Radiodonts, like Stanleycaris, had the brains to evolve into arthropods

Thought this would be yet another ‘heard it here first‘ report,
but see below for an overlooked Ruedemann 1916 hypothesis listing trilobites as crustaceans.

Moysiuk J and Caron J-B 2022 report:
“In addition to being among the most iconic and bizarre-looking Cambrian animals, radiodonts are a group that offers key insight into the acquisition of the arthropod body plan by virtue of their phylogenetic divergence prior to all living members of the phylum.”

This is correct. Two years ago we looked at radiodonts (Fig 1) evolving into trilobite arthropods from polyclad flatworm ancestors (Fig 2). Then in March 2022 a series of posts looked at radiodonts evolving into onychophorans and tardigrades (Fig 3), trilobites into insects (Fig 4) and other arthropods. Nice to get confirmation from a published peer-reviewed study on these, but they still need to include ancestral polyclad flatworms (Fig 5) and trilobites to understand the backstory.

According to wildsingapore.com.
“Many flatworms are carnivores that prey on tiny animals (protozoa, copepods, worms) or feed on immobile animals such as bryozoans, ascidians and molluscs. Being flat, they slip easily between the shells of bivalves and some flatworms are considered pests of oyster farms. Some are scavengers, feeding on dead animals.”

Based on phylogenetic bracketing the above panorama of feeding styles most likely characterizes that of radiodonts. As in flatworms, radiodonts lacked hinged mouth parts. So they were not capable of ferocious predation on large, mobile, armored animals. They were key transitional taxa in the evolution of several arthropod and velvet worm clades.

References
Moysiuk J and Caron J-B 2022. A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation. Current Biology 32(115):3302–3316. online.
Pates S, Daley AC and Ortega-Hernández J 2018. Reply to Comment on “Aysheaia prolata from the Utah Wheeler Formation (Drumian, Cambrian) is a frontal appendage of the radiodontan Stanleycaris” with the formal description of Stanleycaris. Acta Palaeontologica Polonica. 63 (1): 105–110.
Ruedemann R 1916. ON the presence of a median eye in trilobites. New York State Museum.

wiki/Stanleycaris
ivescience.com/three-eyed-cambrian-fossil-stanleycaris