Scientists studying shark embryos have uncovered evidence that the basic blueprint for building faces in jawed animals has remained largely unchanged for more than 400 million years.
The research, published in Development, focused on the small-spotted catshark, a small species of shark that may help scientists understand how faces first evolved in ancient vertebrates.
The study was led by researchers at the Max Planck Institute for Evolutionary Biology, including developmental biologist Markéta Kaucká.
Most previous studies on face development have focused on bony animals such as mice, chickens, and zebrafish.
Sharks and other cartilaginous fishes have been studied far less, even though they split from bony vertebrates hundreds of millions of years ago.
Because of this gap, scientists have struggled to understand how facial structures first evolved in early jawed animals.
To investigate, the researchers studied cranial neural crest cells, a special group of cells that help form the face during embryonic development.
These cells are unique to jawed vertebrates and play a major role in creating the skull, cartilage, connective tissues, and parts of the nervous system.
In embryos, these cells begin near the developing brain before moving to different parts of the growing head and face. Once they arrive, they transform into many different tissues that shape the face.
Using advanced imaging techniques and single-cell genetic analysis, the team tracked these cells inside developing catshark embryos. They discovered that the early developmental program of shark facial cells is remarkably similar to the one seen in bony vertebrates.
This suggests that the fundamental instructions for building a vertebrate face were already established very early in evolution and have been preserved ever since.
The scientists were surprised by how strongly these ancient developmental programs had remained conserved across such enormous evolutionary distances.
However, the study also revealed an important difference. While the basic genetic program was similar, the behavior of the cells later in development differed between sharks and animals such as mice or chickens.
In the catshark, the daughter cells produced by cranial neural crest cells gather behind the eye and pause there instead of moving directly toward the front of the face. Despite taking this different developmental route, the cells still eventually form equivalent facial structures.
“We expected that the unique shark facial morphology arises from distinct properties of CNCC; however, that is not the case,” said Elio Escamilla-Vega, the study’s first author.
Studying shark embryos is particularly challenging because they develop slowly inside tough protective egg cases, making them difficult to observe and manipulate compared to common laboratory animals.
To overcome this problem, the researchers worked with scientists at DESY and used powerful synchrotron X-ray imaging technology to create highly detailed 3D images of developing shark embryos at cellular resolution.
The team has also made all of their data publicly available so other researchers can continue exploring shark development.
The findings provide an important new window into the deep evolutionary history of vertebrates and suggest that the ancient biological instructions that shape human faces today may have first appeared long before dinosaurs—or even the earliest land animals—ever existed.
