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in Parry, Lerosey-Aubril, Weaver & Ortega-Hernández, 2021. |
Highlights
• Two species of rare fossil ctenophores are described from the Cambrian of Utah
• Fossil ctenophores preserve remains of nervous tissue and sensory structures
• Neurological structures include an oral nerve ring and giant longitudinal axons
• Cambrian ctenophores had a more complex neuroanatomy than living species
Summary
Ctenophores are a group of predatory macroinvertebrates whose controversial phylogenetic position has prompted several competing hypotheses regarding the evolution of animal organ systems. Although ctenophores date back at least to the Cambrian, they have a poor fossil record due to their gelatinous bodies. Here, we describe two ctenophore species from the Cambrian of Utah, which illuminate the early evolution of nervous and sensory features in the phylum. Thalassostaphylos elegans has 16 comb rows, an oral skirt, and an apical organ with polar fields. Ctenorhabdotus campanelliformis has 24 comb rows, an oral skirt, an apical organ enclosed by a capsule and neurological tissues preserved as carbonaceous films. These are concentrated around the apical organ and ciliated furrows, which connect to a circumoral nerve ring via longitudinal axons. C. campanelliformis deviates from the neuroanatomy of living ctenophores and demonstrates a substantial complexity in the nervous system of Cambrian ctenophores.
Keywords: Ctenophora, Marjum Formation, Cambrian, Nervous system, Metazoa
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| Ctenorhabdotus campanelliformis (top) and Thalassostaphylos elegans (bottom). Reconstruction by Holly Sullivan |
Systematic Paleontology
Phylum: Ctenophora Eschscholtz 1829
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| Holotype fossil specimen of Thalassostaphylos elegans from the mid-Cambrian Marjum Formation in Utah. Light photograph (left), interpretative drawing (right), and magnification of polar fields (bottom left). |
Genus: Thalassostaphylos gen. nov
Etymology: Genus name from Greek Thalassa (sea) and staphylos (grape).
Type species: Thalassostaphylos elegans nov.
Diagnosis: Ctenophore with rounded body outline in lateral view with broad comb rows that
16 abut each other laterally. Comb rows terminate at the margin of an extensive oral skirt surrounding a large mouth opening. Oral skirt has a scalloped oral margin, with eight lobes present around its circumference. Apical sense organ with paired polar fields.
Thalassostaphylos elegans sp. nov.
Etymology: From Latin elegans (elegant), in reference to the skirt and its scalloped margin.
Type material: UMNH.IP.6086 (holotype and only known specimen).
Locality and Horizon: House Range of western Utah, USA (see methods for locality details). Drumian strata (lower Ptychagnostus punctuosus Zone) of the middle part of the Marjum Formation, Miaolingian, Cambrian (see Methods below).
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| Fossil specimen of Ctenorhabdotus campanelliformis from the mid-Cambrian Marjum Formation in Utah. Light photograph (left), elemental map showing nervous system as carbon films (right), and interpretative drawing (bottom left). |
Genus: Ctenorhabdotus Conway Morris and Collins 1996
Type species: Ctenorhabdotus capulus (Conway Morris and Collins, 1996).
Ctenorhabdotus campanelliformis sp. nov.
Etymology: From Latin campanella (small bell) and formis (shape), in reference to the bell-shaped outline of the body.
Type material: UMNH.IP.6125 (holotype and only known specimen).
Locality and Horizon: House Range of western Utah, USA (see methods for locality details). Most likely recovered from the Drumian strata (lower Ptychagnostus punctuosus Zone) of the middle part of the Marjum Formation, Miaolingian, Cambrian (see Methods below).
Diagnosis: Ctenophore with bell-shaped body outline in lateral view with 24 comb rows. Comb rows terminate at the margin of an extensive oral skirt surrounding a large mouth opening. Aborally, comb rows merge with trifurcating ciliary grooves arising from the apical organ. Apical sense organ enclosed in a capsule.
Luke A. Parry, Rudy Lerosey-Aubril, James C. Weaver and Javier Ortega-Hernández. 2021. Cambrian Comb Jellies from Utah illuminate the early Evolution of Nervous and Sensory Systems in Ctenophores. iScience. 102943. DOI: 10.1016/j.isci.2021.102943
