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Nature can be ... weird. And if you've ever seen a coconut crab or an aye-aye, then you know exactly what I mean. But recently, researchers have been studying some animals that even they admit are strange. For example, a group of paleontologists think it's figured out the evolutionary story behind one of the weirdest-looking animals that ever lived, the Tully Monster. 

Paleontologist Victoria McCoy, now at the University of Leicester, has been fascinated with the ancient see creature since she was a child. She recently described the Tull monster as being "just about at the top of the scale of weirdness." But how weird are we talking exactly? Let me put it this way; if the cantina in Star Wars had an aquarium, a Tully monster would've fit right in.

It looks like it was cobbled together from the spare parts of random animals, with some extra bits thrown in. It had a chunky body, eyes sticking out from its on rigid stalks, and vicious little teeth inside a mouth shaped like a crab claw, at the end of a long trunk. and even though it sounds like something out of a George Lucas fever dream, this creature was very real. It swam around 300 million years ago in what is now Illinois. Okay, but what was it?

Ever since it was first discovered in the 1950s, by an amateur fossil hunter named Francis Tully, scientists have been stumped by it. But McCoy and her colleagues examined more than 1200 fossilized Tully monsters that've been found over the past 60 years, and they announced last week in the Journal Nature, that they had solved the mystery.

For the most part. While studying high-resolution photographs of all of the known fossils of the creature, which is officially known as Tullimonstrum, they found some crucial features that had been overlooked before. For example, Tully monsters have a pale band running through the middle of their bodies. This was originally assumed to be a gut tube, a sort of primordial digestive system, but that wasn't very helpful, considering that most animals have some kind of gut. But gut tubes tend to be much darker when they show up in fossils, and they stop before reaching the tail, at the anus. But the pale band found in the monsters extended clear through the tail.

Furthermore, some Tully monsters showed two bands, a dark one and a light one. So the light band had to be something else. It turns out, it was a rudimentary spinal cord. This meant Tully monsters weren't giant worms or slugs, they were vertebrates. With that important clue, the scientists searched branch after branch of the tree of life, looking for similarities with other creatures. In time, some features that they'd noticed before began to make more sense. The backward-pointing teeth made of keratin, for example, and the faint outline of a simple brain, and its single nostril. All of these traits are shared by Tully monsters and one other known animal; lampreys, long fish with toothy, jawless mouths. 

So, McCoy and her colleagues concluded that Tullimonstrum was probably an ancient relative of lampreys. But there's still a lot left to learn about it, from how it might have lived, to why there aren't any animals that look much like it today. 

While we're on the subject of fish that are really freaking weird, one fish in a UK lab tank did something so unexpected, it got a whole research paper dedicated to it! Scientist were keeping a bunch of cichlid fish in isolation, in separate tanks, as part of a study on species hybridization. and it seems that one of the female fish got bored or lonely or something, because it apparently fertilized its own eggs, and had dozens of babies, all by itself. Researchers have called this solo style of sexual reproduction "selfing". It turns out that this fish had fourteen broods of male and female baby fish, without ever mating. Some of the off-springs went on to have babies of their own, produced the regular way. That means those fish had two parents, but just three grandparents!

But this wasn't a case of cloning or parthenogenesis, sometimes called "virgin birth", neither of which requires sperm. Instead, this fish managed to achieve true self-fertilization, using sperm and egg cells from the same organism. This kind of reproduction is well-documented in plants and many invertebrates, but among vertebrates it's almost unheard of. But, how does one go about selfing oneself? Well, in the cichlid's case, it managed to develop a functional testis. Basically, one of its ovaries started producing spermatocytes, the precursors to sperm cells. So now, scientists are trying to figure out how she managed to pull this off. Sex determination in cichlid fish is pretty complicated. Each species has its own system, controlled by genes, the environment, or both. And the fact that this fish was a hybrid of two closely related species further complicates things. But for now, researchers think that selfing might be a rare evolutionary strategy that some animals can use to reproduce in a new or changing environment, place where weird risk are more likely to pay off. So, thank nature, you're really weird. 

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