Opabiniid Described 100 Years Later: Researchers Confirm It Is Different from Radiodont

An international research team led by Harvard University has recently confirmed that a sample previously considered a radiodont is actually an "opabiniid."

As indicated in a Phys.org report, in the book of Stephen Jay Gould, former professor in the Department of Organismic and Evolutionary Biology at Harvard, made popular the so-called "weird wonder" stem-group arthropods "Opabinia and Anomalocaris," found in the Cambrian Burgess Shale, turning them into icons in famous culture.

Whereas the "terror of the Cambrian Anomaloaris," along with its circular mouth and "spiny grasping appendages" is a radiodont that has many relatives. The Opabinia that has five eyes, with its unique frontal proboscis stays the only opabiniid ever found. That is until today.

Utaurora Comosa

The new research published in Proceedings of the Royal Society B used fresh and strong phylogenetic approaches to validate Utaurora comosa as just the second opabiniid ever found and the first in more than a hundred years.

Utaurora comosa, discovered in Utah's 500-million-year-old Cambrian Wheeler Formation, was first described in the late 2000s as a radiodont.

According to co-lead author Stephen Pates, former postdoctoral in the Department of Organismic and Evolutionary Biology at Harvard, initially encountered the sample at the University of Kansas Biodiversity Institute & Natural History Museum while he was a graduate student.

Pates was examining the radiodonts' diversity and felt this sample did not exactly suit with an actual radiodont. When he joined senior author Professor Javier Ortega-Hernandez's lab in OEB, the co-lead author worked with Jo Wolfe, an OEB postdoctoral fellow studying the associations of fossil and living arthropods, to identify where Utaurora best suit in the tree of life.

'Opabiniids'

Opabiniids are the first group to have a mouth that's posterior-facing. Their dorsal intersegmental furrows are originators to full body segmentation and their lateral swimming flaps are antecedents to appendages.

Essentially, Utaurora is sharing characters and morphology with both Opanbinia and radiodonts. While the anterior structure and eyes of Utaurora were inadequately preserved, Opabinia is most identifiable from its frontal proboscis and five eyes, the intersegmental furrows on the back, and paired serrated spines on the tail were completely observed.

What led Pete and Wolfe to use polygenic assessment when they compared Utaurora with more than 40 fossils and 11 living taxa of radiodonts, arthropods, and other panarthropods were the limited morphological observations.

According to Wolfe, the preliminary phylogenetic analysis showed it was most nearly most closely associated with Opabinia. He added, they followed up with more tests to cross-examine that finding using various models of evolution and sets of data to visualize the various kinds of associations such fossils may have had.

Creation of the 'Dinocarids' Group

Different from Opabinia, which was found in the Cambrian Burgess Shale of British Columbia in Canada, Utaurora was discovered in Utah, and still, Cambrian is a few million years younger than the former. Meaning, Opabinia was not the lone opabiniid. More so, it was not as distinctive a species as it has been thought, said Pates.

Lastly, according to a similar Bioengineer.org report, when Utaurora was initially described as a radiodont in 2008, researchers thought opabiniids are radiodonts created monophyletic group identified as "dinocarids."

Nevertheless, over the past decade to decade-and-a-half, scientists have found more than 10 new species of radiodonts, making it possible to find out that opabiniids and radiodonts are a little different.

Related information about the opabiniid discovery is shown on Wonder World's YouTube video below:

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