Yuyuanozoon

Not to be confused with Yunnanozoon.

Yuyuanozoon Temporal range: Cambrian Stage 3 PreꞒ Ꞓ O S D C P T J K Pg N
Holotype
Life restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade?:	†Vetulicolia
Class:	†Vetulicolida
Order:	†Vetulicolata
Family:	†Didazoonidae
Genus:	†Yuyuanozoon Chen et al., 2003
Type species
†Yuyuanozoon magnificissimi Chen et al., 2003

Yuyuanozoon magnificissimi, from the Cambrian Stage 3 Chengjiang lagerstatte, is the largest known vetulicolian, with specimens up to 20 cm in length compared to 5–14 cm for other vetulicolian species.[1]

Etymology

The generic name translates as "Animal of Yu Yuan," Yu Yuan being an ancient name for Chengjiang County. The specific name, magnificissimi, translates as "magnificent," in reference to the great size of the holotype.[2]

Description

Its body is non-biomineralized and consists an elongate ovoid anterior section, with a segmented posterior section roughly one-third of the width and half the length of the anterior. The anterior opening is wide, with a narrow, raised circumventing rim 5 mm posterior to the opening. The anterior section is divided into six subdivisions by five circumventing lines, with gill openings placed symmetrically on each side, coinciding with the lines.[3] In the holotype, gill filaments are seen growing from the posterior side of the gill bars,[2] but no filaments have been seen on the three more recently-examined specimens.[3]

The posterior region consists of seven segments, each of which has five to six annulations (as also seen in Didazoon.[3] It is more cylindrical than the posterior sections of other vetulicolians.[2]

Taxonomy

Yuyuanozoon is a member of the Didazoonidae. It was originally placed incertae sedis with in the phylum Vetulicolia,[2] then moved under the Vetulicolidae in a comprehensive review of the phylum,[4] and most recently reassigned to the Didazoonidae based on additional specimens that clearly show the details of the anterior opening as well as annulations on each posterior segment.[5]

A 2024 study has found the Didazoonidae to be a paraphyletic grade of the vetulicolians closest to crownward chordates as shown in this simplified cladogram:[6]

Chordata	Banffia† Heteromorphus† Skeemella† Nesonektris† Vetulicolidae† Didazoon† "Didazoonidae" Pomatrum† Yuyuanozoon† Yunnanozoon† Cathaymyrus† Pikaia† Chordata (crown group)
(total group)

An earlier study in 2014 placed vetulicolians as the sister-group to tunicates, but was unable to resolve any relationships among vetulicolians as a group:[7]

Vetulicolia†	Vetulicola† Beidazoon† Ooedigera† Pomatrum† / Xidazoon† "Didazoonidae" Didazoon† Yuyuanozoon† Banffia† Heteromorphus† Nesonektris†
	Tunicata

See also

• Maotianshan shales

References

1. Li et al. 2018, p. 1081
2. Chen et al. 2003, p. 282
3. Li et al. 2018, pp. 1085–1086
4. Aldridge et al. 2007
5. Li et al. 2018, p. 1082
6. 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)
7. García-Bellido et al. 2014, p. 9

Works cited

• Aldridge, Richard J.; Hou, Xian-guang; Siveter, David J.; Siveter, Derek J.; Sarah E., Gabbott (2007). "The systematics and phylogenetic relationships of vetulicolians". Palaeontology. 50: 131–168. doi:10.1111/j.1475-4983.2006.00606.x. S2CID 85722738.
• Chen, Ailin; Feng, Hongzhen; Zhu, Maoyan; Ma, Dongsheng; Li, Ming (2003). "A New Vetulicolian from the Early Cambrian Chengjiang Fauna in Yunnan of China". Acta Geologica Sinica. 77 (3): 281–287. doi:10.1111/j.1755-6724.2003.tb00742.x. S2CID 128895860.
• 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.
• 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.