Contemporary understanding was that an ancient group of fishes called jawless fishes (which still exist today) evolved into five different groups of fishes these being; placoderms (now extinct), spiny sharks (also extinct), fin-ray fishes (modern fishes), cartilaginous fishes (sharks and rays) and lobe-fin fishes. One group, the lobe-ray fishes evolved into tetrapods that became the land animals like mammals, amphibians, reptiles and birds. In this video from the Melbourne Museum, Wayne Gerdtz explains this.
However new research has revealed that fin rays in fin-ray fishes and fingers and toes in humans are related! Scientists from the University of Chicago have shown that the cells that make fin rays in fish also form fingers and toes of land creatures, including humans.
The researchers used a gene-editing technique to delete various combinations of limb-building genes (also known as Hox genes) in zebrafish. They then cross-bred the mutant fish and discovered that the deletion of Hox genes hindered the full development of fin rays.
The researchers also used cell-labelling techniques to monitor cell migration during development. This showed that the cells found in the wrists and fingers of humans are also found exclusively in the fin rays of fish.
Markers of the wrists and digits in the limb of a mouse (left) are present in fish and demarcate the fin rays (right). Credit: SHUBIN LABORATORY
This new research raises questions about our understanding of where terrestrial (land) animals evolved from and suggests that one day fin-ray fishes like flathead may evolve into new groups of land animals to escape the south east trawl fleet.