Ancient fish had flexible joints like humans

Ancient fish once roamed the waters with features that preceded human elbows and knees. Scientists have revealed that our flexible joints can be traced to the earliest jawed fish, bridging the distant past with our daily movements.

Research on ancient fossils has shown that skeleton flexibility is not a modern trait. Jawless species do not appear to share this structural hallmark, signaling a major shift in vertebrate history.

Neelima Sharma of The University of Chicago is part of the team that investigated fossil evidence and living examples to see where these joints first emerged.

Sharma’s work reveals that these articulated connections, once believed unique to bony species on land, appeared in ancient aquatic creatures long before limbs evolved.

Exploring flexible connections

Synovial joints are typically found in creatures that require movement with reduced friction. They appear as spaces, or cavities, between bones or cartilage, lubricated by a thin fluid.

This arrangement provides a blend of strength and range. It is more complex than joints that simply fuse or cartilaginous links that have limited motion.

What sets synovial joints apart

Bone surfaces involved in this flexible setup often show specialized cells and proteins. These features help maintain smooth motion and prevent harmful rubbing.

Scientists once thought that this design was mostly found in land vertebrates. That assumption is now questioned by new analyses on certain fish skeletons.

Sea lampreys, which belong to a lineage without jaws, do not display synovial cavities. Their skeletal elements meet in ways that lack the lubricated space.

Bamboo sharks and little skates, both cartilaginous fish, present a different picture. Joints in these species have the layered tissues and proteins that connect to the type of architecture previously linked to synovial structures.

Fossil scans reveal ancient fish joints

The team used advanced imaging techniques to study a fossil fish known as Bothriolepis. This specimen exhibited a cavity between skeletal components – a trait places it among the oldest creatures with a documented synovial joint.

Cartilaginous fish from modern times share some of these patterns with the fossil. Researchers see this as a sign that their common ancestor had joints that could bend with less wear.

Flexible joints helped fish move better

Changing from rigid junctions to more mobile connections offered new avenues in feeding and locomotion. Evolving jaws was one major step, but flexible joints around those jaws opened even more possibilities.

Joint evolution also affected survival. Fish that could maneuver more freely had advantages in escaping predators or capturing prey.

Future research directions

“The origin of mobile joints in our fish ancestors enabled them to move about and feed in new ways. This study shows that the developmental processes that are responsible for these joints arose deep within the fish evolutionary tree,” said Sharma.

There is ongoing interest in how other fossil groups fit into the timeline. Scientists aim to look at additional specimens, hoping to see exactly when these structural traits appeared in different fish branches.

Clues from embryonic development

Developing embryos often hold secrets about evolutionary history. The researchers found that the little skate embryo forms joints in a way similar to tetrapods. Specific proteins appear during development, signaling joint formation in ways that match land vertebrates.

Muscle activity also plays a crucial role. When scientists temporarily paralyzed developing little skates, their joints failed to form properly. This suggests that movement itself is key in shaping these structures, much like in zebrafish and tetrapods.

What this means for human joints

Understanding where our synovial joints originated could help scientists explore joint disorders. Conditions like osteoarthritis involve the breakdown of joint cartilage, leading to pain and stiffness.

Studying how these joints evolved may offer insights into preventing or treating such diseases.

The research also has implications for regenerative medicine. If scientists understand how these joints first formed, they may uncover ways to encourage cartilage repair.

Future studies could look at whether some of the ancient joint-forming proteins could be used in therapies for joint damage.

The study is published in the journal PLOS Biology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–