Trilobozoans (also known as triradialomorphs) are some of the more enigmatic members of the Ediacaran biota. In the past their unique three-way-symmetrical body plan was interpreted as linking them to groups like sponges, cnidarians, or echinoderms, but currently they’re considered to be their own weird little phylum with uncertain evolutionary affinities, classified no more specifically than “probably some sort of early eumetazoan animal“.
Lobodiscus tribrachialis is a newly-described member of this mysterious lineage. It lived in warm shallow marine waters covering what is now Southwestern China, and with an age of around 546 million years it’s currently the youngest known trilobozoan, extending the group’s time range by several million years.
About 3.7cm in diameter (~1.5″), it had the characteristic trilobozoan disc-shaped shield-like body, with a central depression surrounded by three triradially-symmetric lobes with branching ridges and grooves.
Its body would have been soft but fairly rigid, and it’s not clear if it was capable of moving over the seafloor or if it had a more static lifestyle. Like its relative Tribrachidium it was probably a filter feeder, with the grooves on its surface directing water flow towards the central depression – and this surface ornamentation may also have been covered with cilia that actively caught and transported suspended food particles.
References:
- Ivantsov, A. Yu, and M. A. Zakrevskaya. “Trilobozoa, Precambrian tri-radial organisms.” Paleontological Journal 55 (2021): 727-741. https://doi.org/10.1134/S0031030121070066
- Ivantsov, Andrey, Aleksey Nagovitsyn, and Maria Zakrevskaya. “Traces of locomotion of Ediacaran macroorganisms.” Geosciences 9.9 (2019): 395. https://doi.org/10.3390/geosciences9090395
- Hall, C. M. S., et al. “The short-lived but successful tri-radial body plan: a view from the Ediacaran of Australia.” Australian Journal of Earth Sciences 67.6 (2020): 885-895. https://doi.org/10.1080/08120099.2018.1472666
- Rahman, Imran A., et al. “Suspension feeding in the enigmatic Ediacaran organism Tribrachidium demonstrates complexity of Neoproterozoic ecosystems.” Science Advances 1.10 (2015): e1500800. https://doi.org/10.1126/sciadv.1500800
- Zhao, Mingsheng, et al. “A putative triradial macrofossil from the Ediacaran Jiangchuan Biota.” Iscience 27.2 (2024). https://doi.org/10.1016/j.isci.2024.108823
- Wikipedia contributors. “Lobodiscus.” Wikipedia, 29 Mar. 2024, https://en.wikipedia.org/wiki/Lobodiscus
- Wikipedia contributors. “Trilobozoa.” Wikipedia, 10 Mar. 2024, https://en.wikipedia.org/wiki/Trilobozoa