Fossil Shrimp With Five Eyes Could Be Elusive ‘Transitional Species’

Chimeric early arthropod lived half a billion years ago and combines features of all sorts of later arthropods, including huge frontal claws

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Artist's impression of Kylinxia zhangi
Artist's impression of Kylinxia zhangiCredit: D.-Y. Huang & H. Zeng
Ruth Schuster
Ruth Schuster

We’re so egotistical about our morphology that we even portray alien beings from distant galaxies as looking like us, but green. Two eyes, two ears, a proboscis, etcetera. So first of all we apparently have a vestigial third eye in our brains and secondly, the world keeps showing us alternatives. On Wednesday, scientists at the Chinese Academy of Sciences disproved our conservatism yet again with a report on a strange sort-of-shrimplike ancestral creature that lived around half a billion years ago and had five eyes.

Kylinxia zhangi, named for a chimera in Chinese mythology named Kylin and the Chinese word for shrimp, was an arthropod. The main oddity of this early Cambrian proto-shrimp is actually that it combined features we know from other arthropods. Perhaps, Diying Huang and colleagues suggest in Nature, the lovely Kylinxia was a “transitional species.”

The fossil of Kylinxia zhangiCredit: D.-Y. Huang & H. Zeng

In other words, along the evolutionary road it appears to be a chimera of arthropod groups that would take shape in its future. Does that mean Kylinxia was ancestral to today’s arthropods? Not necessarily, but it may have been.

Transitional fossils, an animal on the cusp of divergence, are a holy grail to evolutionary biologists. Charles Darwin was embarrassed by the failure to identify fossils as transitional, ostensibly weakening his theory of evolution (published in 1859), blaming the absence on the spotty fossil record. Happily for his sanity, the transitional dinobird Archaeopteryx was discovered in 1861 – a transitional animal between non-avian and avian dinosaurs.

Now Huang and the team believe they have found a transitioning arthropod that has five compound eyes on stalks, like Opabinia; two large frontal claws like Anomalocaris (whose name means “unlike other shrimp”); and a basic body structure like the class Megacheira. Its head shield is fused like deuteropods. Its mouth is similar to that of the ancestral scorpion, the Chelicerata, and its feelers are reminiscent of the mandibulate arthropods, which includes everybody from millipedes to insects.

Opabinia regalisCredit: Nobu Tamura / http://spinops.blo
Anomalocaris.Credit: PaleoEquii

Those frontal claws were orientated upward, by the way, and were spiny. Its tail fan was shrimplike, with three lobes. In today’s arthropods these tail lobes, called uropods, may be modified to serve as claspers to hold onto the female during mating. We cannot know what Kylinxia got up to with its uropods.

Summing up, Kylinxia seems like a transitional animal between the Radiodonta (stem-group arthropods, including some absolute monsters) and their cousins the Deuteropoda (which sport appendages on the second head segment), the team writes. It features characteristics of both: that fused head shield and “arthropodized” torso are pure deuteropodic, while the five eyes scream of radiodont.

Your third eye, by the way, evolved into your pineal gland, to somewhat oversimplify matters. The relic lizard called tuatara still has a relatively developed third eye on the top of its head. That third eye usually scales over in the reptile’s adulthood.

Artist's impression of Kylinxia zhangi.Credit: D.-Y. Huang & H. Zeng
Megacheirans.Credit: Junnn11

So there we have it. Does having five compound eyes mean it saw well? Half a billion years after the event, it’s hard to say. We can say that some extant shrimp see exceptionally well. The Mantis shrimp have extraordinarily advanced eyes: capable of seeing colors, ultraviolet light, polarized light and even circularly polarized light. You can’t do that. And they can move each of their (two) eyes independently. They also pack a punch that would put Rambo to shame. Shame that they can see you coming but still don’t get out of the way.

Here’s a video by Ze Frank about the mantis shrimp. Enjoy.

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