:en:Utahnax
{{Short description|Extinct genus of gilled lobopodian}}
{{Speciesbox
| fossil_range = {{Fossil range|Drumian}}
| image = M835334.png
| image_caption = Fossil of Utahnax
| image2 = 20231215 Utahnax vannieri diagrammatic reconstruction.png
| image2_caption = A reconstruction of the known parts of Utahnax
| genus = Utahnax
| parent_authority = Lerosey-Aubril and Ortega-Hernández, 2022
| species = vannieri
| authority = Lerosey-Aubril and Ortega-Hernández, 2022
}}
Utahnax is a genus of kerygmachelid{{Cite journal |last=McCall |first=C. R. A. |year=2023 |title=A large pelagic lobopodian from the Cambrian Pioche Shale of Nevada |journal=Journal of Paleontology |pages=1–16 |doi=10.1017/jpa.2023.63}} lobopodian from the Drumian of Utah, containing one species, Utahnax vannieri, either from the Marjum or Wheeler formation.
Description
Utahnax's preserved section is roughly {{cvt|6|cm}} long, with at least eight pairs of ventral flaps similar to those found on Kerygmachela. Unusually, it does not appear to have had legs, suggesting the ventral flaps are broadened lobopods similar to the ventral flaps on radiodonts, and casting doubt on whether Kerygmachela had legs or whether reported “lobopods” are actually muscles of the flaps.{{cite journal |last1=Lerosey-Aubril |first1=R. |last2=Ortega-Hernández |first2=J. |year=2022 |title=A new lobopodian from the middle Cambrian of Utah: did swimming body flaps convergently evolve in stem-group arthropods? |journal=Papers in Palaeontology |volume=8 |issue=3 |pages=e1450 |doi=10.1002/spp2.1450 |bibcode=2022PPal....8E1450L |s2cid=250076505 }} In addition, it may have borne complex digestive glands similar to those of radiodonts.
Ecology
As Utahnax nests firmly within the predatory clade of “gilled lobopodians”, it can be assumed that it was also predatory. Its lack of lobopods also suggests it was primarily if not wholly pelagic, occupying a similar niche to radiodonts. This may explain the paucity of gilled lobopodians in the fossil record, as they may have competed with radiodonts in the pelagic predatory niches.
Etymology
Distribution
Utahnax is known from only a singular part and counterpart. As the fossil was not precisely labelled, it is unknown where exactly it was found in Utah, although an origin in the Weeks Formation or most of the Wheeler Shale can be ruled out due to differing fossil preservation methods.
References
{{reflist}}
{{Lobopodia}}
{{Dinocaridida}}
{{taxonbar|from1=Q125019781}}
Category:Fossils of the United States