Omnidens
| Omnidens Temporal range:
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| Size estimation of Omnidens as a gilled lobopodian, with the only evident region (mouthparts) highlighted in dark grey. (Note: speculative frontal appendage morphology is now known to be incorrect) | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| (unranked): | Panarthropoda |
| Genus: | †Omnidens Hou, Bergström, and Yang, 2006 |
| Type species | |
| Omnidens amplus Hou, Bergström, and Yang, 2006
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| Species | |
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Omnidens, meaning "all-tooth", is an extinct genus of large Cambrian animal known only from a series of large mouth apparatus and sclerotized talon-like structures, originally mistaken as the mouthparts of anomalocaridids.[1] When first named, it was interpreted as a giant priapulid,[1] but is now considered a panarthropod.[2] Its mouth apparatus closely resembles that of the smaller gilled lobopodian Pambdelurion, indicating it is likely to have been a close relative of that species, potentially even synonymous.[2] With a maximum estimated body length of 1.5 metres (4.9 ft), Omnidens is suggested to have been the largest known free-living Cambrian organism.[2] Omnidens fossils are found in the Maotianshan Shales.[1]
History
[edit]The first-described specimen of Omnidens was first described in 1994. At the time, it was interpreted as the oral cone of an anomalocaridid, and it was used as evidence to claim that anomalocaridids could reach a maximum body length of up to 2 meters (6.6 ft).[3] Omnidens fossils were later described as specimens of Peytoia and Parapeytoia until finally being recognized as a distinct species in 2006 and named Omnidens amplus.[1] At this time, it was reinterpreted as a gigantic priapulid, at least 1 metre (3.3 ft) long, far exceeding most known priapulids in size. Its specific name, amplus, means "large" or "giant". Omnidens was later identified as a close relative of the gilled lobopodian Pambdelurion.[2] In 2024, additional remains were described from Xiaoshiba Lagerstätte, which were proposed as a new species, O. qionqii, after the mythical, man-eating Qiongqi, one of four ancient creatures in Chinese mythology, whose name means "distressingly strange".[4]
Description
[edit]
Omnidens is known primiarly from large mouthparts, and more recently, distal portions of the frontal appendages. The preserved mouthparts would have formed a short muscular, potentially protrusible pharynx surrounded by circles of spiny sclerites, which were reminiscent of the scalids of priapulids, kinorhynchs, and loriciferans. The inside of the pharynx was also lined with several rows of pharyngeal sclerites. Based on the large size of its preserved mouthparts, Omnidens is estimated to have reached a length of up to 1.5 metres (4.9 ft).[2] Its overall appearance was likely similar to that of its close relative Pambdelurion. The mouth, unlike the oral cones of radiodonts, was arranged bilaterally, forming two laterally opposing sets of "jaws", composed of a number of tooth-plates, which are further divided into a basal plate and a nail-like spine. The frontal appendages are known from their distal-most portions, which appear as wide, heavily sclerotized bases, bearing a bilaterally symmetrical series of long talons. Additionally, elements which may represent bilaterally symmtrical head carapaces, and a number of small setal-blade like strucures, have been found associated with the mouthparts and talons.[4]
Classification
[edit]| Phylogenetic relationships of Panarthropoda,[5] with possible bearers of the Omnidens mouthparts bolded |
Omnidens is classified as a stem-group arthropod.[2] and, due to the striking similarities in their unconventional mouthparts, Omnidens is consistenlty found as a sister-taxon to the "gilled lobopodian" Pambdelurion whittingtoni.[2][4][6]
Distribution
[edit]Omnidens is found in both the Chengjiang Biota and the Xiaoshiba Lagerstätte of China, putting their age at approximately 520 Ma, during Cambrian Stage 3.[7] O. amplus and O. qiongqii are both known from the Chengjiang, but O. qiongqii is the only Omnidens species present at Xioashiba, where it is found in relative abundance (hundreds of specimens, primarily mouthparts).[4][8] Pambdelurion, which has mouthparts nearly identical to those of Omnidens, is from the Sirius Passet Lagerstätte of Greenland.[2]
References
[edit]- ^ a b c d Hou, Xianguang; Bergström, Jan; Jie, Yang (2006). "Distinguishing anomalocaridids from arthropods and priapulids". Geological Journal. 41 (3–4): 259–269. Bibcode:2006GeolJ..41..259X. doi:10.1002/gj.1050. S2CID 83582128.
- ^ a b c d e f g h Vinther, Jakob; Porras, Luis; Young, Fletcher J.; Budd, Graham E.; Edgecombe, Gregory D. (2016). "The mouth apparatus of the Cambrian gilled lobopodian Pambdelurion whittingtoni". Palaeontology. 59 (6): 841–849. Bibcode:2016Palgy..59..841V. doi:10.1111/pala.12256. hdl:1983/16da11f1-5231-4d6c-9968-69ddc5633a8a. ISSN 1475-4983. S2CID 88758267.
- ^ Chen, Jun-Yuan; Ramskold, Lars; Zhou, Gui-Qing (1994). "Evidence for Monophyly and Arthropod Affinity of Cambrian Giant Predators". Science. 264 (5163): 1304–1308. Bibcode:1994Sci...264.1304C. doi:10.1126/science.264.5163.1304. PMID 17780848. S2CID 1913482.
- ^ a b c d Li, Wei; Yang, Jie; Yang, Xiaoyu; Dhungana, Alavya; Wang, Yu; Zhang, Xiguang; Smith, Martin R. (November 2024). "Omnidens appendages and the origin of radiodont mouthparts". Papers in Palaeontology. 10 (6). doi:10.1002/spp2.1600. ISSN 2056-2799.
- ^ Howard, Richard J.; Hou, Xianguang; Edgecombe, Gregory D.; Salge, Tobias; Shi, Xiaomei; Ma, Xiaoya (2020). "A Tube-Dwelling Early Cambrian Lobopodian". Current Biology. 30 (8): 1529–1536.e2. doi:10.1016/j.cub.2020.01.075. ISSN 0960-9822. PMID 32109391.
- ^ McCall, Christian R. A. (September 2023). "A large pelagic lobopodian from the Cambrian Pioche Shale of Nevada". Journal of Paleontology. 97 (5): 1009–1024. doi:10.1017/jpa.2023.63. ISSN 0022-3360.
- ^ Hofmann, M. H.; Li, X. H.; Chen, J.; MacKenzie, L. A.; Hinman, N. W. (2016). "Provenance and temporal constraints of the Early Cambrian Maotianshan Shale, Yunnan Province, China". Gondwana Research. 37: 348–361. Bibcode:2016GondR..37..348H. doi:10.1016/j.gr.2015.08.015.
- ^ Li, Wei; Yang, Jie; Zhang, Xiguang (2018). 寒武系第3阶小石坝化石库Omnidens-like口器研究. 中国古生物学会第十二次全国会员代表大会暨第29届学术年会论文摘要集.
External links
[edit]- "Arthropod ancestor had the mouth of a penis worm". Natural History Museum. Archived from the original on 2023-06-04.
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