Glimpses of the heads of lizards and snakes

The evolution of animal heads is a remarkable example of how diverse anatomical features have co-evolved to adapt to different ecological niches, behaviors and functions. But the intricate details of why vertebrate heads vary so widely in shape remain elusive.

The crux of the problem lies in the great anatomical diversity and complex nature of animal growth and development, often exacerbated by studies focusing only on specific stages of an animal’s life or on isolated components of the head, especially in adulthood.

In a collaborative effort, researchers from the HiLIFE Institute of Biotechnology at the University of Helsinki, together with international collaborators, studied the exceptional morphological diversity of squamate reptiles, including lizards and snakes, to unravel the long-standing mystery surrounding the various shapes of vertebrate heads. Their comprehensive analysis covered head development from early embryonic formation to fully formed adult bones and organs.

The work is published in the journal Ecology and evolution of nature.

This research highlights the importance of understanding embryo growth, overall organism development, and the complex interactions between different tissues in the formation of vertebrate heads.

By meticulously comparing the shapes of skull bones and soft tissues, the results shed light on the gradual emergence of distinctions between snake and lizard heads during their development. Various mechanisms, including shape formation and rate of development, contribute to these differences.

“Our study provides a framework for future animal studies aimed at analyzing patterns of variation in the skull and other tissues from an evolutionary and developmental perspective,” says lead researcher Nicolas Di-Poï, research director at the Institute of Biotechnology of the University of Helsinki.

“The origin of snake skulls has been linked to changes in developmental timing. However, the evolution of snakes cannot be explained solely by a single type of change. Multiple changes play a role in the formation of their skull and head. In early embryos, snake development “diverges from lizards in both shape and position, followed by temporal differences in later stages,” explains the study’s first author, Ph.D. Joni Ollonen.

The study also reveals dynamic changes in how skull bones integrate with surrounding brain tissue and sensory organs.

“What’s fascinating is that snakes have a more integrated head during development, where changes in one area affect others. This limits the shape of their head during growth but allows their skull to take extreme forms that lizards cannot,” describes Di-Poï.

Key areas around the eyes, nasal cavity and Jacobson’s organ are found to be essential in the formation of snakes’ skulls, highlighting the important role of changes in vital senses like vision, smell and smell. specialized organ for detecting odors in the evolution of the snake.

This research marks a significant advance in understanding the adaptive nature of reptile heads, providing valuable insight into how different skull bones and surrounding organs are connected in vertebrates. This new knowledge offers insight into the fascinating world of how form, development and function are intertwined in the diversity and design of nature.