Fossil discovery sheds light on the early evolution of animal nervous systems

An international team of scientists has solved a fascinating piece of the evolutionary puzzle. That’s how the ventral nerve cord, a key component of the central nervous system, evolved in ecdystes, a group that includes insects, nematodes, and priapulid worms.

Their findings, published in a paper titled “Conservation and early evolution of the scalidophoran ventral nerve cord” in Science Advances, provide valuable insight into the origin of these structures in the Basal Cambrian.

The research team consisted of Dr. Deng Wang (Northwest University), Dr. Jean Vannier (University of Lyon), Dr. Chema Martin-Durán (Queen Mary University of London), and Dr. María Herranz (University Rey Juan Carlos). Masu. They analyzed highly preserved fossils from major Cambrian deposits. These fossils include representatives of the early-evolving Scalidophora, a member of the Ecdynozoan subgroup, and provide a rare glimpse into the nervous system structure of ancient animals.

Ecdynozoans include arthropods (such as insects and crabs), nematodes (roundworms), and even smaller groups such as kinolynches (“mud dragons”) and priapulids (“penis worms”). Their central nervous system, including the brain and ventral nerve cord, has long intrigued scientists seeking to understand the evolutionary relationships between these groups.

For example, priapulidids exhibit a single ventral nerve cord, whereas loriciferans and quinorhynchids have paired nerve cords, and quinorhynchids also develop paired ganglia. Did the ancestral molt have a single or paired ventral nerve cord?

Additionally, loriciferans and quinolhynchians share similar nervous system design with arthropods, but are phylogenetically distant. Are these similarities the result of convergent evolution or do they reflect a common evolutionary origin?

Scaridophorans, which include priapulids, loriciferans, and quinolhynchians, first appeared in the early Cambrian. They represent an important lineage for studying the evolutionary trajectory of the ventral nerve cord in ecdysizoans.

The researchers found fossils from the Fortunian-Quanchuan Formation (such as Eopliaprites and Eochinorrhynx), the Chengjiang biota (such as Xiaoheitingera and Maffanscorex), and the Goryuan Ottoia prolifica. By studying these, they identified an elongated structure that ran along the ventral sides of these ancient creatures.

“These structures closely resemble the ventral nerve cords found in modern priapulids,” explained Dr. Deng Wang and Dr. Jean Vannier. Their analysis shows that these fossils preserve traces of a single ventral nerve cord, shedding light on the likely ancestral state of caridophorans.

Phylogenetic analyzes support the hypothesis that a single ventral nerve cord was the ancestral state of caridophorans. Furthermore, the evolutionary grouping of Nematoda and Panarthropoda (a clade that includes arthropods, tardigrades, and onychopods) suggests that their common ancestor may also have had a single nerve cord. It suggests that it is high.

“This suggests that the common ancestor of all ecdysids had a single ventral nerve cord,” said Dr Chema Martín Duran. “The paired nerve cords observed in arthropods, loriciferans, and quinorhynchians likely evolved independently and represent derived traits.”

This study also highlights the link between the evolution of paired ventral nerve cords, ganglia, and body segmentation. Loriciferans, Kinorhynchians, and Panarthropods exhibit varying degrees of body segmentation, suggesting that these structural changes may have coevolved with changes in the nervous system.

Dr Maria Herranz says: ‘The appearance of paired nerve cords likely facilitated greater coordination of locomotion, especially in segmented animals.During the Precambrian-Cambrian transition, the nervous system and muscles “Changes in the system are coupled with the development of appendages, allowing us to do more.” complex movement. ”

This discovery deepens our understanding of ecdysozoan evolution and highlights the role of the fossil record in answering important questions about early animal development.

By linking the structure of the nervous system to broader evolutionary trends, this study provides a clearer picture of how diverse ecdysizoan lineages arose and adapted to their environments. be.