An “intermediate” fossil:
Despite being just two centimeters in length, the remarkably preserved soft tissues of the Gyaltsenglossus fossils reveal incredibly detailed anatomical structures. These details include the oval-shaped proboscis of acorn worms and a basket of feeding tentacles similar to those of pterobranchs. The age of these fossils, combined with the unique morphological combination of the two major hemichordate groups, makes this discovery a critical find for understanding early hemichordate evolution.
“An ancient animal with an intermediary anatomy between acorn worms and pterobranchs had been hypothesized before but this new animal is the clearest view of what the ancestral hemichordate may have looked like,” says Dr. Christopher Cameron, Associate Professor at the University of Montreal and a co-author on this study. “It’s exciting to have so many new anatomical details to help drive new hypotheses about hemichordate evolution.” …
In this particular case, Gyaltsenglossus suggests that the ancestral hemichordate may have been able to use the feeding strategies of both of the modern groups. Like acorn worms, the long proboscis may have been used to feed on nutrient-filled marine mud, while at the same time, and like the pterobranchs, the array of six feeding arms was probably used to grab suspended food particles directly from the water above where it was crawling.
Hemichordates belong to a major division of animal life called Deuterostomia, which includes chordates like fish and mammals, and not the division of animal life called Protostomia, that includes arthropods such as insects and annelids such as earthworms. Dr. Nanglu explains, when looking at Gyaltsenglossus, we’re actually looking at a very, very distant relative of our own branch of vertebrate and human evolution.
Royal Ontario Museum, “Early Cambrian fossil: Bizarre half-billion-year-old worm with tentacles solves evolutionary mystery” at ScienceDaily
Paper. (open access)
The importance of the controversy that is said to be settled now does not seem nearly as great as the significance of the Cambrian explosion itself.