A giant stem-group chaetognath

[erik simpson]

https://www.science.org/doi/10.1126/sciadv.adi6678

Abstract
"Chaetognaths, with their characteristic grasping spines, are the oldest
known pelagic predators, found in the lowest Cambrian (Terreneuvian).
Here, we describe a large stem chaetognath, Timorebestia koprii gen. et
sp. nov., from the lower Cambrian Sirius Passet Lagerstätte, which
exhibits lateral and caudal fins, a distinct head region with long
antennae and a jaw apparatus similar to Amiskwia sagittiformis. Amiskwia
has previously been interpreted as a total-group chaetognathiferan, as
either a stem-chaetognath or gnathostomulid. We show that T. koprii
shares a ventral ganglion with chaetognaths to the exclusion of other
animal groups, firmly placing these fossils on the chaetognath stem. The
large size (up to 30 cm) and gut contents in T. koprii suggest that
early chaetognaths occupied a higher trophic position in pelagic food
chains than today."

When they say "giant", context is important: 2oo mm in length, 290 mm
including the antennae. It was discovered in the Sirius Passet
lagerstatte in northen Greenland. It's similar to and closely related
to Amiskwia, a familiar fossil known in the Burgess Shale.

It and others represent a stem clade sister to crown rotifers.

[John Harshman]

For Cambrian Stage 2, 20cm is huge. This is way cool.