The Yanjiahe Formation has been dated through various methods. The top of the formation is dated at 526.5±1.1Ma and 526.4±5.3Ma using radiometric dating on ash beds within the area. Likewise, the base of the formation has been dated to between 542±0Ma to 526±0Ma through carbon isotopic correlations.[1]
The Yanjiahe Formation contains a wide range of unique organisms from the base of the Cambrian, from the probable earliest stem group echinoderm Yanjiahella, to the ecdysozoan Beretella, alongside a large wealth of early molluscs, such as Watsonella and Scenella.[3] The formation is also home to several large but incomplete ecdysozoan-like cuticles, exceeding the other fully complete ecdysozoans like Beretella and Saccorhytus in size. Despite their incompleteness, they still offer an insight into the already varied biodiversity of ecdysozoans during the early Cambrian.[5]
Four specimens with a vermiform morphology that is annulated in appearance, maximum known length is 3.1mm (0.1in). Surface ornamentation noted to resemble that seen in the pancrustacean Yicaris from the Yu’anshan Formation, as well as the ecdysozoan Saccorhytus from this formation.
A singular specimen of a trunk segment covered in spines of varying sizes, maximum length of the specimen is 2.7mm (0.1in). Is comparable to various ecdysozoan groups, such as lobopods, and more so to the extant kinorhynchs. It is noted that if the latter interpretation is valid, the specimen would likely be placed as a crown-group kinorhynch, although more evidence is needed.
The most abundant, with seventeen specimens known, and found in two modes of preservation. Specimens are covered in fractured spines of varying shapes, and the maximum known length of this form being 4.3mm (0.2in). Is noted to be comparable to various small shelly fossils such as Protohertzina and Mongolodus, and several ecdysozoans such as Eokinorhynchus, Scalidodendron, and Saccorhytus.
Two specimens with a vermiform morphology, and is only known to attain a length of 1.8mm (0.1in), making it the smallest of the known forms. These specimens have been compared to the likes of Eopriapulites and Palaeoscolex.
Two specimens, which are evenly covered in small papillate knobs, and attain a maximum known length of 4.9mm (0.2in). They have been compared to a wide range of papillate knob-bearing acritarchs, embryos, algae-like forms, and tentative sponges, such as Bacatisphaera, Archaeooides, Shaanisphaera, and Aetholicopalla respectively.
Five specimens with a dense covering of short coniform to hook-like spines, and are the largest of the forms, attaining a maximum length of 8.9mm (0.4in). The five specimens are noted to bear a striking resemblance to Saccorhytus, although they are also notably much larger, suggesting that saccorhytids may have attained much larger sizes than currently known.
12345678910Liu, Zhanhong; Algeo, Thomas J. (June 2025). "Appearance of SSFs in earliest Cambrian seas of South China linked to salinity conditions". Chemical Geology. 683 122761. doi:10.1016/j.chemgeo.2025.122761.
1234567Chang, Shan; Feng, Qinglai; Clausen, Sébastien; Zhang, Lei (May 2017). "Sponge spicules from the lower Cambrian in the Yanjiahe Formation, South China: The earliest biomineralizing sponge record". Palaeogeography, Palaeoclimatology, Palaeoecology. 474: 36–44. Bibcode:2017PPP...474...36C. doi:10.1016/j.palaeo.2016.06.032.
↑Guo, Junfeng; Han, Jian; Van Iten, Heyo; Song, Zuchen; Qiang, Yaqin; Wang, Wenzhe; Zhang, Zhifei; Li, Guoxiang; Sun, Yifei; Sun, Jie (May 2020). "A new tetraradial olivooid (Medusozoa) from the lower Cambrian (Stage 2) Yanjiahe Formation, South China". Journal of Paleontology. 94 (3): 457–466. Bibcode:2020JPal...94..457G. doi:10.1017/jpa.2019.101.
