Looking hundreds of millions of years into the past can reveal startling discoveries – as was the case with the discovery of a second species of opabiniidae, a soft-bodied arthropod with a segmented exoskeleton that lived on the seabed during the Miaolingian (509-497 million years ago).
The original opadinide, Opabinia regaliswas first described over a century ago in 1912 and has several notable physical characteristics, including the five protruding eyes on the stalks of its head, a backward-facing mouth, and its hollow tubular proboscis.
Now there is another one: Opabinia regalis is not as unique a species as previously thought, as it was joined by Utaurora comosa. This creature was previously thought to belong to a different group of animals known as radiodonts, but it has now been reclassified as an opabiniid after extensive research.
“Initial phylogenetic analysis showed it to be most closely related to Opabinia“, explains paleontologist Jo Wolfe of Harvard University.
“We followed up with more tests to interrogate this result using different evolutionary models and datasets to visualize the different kinds of relationships this fossil may have had.”
U. comosa was first described as a radiodont in 2008, after it was originally discovered in a fossil site known as the Wheeler Formation in Utah. It’s a few million years younger than Opabiniaand was found in a different location – Utah rather than Canada.
While Utaura shares characteristics and morphology with radiodonts and Opabinia, the researchers behind the latest study decided to dig deeper. The team compared the Utaura fossil with 43 other fossils, plus 11 living taxa, covering arthropods, radiodonts and other panarthropods.
Due to their similarities, opabiniids and radiodonts were originally thought to have the same common ancestor and were grouped together as “dinocarids”.
However, over the past 15 or so years, more tools for studying evolutionary history have been developed – and just as importantly, several new species of radiodonts have been discovered, highlighting the differences between these creatures and the opabiniids.
“Based on morphology alone, you could argue for Utaura being a bizarre radiodont and also for bringing back the concept of ‘dinocarid’,” says paleontologist Stephen Pates, from the University of Cambridge in the UK.
“But our phylogenetic dataset and analyzes supported Utaura as an opabiniid in 68 percent of the trees recovered by analyzing the data, but only in 0.04 percent for a radiodont.
While the front of U. comosa fossil was poorly preserved, researchers noted the intersegmental furrows along the back and the paired serrated spines on the tail. Along with the evolutionary tree analysis carried out by the team, a new species has emerged, half a billion years after its disappearance.
“Dissection of phylogenetic support demonstrates that while the evidence for radiodont paraphyly is weak, Utaura can be confidently reassigned to Opabiniidae,” the researchers write in their paper.
“The Strangest Cambrian Wonder No Longer Stands Alone.”
Now that the classification has been made, future research can use U. comosa to help trace the evolution and ecology of the opainiid, and this is unlikely to be the last we hear of this strange-looking animal.
the Opabinia shares a scientific history with another group of arthropods known as Anomalocaris, and both were originally described as “strange wonders” of the Middle Cambrian. It is only now that the differences between them really emerge.
“We now know that these animals represent extinct evolutionary stages that are related to modern arthropods,” says Wolfe.
“And we have tools beyond qualitative comparison of morphological characteristics for more definitive placement in the animal tree of life.”
The research was published in the Proceedings of the Royal Society B Biological Sciences.