Characterized by a finless torpedo-shaped body, Nuucichthys rhynchocephalus is the first soft-bodied vertebrate known from the American Great Basin.
Nuucichthys rhynchocephalus was a pelagic organism with limited swimming abilities. Image credit: Franz Anthony.
Nuucichthys rhynchocephalus swam in the Cambrian oceans between 505 and 500 million years ago.
The ancient animal had a finless torpedo-shaped body that includes a number of markers characteristic of vertebrates.
It is one of only four species documenting the early evolutionary stage of vertebrate lineage.
“The discovery of Nuucichthys rhynchocephalus is a valuable contribution to early vertebrate evolution and biodiversity because of the dearth of these types of organisms in Cambrian fossil sites — including South China, the Northeastern United States, and British Columbia,” said Harvard University paleontologists Rudy Lerosey-Aubril and Javier Ortega-Hernández.
“Early vertebrates start to have big eyes and a series of muscle blocks that we call myotomes, and this is something we recognize very well in our fossil.”
The studied material of Nuucichthys rhynchocephalus consists of a single partial fossil discovered in the Marjum Formation in the House Range of western Utah, the United States.
“Nuucichthys rhynchocephalus is the first soft-bodied vertebrate to be discovered in the Marjum Formation of the American Great Basin,” the paleontologists said.
The new species also confirms that, despite their overall similarities to larval fish — having a cavity that is a sort of rudimentary gill system — they were devoid of fins and therefore had limited swimming capabilities.
“But all of these characteristics clearly point to some vertebrate affinities,” Dr. Lerosey-Aubril said.
“And because it’s very early in the evolution of the vertebrates, they don’t have bones yet — this is why these fossils are exceedingly rare.”
The authors speculate that Nuucichthys rhynchocephalus likely lived high up in the water column of the ocean.
Because of this, and because it possessed no biomineralized parts like bones or a shell, it was particularly prone to rapid post-mortem degradation and decay, which explains why they were fossilized so rarely.
“What’s interesting with this new species is that understanding how the morphology evolved from the invertebrate type to the vertebrate type is difficult without fossils, and this new fossil tells us a little bit about that,” Dr. Ortega-Hernández said.
The discovery of Nuucichthys rhynchocephalus is reported in a paper in the journal Royal Society Open Science.
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Rudy Lerosey-Aubril & Javier Ortega-Hernández. 2024. A long-headed Cambrian soft-bodied vertebrate from the American Great Basin region. R. Soc. Open Sci 11 (7): 240350; doi: 10.1098/rsos.240350