123456789101112Steiner, Michael; Yang, Ben; Hohl, Simon; Zhang, Lei; Chang, Shan (September 2020). "Cambrian small skeletal fossil and carbon isotope records of the southern Huangling Anticline, Hubei (China) and implications for chemostratigraphy of the Yangtze Platform". Palaeogeography, Palaeoclimatology, Palaeoecology. 554 109817. Bibcode:2020PPP...55409817S. doi:10.1016/j.palaeo.2020.109817.
12345678910111213Yang, Lei; Yang, Ben; Shang, Xiaodong; Steiner, Michael (June 2025). "Palaeogeographic and stratigraphic significances of Fortunian small skeletal fossils from the southern Shennongjia Region (China)". Palaeogeography, Palaeoclimatology, Palaeoecology. 668 112910. Bibcode:2025PPP...66812910Y. doi:10.1016/j.palaeo.2025.112910.
↑Guo, Junfeng; Han, Jian; Iten, Heyo Van; Wang, Xing; Qiang, Yaqin; Song, Zuchen; Wang, Wenzhe; Zhang, Zhifei; Li, Guoxiang (January 2020). "A fourteen-faced hexangulaconulariid from the early Cambrian (Stage 2) Yanjiahe Formation, South China". Journal of Paleontology. 94 (1): 45–55. Bibcode:2020JPal...94...45G. doi:10.1017/jpa.2019.56.
↑Song, Zuchen; Guo, Junfeng; Han, Jian; Van Iten, Heyo; Qiang, Yaqin; Peng, Jiaxin; Sun, Jie; Zhang, Zhifei (June 2022). "A New Species of Septuconularia (Hexangulaconulariidae, Cnidaria) from Cambrian Stage 2, South China". Acta Geologica Sinica - English Edition. 96 (3): 757–765. Bibcode:2022AcGlS..96..757S. doi:10.1111/1755-6724.14917.
↑Guo, Junfeng; Han, Jian; Van Iten, Heyo; Song, Zuchen; Qiang, Yaqin; Wang, Wenzhe; Zhang, Zhifei; Li, Guoxiang (September 2021). "A ten-faced hexangulaconulariid from Cambrian Stage 2 of South China". Journal of Paleontology. 95 (5): 957–964. Bibcode:2021JPal...95..957G. doi:10.1017/jpa.2021.25.
12Chang, Shan; Clausen, Sébastien; Zhang, Lei; Feng, Qinglai; Steiner, Michael; Bottjer, David J.; Zhang, Yan; Shi, Min (September 2018). "New probable cnidarian fossils from the lower Cambrian of the Three Gorges area, South China, and their ecological implications". Palaeogeography, Palaeoclimatology, Palaeoecology. 505: 150–166. Bibcode:2018PPP...505..150C. doi:10.1016/j.palaeo.2018.05.039.
↑Chang, Shan; Feng, Qinglai; Zhang, Lei (August 2018). "New Siliceous Microfossils from the Terreneuvian Yanjiahe Formation, South China: The Possible Earliest Radiolarian Fossil Record". Journal of Earth Science. 29 (4): 912–919. Bibcode:2018JEaSc..29..912C. doi:10.1007/s12583-017-0960-0.
12345Chang, Shan; Zhang, Lei; Feng, Qinglai (September 2025). "Diverse organic-walled microfossils from the basal Cambrian Yanjiahe Formation in the eastern Three Gorges area". Review of Palaeobotany and Palynology. 340 105361. Bibcode:2025RPaPa.34005361C. doi:10.1016/j.revpalbo.2025.105361.
1234Ahn, Soo Yeun; Zhu, Maoyan (November 2017). "Lowermost Cambrian acritarchs from the Yanjiahe Formation, South China: implication for defining the base of the Cambrian in the Yangtze Platform". Geological Magazine. 154 (6): 1217–1231. Bibcode:2017GeoM..154.1217A. doi:10.1017/S0016756816001369.
P. Chen. 1984. Discovery of Lower Cambrian small shelly fossils from Jijiapo, Yichang, west Hubei and its significance. Professional Papers of Stratigraphy and Palaeontology 13:49-64
