Liu et al., Palaeogeogr. Palaeoclimatol. Palaeoecol., 2025
Tiny embryos discovered in China
Objects found in China may reveal that the first ancestors of the group they were part of had a sac-shaped body — the worm shape may only have appeared later.
They are millimeter-sized objects, says , but they are a great discovery. They belong to animals that lived at the beginning of the Cambrian period, about 535 million years ago.
There are several animals, and they belong to the group Ecdysozoawhich includes insects, spiders, crustaceans and worms. In total, they are 7 new fossilsdiscovered in the Kuanchuanpu Formation in China.
The team of paleontologists led by Mingjin Liufrom Chang’an University, in China, believes that the adult forms of embryos may be closely related to Saccorhytusa genus represented by a single species — a tiny and peculiar creature from the Cambrian era, who didn’t have a tail, suggest in what will be published in Palaeogeography, Palaeoclimatology, Palaeoecology in the February edition.
These embryos, nicknamed ecdysozoans they are much rarer than those of crabs or other animals with tough carcasses because they are considerably more delicate.
The once soft tissues that made up each embryo have long been replaced by calcium phosphate minerals as they decomposed in the bottom sediments of a marine environment. This fossilization process preserved the three-dimensional anatomy of embryos with impressive detail, points out Science Alert.
Based on the number and arrangement of the plates that form the embryos’ exoskeletons, called sclerites, the researchers classified the tiny organisms as two new taxa (a group of one or more populations of an organism): Saccus xixiangensis e The sack.
The lack of deformation in the exoskeleton suggests the cuticle formationwhich would mean that the embryos were almost ready to hatch at the time of their death. Despite this, they were still in a phase of embryonic development prior to the formation of a mouth or anus.
The tax Saccorhytus coronarius was found in the same Kuanchuanpu formation as o Sack. It also had no limbs, no eyelashes, it had a bag-shaped body, a giant mouth with radial structures aroundbilateral symmetry and had no anus. And it measured about one millimeter in diameter.
If they were similar, both the Sack like the Saccorhytus may both be basal Ecdysozoans, suggesting that the group’s earliest ancestors had a sac-shaped body, having the worm shape only appeared later.
All this discovered from seven small balls of calcium phosphate.
