Emeraldella is a genus of arthropod known from the Middle Cambrian of North America. The type species E. brocki was described in 1912 from the Burgess Shale.[1] 21 specimens of Emeraldella are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community.[2] A re-study on the species was done in 2012.[3] A second species E. brutoni is known from the Wheeler Shale, which was described in 2011.[4] An additional specimen of E. brutoni was described in 2019, which revealed more of the anatomy.[5] It has been placed as a basal member of the clade Vicissicaudata within Artiopoda, a group of arthropods containing trilobites and their relatives.[5]
| Emeraldella Temporal range:
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|---|---|
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| Emeraldella brocki | |
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| Emeraldella brutoni | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| (unranked): | †Artiopoda |
| (unranked): | †Vicissicaudata |
| Genus: | †Emeraldella Walcott, 1912 |
| Type species | |
| Emeraldella brocki Walcott, 1912
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| Other species | |
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Emeraldella brutoni Stein, Church & Robison, 2011 | |
Description
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Emeraldella species reached around 5–6 centimetres (2.0–2.4 in) in length, excluding the long telson/tailspine at the end of the body, which is longer than the trunk region of the body.[3][5] The semicircular head bore an elongate pair of antennae, sometimes exceeding over 80 segments in E. brocki. Eyes were present in E. brutoni, but absent in E. brocki. The head has 3 pairs of post-antennae limbs, the first of which was uniramous (only composed of one branch), composed of an endopod (leg-like part) with nine segments/podomeres, which were covered in spines, while the other two pairs were biramous (two branched). The trunk is made up of 10 (in E. brutoni) or 11 in (E. brocki) segments/tergites, which have well developed pleurae, which are followed by a cylindrical segment to which "caudal flaps" attached, followed by the tailspine. Pairs of biramous (two branched) limbs run down the body. The shape of the endopods (inner, leg-like branch) of the biramous limbs strongly varied in proportion along the body length but generally curved outward towards where it attached to the body and then downwards near their tips at the fifth segment (podomere). The exopod (outer branch of the biramous limb) is paddle-shaped and divided into three segments, the one closest to the body was covered in lamellae, while the two further away were covered in setae (hair-like structures). The caudal flaps were modified exopods, and were also fringed with setae.[5]
Taxonomy
editIn 1923, Emeraldella was placed, along with Sidneyia, as part of the group "Xenopoda". Today, both Sidneyia and Emeraldella are placed as part of the clade Vicissicaudata within Artiopoda, which includes trilobites and other arthropods with similar bodyforms. However, Sidneyia and Emeraldella are usually not recovered as each others closest relatives within Vicissicaudata, rendering "Xenopoda" invalid.[6]
References
edit- ^ "II.—Cambrian Geology and Palæontology. No. 6: Middle Cambrian Beanchiopoda, Malacostraca, Trilobita, and Merostomata. By C. D. Walcott. Smithsonian Miscellaneous Collections, vol. lvii, No. 6 (publication 2051), 1912". Geological Magazine. 9 (8): 376–377. August 1912. Bibcode:1912GeoM....9..376.. doi:10.1017/s0016756800115006. ISSN 0016-7568.
- ^ Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS. 21 (5): 451–65. Bibcode:2006Palai..21..451C. doi:10.2110/palo.2003.P05-070R. JSTOR 20173022. S2CID 53646959.
- ^ a b Stein, Martin; Selden, Paul A. (June 2012). "A restudy of the Burgess Shale (Cambrian) arthropod Emeraldella brocki and reassessment of its affinities". Journal of Systematic Palaeontology. 10 (2): 361–383. doi:10.1080/14772019.2011.566634. ISSN 1477-2019. S2CID 55018927.
- ^ "A new Cambrian arthropod, Emeraldella brutoni, from Utah". Paleontological Contributions. 2011-09-29. doi:10.17161/PC.1808.8086. hdl:1808/8086. ISSN 1946-0279.
- ^ a b c d Lerosey-Aubril, Rudy; Ortega-Hernández, Javier (2019-10-31). "Appendicular anatomy of the artiopod Emeraldella brutoni from the middle Cambrian (Drumian) of western Utah". PeerJ. 7: e7945. doi:10.7717/peerj.7945. ISSN 2167-8359. PMC 6825744. PMID 31687274.
- ^ Briggs, Derek E. G.; Siveter, David J.; Siveter, Derek J.; Sutton, Mark D.; Legg, David; Lamsdell, James C. (August 2023). "A vicissicaudatan arthropod from the Silurian Herefordshire Lagerstätte, UK". Royal Society Open Science. 10 (8): 230661. doi:10.1098/rsos.230661. ISSN 2054-5703. PMC 10394423. PMID 37538743.
External links
edit- "Emeraldella brocki". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011. Archived from the original on 2020-11-12. Retrieved 2023-01-21.
- "Emeraldella, Cambrian Problematic Soft-bodied Fossil". fossilmuseum.net. Archived from the original on 2021-11-29.