The Cambrian geological period, more than 500 million years ago (Ma), is an important time because the first fossils of many groups of animals are known there. Some of them are enigmatic due to their strange appearance and the small number of fossils found. This is the case of the tommotidae, an extinct subgroup belonging to the lophophora, some of whose current representatives resemble shells called brachiopods. The precise morphology and relationship of some tommotids to other groups of animals remains obscure.
But paleontologists have discovered a complete tommotiid fossil in Chengjiang (China) dated 518 Ma. This discovery is published in the journal current biology September 27, 2022 sheds more light on the place of representatives of this group in the animal kingdom and better understands how animals diversified more than 500 Ma ago.
A tiny “phoenix” from the ancient seas
Here’s a phoenix… even if it doesn’t look like much! In any case, this is where the name of this new fossil species is taken: Wufengella bengstoni ; “wufeng“which means” dancing phoenix “. This fossil shows that, during its life, the animal was small: less than 2 cm long. Certainly small, but rare, the fossil is almost complete! It allows us to know that it was a strange worm formed by segments -metameres- covered in the middle of the back by two sets of asymmetrical plates, and a series of small plates on each side of the back.
These plates do not have any particular ornamentation, apart from the growth striae that allow us to determine how these plates developed during the growth of the animal. But could it have wings like the phoenix? Almost ! Well, not wings, but fine bristles made of chitin. setae – lining the sides of the worm, preserved as tracks or sometimes as masses of pyrite. “It looks like the unlikely offspring between a hairy worm and a mollusk.study co-author Jakob Vinther said in a press release, before adding that despite this “does not belong to any of these groups“.
The Cambrian geological period, more than 500 million years ago (Ma), is an important time because the first fossils of many groups of animals are known there. Some of them are enigmatic due to their strange appearance and the small number of fossils found. This is the case of the tommotidae, an extinct subgroup belonging to the lophophora, some of whose current representatives resemble shells called brachiopods. The precise morphology and relationship of some tommotids to other groups of animals remains obscure.
But paleontologists have discovered a complete tommotiid fossil in Chengjiang (China) dated 518 Ma. This discovery is published in the journal current biology September 27, 2022 sheds more light on the place of representatives of this group in the animal kingdom and better understands how animals diversified more than 500 Ma ago.
A tiny “phoenix” from the ancient seas
Here’s a phoenix… even if it doesn’t look like much! In any case, this is where the name of this new fossil species is taken: Wufengella bengstoni ; “wufeng“which means” dancing phoenix “. This fossil shows that, during its life, the animal was small: less than 2 cm long. Certainly small, but rare, the fossil is almost complete! It allows us to know that it was a strange worm formed by segments -metameres- covered in the middle of the back by two sets of asymmetrical plates, and a series of small plates on each side of the back.
These plates do not have any particular ornamentation, apart from the growth striae that allow us to determine how these plates developed during the growth of the animal. But could it have wings like the phoenix? Almost ! Well, not wings, but fine bristles made of chitin. setae – lining the sides of the worm, preserved as tracks or sometimes as masses of pyrite. “It looks like the unlikely offspring between a hairy worm and a mollusk.study co-author Jakob Vinther said in a press release, before adding that despite this “does not belong to any of these groups“.
Photo of the Wuffengella fossil (left) and its interpretive drawing (right). Asymmetrical plaques (yellow and blue) and hairs (red lines) are highlighted. Credits: Jakob Vinther and Luke Parry
The ancestors of brachiopods were worms with moving plates.
Until now, the known fossils of this type of tommotidae were isolated plates that did not allow us to have a precise idea of the morphology of this group. These fossil organisms, typical of the Cambrian, are best known from animals with shells or tubes; well adapted to a fixed life form, such as today’s brachiopods. This study shows that wufengella does not correspond to this plan of organization and that this animal had a mobile life form. It more closely resembles an annelid, segmented worms lined with small hairs, found in close proximity to tommotidae according to previous studies.
Here, segmentation and the presence of hairs are common characters that suggest a close proximity between the oldest lophophores and the annelids. “Now we can see that these similarities are a reflection of a common ancestry. The common ancestor of the lophophorates and the annelids had an anatomy more similar to that of the annelids.says Jakob Vinther in a press release. It seems here that the fixed way of life appeared later in the lophophorates and that their oldest representatives, the tommotiids, had a mobile way of life similar to that of the annelids.
Simplified reconstruction of lophophorate evolution. The current lineages, unsegmented and with a fixed lifestyle, are the phoronids, the bryozoans and the brachiopds. Credits: Luke Perry
Thus, this study confirms the hypotheses that the ancient lophophores such as certain tommotids were segmented “worms” with dorsal plates provided with setae. In fact, the current lophophores, like the organisms fixed to the shell that are the brachiopods, derive from worms with mobile plates. It also helps support the very close relationship between annelids and lophophorates. Finally, the fact that wufengella being mobile shows that the fixed life form spread later in the evolution of the group. “At some point, the tommotiid ancestor of lophophorates settled and evolved by feeding […] suspended particles in the water. Thus, a long, vermiform body with many repeating body units became less useful and was reduced.” emphasizes the Jakob Vinther in a press release.