New Cambrian basal vertebrate: Nuucichthys

Lerosey-Aubril and Ortega-Hernández reported,
“Here, we describe the first soft-bodied vertebrate from the American Great Basin, the Drumian Marjum Formation of Utah. Nuucichthys rhynchocephalus gen. et sp. nov. is characterized by a finless torpedo-shaped body that includes a snout-like anterior head bearing anterolateral eyes, approximately 25 thick myomeres, a large branchial chamber with a keel and approximately seven putative dorsal bars and a spiniform caudal process. Our analysis recovers Nuucichthys within the vertebrate stem, where it forms a polytomy with its Laurentian relatives, Emmonsaspis and Metaspriggina. Based on the eye orientation and absence of fins, we tentatively reconstruct Nuucichthys as a pelagic organism with limited swimming abilities (planktonektic).”

In many ways, Nuucichthys was still a lancelet, = a tiny, very short, Cambrian hagfish.

Figure 1. Nuucichthys rhynchocephalus in situ. ” data-image-caption=”

Figure 1. Nuucichthys rhynchocephalus in situ.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-rhynchocephalus588-1.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-rhynchocephalus588-1.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87806″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-rhynchocephalus588-1.jpg” alt=”Figure 1. Nuucichthys rhynchocephalus in situ.” width=”584″ height=”236″ />

Figure 1. Nuucichthys rhynchocephalus in situ. Here flipped left to right following presentation convention.

Figure 1. Original reconstruction of Nuucichthys identifying the terminal dark spot as an eye. ” data-image-caption=”

Figure 1. Original reconstruction of Nuucichthys identifying the terminal dark spot as an eye.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-rhynchocephalus-reconstruction588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-rhynchocephalus-reconstruction588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87818″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-rhynchocephalus-reconstruction588.jpg” alt=”Figure 1. Original reconstruction of Nuucichthys identifying the terminal dark spot as an eye. ” width=”584″ height=”190″ />

Figure 1A. Original reconstruction of Nuucichthys identifying the terminal dark spot as an eye. See figure 2.

Lerosey-Aubril and Ortega-Hernández reported,
“The studied material consists of a single fossil (part only) discovered in the Drumian Marjum Formation in the House Range of western Utah, USA, and housed in the collections of Invertebrate Paleontology of the Natural History Museum of Utah (UMNH.IP.6084). Its precise geographic origin and stratigraphic position within the formation were not provided on the label accompanying the specimen”

Sounds like the holotype and sole specimen (UMNH.IP.6084, Figs 1–3) was found in the stacks, brought to the museum by an unnamed collector at some time in the past.

Figure 2. Nuucichthys anterior. DGS colors and labels added here. ” data-image-caption=”

Figure 2. Nuucichthys anterior. DGS colors and labels added here.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-head588.gif?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-head588.gif?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87807″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys-head588.gif” alt=”Figure 2. Nuucichthys anterior. DGS colors and labels added here.” width=”584″ height=”373″ />

Figure 2. Nuucichthys anterior. DGS colors and labels added here. Note the atrium is punctured by gill openings. The oral cavity retains small, hard, stem-like teeth. The nares were originally identified as an eye.

Lerosey-Aubril and Ortega-Hernández reported,
“We find no traces of dorsal or caudal fins in Nuucichthys, despite the colour difference between the fossil and the surrounding matrix along most of the body margins.”

This is a very primitive vertebrate with only a few modifications more advanced than lancelets and hagfish. Nuucichthys appears to be streamlined (Fig 1). The overlooked tiny caudal fin and massive undulatory muscles = myomeres indicate perhaps a better swimmer than similar lancelet juveniles, and very different from eel-like extant hagfish.

All three share subsurface non-terminal eyes.

Figure 3. Nuucichthys posterior. DGS colors added here. ” data-image-caption=”

Figure 3. Nuucichthys posterior. DGS colors added here.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys.tail_.gif?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys.tail_.gif?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87808″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/nuucichthys.tail_.gif” alt=”Figure 3. Nuucichthys posterior. DGS colors added here.” width=”584″ height=”281″ />

Figure 3. Nuucichthys posterior. DGS colors added here.

Lerosey-Aubril and Ortega-Hernández reported,
“A comparison with decay patterns of amphioxus and modern vertebrates allows a tentative assessment of the duration and impact of decay in the Marjum specimen.”

The DGS color additions to the published images
(Figs 1–3) follow lancelet and hagfish Bauplans.

Figure 4. Two Metaspriggina specimens married together to show the terminal orbit morphology is the result of incomplete = buried data. ” data-image-caption=”

Figure 4. Two Metaspriggina specimens married together to show the terminal orbit morphology is the result of incomplete = buried data.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/metaspriggina_walcotti3-588.gif?w=140″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/metaspriggina_walcotti3-588.gif?w=479″ tabindex=”0″ role=”button” class=”size-full wp-image-87816″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/metaspriggina_walcotti3-588.gif” alt=”Figure 4. Two Metaspriggina specimens married together to show the terminal orbit morphology is the result of incomplete = buried data. ” width=”584″ height=”1249″ />

Figure 4. Two Metaspriggina specimens married together to show the terminal orbit morphology is the result of incomplete = buried data. Two dorsal exposure burials point to a wider cross-section than current reconstructions indicate. That, along with the buccal ciri fringing the leading edges of the skull point to a bottom feeder, like a vacuum cleaner. Note the separate elements in the skull.

Here
in the large reptile tree (LRT, 2323 taxa) Nuucichthys nests between hagfish and Metaspriggina + lampreys + all higher chordates. That matches the authors’ analysis. Since both tests recovered Metaspriggina as a sister taxon, we have to talk about it.

The Metaspriggina cantilevered eye problem.
The Cambrian chordate, Metaspriggina, is known from several Burgess Shale specimens. Two are shown here (Fig 4). One seems to show terminal eyes, but those were dug out, exposed above the matrix, perhaps leaving more of the specimen below the surface, as the other specimen (Fig 4) indicates. The other specimen shows non-terminal orbits on a triangular skull, superficially quite different in morphology. Here the two morphologies are married together (Fig 4).

This solution to the Metaspriggina cantilevered eye problem has bearing on the identity of the dark spot at the tip of the rostrum in Nuucichthys. Here that dark spot is reidentified as a pair of terminal nares.

Two dorsal exposure burials (Fig 4) indicate a wider cross-section than current narrow cross-section reconstructions indicate. That, along with the buccal ciri fringing the leading edges of the skull (Fig 4) suggest Metaspriggina was a bottom feeder, its wide triangular skull fringed by cirri acting like a vacuum cleaner.

With these hypothetical solutions (Figs 2, 4) perhaps no Cambrian vertebrate taxa had terminal eyes. Presently no tested Cambrian vertebrates had this Bauplan.

References
Lerosey-Aubril R and Ortega-Hernández J 2024. A long-headed Cambrian soft-bodied vertebrate from the American Great Basin region, Royal Society Open Science (2024). DOI: 10.1098/rsos.240350   online.

wiki/Metaspriggina
wiki/Nuucichthys – not yet posted

Publicity
phys.org/news/2024-07-soft-needle-oceanic-haystack
“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,” Lerosey-Aubril 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. “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,” Ortega-Hernández said.”