Pomatrum
| Pomatrum Temporal range:
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|---|---|
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| Artist's conception | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade?: | †Vetulicolia |
| Class: | †Vetulicolida |
| Order: | †Vetulicolata |
| Family: | †Didazoonidae |
| Genus: | †Pomatrum Luo and Hu, in Luo et al., 1999 |
| Species: | †P. ventralis
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| Binomial name | |
| †Pomatrum ventralis Luo and Hu, in Luo et al., 1999
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| Synonyms | |
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Xidazoon stephanus[1] | |
Pomatrum is an extinct vetulicolian, the senior synonym of Xidazoon; the latter taxon was described by Shu, et al. (1999) based on fossils found in the Qiongzhusi (Chiungchussu) Formation, Yu'anshan Member (Eoredlichia zone), Lower Cambrian, Haikou, (Kunming), about 50 km west of Chengjiang, China.[2]
The fossils show that the body of the animal was divided into two parts. The anterior part of the body is moderately inflated, with a prominent mouth circlet. It has faint transverse divisions towards the front, but is otherwise smooth. The mouth circlet consists of about 30 plates divided into inner and outer regions. The anterior section has five structures on each side, which are interpreted as gills. A dark region running close to the ventral and posterior margins is interpreted as an endostyle. The condition of the anterior portion of the fossils suggests that it was thin-walled, i.e., that the anterior portion was largely hollow. The posterior part of the body tapers towards front and back (diamond-shaped), and is divided into seven segments covered in cuticle with three less well-defined segments at the anterior end.[3] There are short spines at the posterior tip. The authors describe an alimentary canal with terminal openings and a rectum with what might be dilator muscles.
Taxonomy
[edit]Pomatrum is a member of the Didazoonidae, which one 2024 study has found to be a paraphyletic grade of the vetulicolians closest to crownward chordates as shown in this simplified cladogram:[4]
An earlier study in 2014 was unable to resolve any relationships among vetulicolians as a group:[5]
Relationship to Xidazoon
[edit]
Based on a comparison of the incomplete/damaged holotype with the incomplete/damaged holotype of Pomatrum ventralis, a comprehensive examination of the vetulicolian systematics published in 2007 accepted a 2002 proposal that X. stephanus was a junior synonym of P. ventralis because the anterior portions of the two species are largely identical.[1] This proposal has been accepted by a number of other workers,[5][8] although in some cases only tentatively.[9]
Prior to this, Xidazoon had been treated as a separate genus by workers aware of Pomatrum,[10] who argue that Pomatrum has more than the seven posterior segments found in Xidazoon.[11] Some workers have continued to treat the genera as separate at least as recently as 2023.[12]
Possible Relationship to Pipiscius
[edit]Upon its discovery, Xidazoon was likened to the Carboniferous chordate Pipiscius on account of having a similar anterior circlet, although it was noted that the similarities could be due to convergence.[2] A later assessment of chordate phylogeny noted the possible connection while discussing Pipiscius as a possible hagfish relative, but also noted that the position of Xidazoon among the chordates was not certain.[13] A recent phylogenetic analysis of vetulicolians and other early chordates did not including Pipiscius.[4]
See also
[edit]
References
[edit]- ^ a b Aldridge et al. 2007, pp. 145–147
- ^ a b Shu et al. 1999
- ^ Shu 2005
- ^ a b Mussini et al. 2024, pp. 6–7 (Note: The cladogram is simplified using the definition of Vetulicolidae from Li et al. 2018, cited elsewhere on this page)
- ^ a b García-Bellido et al. 2014, p. 9
- ^ Shu 2005, p. 2348
- ^ Aldridge et al. 2007, pp. 142–143
- ^ Li et al. 2018, pp. 1083–1084
- ^ McMenamin 2019, p. 10
- ^ Shu et al. 2001
- ^ Shu 2005, p. 2345
- ^ Yang et al. 2023
- ^ Rowe 2004, p. 392
Works cited
[edit]- Aldridge, Richard J.; Hou, Xian-Guang; Siveter, David J.; Siveter, Derek J.; Gabbott, Sarah E. (2007). "The Systematics and Phylogenetic Relationships of Vetulicolians". Palaeontology. 50: 131–168. doi:10.1111/j.1475-4983.2006.00606.x. S2CID 85722738.
- García-Bellido, Diego C.; Lee, Michael S. Y.; Edgecombe, Gregory D.; Jago, James B.; Gehling, James G.; Paterson, John R. (2014). "A new vetulicolian from Australia and its bearing on the chordate affinities of an enigmatic Cambrian group". BMC Evolutionary Biology. 14: 214. doi:10.1186/s12862-014-0214-z. PMC 4203957. PMID 25273382.
- Li, Yujing; Williams, Mark; Gabbott, Sarah E.; Chen, Ailen; Cong, Peiyun; Hou, Xianguang (2018). "The enigmatic metazoan Yuyuanozoon magnificissimi from the early Cambrian Chengjiang Biota, Yunnan Province, South China". Journal of Paleontology. 92 (6): 1081–1091. doi:10.1017/jpa.2018.18.
- McMenamin, Mark A. S. (2019). "Cambrian Chordates and Vetulicolians". Geosciences. 9 (8): 354. Bibcode:2019Geosc...9..354M. doi:10.3390/geosciences9080354. ISSN 2076-3263.
- Mussini, G.; Smith, M. P.; Vinther, J.; Rahman, I. A.; Murdock, D. J. E.; Harper, D. A. T.; Dunn, F. S. (2024). "A new interpretation of Pikaia reveals the origins of the chordate body plan". Current Biology. 34 (13): 2980–2989.e2. doi:10.1016/j.cub.2024.05.026. PMID 38866005.
- Rowe, Timothy (2004). "Chordate Phylogeny and Development". In Cracraft, Joel; Donoghue, Michael J. (eds.). Assembling the Tree of Life. Oxford University Press.
- Shu, Degan (2005). "On the Phylum Vetulicolia". Chinese Science Bulletin. 50 (20): 2342–2354. Bibcode:2005ChSBu..50.2342S. doi:10.1007/BF03183746. S2CID 86827605.
- Shu, D.-G.; Conway Morris, S.; Han, J.; Chen, L.; Zhang, X.-L.; Zhang, Z.-F.; Liu, H.-Q.; Li, Y.; Liu, J.-N. (2001). "Primitive deuterostomes from the Chengjiang Lagerstätte (Lower Cambrian, China)". Nature. 414 (6862): 419–424. Bibcode:2001Natur.414..419S. doi:10.1038/35106514. PMID 11719797. S2CID 4345484.
- Shu, D.; Conway Morris, S.; Zhang, X-L.; Chen, L.; Li, Y.; Han, J. (1999). "A pipiscid-like fossil from the Lower Cambrian of south China". Nature. 400 (6746): 746. Bibcode:1999Natur.400..746S. doi:10.1038/23445. S2CID 204995356.
- Yang, Yang; Su, Bi'ang; Ou, Qiang; Cheng, Meirong; Han, Jian; Shu, Degan (2023). "An enigmatic structure in the tail of vetulicolians from the Cambrian Chengjiang biota, South China". Papers in Paleontology: e1537. doi:10.1002/spp2.1537.
