used its spikes to attach to other animals and get more easily transported from area to area.
Sort of like the modern-day remoras.
3. For mating.
Let's be real — it's almost always for mating. After all, BBC noted that only males have that bristly top fin. The Journal of Vertebrate Paleontology reported that some scientists believe the denticles to have been weapons for breeding males to use against other males for a female's affection.
And, the Journal noted that some believe the flat fin structure was inflatable.
So, it could grow to a larger ironing board — perhaps to better attract mates with?
One thing is pretty easy to assume, though: As ReefQuest noted, the shark certainly couldn't glide through the water with ease.