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| Mobulavermis adustus McCall, 2023 DOI: 10.1017/jpa.2023.63 |
Abstract
Lobopodians are an iconic and diverse group of animals from the Cambrian, which alongside radiodonts, present an important window into the evolution of arthropods and the development of Paleozoic ecosystems. Of these, a rare few species outside of Radiodonta possess lateral swimming flaps. The recent discovery of Utahnax provided much-needed insight into the evolution of swimming flaps, suggesting that the ventrolateral flaps of Kerygmachela evolved independently from other flap-bearing lobopodians and radiodonts. Here a new pelagic lobopodian species is described, Mobulavermis adustus new genus new species, the first lobopodian to be reported from the Cambrian-age Pioche Shale of Nevada. Mobulavermis adustus was large and possessed more ventrolateral flap pairs than any other known lobopodian or radiodont. It is found to be a close relative of both Kerygmachela and Utahnax, allowing the establishment of the new lobopodian family Kerygmachelidae new family. In addition, an indeterminate euarthropod fossil from the Pioche Formation is described in brief, and the recently described Chengjiang species Parvibellus avatus Liu et al., 2022, thought to have been related to the “gilled lobopodians,” is reinterpreted as a juvenile siberiid lobopodian.
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| Mobulavermis adustus KUMIP 298510 (holotype) from the Pioche Shale, middle Cambrian, Nevada: (1) KUMIP 298510a (part), immersed, showing curving body and caudal spine preserved in negative relief; (2) KUMIP 298510b (counterpart), immersed, with caudal spine in strong positive relief; (3) KUMIP 298510b (counterpart), dry, closeup of caudal spine in positive relief and some reduced terminal flaps; (4) KUMIP 298510a (part), immersed, closeup of trunk interior, showing digestive tract, possible gut gland, and possible evidence of strong trunk annulation; (5) KUMIP 298510b (counterpart), dry, closeup of flap surfaces near anterior of specimen. Scale bars = 10 mm. afm = anterior flap margin; an = annulations; bw = body wall; cs = caudal spine; dt = digestive tract; fo = flap ornamentation; mg = midgut gland; pfm = posterior flap margin; tf = terminal reduced flaps. |
Systematic paleontology
Superphylum Panarthropoda Nielsen, Reference Nielsen1995
Family Kerygmachelidae new family
Type genus: Kerygmachela Budd, 1993.
Other taxa included: Utahnax Lerosey-Aubril and Ortega-Hernández, 2022, Mobulavermis n. gen.
Diagnosis: Lobopodians with lobopod-derived ventrolateral swimming flaps and lacking dorsal flaps or setal blades; trunk elongate, roughly cylindrical, and annulated; paired frontal appendages large and raptorial.
Genus Mobulavermis new genus
Type species: Mobulavermis adustus, by monotypy.
Etymology: From Mobula, the genus name of extant manta rays and devil rays, drawing comparison to the elongate flexible caudal spines and broad swimming flaps of Mobula rays, which resemble the outline of the new taxon, combined with the Latin vermis, meaning “worm.”
Mobulavermis adustus new species
Anomalocaridid gen. indet. sp. indet.; Lieberman, 2003; p. 683, fig. 6.4.
indeterminate anomalocaridid; Lerosey-Aubril and Ortega-Hernández, 2022; p. 15.
Diagnosis: Lobopodian with vermiform body terminating in an elongate, flexible caudal spine; numerous broad, densely packed, lobopod-derived ventrolateral body flaps strongly overlapping successively; posterior ventrolateral body flaps decreasing in size linearly toward base of caudal spine until becoming flush with trunk; ventrolateral body flap posterior margins convex, anterior margin begins perpendicular to body wall before gradually curving posteriorly.
Occurrence: Pioche Formation, Combined Metals Member (Cambrian Series 2, Stage 4, Nephrolenellus multinodus Biozone), Lincoln County, Nevada; ....
Etymology: From the Latin adustus, meaning “burnt,” “singed,” or “sun-burnt,” in reference to the dramatic yellow, red, and black coloration of the two known specimens and to the arid conditions of the type locality.
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| Digital life reconstruction of Mobulavermis adustus, shown swimming in a Cambrian ocean alongside small bivalved arthropods and early chordates (speculative anterior morphology based on Kerygmachela kierkegaardi). |
Christian R.A. McCall. 2023. A large pelagic lobopodian from the Cambrian Pioche Shale of Nevada. Journal of Paleontology. First View. DOI: 10.1017/jpa.2023.63
Non-technical Summary: Lobopodians are an iconic group of animals from the Paleozoic that includes Hallucigenia and Opabinia, as well as living animals such as tardigrades and velvet worms. They would also eventually give rise to the first arthropods by developing a hard, sclerotized exoskeleton. During the Cambrian, a rare subset of lobopodians possessed large swimming flaps, sometimes alongside ventral walking limbs. A new, large-bodied pelagic lobopodian from the Cambrian of Nevada is described, possessing more swimming flaps than any other lobopodian or radiodont.
