Chaetae are stiff bristles made of chitin that characterize many species of annelid worms.
Reconstruction of Shaihuludia shurikeni from the Spence Shale of Utah. Image credit: Rhiannon LaVine.
Shaihuludia shurikeni inhabited the Cambrian seas approximately 507 million years ago.
The ancient creature was a type of annelid, a diverse group of segmented worms found in terrestrial, freshwater and marine environments all over the world.
Shaihuludia shurikeni was 7 to 8 cm (2.8-3.1 inches) long, had a wide body and flattened fans of fused blade-like chaetae.
“Annelids are an extremely diverse phylum (around 21,000 described species) and have conquered a variety of terrestrial, freshwater, and marine environments,” said Dr. Julian Kimmig, a paleontologist at the Staatliches Museum für Naturkunde Karlsruhe and the University of North Dakota.
“However, their whole-body fossil record is sparse. Their soft-bodied nature typically results in rapid decay, restricting most of their fossil occurrences to Lagerstätten-type deposits.”
“The oldest accepted whole-body annelids appear in the early Cambrian of China and Greenland and are present from this point forward in the Lagerstätten of the Cambrian.”
“They reach a peak known-diversity within the period by the middle Cambrian, with six species from the Burgess Shale alone.”
“Most annelid taxa known from the Cambrian belong to the annelid stem group,” they added.
“These organisms typically show homonymous segmentation with a single pair of head appendages and in some cases with a median antenna.”
Shaihuludia shurikeni. Image credit: Kimmig et al., doi: 10.1080/08912963.2023.2196685.
The single specimen of Shaihuludia shurikeni was collected from the Spence Shale Member of the Langston Formation in northern Utah and southern Idaho, the United States.
“The Cambrian Spence Shale Lagerstätte of northeastern Utah and southeastern Idaho preserves one of the most diverse Burgess Shale-type biotas in Laurentia,” the paleontologists said.
“Its fauna comprises over 90 species, of which about one-third are soft-bodied.”
“The soft-bodied remains are dominated by arthropods, but also include algae, cyanobacteria, deuterostomes (hemichordates), scalidophorans, and sponges.”
The authors analyzed the specimen using scanning electron microscopy and energy dispersive X-ray spectrometry.
“Shaihuludia shurikeni is especially interesting, as it had some very impressive chaetae, which makes it unique among the Cambrian annelids,” Dr. Kimmig said.
“The way that the fossil is preserved is also of particular interest, because most of the soft tissue is preserved as an iron oxide ‘blob,’ suggesting the animal died and was decomposing for a while before it was fossilized.”
“However, with the analytical methods used in the paper, we show that even with limited preservation you can identify fossils.”
In their research, the team also reexamined a fossilized annelid previously found in the Spence Shale and reclassified it as Burgessochaeta — a surprise because until then, this genus have only been found in another famed fossil deposit in British Columbia, Canada.
“Burgessochaeta is really only known from the Burgess Shale,” said Dr. Rhiannon LaVine, a paleontologist at the University of Kansas.
“A similar worm was collected in our Spence Shale decades ago, and it was named Canadia, which is kind of a wastebasket genus for a lot of the annelids that come out of these types of deposits.”
“Nobody really looked into it for a long time, but when we got this one, we took a little closer look at the other annelid found there. Maybe this was another version of it, or it was related in some way.”
“We determined the other annelid from the Spence Shale is actually closer to Burgessochaeta — this is the first time it’s been described outside of the Burgess Shale.”
The discovery is reported in a paper in the journal Historical Biology.
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Julien Kimmig et al. Annelids from the Cambrian (Wuliuan Stage, Miaolingian) Spence Shale Lagerstätte of northern Utah, USA. Historical Biology, published online April 8, 2023; doi: 10.1080/08912963.2023.2196685
